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VK3EM SLA Charger - The Repeater Builder`s Technical Information

1. 9 Solder the screw terminal blocks if your using them 10 Solder the current sense resistors R2 and R3 11 Solder the main electrolytic capacitor Use a dab of hot melt glue to keep it firm on the PCB 12 Install and solder U4 the 7812 voltage regulator The metal TAB should be facing outwards from the centre of the PCB Make sure you install it in the right spot U4 is located near the binding post and the battery charger output connector J2 13 Install binding posts in the four corner holes It is suggested that you mount posts on both side of the pcb as shown in the front cover photo This helps keep the PCB stable during testing 14 Solder diodes temporarily into place for D8 D9 and D10 You could use surface mount diodes or leaded ones The anode is the chamfered end as shown on the silk screen 15 Install Q1 the TIP32C pass transistor You should mount this transistor on the heatsink and use short length of hook up wire Suitable gauge to connect to the PCB Make sure you get the pin out right It is printed on the solder side of the board If you substitute another pass transistor it might have another pinout 16 Cut the track and lift it from the PCB as shown in the picture below This is part of the charger reset modification described in the Design Documentation Zei 2000 UKIEN httpt uuu gece ties com vk3em SH Ms CA di R y RS e R2 E zo gei cau Charger Sealed Lead Acid Battery Charger Mk
2. Rb Rsum Ra Rb 14 926kQ Now calculate Rt _ Vin Vt Vref Ris It Rt 1680hm We now know all the theorectical resistor values for our batterv charger But whv are they theorectical Well as Murphev s Law states there is always something vou don t factor in In this case its the Vce voltage drop across the open collector resistor at Pin 7 Power Indicate Huh What do you mean Remember Pin 7 is being used as the ground reference instead of ground This means the charger does not draw current via the resistor divider string when the battery charger is off No supply The problem is Pin 7 is grounded via a Transistor When turned hard on and with a collector current of 70uA there is a voltage drop across the transistor If this voltage drop is not factored into the equation you will get an error in your battery charger transistion and float voltages The voltage on my prototype turned out to be 27mV This may vary from unit to unit but at 66uA equates to approximately 415 Ohms Subsequently the theorectical value of Rc and the real value of Re differs by this amount So the final theorectical values are Rc 34 5 kOhm So this could be implemented as a 33k and 1k5 Rd 809 kOhm This could be 680k 150k 1M Ra 161 kOhm This would best be 150k 22k 22k Rb 15 kOhm Well obviously 15k is the best value Rt 168 Ohms so either 150 or 180 Ohms would suffice 22 i 4954EUJ 1129 199 15385 ae
3. O 3 N lt bg L m 3 N 106 553 mm SLA Charger Mk Il Bill of materials Rev 1 3 Part Type Qiy Designators ates OR Wire Link 8 JRIS R28 R34 R35 R55 R56 R64 RG6 Jxial Style R Resistor 5 M Ohm Resistor 5 N5404 Diode K Ohm Resistor 1 9 R43 R50 R51 0805 SMD K Ohm Resistor 5 7 R15 nF Capacitor 21 C22 C23 k2 Ohm Resistor 1 48 R49 Ok Ohm Resistor 1 4 R8 R52 R53 Ok Ohm Resistor 5 11 R16 R46 u7 35v Tantalum u7 16v Tantalum 5k Ohm Resistor 5 2k Ohm Resistor 5 3k Ohm Resistor 5 00k Ohm Resistor 5 65 parallel with 330k OOnF Capacitor 35v 9 C10 C11 C12 C13 C14 C25 OOpF Ceramic Cap 18 020 50k Ohm Resistor 5 25 R26 70R Resistor 5 20R Resistor 5 R54 30k Ohm Resistor 1 7 R22 R65 parallel with 100k 80k Ohm Resistor 5 200uF 35 Electrolytic 812 12v 1Amp Regulator C817 C857 M358 M393 IP32C TO 220 C3906 DIP 16 2 WAY Screw Terminal Block J1 J2 J3 J4 J5 J7 0 2 Pin Spaced 3 WAY Screw Terminal Block J6 0 2 Pin Spaced H H olcjommmjou PTR OOH Toya Gel ke O O Fo O X We E CIC Design Documentation The UC3906 has a well defined design process for determining the batterv charging characteristics This is a fancv wav of saving thev were not plucked out of the air Individual requirements might vary so here is the design process l used for the VK3EM Sealed Lead Acid Charger The voltages used in this design process were chosen a
4. the use of ferrite beads on these leads inside a shielded box is recommended This output does not need to be fused The square pad is goes to the positive terminal of the battery and the round pad to the negative terminal J3 Float Charge Indicator LED Green An external green LED can be connected to this point When the LED is on the charger is in the Float state The square pad connects to the Anode long lead of the LED and the round pad to the cathode short lead Current is limited to 10mA J4 Charge Current Monitor LED Red An external red LED can be connected to this point When the LED is glowing brightly the battery is accepting a large charge current When the LED is glowing slightly the battery is accepting a small charge current When the LED is off the battery is accepting negligible current The square pad connects to the Anode long lead of the LED and the round pad to the cathode short lead Current is limited to 20mA J5 Over Charge Indicator LED Amber An external orange LED can be connected to this point When the LED is on the charger is in the Over Charge state The square pad connects to the Anode long lead of the LED and the round pad to the cathode short lead Current is limited to 10mA J6 Current Sense Resistor Selection An external switch which can select one out of two current sense resistors Recommended values are 1 Ohm For 250 mA amp bulk charge and 0 27 Ohm For 1 amp bulk charge Ensure t
