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1. x CHARGING CURVE NICKEL IRON BATTERY FIG II 2222 TIME CHARGING CURVE LEAD ACID BATTERY FIG 12 x VOLTAGE TIME CHARGING CURVE LITHIUM BATTERY IRON SULFIDE ELECTRODE FIG 13 VOLTAGE TIME CHARGING CURVE SILVER CADMIUM BATTERY FIG 14 CURRENT ge e TIME CONSTANT VOLTAGE CHARGING CURVE NICKEL CADMIUM BATTERY 4 392 101 1 OF CHARGING BATTERIES AND APPARATUS THEREFOR This is a continuation of application Ser No 911 554 filed May 31 1978 and now abandoned CROSS REFERENCE TO RELATED APPLICATION The subject matter of the present application is re lated to that disclosed in co pending and commonly assigned U S patent application Ser No 337 296 co filed on Jan 5 1982 entitled Apparatus and Method for Charging Batteries which application is a continu ation of U S patent application Ser No 911 268 filed May 31 1978 now abandoned FIELD OF THE INVENTION This invention pertains to battery chargers in general and specifically to a method and apparatus for charging batteries which permits any battery to be brought to its full state of charge at a very rapid rate and also at maxi mum efficiency without danger of damage to the bat tery or to the charger This invention will be described with particular reference to nickel cadmium batteries but it is also capable of charging many other types of batteries i
2. Maximum Slope and Maximum Voltage Sum respectively The Minimum Slope register is set to a large number while the imum Slope and Maximum Voltage Sum registers are each set to a large negative number such as 10 000 The use of these registers will be described below Thereafter the program moves to block 130 designated loop 2 This is a common return location to which the program is redirected after each of several alternative sequences have been completed In this in stance after the three registers have been initialized as described above the program moves through block 130 to block 132 In block 132 the stated interrogation is has two seconds gone by Block 132 together with the closed loop 133 for a negative response to this interrogation simply amount to a delay circuit to prevent the program from proceeding until a period of time arbitrarily se lected to be two seconds has passed since the last time that the time register was incremented in accordance with block 114 After each such increment a two sec ond timer is restarted and it runs while the computer program proceeds through its next sequence of steps At the end of the sequence the program returns to block 130 and the computer is held in the delay loop until two seconds have passed The time register is then incre mentally increased and the computer proceeds to its next sequence of steps The program the
3. controlling the supply of electrical energy to the battery on the basis of the so determined occur rence 3 A method of rapidly and efficiently charging a battery of the type in which the voltage characteristic thereof varies with the state of charge of the battery and in which the voltage characteristic varies with time during charging to exhibit an inflection point prior to the battery attaining substantial full charge the inflec tion point characterized by a change in sign of the sec ond derivative of the voltage characteristic variation with time from a positive to a negative value the method comprising the steps of supplying electrical energy to the battery for charg ing thereof monitoring said voltage characteristic of the battery during charging analyzing the variation of said monitored voltage characteristic with time to determine the occur rence of the inflection point exhibited prior to the battery attaining substantial full charge by deter mining a change in sign from a positive to a nega tive value of the second derivative of said voltage characteristic variation with time and controlling the supply of electrical energy to the battery basis of the so determined rence 4 A method of rapidly and efficiently charging a battery of the type in which the current characteristic drawn by the battery during charging varies with the state of charge of the battery and in which the current ch
4. 4 392 101 5 1983 Sheet 3 of 6 U S Patent AV1dSIQ J 2031 ASt I i I s E U S Patent Jul 5 1983 Sheet 4 of 6 4 392 101 Loop 133 FIG 5 START Y SECONDS Y N TOTAL TIME GONE BY TO 2 INCREMENT THE TOTAL TIME 122 REGISTERS 124 INITIALIZE MIN 18 SLOPE A LARGE Y STOP NUMBER CHARGING 126 INITIALIZE MAX SLOPE TO A SMALL NUMBER 128 130 INITIALIZE VOLT SUM FIG 6 LOOP 2 SMALL NUMBER READ THE VOLTAGE AND Y i PUT IN TEMPSUM lt 145 CALCULATE pS STOP DIFF K CHARGING 138 139 Y N STOP 146 CHARGING 15 IT TIME N TO DO A SLOPE Y CALCULATION 2 142 140 15 TEMPSUM gt VOLT SUM y TEMPSUM IN VOLT SUM U S Patent Jul 5 1983 Sheet 5 of 6 _ 4 392 101 FIG 7 148 SUM IN OLDSUM 150 IN SUM SLOPE SLOPE lt 0 152 154 CALCULATE 164 SUM OLDSUM N Y AND PUT IN SLOPE Is 5156 237 FURTHR IN MIN SLOPE Y SLOPE 202 FIG 8 FIG 9 IS SLOPE MIN SLOPE K4 20 SLOPE MAX SLOPE t 5 gt 0 oe a U S Patent Jul 5 1983 Sheet 6 of 6 4 392 101 16 10 lt re gt
5. amplifier 1 from a voltage divider comprising the parallel resistors Rs3 and a binary coded combination of the resistor 5 20 25 35 40 45 55 60 65 14 ladder as selected the computer Resistors R44 Rso each have values which twice the value of the preceding sequential resistor The computer under the instruction of its program as will be described here inafter selects an initial minimum value for example by turning on only This develops a voltage across IC gt c which is compared in IC3 to the signal received from the battery If this minimum voltage supplied from the computer is not equal to or greater than the battery voltage then successively increased values are tried by the computer until a match is reached This information is communicated back to the computer from the output of IC3 and the computer uses the last input to com parison circuit as the battery voltage In reset circuit 28 the comparator amplifies a signal derived from the 25 volt supply and compares it to a 5 volt reference If the 25 volt signal goes below approximately 10 volts as would occur upon the re moval of power from the system either due to a power failure or due to the operator unplugging the charger the output signal from the comparator instructs the computer to return all of its programming functions to the initial conditions that is those which must b
6. ance capability of the battery that is of its internal and external connections and of its internal plates and also by its internal ion transit time This level is generally given by the manufacturer For example sub C size nickel cadmium batteries available from General Elec tric can accept fast charge current at the 4C rate lead acid batteries of the sealed type available from Gates Energy Products Inc can accept fast charge current at the 0 3C rate Even though batteries could accept such fast charge currents presently known chargers are not capable of shutting off the fast charge current at the proper mo ment and even batteries which structurally could accept fast rate currents can only be charged at the trickle charge rate In general any charge rate above the 5 hour rate 0 2C has previously required a special bat tery design Because of the accuracy with which the present in vention determines the full charge level the present charging method permits the use of fast charge currents with many batteries which could previously be charged only by slow trickle charge rates This is particularly 25 true in the categories of nickel cadmium batteries and lead acid batteries which predominate among the re chargeable battery couples presently available Thus the present method permits essentially all of nickel cadmium batteries presently in use by consumers to be recharged in a time on the order of 1 hour Lead acid batteri
7. 120 240 volt AC input 10 20 volt AC output 1 5 amps LED 7 segment light emitting diode display common cathode LED2 7 segment light emitting diode display common cathode Slow blow fuse amp F2 Fuse 5 amps TH Thermistor RL28F1 5 Switch 3 pole double throw 3 amp contacts 52 Switch SPST N O momentary 53 Switch 5 5 54 Switch SPST Ss Switch SPST FLOW CHART MICROCOMPUTER OPERATION FIGS 5 8 comprise a flow chart of the basic opera tions which are performed within the microcomputer The flow chart illustrated in FIGS 5 8 summarizes the program steps and has been prepared at a level of detail which would permit an experienced programmer to complete the detaled implementation of this invention in a type 8048 microcomputer but which at the same time is not so detailed as to require repetitious descrip tion of iterative steps As has previously been noted when power is first applied to the system the reset circuit 26 automatically 10 15 20 25 30 35 45 50 55 60 65 16 sets all operations of the computer 18 to an initial reset mode In the flow chart the start block 110 signifies the application of the start signal to the com puter due to the closing of the start switch 16 of FIG 2 Immediately the internal total time register is set at 0 This is indicated by block 112 The further steps of the process shown in FIGS 5 8 are then performed by the microcomputer The next
8. Dio are provided to pro tect the computer 18 Alternatively this selection could be provided automatically by using different sets of unique terminals to which different battery types are connected Also the entire selection circuit 24 might be omitted if the charger is intended for use with only a single battery type Temperature cut off circuit 26 comprises a safety circuit to prevent operation at temperatures outside a predetermined permissible range In the particular ar rangement shown the voltage at the midpoint of the voltage divider comprising resistor R36 and thermistor TH controls the input to both sides of the comparator amplifier In the case of a high temperature e g 125 F the resistance of TH is low which reduces the voltage input to the positive side of in the case of low temperature e g 25 F the resistance of TH is high which increases the voltage at the negative side of Either extreme produces low output signal from 1 which instructs the computer to discontinue charg ing In subcircuit 22 the battery develops an input signal across the voltage divider R4 Rg7 which is amplified in operational amplifier 1224 The resistances R64 Res and and capacitors and Cio comprise a filter on the output of ICz4 and this signal 15 used as one input to comparator amplifier IC3 At the same time another input to comparator IC3 is developed through operational
9. No 98 270A pub lished by the Intel Corporation of Santa Clara Calif 95051 When the start switch 16 is actuated which could be accomplished automatically on connection of a battery to the output lines the microcomputer 18 first allows 40 45 60 65 12 the full charge current to be applied to the battery through the amplifier 12 for a predetermined period of time usually between 30 and 60 seconds which allows the battery to be brought through the segment of FIG 1 identified as Region I For nickel cadmium batteries of the sub C size the preferred time is 40 seconds This application of power can be at full rated current since even a defective battery or a fully charged battery will not be seriously damaged by the application of this power for this short an interval The application of power is controlled by the micro computer 18 by its selection of the appropriate current control resistor 20 through which to apply the input signal to the current amplifier 12 After an appropriate period of time has passed as described above the microcomputer 18 makes use of the analog to digital converter A D 22 to de termine the battery voltage The converter 22 is prefer ably of the successive approximation type in which successive approximate digital values of battery voltage generated by the microcomputer 18 are compared to the actual battery voltage until a close approximation is achieved This information is then fed bck into the
10. and efficiently charging a battery of the type having a characteristic associated therewith that varies with the state of charge of the battery and in which the variation of the characteristic with time during charging exhibits a first and a succeed ing inflection point prior to the battery attaining a pre determined charge level the method comprising the steps of supplying electrical energy to the battery for charg ing thereof monitoring said characteristic of the battery during charging analyzing the variation of said monitored characteris tic with time to determine the occurrence of the succeeding inflection point and controlling the supply of electrical energy to the battery on the basis of the so determined occur rence 8 A method of rapidly and efficiently charging a battery of the type having a characteristic associated therewith that varies with the state of charge of the battery and in which the variation of the characteristic 4 392 101 29 with time during charging exhibits opposed pair of Inflection points prior to the battery attaining substan tial full charge the method comprising the steps of supplying electrica energy to the battery for charg ing thereof monitoring said characteristic of the battery during charging analyzing the variation of said monitored characteris tic with time to determine the occurrence of last inflection point of the opposed pair of inflec tion points a
11. and for controlling said supply means to control the supply of electrical energy to the bat tery 35 An apparatus for charging a battery of the type having a characteristic associated therewith that varies with the state of charge of the battery and in which the variation of the characteristic with time during charg ing exhibits a first and a succeeding inflection point prior to the battery attaining substantial full charge said apparatus comprising means for supplying electrical energy to the battery for charging thereof and means connected to said supply means for monitoring the characteristic during charging for analyzing the so monitored characteristic with time to deter mine the occurrence of the succeeding inflection point and for controlling said supply means to controi the supply of electrical energy to the bat tery 36 An apparatus for charging a battery of the type having a characteristic associated therewith that varies with the state of charge of the battery and in which the variation of the characteristic with time during charg ing exhibits an opposed pair of inflection points prior to the battery attaining a predetermined charge level said apparatus comprising means for supplying electrical energy to the battery for charging thereof means connected to said supply means for monitoring the characteristic during charging means connected to said monitoring means for ana lyzing the so monitored characteri
12. at that point this being accomplished without regard to the actual voltage of the battery individual cell characteristics individual charging history of the particular battery or the actual ambient temperature In another aspect it is an object of this invention to provide a universal method for rapidly charging various types of batteries and to further provide an apparatus which selects the proper sub method required to rap idly charge a battery of a particular type In a further aspect an object of this invention is the provision of an apparatus for applying charge current to a battery and determining accurately the moment when a battery has reached its full state of charge Still another object of this invention is the provision of an improved method and apparatus for fast charging batteries which recognizes accurately when a battery has reached a full state of charge which thereupon terminates the fast charge mode and which subse quently supplies a topping charge current to the battery to compensate for batteries which due to a particular charging history may produce a false indication of full state of charge Still another object of this invention is the provision of a method and apparatus for charging batteries which identifies intermediate states in the charging cycle of a particular battery and adjusts the rate of charging cur rent applied so as to maintain the applied current at the optimum level for rapid efficient and n
13. electrical energy to the battery upon the first occurrence of a one of a said first mentioned inflection point 0 15 20 25 30 40 45 55 60 65 32 b control indicium for reducing the supply of electrical energy to the battery 18 method of rapidly and efficiently charging battery type having a characteristic associated therewith that varies with the state of charge of the battery and in which the variation of the characteristic with time during charging exhibits a sequence of a first and a successive inflection point prior to the battery attaining substantial full charge the method comprising the steps of supplying electrical energy to the battery for charg ing thereof monitoring said characteristic of the battery during charging analyzing the variation of said characteristic with time to determine the occurrence of said sequence of a first and a successive inflection point and to determine the occurrence of a predetermined vari ation of said characteristic that comprises a control indicium for reducing the supply of electrical en ergy to the battery and reducing the supply of electrical energy to the battery upon the first occurrence of a one of a said sequence of a first and a successive inflection point b control indicium for reducing the supply of electrical energy to the battery 19 A method of rapidly and efficientiy charging a nickel ca
14. indicate that charging is in process In the case of a complex battery charger used by a qualified technician the display circuit may provide for the display of a variety of different information which may be of use to the technician in evaluating the condi tion of the battery FIGS 3 and 4 together comprise a schematic dia gram of one suitable embodiment of FIG 2 The respec tive segments of the circuit as identified in FIG 2 are enclosed in dotted line boxes identified by correspond ing numbers In the specific embodiment of these figures a conven tional line plug 8 is provided for connection to a source of power The power supply 10 includes a transformer Ti and a full wave bridge rectifier made up of diodes Di D4 The output from the bridge which may be approximately 20 volts D C is applied through ampli fier 12 and switch 14 to the battery shown in dotted 4 392 101 13 line illustration portion of the bridge output is also applied to a filter made up of resistor Ri diode Ds and capacitor C and to voltage regulator IC Regulated voltages of 25 volts and 5 volts for use in the other portions of the circuit are taken at the indicated output terminals The resistor controlled current amplifier 12 operates according to outputs taken from the microcomputer 18 through current control resistors 20 shown in FIG 4 In accordance with its internal program the computer 18 selects a current level by c
15. mi crocomputer 18 which then proceeds to execute its program so as to charge the battery in accordance with the method described above In addition to the basic elements of the block diagram already mentioned the circuit should provide certain additional features If the battery charger is of a type adapted to handle a variety of battery sizes and types a battery type selection circuit 24 is included which se lects the specific program for the given battery type from several stored in the computer This may be done either by the operator or automatically by some identifi cation means such as particular terminal types provided on the battery itself The system also preferably includes a temperature cutoff circuit 26 The purpose of this circuit is to pre vent charging if the ambient temperature is either so low or so high as to cause damage to the battery or to the charging circuit itself Reset circuit 28 is provided to reset the entire mi crocomputer program to time zero as soon as power is supplied to the system or in the event of a power inter ruption This is done to prevent unpredictable charging effects which might occur if the computer were to be initiated at an incorrect point in its program Finally the operator display circuit 30 provides for communicating such information as may be appropriate to the operator In the case of a simple charger for use by a consumer the display 30 may consist only of an illumination lamp to
16. points Control ling the proper charge mode may then involve simple conversion from a high rate fast charge mode to a suit able maintenance mode which prevents or compensates for self discharge of the battery In other cases proper control of the battery charging sequence may involve a combination of inflection point determination with other analyses of the variation of voltage with respect to time or of the actual voltage at a particular time In all of these cases a significant aspect of this invention is the determination of inflection points in the curve _ which represents the electrochemical potential of the battery as a function of time By way of illustration of the above general method the following specification describes appropriate varia tions on the specific type of analysis which may be 4 392 101 5 performed to determine the inflection points and also describes variations in the analysis which may be neces sary to accommodate differing modes of battery charg ing such as constant voltage constant current etc Spe cific applications include techniques for charging such batteries as nickel cadmium lead acid and silver cad mium In further accordance with the present invention apparatus is described for implementing these various methods In a preferred embodiment the apparatus includes a suitable source of electrical energy an analyt ical device for determining the necessary controlling parameters a
17. prevent even the possibility of such degradation a surcharge current of 0 1C can be applied for a few hours after the second inflection point has been reached The above described maintenance cycle may then begin In the case of lead acid batteries as has previously been discussed an interval of low rate charging may be useful to completely charge the battery thereafter an appropriate maintenance mode is used to compensate for self discharge In other battery couples other finish ing techniques may be utilized as appropriate SUMMARY The foregoing specification describes battery charging method which basically utilizes the inflection point analysis method to identify very precisely signifi cant points in the variation of the electrochemical en ergy in a battery during its charge cycle Accordingly the appended claims are broadly directed to this method and are intended to include all variations of this method as may be obvious to those skilled in the art Among the many possible variations it should be noted that the above apparatus particularly described has made use of an approximation technique for deter mining the occurrence of an inflection point It is of course fully within the contemplation of this invention to use this or other approximation techniques for locat ing critical points in a profile or to provide a circuit which is capable of directly monitoring the second derivative for a change in sign Similar va
18. so monitored characteristic with time to deter mine the occurrence of the inflection point that occurs just prior to the battery attaining substantial full charge and the occurrence of a predetermined variation of the monitored characteristic that com prises control indicium for controlling said supply means and for controlling said supply means to control the supply of electrical energy to the bat tery 45 An apparatus for charging a battery of the type having a characteristic associated therewith that varies with the state of charge of the battery and in which the variation of the characteristic with time during charg ing exhibits an inflection point prior to the battery at 30 35 45 50 55 60 65 38 taining a predetermined charge level and another inflec tion point that precedes first mentioned inflection point said apparatus comprising means for supplying electrical energy to the battery for charging thereof means connected to said supply means for monitoring the characteristic during charging means connected to said monitoring means for ana lyzing the so monitored characteristic with time to determine the occurrence of the first mentioned inflection point and the occurrence of a predeter mined variation of the monitored characteristic that comprises control indicium for controlling said supply means and means connected to said supply means to control the supply of electric
19. supply means for monitoring the voltage characteristic during charging for ana lyzing the so monitored characteristic with time to determine the occurrence of the last inflection point of the opposed pair and the occurrence of a predetermined variation of the monitored charac teristic that comprises control indicium for control ling said supply means and for controlling said supply means to control the supply of electrical energy to the battery 48 The apparatus claimed in claim 29 31 33 35 38 or 44 wherein said second mentioned means comprises a stored program controlled means 49 The apparatus claimed in claim 48 wherein said stored program controlled means comprises a stored program processor controlled means 50 The apparatus claimed in claim 48 wherein said stored program controlled means further comprises means for analyzing the so monitored characteristic with time to determine the occurrence of a prede termined variation of the monitored characteristic that comprises a control indicium for controlling the supply of electrical energy to the battery 4 392 101 39 51 The apparatus claimed in claim 50 wherein said means for analyzing to determine the occurrence of a control indicium comprises means for determining the occurrence of a one of the variation of the characteristic ceasing to be mono tonic the value of the characteristic decreasing to prede termined limtt the value of the characteris
20. the additional application of a surcharge after the second inflection point has been reached This is due to the internal chemistry of the lead acid battery which causes the final addition of energy to occur at a slower rate than in the case of a nickel cadmium battery Therefore the optimum charge method for lead acid batteries is to apply the inflection point method of analysis as previ ously described and when the second inflection point between Regions III and is identified the microcom puter is instructed to shift charging rate to an inter mediate level This intermediate rate is then applied for a fixed period of time In general lead acid batteries have structure which permit the constant current to be about 2C in 4 392 101 _ 0 15 20 25 35 45 50 60 65 22 fast charge mode The surcharge rate selected is gener ally about one half of the full charge rate The fixed period of time is calculated by determining how long it takes to add 25 of the full battery capacity to the battery at the surcharge rate At the end of that time the battery charger automatically terminates the full charge mode and begins a maintenance mode cycle which simply compensates for self discharge FIG 12 illustrates the charging curve for a lithium battery having an iron sulfide electrode In this case the inflection points occur much earlier in the charge cycle and there are almost no di
21. the curve traced by the change in current with time Actually the term constant voltage is applied equally to systems in which the actual applied voltage is constant throughout the charge period to systems in which the current is always measured when the voltage is at a preselected value or to systems in which a pulsat ing applied voltage has a constant average and in which the measured current is correspondingly averaged All of these systems produce a curve of current against time which has the same general form and which may be treated by means of the same inflection point analysis accordingly this profile is referred to herein as the current profile In the particular case of a nickel cadmium battery the current profile is illustrated in FIG 14 In fact this curve is exactly the same in form as that shown in FIG 1 except that the entire curve is inverted Thus the method of inflection point analysis as applied to this profile is exactly the same as has been described in con nection with FIG 1 except that all of the pertinent analyses regarding signs direction of change etc are reversed Initially the current decreases in a manner corresponding to that in Region I in which the voltage of FIG 1 increased This is followed by an interval in which the current decreases slowly this is normally the longest time interval and the one in which the major increase occurs in the energy stored in the battery This correspond
22. with time of a characteristic of the battery which is indicative of the variation in stored chemical energy as the battery is charged The method specifically comprises analyzing the profile for the occurrence of a particular series of events preferably including one or more inflection points which precisely identify the point in time at which the application of a fast charge rate should be discontinued Additional methods of analysis provide for termination or control of the charging current upon the occurrence of other events such as limiting values on time voltage or voltage slope or a negative change in the level of stored energy Apparatus for performing these methods comprises a suitable power supply and a microcomputer for analyz ing the profile and controlling the power supply 64 Claims 14 Drawing Figures NICKEL CADMIUM BATTERY CHARGING CYCLE U S Patent ul 5 1983 Sheet 1 of 6 4 392 101 VOLTAGE s NICKEL CADMIUM BATTERY CHARGING CYCLE FIG 2 TO BATTERY A C POWER 14 FY SUPPLY EZE _ CONTROLLED ali VOLTAGE D C CURRENT AMP SWITCH 16 CURRENT START SWITCH CONTROL RESISTORS BATTERY TYPE COMPUTER CONVERTER 24 SELECTION 8048 CIRCUIT 588 26 30 28 TEMPERATURE OPERATOR RESET CUT OFF DISPLAY CIRCUIT CIRCUIT CIRCUIT 4 392 101 Jul 5 1983 Sheet 2 of 6 U S Patent 1 Wg gi
23. 3 Of course in devising the method and system for each of the batteries mentioned in connection with FIGS 10 13 the additional safeguards to prevent seri ous overcharge and to shut the system off in the event that either the battery or the charger is defective are also included thus a maximum total time limit a maxi mum voltage limit a negative change in voltage and a negative slope limit may all be included as appropriate CURRENT PROFILE ANALYSIS The description of this invention as set forth above has been given in terms of the battery analysis method which applies when the state of charge of the battery is measured under constant current conditions In addi tion it is possible to charge the battery in a constant voltage mode to measure the change in current with the passage of time and to apply similar methods of inflection point analysis to the resultant profile of changing current with time This technique involves the selection of a constant voltage to be applied to the bat tery by the charger the voltage chosen is selected so that the current which it applies to the battery during the bulk of the charge time is reasonable on the basis of the same parameters as described in the case of the constant current charger namely the charge efficiency the cost and the time required to fully charge a dis charged battery Once again this application of con stant voltage produces a known and predictable form for
24. 3 plus any integral number of minutes the se quence goes on to block 154 where the difference in 4 392 101 19 value between the Sum register and Oldsum register is calculated and put into a register location called Slope The sequence then continues to block 156 In step 156 the register Min Slope which was set to an initial large value in step 124 is used Specifically the value in Slope is subtracted from the value in Min Slope and the result tested to see if it is greater than or equal to 0 If the Slope register is less than the previous Minimum Slope register which had been initialized to a very large number the Slope value is put into the Minimum Slope register Thus once per minute each time through this program sequence a slope is calculated and a check is done to see if the new value of slope is less than the previous lowest slope reading If it is this new slope is put into the Minimum Slope register in block 158 and the sequence continues to block 160 If the newest slope is not less than the minimum slope the sequence also goes to block 160 Here the slope reading just taken is subtracted from the Max Slope register which was initialized at block 126 to a very small number If this difference is less than 0 meaning that the new value in the Slope register is greater than the previous value in the Max Slope register then t