5. CHG ENB R3 1831 l CSOUT oR WE np OGTRM 8 06784 TKLBIAS 10 SLC R39 R29 R40_R26 Op R62 SLC T OG IND 7 680k iM OR 8 PWR IND 14 6 NF 150k R4PIR32 U2 334 JNF UC39066 020 RD 100p RC R63 R4 033 OR ik INF 4 4 l H L 7023 arger Control Circuitry T BEI BEI 1 R10 R7 NF Un c13 100n K E XM L D8 2 NF l EXT GREEN LED col a3 1 R16 80857 SLC E Tok LM393 Ai USA C12 100n Elevated Charge Indicator Float Charge Indicator Bi 012 1815 INF 1k J5 1 D10 SZ SNE 2 04 pt 80857 10k 12v R14 NF J7 2 R19 1 NE NF R20 NF R21 NF Not Fitted EXT ORANGE LED R60 VSENSE Ra7NF INF Q5 NF Pei OCTRM MKII Battery Charger c 2000 Luke Enriquez Number Revision 1 3 22 Nov 2000 Sheet of E Electronics Projects SRESU SLA ch rea BandSchematics SLA Charger 7 8 e Batterv Charger Wiring Diagram for a Tvpical Applicat
6. a minimum use C 6 2 Select the appropriate charge current with the charge current selection switch 3 Turn the charger on When power is applied and NO battery is connected the battery charger enters the float state and the green LED will turn on If the green LED does not turn on the battery charger is faulty and you should contact your network administrator Connecting the charger to a battery may cause one of several things to happen If the battery voltage is less than 12 6 volts the charger will enter the bulk state and the charge current LED will turn on If the battery voltage is greater than 12 6 volts the charger will remain in the float charge state green LED on but the charge current LED may turn on To reset the state of the battery charger the reset switch must be depressed This will cause the battery charger to return to the bulk state or the over charge state In either case the battery charge cycle will begin and the charge current LED RED will glow brightly As the battery is charged the terminal voltage increases When the battery voltage reaches 13 7 volts the Over Charge State LED will turn on As the battery continues to charge the terminal voltage will rise to 14 5 volts and the charge current will decrease When the battery is fully charged the charger will switch to the float state which is appropriate for long term maintenance of the battery The battery can be left permanently connected the battery charge
7. resistor Sealed Lead Acid Battery Charger MkII Manual Rev 1 3 Page 5 J6 allows the current sense resistors to be selected using a switch If vou want both 1 Amp and 0 25 Amps or whatever current sense resistor vou choose make sure vou use a DPDT switch and parallel both sides of the switch Even good DPDT switches have enough switch contact resistance to effect the bulk charge current Poor qualitv vum cha brand and rotarv switches are not recommended Don t use them Q1 Base current is sinked by Pin 16 of U2 the UC3906 and added back to the charger output via Pin 15 R45 sets the trickle bias current when the battery is below the trickle bias threshold of 10v in this case Pin 14 has two capacitors to ground that provide loop stability 100nF is the main compensation capacitor 100p helps with RF by pass C11 gives some noise protection to the over charge state terminate input Too high a value causes the charger to start up in the over change state Too low a value causes the charger to prematurely trip to the float voltage state The calculation of RA RB RC and RD are shown in the Design Calculations see Appendix A Print it out for future reference or tweaking Each resistance value is made of up two resistors in parallel and then two of these parallel combinations in series In other words it is highly unlikely potentiometers are required You can use potentiometers if you want to but good ones are expensive Yum Cha potentiometers a
8. the loaded AC voltage of your transformer In the case of DC input power supply they do not need to be fitted although fitting a small value would be recommended So long the DC voltage across the capacitors is never less than 17v at your lowest mains supply voltage you should be safe make particular mention of this because designers sometimes forget that 240v AC mains does not mean you will have 240v AC RMS at all times I ve seen the voltage at my power points vary from 260v AC RMS to 222v AC RMS When designing also ensure your electronics will cope with the change in transformer secondary voltage due to change in primary voltage U4 provides a regulated 12v output for the operation of the other circuitry This is required due to the possibility of many and varied input supply voltages It became too hard to try and limit the current through the leds with a wildly varying power supply Unfortunately this regulator is a source of heat and thus will contribute to the temperature sensing error of the UC3906 battery temperature compensation U4 is located close to the rear edge of the PCB so it can be mounted on a heatsink or have a small heatsink added It is recommended that you mount this device on the heat sink and run some short leads back to the PCB Be careful though as long leads might cause the regulator to oscillate Charger Control Circuitry The exact operation of the UC3906 battery charger is a bit complex to detail here Not only th