25. United States Patent 9 4 392 101 Jul 5 1983 11 45 Saar et al 54 METHOD OF CHARGING BATTERIES AND APPARATUS THEREFOR 75 Inventors David A Saar Timonium Richard Waiter Baltimore both of Md 73 Assignee Black amp Decker Inc Newark Del 2 Appl No 337 174 22 Filed Jan 5 1982 Related U S Application Data 63 Continuation of Ser No 911 554 31 1978 aban doned 51 Int Cl 2 sansaq H01M 10 44 152 U S Ch Jawa sanaw 320 20 320 39 58 Field of Search 320 20 22 24 320 39 40 48 56 References Cited U S PATENT DOCUMENTS 3 289 065 11 1966 Dehmelt et al 320 40 3 424 969 1 1969 3 660 748 5 1972 Clayton 3 703 675 11 1972 Alric et al 320 31 3 794 905 2 1974 Long 320 20 3 864 617 2 1975 Smith et al 320 23 3 890 556 6 1975 Melling et al 3 938 021 2 1976 Kosmin 320 40 4 034 279 7 1977 Nillson 320 20 BATTERY VOLTAGE 4 114 083 9 1978 Benham etal 4 118 661 10 1978 Siekierski FOREIGN PATENT DOCUMENTS 1438002 10 1968 Fed Rep of Germany 320 46 Primary Examiner William M Shoop Attorney Agent or Firm R B Sherer Harold Weinstein E D Murphy 57 ABSTRACT A method of fast charging batteries by means of precise analysis of the profile of the variation
26. al energy to the battery in re sponse to said analyzing means 46 An apparatus for charging a battery of the type having a characteristic associated therewith that varies with the state of charge of the battery and in which the variation of the characteristic with time during charg ing exhibits a sequence of a first and a successive inflec tion point said apparatus comprising means for supplying electrical energy to the battery for charging thereof means connected to said supply means for monitoring the characteristic during charging means connected to said monitoring means for ana lyzing the so monitored characteristic with time to determine the occurrence of a sequence of the first and successive inflection points and the occurrence of a predetermined variation of the monitored characteristic that comprises control indicium for controlling said supply means and means connected to said supply means to control the supply of electrical energy to the battery in re sponse to said analyzing means 47 An apparatus for charging a nickel cadmium bat tery of the type having a voltage characteristic associ ated therewith that varies with the state of charge of the battery and in which the variation of the voltage char acteristic with time during charging exhibits an opposed pair of inflection points said apparatus comprising means for supplying electrical energy to the battery for charging thereof and means connected to said
27. ance charge which is used to compensate for the internal self dis charge characteristics of all electrochemical cells in cluding nickel cadmium cells Nickel cadmium cells can self discharge as much as 10 to 30 per month depending on the storage temperature and the particu lar characteristics of the cell One method of mainte nance charging is to apply a low to medium charge current for a short period of time one or more times per day The preferred rate is a charging rate of C charge rate representing the same number of amperes of charge as the ampere hour rated capacity of the cell for 15 to 30 seconds every 6 hours This provides approxi mately twice the typical loss rate in ampere hours of the cell without causing any significant heating or pressure buildup in the cell The particular charge rate and par ticular choice of charged time to resting time can be varied over a very wide range The method is merely to replace the calculated or measured energy lost to self discharge of the cell CHARGING APPARATUS FIG 2 is a block diagram showing the major ments of electronic circuitry which are used in accor dance with this invention to implement the above de scribed charging method The flow of charging current in FIG 2 runs from an AC power input plug 8 connect able to an ordinary source of line current to a power supply 10 which converts the AC input to low voltage DC Next the current passes through a resi
28. and used by those familiar with batter ies and the art of battery charging to provide improved techniques of fast battery charging without departing from the spirit of the present invention In addition the present invention presents numerous subcombinations of this method which have not previ ously been known the many variations of these combi nations which will readily occur to those familiar with the battery and battery charging art are also intended to be included Particular emphasis has also been placed on the charging of nickel cadmium batteries and lead acid batteries in view of the importance of these couples The specific methods perfected for charging such bat teries are also fully within the contemplation of the present invention Finally a specific apparatus has been disclosed for performing the method of this invention A great many obvious variations of this apparatus will be readily ap parent which correspond generally to the alternative methods described It is fully intended that the appara tus claims in this application be extended to cover all such alternative embodiments of this basic apparatus We claim 1 A method of rapidly and efficiently charging a battery of the type having characteristic associated therewith that varies with the state of charge of the battery and in which the characteristic varies with time during charging to exhibit a plurality of inflection points prior to the battery attainin
29. any normal battery that is any battery which is not defec tive can be changed at a relatively high rate In using previously known battery charging methods it has been necessary to limit the application of high rate charging currents to batteries which are especially adapted to accommodate the inadequate shut off modes in use This is due to the fact that previous methods cannot stop the fast charge current at the proper moment and the various harmful effects previously noted can occur Only batteries designed to withstand these effects can be used and even such batteries experience shortened lives etc In contrast the method of the present invention pro vides such precise control over the application of en ergy to the battery that it can be used to fast charge even those batteries which were previously intended for charging only by slow rate methods The term trickle charge usually refers to a charge rate such that the battery receives its full charge only over a period of 12 to 24 hours Thus typical trickle chargers apply a current of between 0 05 and 0 1C In accordance with previous methods the terms fast charge or quick charge are generally applied to rates in excess of 0 2C that is charge rates which would charge a battery in less than 5 hours All batteries accept currents of the fast charge level for limited periods of time The upper limit for a particular battery is governed by the current accept
30. any nickel cadmium battery cell in a minimum time considering reasonable system cost Up to the present time rapid charging techniques for batteries have carried the risk of serious damage to the battery To help in avoiding this problem ordinary battery cells are usually manufactured for use in con junction only with so called trickle chargers which require some 16 24 hours to bring a battery from a substantially discharged state to approximately its fully charged state Even when this time penalty is accepted such chargers can be harmful to the battery cells over a long period of use Rapid chargers are available for nickel cadmium cells which will bring a battery to approximately full charge within approximately one hour However these char gers require the use of high priced cells manufactured by special techniques so that the cells are capable of withstanding the possible harmful effects of rapid charging This is due to the fact that the chargers cut off by one or another of the methods described above with their attendant inaccuracies INFLECTION POINT ANALYSIS In accordance with this invention a new method of controlling the battery charge process is provided which identifies exactly the conditions in the particular battery undergoing charge and correspondingly con trols the application of charge current Because of this new technique a high rate charge current can be ap plied to the battery so that the battery is bro
31. aracteristic varies with time during charging to ex hibit an inflection point just prior to the battery attain ing substantial full charge by determining a change in sign of the second derivative of said current characteris tic variation with time the method comprising the steps of supplying electrical energy to the battery for charg ing thereof i measuring said current characteristic drawn by the battery during charging analyzing the variation of said monitored current characteristic with time to determine the occur rence of the inflection point exhibited just prior to the battery attaining substantial full charge by de termining a change in sign of the second derivative of said current characteristic variation with time and 4 392 101 5 _ 0 20 25 45 55 65 28 controlling supply of electrical energy of the battery on the basis of the so determined occur rence 5 method of rapidly and efficiently charging a battery of the type in which the current characteristic drawn by the battery during charging varies with the state of charge of the battery and in which the current characteristic varies with time during charing to exhibit an inflection point prior to the battery attaining substan tial full charge the inflection point characterized by a change in sign of the second derivative of the current characteristic variation with time from a negative to a positive value the method comprising th
32. ation of the characteristic with time during charging exhibits an opposed pair of inflection points prior to battery attaining substantial full charge the method comprising the steps of supplying electrical energy to the battery for charg ing thereof monitoring said characteristic of the battery during charging analyzing the variation of said monitored characteris tic with time to determine the occurrence of a sequence of the opposed pair of inflection points and controlling the supply of electrical energy to the battery on the basis of the so determined sequential occurrence 13 A method for rapidly and efficiently charging a battery of the type having a voltage characteristic asso ciated therewith that varies with the state of charge of the battery and in which the variation of the voltage characteristic with time during charging exhibits inflec tion points prior to the battery attaining substantial full charge in which each inflection point is characterized by a change in sign of the second derivative of the voltage characteristic the method comprising the steps of supplying electrical energy to the battery for charg ing thereof monitoring said voltage characteristic of the battery during charging analyzing the variation of said monitored voltage characteristic with time to determine the occur rence of a sequence of inflection points character ized by a change in the sign of the second deriva tive of said vo
33. azardous condition by the continu ation of a maintenance charge mode after shut down of the high rate due to a negative voltage change VOLTAGE SLOPE ANALYSIS While the charge profile of nickel cadmium batteries does not lend itself to advantageous use of this tech nique other battery couples exhibit profiles wherein termination should be predicated upon the occurrence of a particular voltage slope Thus in a couple wherein Region V involves a slow downward drift of voltage rather than a sharp decrease as the nickel cadmium profile the occurrence of a negative slope is useful in the same manner as the absolute voltage change analysis just described VOLTAGE LEVEL ANALYSIS In some cases of dried or otherwise damaged nickel cadmium cells application of a charging current can cause the voltage to increase to a level significantly beyond the normal voltage of an operative cell Ac cordingly the apparatus of this invention includes the provision of a voltage level sensing means which termi nates charge if a predetermined level of voltage is en countered In other battery couples this may serve as a primary charge termination mode rather than as a sec ondary safeguard TIME ANALYSIS In other defective cells the application of a high charge current may simply be allowed to continue for an undue length of time because the energy is being converted to heat or to oxygen evolution etc In these instances the def
34. be adequate for example if a battery is damaged or defective or if a user inadvertently places a fully charged battery on charge In these cases the normal indicative points may not occur at all or they may possibly occur within the first period of time which the apparatus is not sam pling data In order to protect against these possibilities the present invention further includes the provision of specific controlling techniques or modes which may be used in combination with the basic method described above ABSOLUTE VOLTAGE CHANGE ANALYSIS A first of these techniques which can be incorporated is that of terminating the application of charging cur rent to the battery immediately upon the occurrence of a negative change of voltage By reviewing the curve of FIG 1 it will be noted that there is not point in the normal charge cycle when a negative voltage change occurs Thus if a negative voltage change is encoun tered it must mean that the battery is either defective or that it is already fully charged and that it has entered Region V of the curve Accordingly provision is pref erably included to terminate the high rate charge imme diately upon the occurrence of a negative voltage change Preferably the value of this change should be large enough so that termination is not inadvertently caused by inaccuracies in the monitoring equipment It is also noted that the absolute voltage change anal ysis is utilized to preve
35. be implemented in serveral ways 4 392 101 9 including the apparatus hereinafter described For other types of electrochemical cells or different types of charging systems other sequences of inflection points may be required but the detection of all of these types of second derivative sign changes and specific sequen ces of them are intended to be included within the scope of this general method One principal advantage of inflection point analysis is that it does not depend on the actual value of the volt age of the cell nor does it depend upon the value of the rate of change slope or voltage It is an analysis of those points where the rate of change of voltage that is the slope of voltage changes from decreasing to in creasing or from increasing to decreasing In turn these points are directly relates to the actual chemical occur rences within the battery being charged Thus determination of state of charge and hence the most appropriate time to terminate charge is dependent only upon very universal characteristics of such batter ies and not on the particular cell characteristics or char acteristics which might be due to the history of use such as storage or very heavy use It is thus more reliable and a more valid indication of the most appropriate time at which to terminate charge than previous methods _ In some cases the inflection point technique which is appropriate for normal conditions may not
36. ceeds K2 even in this Region is also indicative of a defective battery K2 may equal 25 milli volts per cell for nickel cadmium batteries The next stage in the process identified as block 146 interrogates the timing system to determine whether a slope calculation should be done This actually repre sents the beginning of the inflection point analysis previ ously described as will be clear from the following description of FIGS 5 and 6 the phrase Slope Calcu lation used in this program identifies the series of steps which locate the inflection points in the curve of FIG 1 As indicated in step 146 the slope calculation is per formed every minute beginning at an arbitrary time identified as K3 seconds is the time interval chosen to allow the battery to pass through the initial stage identified previously as Region I and is usually between 30 and 60 seconds K3 is preferably 40 seconds in the case of nickel cadmium batteries The first several times through the program the in terrogation of step 146 will be answered in the negative and as indicated the program returns to step 130 Thus until the total time registers equal the value K3 the program simply directs the computer to monitor the time and voltage to make sure that neither assigned maximum has been exceeded these checks being per formed at steps 116 and 134 138 respectively and also monitors the voltage for a negative drop in steps 140 144 Once the total t