9. there are a lot of trade offs that one goes through as a designer At some point in time you have to trade off performance reliability manufacturability against cost Otherwise who would want to build a 200 charger OK NASA would but who else Soapbox dis engaged Power Supply J1 is the power input to the charger The AC transformer required should ideally be 18v AC RMS It can be higher but the power dissipated by Q1 the main pass regulator will increase Please be careful with the unloaded voltage on the Electrolytic capacitors They can go pop and are 35v rated for a good reason The input power can also be DC should you already have a DC plug pack lying around The best source of power for this charger are plug packs from old laptops Almost always 18v AC 3Amps The rectifier diodes are type 1N5404 They are 3 Amp 400 v PIV type If you are only building a 250 ma bulk current charger you could replace them with common and cheaper 1N4004 diodes If you have a diode bridge of a suitable rating you could also use that but you might not be able to easily fit it onto the PCB 3 Amp diodes were chosen even though the bulk current maximum is 1 Amp because of input current rush into the electrolytic filter caps at turn on and they were just as cheap as 1N4004 From my source of parts anyway These diodes do get warm at 1 Amp they would be egg frying temperature at 3 amps The value of the main electrolytic capacitors will vary with
10. to reset into the bulk charge mode The way to implement this is shown in the new system wiring diagram which can be found in the Appendecies at the back of this manual Sometime simple solutions are just staring you in the face and often your blind to them This is where it is really handy to give you work to a college or friend and get his suggestions This modification is now standard and forms part of schematic revision 1 3 Note You might ask why can t you use the on off switch The problem with that simple solution is the filter capacitors It does take a considerable time for the charge to bleed off so its not really an elegant solution Modification Note Please be aware this modification requires the removal of a PCB track on the Rev 1 3 PCB Sealed Lead Acid Battery Charger MkII Manual Rev 1 3 Page 7 3 Construction Notes Interface Information The designator J is used to describe a connection from to the Mkil charger The following connections are used J1 18v AC RMS Supply Input This is the main power supply input for the charger The power supply should be fused for safety purposes with a 3 Amp or other appropriate sized fuse Do not short either side of the AC supply to chassis ground J2 Regulated Charger Output The is the regulated charger output that should be connected to some flying leads preferably using flexible heavy gauge wire with large alligator clips If you intend to use the charger near RF fields
11. 1 When the battery voltage eventually reaches 14 5 volts the ORANGE LED should go off and the GREEN LED should come on indicating a fully charged battery More operational advice can be found in the next section 1 2 3 4 5 6 7 8 9 1 1 But it doesn t work Suggestions Are the 7812 and TIP32C devices in the right place Did all voltage match the table Are my diodes in the wrong way around Have then been damaged if they are Are all my power diodes in the wrong way around With no battery connected is anything getting HOT The 7812 will get warm Are all IC s in the right way Have mixed up the BC817 and BC857 transistors Are the 1 resistors really 1 If the above suggestions do not help please contact Luke VK3EMEHOTMAIL COM for further assistance Sealed Lead Acid Battery Charger MkII Manual Rev 1 3 Page 11 Calculating Dissipation of Heat Sink Emphasis within this project has been on the end user to take the partial kit to the fully completed stage That mean choose the required bulk charge rates LED indicators on off switches fuses box power supplv etc However choosing the right heat sink can always be a bit of a hit and miss affair if you simply choose based on the This looks big enough principle The theory behind choosing the right heat sink is simple Unfortunately not all heat sinks especially second hand or recovered heat sinks have known thermal resistances However some suppl
12. II Manual Rev 1 3 Page 9 Smoke Test 1 Apply 18v AC with no battery connected to charger Check for smoke Did you see any If so bugger 2 Check that the green LED D8 is on 3 Check for 18v AC across cathodes of D4 and D3 4 Check the DC voltage across the main electrolytic capacitor Meas 24 8v 5 Check the PIN voltages as per the following table Pin Number U2 UC3906 Volts U1 LM358 Volts U2 LM393 Volts Q1 TIP32C Volts Pin 1 B 0 7 0 05 0 24 4 Pin 2 C 24 8 6 2 15 14 Pin 3 E 24 8 5 96 1 05 24 8 Pin 4 24 8 0 0 Pin 5 24 8 0 05 0 7 Pin 6 0 0 0 6 Pin 7 0 03 0 28 0 Pin8 0 7 11 94 11 94 Pin 9 9 45 Pin 10 2 15 Pin 11 14 3 Pin 12 3 2 Pin 13 2 2 Pin 14 14 7 Pin 15 14 3 Pin 16 24 4 Sealed Lead Acid Battery Charger MkII Manual Rev 1 3 Page 10 System Test Connect a battery of terminal voltage between 11v and 12 5v to the charger output J2 Connect a momentary switch to J7 Apply power to the charger The RED LED D9 should light indicating charge current Disconnect the battery The RED LED should go off and the GREEN LED D8 should light Reconnect the battery Check for 0 25 v drop across the current sense resistor When the battery voltage reaches approximately 13 5 volts the ORANGE LED should light 0 As the battery charges the RED LED should become DIM and go off