37. ction point that precedes first mentioned inflection point said apparatus comprising means for supplying electrical energy to the battery for charging thereof and means connected to said supply means for monitoring the characteristic during charging for analyzing the so monitored characteristic with time to deter mine the occurrence of sequence of the preceding and the first mentioned inflection points and for controlling said supply means to control the supply of electrical energy to the battery 39 An apparatus for charging a battery of the type having a characteristic associated therewith that varies with the state of charge of the battery and in which the variation of the characteristic with time during charg ing exhibits a first and a succeeding inflection point prior to battery attaining a predetermined charge level said apparatus comprising means for supplying electrical energy to the battery for charging thereof means connected to said supply means for monitoring the characteristic during charging means connected to said monitoring means for ana lyzing the so monitored characteristic with time to determine the occurrence of a sequence of the first and the succeeding inflection points and means connected to said supply means for controlling said supply means in response to said analyzing means 40 An apparatus for charging a battery of the type having a characteristic associated therewith that varies wit
38. ction points characterized by a change in the sign of the second derivative of the voltage characteristic from a negative to a positive value and a succeed ing change in sign of the second derivative of the voltage characteristic from a positive to a negative 4 392 101 37 value and for controlling said supply means 10 control the supply of electrical energy to the bat tery 42 An apparatus for oiaren a battery of the type having a current characteristic associated therewith that varies with the state of charge of the battery and in which the variation of the current characteristic with time during charging exhibits inflection points prior to the battery attaining substantial full charge in which each inflection point is characterized by a change in sign of the second derivative of the current characteris tic said apparatus comprising means for supplying electrical energy to the battery for charging thereof and means connected to said supply means for monitoring said characteristic during charging for analyzing the so monitored characteristic with time to deter mine the occurrence of sequence of inflection points characterized by a change in sign of the second derivative of the current characteristic from a positive to a negative value and a succeed ing change in sign of the second derivative of the current characteristic from a negative to a positive value and for controlling said supply means to contro the supply o
39. dmium battery of the type having a character istic associated therewith that varies with the state of charge of the battery and in which the variation of the characteristic with time during charging exhibits an opposed pair of inflection points prior to the battery attaining substantial full charge the method comprising the steps of supplying electrical energy to the battery for charg ing thereof monitoring said characteristic of the battery during charging analyzing the variation of said characteristic with time to determine the occurrence of said opposed pair of inflection points and to determine the occur rence of a predetermined variation of said charac teristic that comprises a control indicium for reduc ing the supply of electrical energy to the battery and reducing the supply of electrical energy to the battery upon the first occurrence of a one of a said opposed pair of inflection points b a control indicium for reducing the supply of electrical energy to the battery 20 The method claimed in claim 16 17 18 or 19 wherein said control indicium for reducing the supply of electrical energy to the battery comprises the occur rence of a one of the variation of said characteristic ceasing to be monotonic the value of said characteristic decreasing to a prede termined limit the value of said characteristic increasing to a prede termined limit the slope of the variation of said characteristic attai
40. e battery will be either over or under charged Most other charging methods which have been used to date are based on combinations of one or more of the above techniques While some problems can be avoided by these combinations at least some of them still exist Even the best fast charge systems require expensive cell constructions but the additional cost only serves to delay the battery deterioration which is caused by the charging system more recent technique illustrated by U S Pat 4 052 656 seeks the point at which the slope of the voltage versus time curve for a given battery is zero However even this technique is subject to difficulties it may detect another point at which the voltage slope is zero but at which the battery is only partially charged in addition even if it properly locates the zero slope point which is close to full charge this inherently over charges the battery and will cause battery deterioration due to heating All of the battery charging systems of which we are presently aware embody one or another of the above techniques and are subject to one or more of the above listed defects This is true despite the fact that most currently known battery chargers are designed to be 3 used with only one type of battery and in general with only one selected number of battery cells of that partic ular type The concept of a battery charger which can accurately and rapidly deliver full charge to a var
41. e steps of supplying electrical energy to the battery for charg ing thereof monitoring said current characteristic drawn by the battery during charging analyzing the variation of said monitored current characteristic with time to determine the occur rence of the inflection point exhibited prior to the battery attaining substantial full charge by deter mining a change in sign of the second derivative of said current characteristic variation from a nega tive to a positive value and controlling the supply of electrical energy of the battery on the basis of the so determined occur rence 6 method of rapidly and efficiently charging a battery of the type having a characteristic associated therewith that varies with the state of charge of the battery and in which the variation of the characteristic with time during charging exhibits an inflection point prior to the battery attaining substantial full charge and another inflection point that precedes the first men tioned inflection point the method comprising the steps of supplying electrical energy to the battery for charg ing thereof monitoring said characteristic of the battery during charging analyzing the variation of said monitored characteris tic with time to determine the occurrence of the first mentioned inflection point and controlling the supply of electrical energy to the battery on the basis of the so determined occur rence 7 method of rapidly
42. e used when a new charge cycle is initiated This can occur either during power down as the power is falling from normal input to zero due to a power failure or during power up as the power is building from zero 10 its nor mal level when the system is first connected to a power source In either case this system is useful to ensure that the computer does not begin a cycle at some indetermi nate midpoint in its cycle with inappropriate informa tion stored in its memory The display system 30 is utilized by the computer to communicate appropriate information to an operator As illustrated the display preferably comprises two seven segment display elements and transistors Q4 and Qs which form conventional strobing control which enables eight output lines to control both displays Al ternatively the display might comprise simply a single indicator lamp Finally element 14 FIG 3 comprises a charge test switch In the normal charge position S14 and 51 con nect the current controlled amplifier 12 and resistor network items 12 and 20 of FIG 2 so that current from power supply 10 is supplied through S44 to transis tors and Q2 to switch 51 to the battery with a return path through resistor Rs In the test position the battery is connected through Si to transistors Q gt through switch Sic to resistor and returning through resistor Rs to the battery For example this could allow the system to be used to dischar
43. ect in the cell may prevent the inflec tion points from occurring and a maximum time cutoff is provided In each of the above cases the exact quantity chosen for the negative voltage change for the negative change in voltage slope for the absolute level of volt age reached or for the maximum time reached is of course a predetermined number based on the type of cell for which the particular charger is intended MAINTENANCE CHARGE MODE After the main charge regime is terminated by one or more of the above five methods of analysis it is pre ferred to proceed into two other charge regimes The first of these is a programed overcharge or surcharge to insure that all possible active material in the cell is fully converted to the charged state and that all possible capacity in the cell will be available to the user The preferred method of overcharge or surcharge is to charge at a relatively low charge rate for a fixed amount of time depending on the type and size of the cell This guarantees that the cell is given a full amount of addi tional charge but at a low enough rate to avoid damage 4 392 101 The fixed time also means that the cell is not subject to long periods of time of overcharge which would subject the cell to increased internal pressures and heat which would eventually damage internal structures such as separators At the end of the surcharge or overcharge period it is very desirable to provide only a mainten
44. energy to the battery for charg ing thereof monitoring said electrical characteristic of the battery during charging analyzing the variation of said monitored characteris tic with time to determine the occurrence of the inflection point exhibited just prior to the battery attaining substantial full charge and discontinuing the supply of electrical energy to the battery on basis of so determined occur rence 61 The method claimed in 60 wherein said discontinuing step further comprises discontinuing the supply of electrical energy to the battery and subsequently supplying electrical en ergy to the battery at a predetermined maintenance rate not less than the internal rate of the battery 62 The method claimed in claim 1 2 3 4 7 15 19 60 wherein said supplying step further comprises supplying the electrical energy to the battery at a rate greater than 0 2 C 63 The method claimed in claim 1 2 3 4 7 18 19 or 60 wherein said monitoring step further comprises monitoring the characteristic on a periodic basis 64 The method claimed in claim 60 wherein said discontinuing step further comprises discontinuing the supply of electrical energy to the battery and subsequently supplying electrical en ergy to the battery for a selected time period on a recurring basis k 65
45. eral method of this invention provides for the identification of un usual conditions which may occur in some cases and which require charge termination to protect either the battery or the charger furthermore this method pro vides for the application of a topping charge in appro priate cases and for the application of a maintenance charge to keep the battery at full charge all of these being accomplished without danger of damaging either the battery the charger All of these objectives accomplished regardless of the actual voltage of the battery despite wide variation in individual cell charac teristics despite previous harmful charging history in the case of a particular battery and despite wide varia tions in the ambient temperature to which the battery and or the charger may be exposed In particular the present invention is based on the discovery that the electrochemical potential of a battery exhibits specific types of nonlinear changes of its value with respect to time as the battery is charged The in vention is further based on the discovery that the true charge state of the battery during charging may be analyzed by noting inflection points which occur as the electrochemical potential changes with respect to time In the case of specific batteries proper charging may involve determining the occurrence of either one or more of such inflection points or of determining a par ticular sequence of ordered inflection
46. es of the gal type can be charged in a time on the order of 2 hours those of the liquid type can be even more quickly charged In general terms the present invention permits the application of a high rate that is a rate in excess of 0 2C and up to the rated current acceptance level of the battery normal batteries so charged by the system of the present invention will receive a full charge and will not be damaged FINISH MODE In the case of nickel cadmium batteries the inflection point analysis described above brings a battery to essen tially 100 charge Thus when the second inflection point has been reached the charger can shift into a maintenance mode in which short pulses of high rate charging current are applied periodically to compensate for self discharge For example a 1C current may be applied for 15 seconds every 6 hours Other mainte nance cycles might be used if desired In actual practice repetitive charging of the battery to exactly the second inflection point may cause minute reversible degradation because this point occurs a small fraction of a percentage point below 100 charge This degradation may be reversed when the battery is left on maintenance or when the operator occasionally places the battery on charge even though it is not discharged This drives the voltage slightly into Region V of FIG 1 so that cut off occurs in accordance with block 145 of FIG 6 which reverses the degradation To completely
47. etermine the occurrence of said inflection point that occurs just prior to the battery attaining substantial full charge and to determine the occur rence of a predetermined variation of said charac teristic that comprises a control indicium for reduc ing the supply of electrical energy to the battery and reducing the supply of electrical energy to the battery upon the first occurrence of a one of a said inflection point b a control indicium for reducing the supply of electrical energy to the battery 17 method of rapidly and efficiently charging a battery of the type having a characteristic associated therewith that varies with the state of charge of the battery and in which the variation of the characteristic with time during charging exhibits an inflection point just prior to the battery attaining a predetermined charge level and at least one other inflection point that precedes said first mentioned inflection point the method comprising the steps of supplying electrical energy to the battery for charg ing thereof monitoring said characteristic of the battery during charging analyzing the variation of said characteristic with time to determine the occurrence of said first men tioned inflection point and to determine the occur rence of a predetermined variation of said charac teristic that comprises a control indicium for reduc ing the supply of electrical energy to the battery and reducing the supply of
48. f electrical energy to the bat tery 43 An apparatus for charging a nickel cadmium bat 5 20 25 tery having a voltage characteristic associated there with that varies with the state of charge of the battery and in which the variation of the voltage characteristic with time during charging exhibits an inflection point prior to the battery attaining substantial full charge and another inflection point that precedes the first men tioned inflection point said apparatus comprising supply means for supplying electrical energy to the battery for charging thereof and stored program controlled means connected 10 said supply means for monitoring the characteristic during charging for analyzing the so monitored characteristic with time to determine the occur rence of the first mentioned inflection point and for controlling said supply means to control the supply of electrical energy to the battery 44 An apparatus for charging a battery of the type having a characteristic associated therewith that varies with the state of charge of the battery and in which the variation of the characteristic with time during charg ing exhibits an inflection point just prior to the battery attaining substantial full charge said apparatus compris ing means for supplying electrical energy to the battery for charging thereof and means connected to said supply means for monitoring the characteristic during charging for analyzing the