13. Sealed Lead Acid Batterv Charger Mk ll Revision 1 3 215 November 2000 c 2000 Luke Enriquez VK3EM Sealed Lead Acid Battery Charger MkII Manual Rev 1 3 Page 1 Disclaimer This batterv charger mav cause serious harm even if used correctiv It could over charge vour batteries and cause a fire burning vour house to ashes and making vour wife girlfriend mum or husband bovfriend dad prettv pissed off In fact l don t recommend using it mvself l suggest vou spend 300 on a commercial one then take them to court when it stuffs up This project is offered in good faith for non commercial purposes oniv If vou build this project vou agree that it is entirely your responsibility if something does go wrong and no damages in any way are the responsibility of VK3EM If after all this you still want to sue me don t bother l don t have any assets I spend all my time designing battery chargers you see This project is offered under the Open Hardware scheme All relevant design and manufacturing details are included You may not in any way shape or form use the information in this project for commercial purposes Revision History Rev 1 0 New development of MkII battery charger New documentation and schematics First build of Rev C PCB Rev 1 1 Added document sections on construction and testing Rev 1 2 Modified circuit for LED Current Monitor Added documentation on heat sink calculation Rev 1 3 Modified circuit to fix
14. When Pin 10 of U2 turns off which occurs when the float state has been entered Pin 2 of U3 is now higher than Pin 3 Pin 1 output goes low drawing base current from Q3 turning it and the LED on Thus the green LED turns on when in the float state Sealed Lead Acid Battery Charger MkII Manual Rev 1 3 Page 6 Elevated Charge Over Charge Indicator Circuitrv The only indication that the charger has changed from State 1 Bulk Charge to State 2 Over Charge is the fact that Pin 9 of U2 UC3906 goes low There is no other electrical change When Pin 9 goes low base current is drawn from Q4 PNP which turns on the orange LED Reseting the UC3906 Many IC s that look fantastic often have one or two problems that are just waiting to appear The reset problem of the UC3906 is one of those The reasoning behind it is quite simple Turn the charger on with no battery connected and the UC3906 defaults to the float charge state because the open circuit load appears to be a fully charged battery accepting no current When you then connect the charger to a battery with a battery voltage above Vs The state where the battery voltage is low enough for the charger to swap from float state to bulk charge state the charger remains in the float the charge state To properly charge the battery the UC3906 needs to be reset to the bulk charge state As with many designs there are always things you over look or fail to test completely My earlier desig
15. arger MkII Manual Rev 1 3 Page 15 3 Appendices 1 Schematics and Wiring Diagram 2 PCB Lavout 3 PCB Overlav 4 Bill of Materials 5 Design Calculations Sealed Lead Acid Battery Charger MkII Manual Rev 1 3 Page 16 BEI D1 D3 ji Ji 1N5404 1N5404 Vin J4 E T 02 D4 18v AC N C5 C6 KS 2 2200u 35v1772200u 35v Vin R48 AI EXT RED LED 1N5404 1N5404 D9 NF 2k2 02 U4 80817 Vin 7812 BEI 1 3 Nin a yout T CurrentSense 849 R53 4 2k2 10k c8 9 Kb c10 TOK S17 35v S47 16v 100n C3 R46 R5 kal For Best Results NF 10k Place 330k in parallel with R65 220R 4 Match R48 and R49 Match R50 and R51 Match R52 and R53 Match R17 and R22 C h C t M 2 HIA n 060 G OR OR oR A n I ss 12 BSE OR OR oR 12V 12V i 9 nos R36 NF denotes Not Fitted OR oR Q1 must be attached to appropiate heat sink Vin a J6 po TIP32C J2 3 N CurrentSense bi d 1 2 OR27 2 1 ati i SS BATTERY CHARGE SELECTION 5 1N5404 R55 09 c18 oF 100n 100p R2 R24 224 22k H RA R2 R27 1504 cs DRV SINK 18 pes Le 4 la 14708 15 me oe y Vin DRV SRC c21 R4 R30 t 3 CS comp bt in 15H INE 025 VIN 13 VSENSE 844 1000 R59 V SENSE RA RB RC and RD should use 1 1 OR 12 oR ii l i RB resistors for best accuracy H i
16. at but it s detailed to the nth degree in the data sheet and application note See links on the VK3EM web page Q1 is the main pass device It is a TIP32C PNP pass transistor The data sheet is provided website on the website for those who want to substitute another transistor When looking for a substitute pay careful attention to the maximum Ic and minimum Beta and Ft Too low a Beta at the UC3906 will be unable to sink enough base current at 1 Amp collector current Too high Ft and you ll end up with a free running RF oscillator Q1 will need to be mounted on a heat sink It is suggested that you use some medium gauge hook up wire to run from the circuit board to the transistor mounted on a heat sink I ve seen too many solder joints fail due to constant expansion contraction of hold cold metalwork See the construction notes Section 3 for details on calculating the size of the heat sink R2 and R3 are the current sense resistors These are the resistors that set the bulk charge current As mentioned before the charger tries to maintain 250mV across these resistors when in the bulk charge state 1 Ohm will give you a bulk charge current of 250mA and 0 25 Ohms will give you a bulk charge current of 1 Amp Just ensure that the value chosen is never lower than 0 25 Ohms Remember RESISTORS HAVE A TOLERANCE AND YOUR RESISTOR MIGHT FALL OUTSIDE THIS RANGE It s best to check it first by making up simple circuit and measuring the voltage drop across the