49. farads 35 volts R40 1 ohm 1 watt C3 10 microfarads 35 volts 1k ohm 1 watt 1 microfarads 35 volts R42 1 8k ohm 1 watt Cs 1 microfarads 35 volts 5k ohm 1 watt 20 picafarads 35 volts 10k ohm 4 watt C7 10 microfarads 35 volts R45 20k ohm 4 watt Cg microfarads 35 volts R46 40k ohm 1 watt Co 10 microfarads 35 volts R47 80k ohm watt 10 microfarads 35 volts Rag 160k ohm 1 watt Di 3 amp 50 volts R49 320k ohm 4 watt D2 3 amp 50 volts Rs 640k ohm 1 watt D3 3 amp 50 volts R52 270 ohm 4 watt D4 3 amp 50 volts Trimpot 3k ohm Ds 1 amp 50 volts R54 10k ohm 4 watt De Zener diode i 5 6 volts 4 watt R55 100k ohm 3 watt 0 1344148 1 amp 50 volts 56 2 2k ohm 4 watt Dg Type IN4148 1 amp 50 volts 10k ohm 1 watt IN4148 gt 1 amp 50 volts Rsg ohm 4 watt Dio Type IN4148 aap ee te 3 lamp 50 volts R59 220k ohm 4 watt IN4148 amp 50 volts 5 1 watt Di 1N4148 50 volts 01 PNP transistor 3 40 volt type 30 Q transistor 15 amp 40 volt type TIP 35 transistor 5 amp 40 volt type MPS 05 NPN transistor 5 40 volt type MPS 05 Qs NPN transistor 5 amp 40 volt type MPS A05 IC Voltage regulator 5 volt 5 amp type 78 05 12 Quad operational amplifier type LM 324 193 Quad comparator type 3302 4 Microcomputer type 8048 T Transformer
50. g duration with little or no increase in voltage During this time most of the internal chemical conversion of the charging pro cess takes place When significant portions of the active material have been converted the battery begins to approach full charge and the voltage begins to increase more rapidly The inflection point A in the curve from a decreasing rate of increase to an increasing rate of increase is identified as the transition from Region II to Region III Region III is characterized by a relatively rapid volt age increase as more and more of the active material is converted to the charged state As the battery ap proaches full charge more closely that is when perhaps 90 to 95 of its active material has been converted chemically oxygen begins to evolve This produces an increase in the internal pressure and also an increase in the temperature of the cell Due to these effects the rapid increase in battery voltage begins to slow and another inflection point occurs in the curve This sec ond inflection point is identified as the transition point between Regions III and IV point B Within Region IV the final portions of the active material are being converted to the chemical composi tion of the fully charged battery At the same time due to oxygen evolution from material already converted the internal pressure increase and the heating contribute to a slowing in the rate of voltage increase until the 65 voltage s
51. g substantial full charge the method comprising the steps of supplying electrical energy to the battery for charg ing thereof monitoring said characteristic drawn by the battery during charging analyzing the variation of said monitored characteris tic with time to determine the occurrence of the last inflection point exhibited prior to the battery attaining substantial full charge and controlling the supply of electrical energy of the battery on the basis of the so determined occur rence 2 A method of rapidly and efficiently charging a battery of the type in which the voltage characteristic 27 thereof varies with the state of charge of the battery and in which the voltage characteristic varies with time during charging to exhibit an inflection point just prior to the battery attaining substantial full charge the in flection point characterized by a change in sign of the second derivative of the voltage characteristic variation with time the method comprising the steps of supplying electrical energy to the battery for charg ing thereof monitoring said voltage characteristic of the battery during charging analyzing the variation of said monitored voltage characteristic with time to determine the occur rence of the inflection point exhibited just prior to the battery attaining substantial full charge by de termining a change in sign of the second derivative of said voltage characteristic variation with time and
52. gard to step 118 If however the latest slope is not less than the Slope by a sufficient increment then the sequence returns to block 130 and continues until one of the four charge method analyses described above causes the charging sequence to stop In this way this flow of operations takes the appara tus through the methods of analysis described above testing at appropriate time intervals for time analysis of excessive total time elapsed for excessively high volt age on the cell or battery indicating possible damage for a drop in voltage from one period to another of sufficient magnitude indicating that the cell or battery is in Region V or for the sequence of second derivative tests indicating that the cell or battery has gone through the transition from Regions III to IV as described in FIG 1 in the change of sign of second derivative test VOLTAGE PROFILE ANALYSIS The present invention as thus far described has been directed to the profile of voltage change with time which occurs in a battery when the charging system used is of the type generally known as a constant cur rent charger This type of voltage change is actually obtainable in several different ways First it may be obtained by applying a steady unchanging charging current to the battery and measuring the change of voltage with time In this method the charger power supply and current amplifier may be chosen to provide a predetermined current
53. ge Thus exactly the same technique can be applied to the nickel iron battery as has been described for the nickel cadmium The only differences are that the constants must be selected in accordance with the needs of the particular battery considering its internal construction and the level of current which it can accept the number of cells and the corresponding maximum voltage and the maximum time or maximum voltage which can be accepted with out damage Also the small scale of the changes in the voltage profile require the system of voltage measure ment to have a higher resolution than is true in the case of a nickel cadmium battery In principle however the method of charging is substantially identical FIG 11 illustrates the charging curve of a representa tive lead acid battery Once again it can be seen that the five Regions as described in connection with FIG 1 are rep ated in the case of the typical lead acid profile and similar inflection points A and B occur The only differences are that the overall change of voltage is larger and the rate of change in Region III is greater However since the Regions are the same and the se quence of inflection points is the same essentially the same method as described in connection with nickel cadmium batteries and nickel iron batteries can again be used for lead acid batteries However it has been found that full 100 charging of a lead acid battery can be better obtained by
54. ge the battery at a pre _ determined rate and by means of appropriate program ming to determine and display the ampere hour capac ity of the battery In addition switch Sig provides an alternate signal to the microcomputer 18 to instruct it to enter the charge program or a separate discharge pro gram wherein it tests the condition of the battery In one embodiment of FIGS 3 and 4 the following circuit elements were used RI 10 ohm 4 Rie 8 2k ohm 1 watt R i watt Ri 10k ohm 1 watt 1k ohm 1 watt Rig Trimpot 100k ohm R4 100k ohm Rio 100k ohm 1 watt Rs ohm 1 watt R20 22k ohm 1 watt 10 1 Ray 10k ohm 1 watt R7 12 ohm 4 watt 220k ohm 1 watt Rg 560 ohm watt R23 10k ohm 1 watt 4 392 101 15 continued Ro 560 ohm 1 watt R24 10k ohm watt Rio 10k ohm watt 10 ohm 4 watt Trimpot 100k ohm 10k ohm watt R12 Ik ohm 4 watt Trimpot 3k ohm 10k ohm 1 watt 8 2k ohm 1 watt 2 2k ohm 1 watt Rag 100k ohm 1 watt Ris 1 Megohm watt R30 12k ohm watt 4 7k ohm 1 watt 10k ohm 1 watt R32 10k ohm watt 1 1 watt 1 1 watt 10k ohm 1 watt 33k ohm 1 watt 47k ohm 1 R35 22k ohm watt R65 33k ohm 4 watt R36 4 7k ohm 1 watt R66 22k ohm 4 watt R37 22k ohm 4 watt 100k ohm 1 watt 33k ohm 1 watt 1000 microfarads 35 volts 680 ohm 1 watt 1 micro
55. ged over a similar time period thus compensating for the cyclic variations in current the voltage profile obtained is exactly the same in form as that shown in 21 FIG 1 and again the same method of analysis be applied A fourth method of obtaining the same profile is to allow the current to vary but to measure the voltage only at the time when the current equals some prese lected constant level again this produces the same results as the other methods just described In all of these instances the voltage profile for a given battery will assume the same general form Since the novel method of analysis described in this specifica tion is a function only of the form of the profile and not of its actual value this method may be applied to any of these charging techniques For convenience all of these methods are commonly referred to by the term voltage profile APPLICATION OF VOLTAGE PROFILE ANALYSIS TO OTHER BATTERY COUPLES FIGS 10 13 illustrate a variety of voltage profiles for particular examples of several different types of batter ies all of which have been developed using the con stant current method referred to above Specifically FIG 10 is a representative profile obtained in the case of a nickel iron battery It will be noted that the general _ appearance of this curve is similar to that of FIG 1 and in particular similar inflection points occur at and as the battery approaches full char
56. h the state of charge of the battery and in which the variation of the characteristic with time during charg ing exhibits an opposed pair of inflection points prior to battery attaining substantial full charge said apparatus comprising means for supplying electrical energy to the battery for charging thereof means connected to said supply means for monitoring the characteristic during charging means connected to said monitoring means for ana lyzing the so monitored characteristic with time to determine the occurrence of a sequence of the opposed pair of inflection points and means connected to said supply means for controlling said supply means in response to said analyzing means 41 apparatus charging battery of the type having a voltage characteristic associated therewith that varies with the state of charge of the battery and in which the variation of the characteristic with time dur ing charging exhibits inflection points prior to the bat tery attaining substantial full charge in which each in flection point is characterized by a change in sign of the second derivative of the voltage characteristic said apparatus comprising means for supplying electrical energy to the battery for charging thereof and means connected to said supply means for monitoring the voltage characteristic during charging for ana lyzing the so monitored characteristic with time to determine the occurrence of a sequence infle
57. herein said means for analyzing further comprises means for analyzing the variation of said monitored characteristic with time to determine the occur rence of a predetermined variation of said charac teristic that comprises a control indicium for con trolling said supply means 57 The apparatus claimed in claim 56 wherein said means for analyzing to determine the occurrence of a 20 30 35 40 45 50 55 40 control indicium comprises means determining the Occurrence of a one of the variation of the characteristic ceasing to be mono tonic the value of the characteristic decreasing to a termined limit the value of the characteristic increasing to a prede termined limit 58 The apparatus claimed in claim 56 wherein said stored program controlled means further comprises means for reducing the supply of electrical energy to the battery upon the passage of a predetermined amount of time 59 The apparatus claimed in claim 29 30 31 34 38 or 44 wherein said battery is a nickel cadmium battery 60 method of rapidly and efficiently charging battery of the type having an electrical characteristic associated therewith that varies with the state of charge of the battery and in which the characteristic varies with time during charging to exhibit an inflection point just prior to the battery attaining substantial full charge the method comprising the steps of supplying electrical
58. his slope value is put into the Max Slope register and replaces the old contents This is done in block 162 Next the sequence flows to block 164 where a test is done to see if the flag F which was cleared in step 122 is set Up to this time it has not so the sequence will proceed through connection point 3 to block 166 At block 166 a test is done to see if the latest slope value is greater than the minimum slope by a preselected incre ment The value of K4 is selected to define some minimum value of positive change which must occur to avoid transient effects before the system is allowed to recognize that the slope has stopped decreasing and is now increasing In the case of nickel cadmium batteries K4 may be 15 millivolts per minute per cell Once this occurs an inflection point will have been identified by approximation If the slope value has not increased over the Mini mum Slope value by this necessary increment the sequence returns to block 130 which is the loop 2 re turn This means that the slope is either continuing to become less or if it is increasing it has not increased sufficiently If the latest slope is greater than Min Slope by K4 meaning that inflection point has been passed or that the sign of the second derivative has changed the sequence flows to block 168 where flag F is complemented set This means referring to FIG 1 that the transition into Region III has been made a
59. iety of different batteries including different number of cells or different types of battery couples is totally beyond the present state of the battery charging art OBJECTIVES The overall object of the present invention is to over come the difficulties inherent in prior techniques of battery charging and to provide a new and improved method of and apparatus for battery charging which fully charges batteries at a very rapid rate and at maxi mum efficiency and without causing either fast or slow deterioration of the battery A more specific object of this invention is the provi sion of a method and apparatus for charging batteries which accurately identifies the moment when the bat tery has reached full charge and which terminates charging without either under or overcharging the battery A further object of this invention is the provision of a method and apparatus for fully charging different bat teries including different numbers of cells at the maxi mum possible rate and efficiency from unknown start ing conditions Another object of this invention is the provision of a method and apparatus for fully charging different bat teries comprising different chemical couples at the max imum permissible rate and efficiency from unknown starting conditions Still another object of this invention is the provision of a method and apparatus for rapidly bringing a battery to its full state of charge and terminating the fast rate charge
60. ign of the second derivative of the current variation with time from a negative to a positive value said apparatus com prising means for supplying electrical energy to the battery for charging thereof and means connected to said supply means for monitoring the current characteristic during charging for ana lyzing the so monitored characteristic with time to determine the occurrence of the inflection point exhibited prior to the battery attaining substantial full charge by determining a change in sign from a negative to a positive value of the second deriva tive of the current characteristic with time and for controlling said supply means to control the supply of electrical energy to the battery 34 An apparatus for charging a battery of the type having a characteristic associated therewith that varies with the state of charge of the battery and in which the variation of the characteristic with time during ing exhibits an inflection point prior to the battery at taining substantial full charge and another inflection 4 392 101 35 point that precedes the first mentioned inflection point said apparatus comprising means for supplying electrical energy to the battery for charging thereof and means connected to said supply means for monitoring the characteristic during charging for analyzing the so monitored characteristic with time to deter mine the occurrence of the first mentioned inflec tion point
61. ime register reaches the interrogation of step 146 is answered in the affirmative and the program passes through connection point 2 and enters the series of steps shown in FIG 7 In FIG 7 the program continues with step 148 which refers two additional register locations in the microcomputer One is called Sum and the other is Oldsum In step 148 the contents of the register Sum are moved into the register location Oldsum and the previous contents of the register Oldsum are cancelled In Block 150 the contents of the latest read ings in Tempsum are transferred into the register location Sum The sequence then moves to block 152 where a test is made to see if the time is equal to K3 seconds If it is the program returns through Loop 2 step 130 Thus the first entry into the steps of FIG 7 at T K3 simply sets a voltage reading in the Sum regis ter which will later be transferred into Oldsum Cal culation of a slope requires at least two points on the line and therefore the first calculation can only be done when the time equals 1 minute plus K3 when the previ ous voltage value is present for comparison to the new value Of course this is really an approximation of the slope rather than an accurate determination Accordingly if the time elapsed equals K3 seconds the sequence goes back to loop 2 block 130 and contin ues for another minute Subsequently when the time equals K
62. ircuit through one of the current control resistors R29 R30 or R31 This controls the input to operational amplifier 1C2 which is taken at the midpoint of a voltage divider made up of the parallel combination of resistors Rig and R17 and the selected current control resistor The output from the amplifier IC2 is compared to the voltage de veloped across a current shunt resistor Rs Any error signal due to a difference is amplified by operational amplifier IC2q and applied to driver transistor The output of transistor Q3 is applied to current control transistors Q and Q2 to produce a very stable constant current which is applied to the battery through Sic If the output current to the battery cannot reach the selected current level for example because there is no battery connected transistor Q3 is turned fully on which through the comparison amplifier IC3a supplies a signal to the computer which turns system off As shown in FIG 3 a momentary contact push but ton switch 16 which may be operator controlled or may be built into the battery socket supplies a signal to the battery to indicate that the charging cycle should be initiated This could also be accomplished by monitor ing for the presence of battery voltage or current flow Selection circuit 24 FIG 3 comprises a plurality of selector switches 53 54 which allow the operator to select a particular computer program appropriate to a particular battery Diodes D7
63. is a test for an excessively high level of battery voltage Thus Ki is preset at a value which for the particular battery being charged represents an excessively high level of voltage which could only be reached by a defective battery Accordingly if the value of voltage in the register equals or exceeds Kj the battery must necessarily be defective or some portion of the charger is defective and the charging sequence must be stopped immediately For example Ki may equal 2 volts per cell for a nickel cadmium battery In normal charging the battery voltage will never equal K and the answer to the interrogation of step 138 will be affirmative so that the program proceeds normally to step 140 In step 138 the register Max Voltage Sum was set to an initial large negative number In step 140 the value in and the value in Max Voltage Sum are compared If the value in Tempsum is greater than that in Max Voltage Sum then the value in Tempsum is placed in the Max Voltage Sum register by instruction 142 and the program proceeds to step 144 If not then the Voltage Sum register value is left unchanged and the program proceeds di rectly to step 144 In step 144 the difference between the values used in Tempsum and in Max Voltage Sum are compared to another constant which is preset according to the battery being charged In fac
64. level at any battery voltage between zero and a value slightly in excess of the volt age of the battery at full charge The current level is chosen on the basis of factors such as the charge effi ciency the cost of the power supply and amplifier and the desired time to fully charge a totally discharged battery In general in nickel cadmium batteries of the C size or sub C size the current applied is about three times the C rate of the battery The C rate of a battery is a current in amperes which is numerically equal to its ampere hour capacity A 3C current would bring a battery to full charge in about 20 minutes In other cases charging rates such as C or 5C may be selected these would fully charge a discharged battery in about one hour or in about 12 minutes respectively A second method of obtaining the voltage profile of FIG 1 is by applying the charging current in pulses and measuring the rest voltage of the battery when the cur rent is zero This is known as trough voltage sensing In a sense the voltage measurements are taken at a stant current level of zero amps The profile of voltage with time will correspond in form although not in scale to that shown in FIG 1 and exactly the same method of analysis as described above may be applied A third method of obtaining this same profile is to apply a current which may vary cyclically but which has a constant average value If the measured voltage is avera
65. ltage characteristic from a negative to a positive value and a succeeding change in sign of the second derivative of said voltage character istic from a positive to a negative value and controlling the supply of electrical energy to the battery on the basis of the so determined sequential occurrence 14 method of rapidly and efficiently charging a battery of the type in which the current characteristic drawn by the battery during charging varies with the state of charge of the battery and in which the variation of the current characteristic with time during charging exhibits inflection points prior to the battery attaining substantial full charge in which each inflection point is characterized by a change in sign of the second deriva tive of the current characteristic the method compris ing the steps of supplying electrical energy to the battery for charg ing thereof monitoring said current characteristic of the battery during charging analyzing the variation of said monitored current characteristic with time to determine the occur rence of a sequence of inflection points character ized by a change in sign of the second derivative of said current characteristic from a positive to a neg ative value and a succeeding change in sign of the second derivative of said current characteristic from a negative to a positive value and 4 392 101 31 controlling the supply of electrical energy to battery on the basis
66. n ing a predetermined limit 21 The method claimed in claim 16 17 18 or 19 20 wherein said reducing step further comprises reducing the supply of electrical energy to the battery upon the passage of a predetermined amount of time 4 392 101 33 22 The method claimed in claims 1 6 10 15 18 19 whrein said monitoring step further comprises monitoring an electrical characteristic of the battery 23 The method claimed in claim 22 wherein the monitoring step further comprises measuring the battery voltage 24 The method claimed in claim 22 wherein the monitoring step further comprises measuring the current drawn by the battery during charging 25 The method claimed in claim 24 wherein the monitoring step further comprises measuring the current drawn by the battery during charging at a constant value of voltage 26 The method claimed in claim 1 2 3 6 7 or 15 wherein said controlling step further comprises discontinuing the supply of electrical energy to the battery 27 The method claimed in claim 1 2 3 6 7 or 15 wherein said controlling step further comprises reducing the rate of supply of electrical energy to the battery to a predetermined rate to prevent self dis charge thereof 28 The method claimed in claim 1 5 6 7 9 10 13 14 in which battery is of the nickel cadmium type 29 An apparaus for charging a battery of the type having a characteri
67. n continues through the previously described loop The interrogation of block 116 is asked and answered in the same manner as previously de scribed and since the maximum allowable time has not 4 392 101 17 yet been reached the program directly to block 120 When the interrogation of block 120 is asked the answer will be in the negative since this is the second time through this sequence At this point the program directs the computer through location 1 in FIG 5 to location 1 in FIG 6 and thus into block 134 This instruction namely to read the voltage and put Tempsum operates analog to digital converter as previously described in connection with FIG 2 and stores the resultant digital statement of the battery volt age in a storage register in the microprocessor This register is referred to as Tempsum The program sequence next proceeds to block 136 where the descriptive step is stated as Calculate Dif ference Tempsum K This is followed immediately by block 138 which inquires whether the difference is negative If the differ ence is either 0 or greater than 0 the answer is no and the computer is directed by step 139 to stop charging This represents a sequence of steps which would be the same as that stated above with regard to block 118 If the difference is negative then the answer is yes and the program proceeds to block 140 In fact the combination of steps 134 136 and 138
68. n the optimum manner for each of those par ticular batteries PRIOR ART Battery usage in various products particularly for the retail consumer has increased tremendously in recent years However batteries are still looked upon with substantial disfavor by many consumers because so much of their experience has been with primary cells which are wasteful which must be frequently replaced and which can cause serious damage if leakage occurs Rechargeable batteries have recently become more popular in various devices but problems are still en countered by the consumer Frequently he discovers that his batteries have self discharged and need recharg ing at exactly the moment when he would like to use the device and recharging in most instances takes an incon veniently long period of time One solution to this is to provide maintenance charg ing systems in which the battery can be left on constant charge between uses Even this system is of no value if the consumer fails to put the battery back on charge after use in addition most maintenance charging sys tems actually cause slow deterioration of the battery with time The solution to all of the above problems would be the provision of an adequate fast charging system which would reliably bring the battery up to its full state of charge in the shortest possible time and without risk of damage While the prior art is replete with attempts to provide good fast charging systems no sati
69. nd controlling the supply of electrical energy to the battery on the basis of the so determined occur rence of the last inflection point of the opposed pair of inflection points 9 A method of rapidly and efficiently charging a battery of the type having a characteristic associated therewith that varies with the state of charge of the battery and in which the variation of the characteristic with time during charging exhibits a plurality of inflec tion points prior to the battery attaining substantial full charge the method comprising the steps of supplying electrical energy to the battery for charg ing thereof monitoring said characteristic of the battery during charging analyzing the variation of said monitored characteris tic with time to determine the occurrence of a second inflection point of the plurality of inflection points and controlling the supply of electrical energy to the battery on the basis of the so determined occur rence 10 A method of rapidly and efficiently charging a battery of the type having a characteristic associated therewith that varies with the state of charge of the battery and in which the variation of the characteristic with time during charging exhibits an inflection point prior to the battery attaining substantial full charge and another inflection point that precedes the first men tioned inflection point the method comprising the steps of supplying electrical energy to the battery fo
70. nd means for controlling the application of energy from the source to the battery In the particular example of a normal discharged nickel cadmium battery a useful charging pattern in accord with this invention is to apply a fast rate con stant charge current to the battery until two consecu tive inflection points are passed specifically a first one at which the sign of the slope of dV dt that is the sign of d2V dt2 changes from negative to positive followed by a second one at which the sign changes from positive to negative These analyses will be further clarified with reference to the voltage variation of a normal nickel cadmium battery in the detailed description hereinafter for the present it is sufficient to note that one basic concept presented herein is that of inflection point analysis Specific techniques of analysis and specific sequences adapted to accommodate different battery couples may readily be developed within the context of this general procedure DESCRIPTION OF THE FIGURES FIG 1 is a graph illustrating the variation of voltage as a function of time during the charge cycle of a nickel cadmium battery FIG 2 is a block diagram illustrating the primary elements in battery charger in accordance with this invention FIGS 3 and 4 together comprise a schematic dia gram illustrating specific circuits which may be pro vided in accordance with this invention to form the block diagram of FIG 2 FIGS 5
71. nd that the charge cycle is well along toward completion From block 168 the sequence also contin ues back to block 130 to continue the process as previ ously described At this point although it is not shown in the flow chart it is usually preferable to replace the value in the Slope register with the value in the Slope register This insures that additional slope values after the first inflection point will be compared to the actual slope at the first inflection point and not to an earlier value which may have been carried because it was slightly larger than the inflection point value Eventually the process will continue through suffi cient cycles so that it will arrive again at step 164 Now the response to this interrogation will be yes and the program will proceed through the connection point 5 25 40 45 65 20 into FIG 9 There sequence contin ues to block 170 where the slope value is tested to see if it is less than the value in register Max Slope by an increment Ks which may be approximately in value as This is the test for the Region III to Region IV transition shown in FIG 1 If the slope is less than Max Slope by Ks then the charge cycle has reached this second inflection point and the charge cycle is complete The sequence then goes to block 172 and the charging process is terminated in the same manner as described in re
72. nt addition of energy to a battery which is fully discharged should produce four consecutive inflection points before full charge is reached In order to fully charge this battery another combi nation of the inflection point analysis method with the alternative charge termination modes previously de scribed will fully charge this battery Specifically the charger 15 arranged to seek the four consecutive inflec tion points which indicate that the battery being charged has gone through its entire cycle from fully discharged to fully charged if this occurs the charger terminates the application of the fast rate charge cur rent However this termination mode alone is not suffi cient In addition the system is instructed to compare the total voltage to some preselected value after each inflection point is measured If the voltage is above the preselected level when an inflection point is reached it will then be known that the battery was not fully dis charged when the charge program was started and that the battery is now fully charged Accordingly the ap plication of the full rate current is discontinued Thus the system accommodates both batteries which are placed on charge while already either fully or partially charged and also batteries which are fully discharged in both cases the charger brings the battery precisely to its full charge capacity without the harmful effects of prior art charging techniques 4 392 101 2