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18. fter careful consultation with the UC3906 datasheet applications note the Gates Energv Products sealed lead acid applications handbook and discussions with engineering friends over a few beers Regards Luke VK3EM 20 8 2000 The Float Voltage defines the long term maintenance voltage This voltage is temperature dependent and tracked by the UC3906 There is NO one correct float voltage Often an acceptable range of float voltages is printed on the side of the battery Use the value appropiate for 25 deg cel Float Voltage Vf 14V The Over Charge Voltage defines when the charger swaps from State 2 Over Charge to State 3 Float When this voltage is reached the battery is fully re charged and ready for use Over Charge Voltage Voc 14 5V The Reference Voltage refers to the on board voltage reference of the UC3906 that temperature tracks with the battery Use the value at 25 deg cel Reference Voltage Vref 2 3V The Threshold Voltage defines when bulk charge can begin Remember your battery might have a shorted cell be connected reverse polarity or even be 6 volts so 10 volts is a good voltage to choose The charger will trickle 25 mA until the battery terminal voltage reaches 10 volts The minimum input supply voltage is also needed for these eqn Threshold Voltage Vt 10V Threshold Trickle Current It 25mA Input Supply Voltage Vin 16 5V The Divider Current refers to the current flowing through the resi
19. he switch has low contact resistance It is recommended you use both sides ie parallel of a DPDT switch J7 Not Used This connection is not used for Rev 1 3 and onwards Special Notes a It is recommended that you print out the bill of materials Rev 1 3 and mark off the items as you solder them on If you are not familiar with the techniques of hand soldering surface mount components download A Guide to Prototyping with SMT from the VK3EM website http www geocities com vk3em b It is recommended that you do not use the charge current monitor circuitry unless you can match resistor values It may be easier to use an analogue meter and sense the voltage drop across the bulk charge setting resistors 1 First solder on all surface mount resistors Remember to check and match 1 resistors 2 Solder on all surface mount capacitors except the Tantalums 3 Solder the 2 surface mount IC s U1 and U3 Pay careful attention to the index Pin 1 The side that contains pins 1 to 4 is usually chamfered 4 Solder the SOT 23 transistors Sealed Lead Acid Battery Charger MkII Manual Rev 1 3 Page 8 5 Solder on the Tantalum capacitors 6 Bend and solder surface mount the 1N5404 power diodes Pav attention to the orientation of the cathode Bending is best achieved using a pair of needle nose pliers 7 Solder in the wire links There are 9 of them 8 Solder U2 the UC3906 IC You can use a quality IC socket if you wish
20. iers such as Farnell Electronics supply pictures dimensions and thermal resistance s of many heatsinks in their catalogue Thus a heatsink of unknown specification can be matched with the pictures and dimensions to estimate the thermal resistance Junetion Temperature 125 deg cel Junction to Case Thermal Resistance 3 125 deg cel per watt Power Dissapated Case to Sink Thermal Resistance 10 Watts 0 7 deg cel per watt Sink to Ambient Thermal Resistance cel per watt Ambient Ar Temperature 50 deg cel Fig A Schematic Diagram for Power Dissipation of TIP32C pass device A thermal system such as a device dissipating heat into an environment can be drawn schematically as shown above The power source is equivalent to an electrical current source Temperatures are equivalent to electrical voltages and thermal resistance s are equivalent to electrical resistance s The designers problem in this projects case is what is a safe value of thermal resistance for the heat sink This depends on what you consider a safe value is In this example the power is being dissipated by the pass transistor a TIP32C The aim is to ensure the junction temperature of the TIP32C does not exceed a safe value There are three things that limit the transfer of heat from the junction to the ambient air The first is the Junction to Case Thermal Resistance or 6jc This thermal resistance is due to the internal construction of the TIP32C and there is nothing
21. ion Normally Closed Push Button Switch zx DPDT Switch Good Quality _ l Parallel Both Sides of switch 7 AC Input Power AC Input Power l Not Used o On Off Switch Amber LED Anode Amber LED Cathode Anode this side LED Side View LED Top View Cathode Anode Cathode this side gt ge Current Sense Resistor a a Current Sense Resistor Electrolytic Electrolytic ve ve ve ve ve ve Terminal Block gt TIP32C Solder wire to hot side of 2k2 resistor or use hole if resistor not fitted ka SE wg Green LED Cathode Green LED Anode RED LED Anode RED LED Cathode Positive Battery Connection Negative Battery Connection Ground to Chassis Case Title Size Number Revision A3 Date 22 Nov 2000 Sheet of File E Electronics Projects SRESU SLA char2ddia B BytS chematics SLA Charger ddb 4 5 7 8 e w Bo pea pareas O L w s Cal D s W E XA UuoD as smmm HEI 106 553 mm 81 28 mm WW 82 18 ASN M H WJEN OOOZ 2 4954eUJ 1199 129 15385 R45 CR E Lu W n lh 20 a oes ECKE vn OI k SZ lvi II et et ku N N D m O N et m 0 d 0
22. n has a fairly simple two transistor circuit that pulled Vsense and OCTRM low which reset the UC3906 into the bulk charge state This solution had one major drawback By fooling the UC3906 into thinking battery volts are low the UC3906 tries to turn the pass device Q1 on harder In other words the current from the charger defaults to the bulk charge current This side effect has two problems If the battery you re trying to charge is close to Voc the instant charge of bulk charge current causes the battery voltage to rise above Va thus keeping the UC3906 in the float state In practice it causes erratic resetting of the UC3906 The device will eventually reset but not if your finger is a bit slow The second problem with the above mentioned side effect is a bit more serious Imagine if you the reset switch accidentally locked on The user would never suspect anything was wrong yet the charger would be locked onto the bulk charge state never able to terminate What a mess that would make Yum cha brand designers wouldn t care since cost is everything If you can always design fail safe systems especially when it involves batteries which can potentially release an enourmous amount of power in a very short time scale It turns out that the solution was really simple but never thought of it because of the way developed my original prototype PCB Just break the input power path between the main filter capacitors and the UC3906 This causes the UC3906
23. or near the bulk charge current 1A or 250mA As the battery is charged the LED will gradually become dim indicating that battery charge current is tapering off When the LED is off charge current is negligible This LED is only a rough indication of charge current ORANGE AMBER LED Over Charge State The Over Charge LED indicates the battery charger is in the Over Charge State In this state the battery terminal voltage will slowly rise to 14 5 volts As the battery approaches this voltage charge current decreases and the charge current will dim The charger attempts maintain 14 5v at the battery terminals until the charge current decreases to B 25 where B is the bulk charge current 40mA or 10mA When the charge current reduces this value the charger will change to the Float State and the green LED will light GREEN LED Float State The Float State LED indicates the battery charger has entered the Float State This state maintains the battery voltage at 14 v 25 deg cel which is suitable for long term battery storage Operation 1 Firstly calculate the appropriate maximum charge current Bulk Charge Current The maximum safe charge current for most sealed lead acid batteries can be calculated by dividing the capacity of the battery in Ampere Hours by six This is referred to as the C 6 charge limit However the maximum capacity of a battery is returned at a charge rate somewhat lower than C 6 When charging time must be kept to
24. r and is ready for use when required Sealed Lead Acid Battery Charger MkII Manual Rev 1 3 Page 14 Special Notes 1 Vou can connect the charger to the batterv then turn the charger on The charger will enter bulk charge state and the charge cvcle will begin In most cases the charger will alreadv be on when connected to a batterv In this case simplv push the reset switch 2 The charger may never finish in the over charge state Amber LED on If this occurs it is a good indication that your battery health is not good and the battery should be replaced or used for low power applications NEVER USE THE CHARGER WITH A LOAD CONNECTED It will cause inaccuracies in charging cycle 3 The charger may never enter the bulk charge state If the battery connected to the charger is only partially discharged the charger may skip the bulk charge state This doesn t really matter as the charge cycle will still be completed 4 The charger may be affected by RF fields This does not seem to be a problem at HF mainly VHF and above If this is causing problems use ferrite beads to help suppress RF interference 5 The charger may swap states at a voltage other than quoted in this manual Firstly don t forget that the charger temperature tracks the battery and this will naturally causes states to change at different voltage with different temperatures Component tolerance will also cause some errors in these voltages Sealed Lead Acid Battery Ch
25. ra gain is provided by U1B which is a standard non inverting DC coupled amplifier any jelly bean op amp that can run from 12v should work For best results match all the resistors in this circuit Even matched the circuit is only a very rough indication of charge current How rough well very rough so don t be too alarmed if it lights slightly even with no battery connected or if its off with over charging no complete It s just a cheaper alternative to a ammeter Note The charge current monitor circuitry really does not work well It s a total pain in the arse to get right The reason is due to the common mode rejection of the diff amp your trying to detect a 250mV difference down to a 25mV difference on a 24 volt DC signal In the partial kit version this circuitry is not loaded due to the time it takes to match resistors If you have the time to match them then it does work and is a lot cheaper and easier in terms of metal work than an analogue ammeter However for most people the use of an analogue meter will be easier due to access to SMT parts Float Charge Indicator Circuitry This is a fairly simple circuit that uses a LM393 or similar comparitor and observes the status of PIN 10 of the UC3906 U2 When bulk or over charging Pin 10 is low close to ground thus Pin 2 of U3 is lower in voltage than pin 3 which causes the output of the comparitor to be open circuit go high and thus the PNP transistor Q3 is off Led off