73. nt fast charging of a fully charged battery which is inadvertently placed on fast charge by the operator Specifically a fully charged battery to which a high current is applied will traverse most if not all of Regions I II and HI very quickly In many cases this will occur in the time period which a normally discharged battery would require to traverse Region I Since the system is instructed not to look for inflection points during the first 30 to 60 second portion of the cycle at least one and perhaps both of the signifi cant inflection points points A and B will pass before the system begins to monitor for them Therefore as monitoring of the fully charged battery begins the battery will be passing through Region IV 20 25 45 50 60 65 10 and entering Region V Within a fairly short time after it has been placed on charge e g 1 3 minutes the battery will enter Region V and its voltage will begin to decrease As soon as the negative voltage change is large enough to indicate to the apparatus that the func tion of voltage with respect to time is no longer mono tonic the apparatus will discontinue the fast charge rate Preferably the charging mode then shifts into a maintenance mode as will be hereinafter described Since the high rate is only maintained for a short period of time the battery will not be damaged by this se quence It is also noted that even defective batteries will not be driven into a h
74. ntrol the supply of electrical energy to the bat tery 32 An apparatus for charging a battery of the type having a current characteristic associated therewith that varies with the state of charge of the battery and in which the variation of the current characteristic with time during charging exhibits an inflection point just prior to the battery attaining substantial full charge the inflection point characterized by a change in sign of the second derivative of the current variation with time said apparatus comprising means for supplying electrical energy to the battery for charging thereof and means connected to said supply means for monitoring the current characteristic during charging for ana lyzing the so monitored characteristic with time to determine the occurrence of the inflection point exhibited just prior to the battery attaining substan tial full charge by determining a change in sign of the second derivative of the current characteristic with time and for controlling said supply means to control the supply of electrical energy to the bat tery 33 An apparatus for charging a battery of the type having a current characteristic associated therewith that varies with the state of charge of the battery and in which the variation of the current characteristic with time during charging exhibits an inflection point prior to the battery attaining substantial full charge the in flection point characterized by a change in the s
75. of the so determined sequential occurrence 15 A method of rapidly and efficiently charging a nickel cadmium battery in which the voltage varies with the state of charge of the battery and in which the variation of the voltage with time during charging ex hibits an inflection point prior to the battery attaining substantial full charge and another inflection point that precedes first mentioned inflection point the method comprising the steps of supplying electrical energy to the battery for charg ing thereof monitoring said voltage characteristic of the battery during charging analyzing the variation of said monitored voltage characteristic with time to determine the occur rence of the first mentioned inflection point and controlling the supply of electrical energy to the battery on the basis of the so determined occur rence of the first mentioned inflection point 16 A method of rapidly and efficiently charging a battery of the type having a characteristic associated therewith that varies with the state of charge of the battery and in which the variation of the characteristic with time during charging exhibits an inflection point just prior to the battery attaining substantial full charge the method comprising the steps of supplying electrical energy to the battery for charg ing thereof monitoring said characteristic of the battery during charging analyzing the variation of said characteristic with time to d
76. on destructive charging additional object of this invention is the provision of a method and apparatus for providing a non destruc tive maintenance charge mode by which a battery can 4 392 101 r 0 45 60 65 4 be kept at its full state of charge without gradual battery deterioration It is an additional object of this invention to provide a novel and unique method of evaluating the state of battery charge and of controlling the applied charge current in response to such evaluation so as to permit the battery to be brought to its full charge state at the maximum possible rate and at maximum efficiency without causing damage or deterioration of the battery such method also including safeguards to protect against damage due to the introduction of a defective cell or to the introduction of a cell which is already at full charge Further objects and advantages of this invention will become apparent as the description and illustration thereof proceed BRIEF DESCRIPTION OF THE INVENTION In general the present invention comprises a method of applying a charge current to a battery monitoring selected battery parameters during the charging infer ting from changes in these parameters an indication of the true charge condition of the battery and controlling the applied charging energy so as to bring the battery to its full charge condition as quickly as possible without damaging the battery In addition the gen
77. r charg ing thereof monitoring said characteristic of the battery during charging analyzing the variation of said monitored characteris tic with time to determine the occurrence of a sequence of the preceding and the first mentioned inflection points and controlling the supply of electrical energy to the battery on the basis of the so determined sequential occurrence 11 A method of rapidly efficiently charging a battery of the type having a characteristic associated therewith that varies with the state of charge of the battery and in which the variation of the characteristic with time during charging exhibits a first and a succeed ing inflection point prior to battery attaining a predeter mined charge level the method comprising the steps of supplying electrical energy to the battery for charg ing thereof monitoring said characteristic of the battery during charging analyzing the variation of said monitored characteris tic with time to determine occurrence of a sequence of the first and the succeeding inflection points and 15 20 25 30 35 45 50 55 60 65 30 controlling the supply of electrical energy to the battery on the basis of the so determined sequential occurrence 12 A method of rapidly and efficiently charging battery of the type having a characteristic associated therewith that varies with the state of charge of the battery and in which the vari
78. riations may also be used with regard to other parametric profiles 4 392 101 0 15 35 40 45 50 55 60 65 26 Another set of variations comprises particular battery characteristic selected for analysis While the present description has been directed particularly to the voltage or current profiles or other characteristics particularly electrical characteristics might also be ana lyzed It is noted that this profile may also vary with other battery conditions in fact as previously de scribed the analysis of this invention partially depends on the fact that other battery conditions affect the pro file In addition to the extremely precise method of inflec tion point analysis as hereinbefore described the pres ent invention also encompasses the analysis for other critical points in the profile of variation with time of a characteristic of the battery which changes with the energy level stored in the battery In addition there fore to inflection point analysis the present invention is also in part directed to improvements in method and apparatus for charging batteries which relate to detailed analyses of the profile of battery characteristics the analyses involving combinations of such factors as limit ing value slope and passage of time By analysing the profile of the particular characteristic for the battery under charge particular combinations of these events may be identified
79. s has relied upon temperature cutoff to termi nate the fast charge mode However these systems are subject to several difficulties they may damage the batteries due to the constant repetition of high tempera ture conditions even in specially manufactured and expensive cells which are theoretically designed to accept high temperatures such systems may not be safe for use with defective cells they actually do not charge a battery to its full capacity in high ambient tempera ture conditions the charge efficiency is low and the systems are therefore wasteful and in low ambient tem perature the battery may be driven to self destruct by venting or possibly explosion Another major category of prior art fast charging systems relies on voltage cutoff However in many types of battery systems including nickel cadmium this termination mode is unreliable due to the large voltage variation which can occur with temperature or due to cell history or individual cell characteristics Thus a voltage cutoff system can destroy a battery through venting Except in unusual ideal conditions it will never properly charge a battery to its full capacity A third major category of prior art battery charging termination is based on simple passage of time How ever the accuracy of this system depends on the bat tery at the beginning of charge having an assumed state of charge There is a very high likelihood that this will not be the case and that th
80. s to the increasing voltage of Region II of FIG 1 The inflection point which must be identified be tween this interval and the next Region of sharply de creasing current occurs at the same point in time as point A in FIG 1 However it identifies a change in the sign of the second derivative of current from positive to negative whereas Point A in FIG 1 identified a change in the sign of the second derivative of voltage from negative to positive Similarly the inflection point be tween Regions III and IV is now identified as that at which the second derivative changes from negative to 10 20 25 30 35 40 45 50 35 60 65 24 positive whereas in FIG 1 the change was from posi tive to negative Thus the entire description of the method of inflec tion point analysis as applied in connection with FIGS 1 9 be converted to a method of inflection point analysis for the constant voltage case by changing the word voltage to current and by reversing all words such as increasing decreasing positive nega tive etc Similarly with regard to FIGS 10 13 the particular batteries identified there can be charged by the constant voltage technique In each case the general method of inflection point analysis as set forth in the specification exactly corresponds to that which has already been described RATE OF CHARGING A primary benefit of the present invention is that
81. sfactory system has yet been developed Most fast charging systems today require very special conditions such as unusually expensive batteries which can accept the output of the fast charge system Even under these special conditions there remains a risk of serious dam age to either the battery or to the charger In addition the present fast charge techniques do not properly charge the batteries Depending on the termination mode used all fast charge techniques of which we are aware either overcharge or under charge the battery _ 0 _ 5 20 5 30 45 55 60 65 2 either of which causes gradual deterioration of the bat tery and premature failure In part the failures of the prior art have been due to the inability to accurately indicate full battery charge this has been due either to the failure of the prior art to select the proper mode of indication or to the fact that even if a reasonably good indicator has been selected the charging requirements of a battery vary substan tially with individual cell chemistry with individual cell history and with ambient temperature Thus even an indication mode which is reasonably well selected for a particular battery type may actually provide an accurate indication only for a few cells having ideal characteristics and only if the cells are charged under proper conditions of ambient temperature For example a major category of previous fast charg ing system
82. step in the process identified as block 114 is to increment the total time register Then the program moves to block 116 which does a comparison between a maximum allowable time as set for the particular bat tery and the time that has elapsed If the comparison shows that the maximum allowable total time has been reached the sequence moves to block 118 which indi cates the execution of the sequence of instructions to stop the charging cycle including either turning off the charging current or turning it to a lower value This may also involve changing to a timed overcharge mode or to a surcharge mode or to a maintenance mode if desired If the total time has not been reached which it will not this first time through the microcomputer goes on to block 120 Here the time register is again used to determine whether this is the first time through this sequence of steps If it is then the program moves to the series of steps 122 128 which direct the computer to set up certain registers within the computer so that they are rady for use later in the program First as indicated at block 122 a flag identified as F is cleared This flag will later be set upon the occurrence of a first inflection point or change in sign of the second derivative The program then continues through block 124 126 and 128 As indicated in the drawing each of these steps controls the placement of an initial value in particular registers namely Minimum Slope
83. stic associated therewith that varies with the state of charge of the battery and in which the variation of the characteristic with time during charg ing exhibits a plurality of inflection points prior to the battery attaining substantial full charge said apparatus comprising means for supplying electrical energy to the battery for charging thereof and means connected to said supply means for monitoring the characteristic during charging for analyzing the so monitored characteristic with time to deter mine the occurrence of the last inflection point exhibited prior to the battery attaining substantial full charge and for controlling said supply means to control the supply of electrical energy to the battery 30 An apparatus for charging a battery of the type having a voltage characteristic associated therewith that varies with the state of charge of the battery and in which the variation of the voltage characteristic with time during charging exhibits an inflection point just prior to the battery attaining substantial full charge the inflection point characterized by a change in sign of the second derivative of the voltage characteristic variation with time said apparatus comprising means for supplying electrical energy to the battery for charging thereof and means connected to said supply means for monitoring the voltage characteristic during charging for ana lyzing the so monitored voltage characteristic with time to de