26. re cheap but they are yuck Horrible nasty hideous little creatures that go open and short and change their value depending on the day of the month Don t use them and don t complain to me if you do Remember you don t need to tweak a pot If you feel like you do consult your doctor RT limits the amount of trickle current when the charger detects a very low battery that may have a shorted cell You defiantly don t want to bulk charge a battery with a shorted cell Ensure that at the maximum supply voltage 25mA is never exceeded The formula for calculating this resistor value is in the appendices D5 stops you letting the smoke out of your pass device and UC3906 IC when you connect the charger up backwards to a battery Hey once bitten twice shy For a 1 Amp bulk charger the 1N5404 3 amp diode provides sufficient headroom Always factor in the idiot factor Even designers are idiots sometimes Usually after 1am and too many beers Charge Current Monitor Circuitry This is basically a differential amplifier that drives a transistor that varies the current through a led which varies its light intensity Take a Breath The problem is most op amps won t work with inputs above their supply rails Subsequently R48 and R49 in combination with R50 and R51 divide the differential DC voltage down to a level acceptable for the inputs on the op amp UTA is the classic differential amplifier circuit It s best if you use 1 or better resistors Ext
27. reset problem Updated schematic and BOM Added wiring diagram Fixed some documentation errors Change schematic revision to match documentation revision Added documentation to locate track to cut for reset circuit modification Thanks go to As with most projects they don t happen without help have been very fortunate and received a lot of help from the following people They deserve a very very big thank you John Wright VK3AJL for countless hours of technical conversation which inspired this project e Bryan Ackerlev VK3YNG for his help manufacturing the PCB s and supplying UC3906 s Adrian Hatherley VK3LK for organising the kit orders making kits up and soldering of surface mount bits Robyn my girlfriend for her patience This project is dedicated to Harold Hepburn VK3AFQ who was one of the most proliferic amateur radio home brewers have been privelidged to meet R I P Sealed Lead Acid Battery Charger MkII Manual Rev 1 3 Page 2 Contents Section 1 Introduction This section details why you should build and use a Sealed Lead Acid Batterv Charger based on the UC3906 IC from Unitrode Section 2 Design Notes This section details how the charger was designed what was considered and why it was done This section would be helpful if you intend to modify the charger to suit your own needs i e change the voltage to 6 volts This section is more for my own reference than anything else Section 3 Cons
28. stor divider string that essentially defines the voltage sensing of the UC3906 The value of this current is very flexible ie it doesn t matter too much but values between 50uA and 100uA are reconmended If vou find vou can t easilv make up the final resistor values with the combination of E12 resistors offered change this value and trv again Vou should eventuallv find a combination of Id and Ra Rb Rc Rd that will utilise E12 resistor values Divider Current Id 66 54 A Everything that can be defined has been defined well sort of Now the calculation can begin Get out your trusty pocket T calculator spend the next 4 hours looking for some batteries that will fit the bloodv thing and continue when your ready Oh yeah kinda progressed from cave man calculator days and use a a mathematics program instead A spreadhseet could be useful too Either way here we go Calculate the voltages for the state transistions V12 and V31 These formulas can be found on page 5 of the UC3906 datasheet V12 0 95 Voc V12 13 775V V31 0 90 Vf V31 12 6V Now calculate Rc _ Vref Id Now calculate Rsum which gives us Ra and Rb Re Re 34 586 KQ Vf Vref Rsum RT Rsum 175 94KQ Now calculate Rd Rd Vref Rsum T Voce NI Rd 809 323 KQ Now calculate Rx which gives us Ra Rc Rd Rc Rd Now calculate Ra Rx Rx 33 169 KQ Vref Vt Ra 161 014KQ Ra Rsum sl Now calculate Rb
29. termine what the maximum safe operating junction temperature will be a Read the datasheet The maximum possible operating junction temperature is 150 deg Use a value 25 deg lower 125 deg for safe reliable operation Thus Tj 125 deg worst case 3 Determine what the maximum ambient temperature will be a Worst case ambient should be based on environment Normal environments can have ambient temperatures up to 50 deg cel Harsh environments could get as high as 70 deg cel Ta 50 deg 4 Determine what the known thermal resistance s are in the system a 3 125 deg cel per watt From Datasheet b 8cs 0 7 deg cel per watt From other research 5 Calculate the maximum thermal resistance of the heat sink sa Refer to Fig A a First note all known parameters Pd 10 Watts Tj 125 deg cel max Ta 50 deg cel max ejc 3 125 deg cel per watt 006 0 7 deg cel per watt b Now remember V IR well guess you do So using the same principles write a system equation Tj Ta Pd 6jc 6cs Osa With a bit of manipulation Tj Ta jc 006 Osa Pd Now fill in the real values to calculate 0sa Thus Osa 3 675 deg cel per watt Sealed Lead Acid Battery Charger MkII Manual Rev 1 3 Page 13 4 User Manual Status Lights RED LED Charge Current The Charge Current LED represents the amount of battery charge current When glowing brightly charge current will be at