84. stic with time to determine the occurrence of the last inflection point of the opposed pair of inflection points and means connected to said supply means for controlling said supply means in response to said analyzing means 37 An apparatus for charging a battery of the type having a characteristic associated therewith that varies with the state of charge of the battery and in which the variation of the characteristic with time during charg ing exhibits a plurality of inflection points prior to the battery attaining substantial full charge said apparatus comprising means for supplying electrical energy to the battery for charging thereof means connected to said supply means for monitoring the characteristic during charging means connected to said monitoring means for ana lyzing the so monitored characteristic with time to determine the occurrence of a second inflection point of the plurality of inflection points and means connected to said supply means for controlling said supply means in response to said analyzing means 38 An apparatus for charging a battery of the type having a characteristic associated therewith that varies with the state of charge of the battery and in which the variation of the characteristic with time during charg ing exhibits an inflection point prior to the battery at 5 15 20 25 30 35 40 45 50 55 60 65 36 taining substantial full charge and another infle
85. stinguishing features of the voltage profile after the second inflection point Be cause of this voltage profile it would be extremely difficult to provide a reliable fast charger for such a battery using only prior art techniques In accordance with the present invention the inflection points can be determined very precisely This indicates that the bat tery is approximately at 45 of capacity Accordingly a charging program for a lithium battery of this type may use the same system for determining inflection points as has been described above coupled with a timing sequence When a battery is attached to the char ger a timer is started and it is set to discontinue the full charge rate when enough time has passed to add ap proximately 55 of the total battery capacity to the battery If no inflection points are encountered during this period the timer alone shuts off the system at the end of the period This accommodates a battery which may be placed on charge although it already has a rea sonably full charge However if the inflection points are encountered before the time has expired then the timer is simply restarted This ensures that a battery which was dis charged or only partially charged initially will receive its full charge FIG 13 illustrates still another variation of voltage profile namely that for a silver cadmium battery In this instance simple determination of two consecutive inflection points is not sufficie
86. stor con trolled current amplifier 12 and then through a char 15 20 25 30 35 ge test switch 14 and finally to the output terminals 15 at which a single or multi cell battery to be charged is connected The power supply may of course be any alternative source of DC power such as larger battery or a converter operated from a DC source The ampli fier is preferably a standard series pass current regulator although other types of controllable current amplifiers could be used The charge test switch normally con nects the current amplifier 12 to the battery for the application of charging current this switch also in cludes a test position for use in a test mode which is described below The remainder of the block diagram illustrates a pre ferred embodiment of the apparatus for performing the method of this invention In the illustrated embodiment a start switch 16 is provided this comprises a momen tary contact switch for initiating the sequence of opera tions It is connected to one input port of a microcom puter 18 In the preferred embodiment of this invention this is an Intel type 8048 microcomputer This is a self contained computer including a program memory for storing instructions a register memory and a central processing unit CPU for controlling the execution of the stored instructions The 8048 microcomputer is more completely described in the publication entitled Microcomputer User s Manual
87. t the test being per formed by the series of program steps 140 142 and 144 is that of checking to see if the voltage has moved downwardly by more than a given minimum amount from a previously achieved maximum value As de scribed above in the section entitled Absolute Voltage Change Analysis if this has occurred this must indicate that the battery has already passed its maximum charge level and is in the region indicated as Region V in FIG 1 or that the battery is defective Accordingly the program is instructed to move to block 145 which stops the charging process in the same manner as steps 118 and 139 If this is not the case that is if the latest value of battery voltage present in is either equal to or greater than the largest value previously recorded 0 15 45 55 60 65 18 then it is known that the battery is somewhere in Re gions I IV and charging can safely continue It should be noted that the value is a small number Its purpose is to prevent spurious or transient errors caused by drift in the electronic circuit values or small negative changes in the battery voltage etc from shut ting down the charging sequence It is also noted that this test is preferably performed even during the initial period identified as Region I of FIG 1 wherein the battery voltage is varying in a somewhat undetermined manner This is because a negative change in battery voltage which ex
88. tabilizes at some peak value for a short period of time This is designated as the transition between Regions IV and V Within Region if charging i is continued the volt of the cell starts to decrease due to additional heat 7 ing as virtually all of the applied energy is converted into heat and the negative temperature coefficient of the battery voltage causes the voltage to decrease Contin ued application of charging energy in this Region would eventually cause damage to the battery either through venting or damage to the separator As previously noted the relative time duration slope or value of any portion of this curve may be modified by such factors as the initial temperature of the battery the charge or discharge history of the battery the par ticular manufacturing characteristics and the individual characteristics of the battery cell However the major aspects of this curve and of each of its Regions will be identifiable in any non defective nickel cadmium bat tery which is brought from a substantially discharged state to a fully charged state at a constant relatively high current In specific accordance with the present invention the above described curve and the information contained therein are utilized in a novel manner to provide improved battery charging method This method is much more accurate than those previously used and is in fact so improved that it permits rapid charging of
89. termine the occurrence of the inflection point exhibited just prior to the battery attaining substantial full charge by determining a change in sign of the second derivative of the voltage charac teristic variation with time and for controlling said supply means to control the supply of electrical energy to the battery 31 An apparatus for charging a battery of the type having a voltage characteristic associated therewith that varies with the state of charge of the battery and in which the variation of the voltage characteristic with 10 20 25 30 35 45 50 55 65 34 time during charging exhibits inflection point prior 10 the battery attaining substantial full charge in flection point characterized by a change in sign of the second derivative of the voltage characteristic variation with time from a positive to a negative value said appa ratus comprising means for supplying electrical energy to the battery for charging thereof and means connected to said supply means for monitoring the voltage characteristic during charging for ana lyzing the so monitored voltage characteristic with time to determine the occurrence of the inflection point exhibited prior to the battery attaining sub stantial full charge by determining a change in sign from a positive to a negative value of the second derivative of the voltage characteristic variation with time and for controlling said supply means to co
90. the preferred method of this invention in volves ignoring the voltage changes which occur within the first 30 60 seconds of the charging cycle the changes which occur in Region I may overlap slightly into the time period within which the data sampling apparatus of this invention is operative In that event an inappropriate inflection point may occur near the begin ning of Region H The apparatus of this invention is designed so that it will ignore such inflection points until those identified above occur in the proper se quence An alternative statement of this technique can be made based on the identification of changes of sign of the second derivative of the voltage with respect to time Specifically Region II is characterized by the gradual decrease of the slope or rate of charge of volt age versus time For a fully discharged battery Region II constitutes the largest portion of the charging period with voltage over most of this period increasing at a relatively low rate As the battery approaches full charge the voltage again starts to increase somewhat more rapidly Thus the slope which had been becoming progressively smaller and smaller starts to become larger again This can be described as an inflection point or a change in sign of the second derivative of voltage with respect to time Thus we have a first such change in sign giving indication that the battery is nearing the full charge state During Region the slope of the
91. through 9 schematically illustrate the se quence of operations performed by the microcomputer shown in FIG 4 FIGS 10 13 are graphs illustrating the variation of voltage as a function of time during the charge cycle of several different batteries and FIG 14 is a graph illustrating the variation of current as a function of time during the charge cycle of a nickel cadmium battery In the following specification an explanation is given of the battery charging process of nickel cadmium bat teries The inventive method for either monitoring or terminating the battery charging process 15 next de scribed including several alternative terminating modes used for either protection or supplemental termination The apparatus of this invention is then presented in cluding a preferred detailed schematic circuit and a preferred embodiment of the operational sequence per formed by the microcomputer Finally general de scription of the application of this invention to other types of batteries and to other charging modes i is pro vided 15 25 35 40 45 50 55 6 BATTERY CHARGING PROCESS In the course of recharging a nickel cadmium battery it has been found that a very typical curve is produced if the increasing battery voltage is plotted as function of time FIG 1 is a representation of a typical curve of this type as taken during a constant current charging cycle A similarly typical curve can be obtained b
92. tic i increasing to a prede termined limit the slope of the variation of the characteristic attain ing a predetermined limit 52 The apparatus claimed in claim 48 wherein said stored program controlled means further comprises means for reducing the supply of electrical energy to the battery upon the _ passage of a predetermined amount of time 53 The apparatus claimed in claim 30 33 34 35 38 or 43 wherein said second mentioned means further comprises means for analyzing the variation of said monitored characteristic with time to determine the occur rence of a predetermined variation of said charac teristic that comprises a control indicium for con trolling said supply means 54 The apparatus claimed in claim 53 wherein said means for analyzing to determine the occurrence of a control indicium comprises means for determining the occurrence of a one of the variation of the characteristic ceasing to be mono tonic the value of characteristic decreasing to a predeter mined limit the value of the characteristic i increasing to a prede termined limit the slope of the variation of the characteristic attain ing a predetermined limit 55 The apparatus claimed in claim 53 wherein said stored program controlled means further comprises means for reducing the supply of electrical energy to the battery upon the passage of a predetermined amount of time 56 The apparatus claimed in claim 37 39 or 40 w
93. ught through its initial stages in the minimum possible time for example as little as 15 minutes for a fully discharged battery As the battery approaches full charge its con dition is identified accurately and the charging current is reduced or cut off at exactly the proper moment in the charge cycle Application of this new technique requires very so phisticated processing of the available information In concise form as applied specifically to nickel cadmium batteries the method of this invention involves the identification of the inflection point between Regions II and III and by the identification of the subsequent or following inflection point between Regions III and IV Once these two inflection points have been identified and it has been confirmed that their occurrence is in 0 20 25 30 35 40 45 55 60 65 4 392 101 8 exactly that order and only then the battery charging current can be discontinued or reduced to a mainte nance or topping mode if desired with absolute assur ance that the battery has been brought to a full state of charge regardless of its temperature history or individ ual cell characteristics Because of the accuracy of this determination this method can even be applied to bat teries which are constructed for use only with trickle chargers It should be noted that the exact sequence of occur rence of these inflection points is critical to this inven tion While
94. voltage time curve increases further and further as the battery comes closer to full charge At or near the full charge point there is the transition between Regions III and IV at which the slope of voltage stops increasing and starts decreasing to smaller and smaller values as Region IV progresses Here again a change in the sign of the sec ond derivative of the voltage time curve occurs This decreasing slope in Region IV indicates that virtually all of the active material in the cell has been changed to the charged state and that the energy going into the cell is beginning to convert into heat rather than continuing the charging process Thus it is desirable to terminate charge during the early or middle part of Region IV of the voltage time curve These two above described changes in sign of the second derivative of the voltage time curve are charac teristic of nickel cadmium and other electrochemical cells during the charging process They provide a unique and reliable indication of the state of charge of the battery A particularly important aspect of the method of this invention is accordingly the use of one or more of these observable changes of sign of the sec ond derivative of the voltage time curve to determine when to terminate battery charging The method of this invention of observing these in flection points or of changes in the sign of the second derivative of the voltage time curve of the battery charging process can
95. y plotting current against time during a constant voltage charging cycle and a reproducible pattern also occurs if neither voltage nor current are held constant This curve may be divided into significant regions as indicated by the Roman numerals between the vertical lines superim posed on the curve While the curve is subject to varia tions in specific values of voltage or of time the general form is similar for all nickel cadmium batteries includ ing one or more cells and the following discussion applies equally to all such batteries Region I of FIG 1 represents the initial stage of voltage change which occurs when the charging cycle is first started In this Region the voltage is subject to significant variations based on the initial charge level of the battery its history of charge or discharge etc Since the shape of this Region can vary it is indicated in FIG 1 by a dotted line Because the information in Region I varies it is usu ally preferable to ignore this segment of the curve The battery will generally traverse Region I completely within the first 30 to 60 seconds of charging and enter Region II in general the voltage in the Region I and period increases relatively rapidly from the initial shelf voltage and the short peaks which may occur in this Region are not harmful battery approaches a more stable charging regime it enters the portion of the curve designated Region II Region may be of fairly lon

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