30. that can be done about it 6jc is quoted in the TIP32C datasheet as being 3 125 deg cel per watt This means for each watt dissipated the junction temperature will be 3 125 deg hotter than the case When the TIP32C is mounted on a heatsink some sort of insulating washer is usually used due to the metal tab of the TIP32C being electrically connected to the collector You don t have to use an insulating washer you can insulated the heat sink instead but it is usually easier to insulate the transistor with an insultating washer Unfortunately this adds more thermal resistance to the system This is known as Case to Sink thermal resistance s or 005 Using thermal grease and good mechanical compression with a flat surface heatsink helps to minimise cs Using a good thermal conducting rubber washer compression and thermal grease would result in a thermal resistance close to 0 7 deg cel per watt 0056 will depend on the type of washer you use so if your unsure use 1 deg cel per watt to be on the safe side The final thermal resistance in the system is the heatsink itself known as sink to ambient thermal resistance or 058 To determine what heat sink we need to use the maximum value of 6sa for the heat sink needs to be calculated Before this can be calculated the parameters of the system must first be defined When it comes to component lifetime it is always wise to err on the side of caution For instance according to the TIP32C datasheet the ma
31. truction Notes This section details how to construct the charger with a MkII PCB and the appropriate components It also contains hints and tips if you are building your own charger on vero board or by some other means Section 4 User Manual This section details how the charger works and what those funny lights mean Section 5 Appendices This section details 1 Schematics and wiring diagram 2 PCB Layout 3 PCB Overlay 4 Bill of materials and 5 Design Calculations Please Note have spent many hours documenting as much information as possible If this documentation does not answer a question or concern try reading the Frequently Asked Questions on the website If that does not help e mail me at VKZEM HOTMAIL COM All information intellectual property circuits and circuit boards documented are c 2000 VK3EM They are for non profit use only Refer to the website for up to date information This project has been placed in the public domain for the purposes of education Sealed Lead Acid Battery Charger MkII Manual Rev 1 3 Page 3 1 Introduction Why use a special charger A lot of people have their own view on charging batteries A lot of people get it wrong What do mean by wrong If you spend big dollars on batteries or vou obtain good batteries for free vou want to get two things maximum life and maximum capacitv A significant influence on these two factors is the wav the batterv is re charged especiall
32. ttery 2 The failure to temperature track a float charger and 3 The excessive discharging of a battery Where to find further information One of the best sources of information is the Gates Energy Products applications manual for sealed rechargeable batteries As Murphy s law dictates it s out of print and not available in PDF form It should be because there are many hours of informative reading to be had with this book The next best source is Unitrode Application Note U 104 This application note can be downloaded at the VK3EM website It is also available via Texas Instruments who now own Unitrode Please Note It is impossible to detail exactly how to recharge a sealed lead acid battery It will vary with different manufacturers materials constructions electrolytes discharge cycles etc All wish to point out with this project is that using a UC3906 based charger is a few orders of magnitude better than a voltage regulator set at 13 8 volts Sealed Lead Acid Battery Charger MkII Manual Rev 1 3 Page 4 2 Design Notes Introduction Please make sure you have a copy of Mk II schematics and design calculations in front of you when you read this section You will find them in the Appendices This section of the manual should give you a fair idea of what s going on inside my head when designed this charger As always might have done some things differently with hindsight encourage constructive criticism but remember
33. v seal lead acid cells with gel electrolvte Get it wrong and vour getting less life and capacitv than vour batterv can offer Sealed lead acid batteries are quite expensive so building a good charger is a worthwhile investment Buving one is the next best option but good ones are verv expensive The VK3EM Sealed Lead Acid Batterv charger is based around a UC3906 integrated circuit from Unitrode Now owned by Texas Instruments specifically designed for charging SEALED lead acid batteries It is not a cheap and nasty battery charger It is an accurate battery charger designed specifically to get maximum life and capacity from your batteries It can also be built for a modest price Some key points about recharging sealed lead acid cells can be detailed here 1 The chemistry of sealed lead acid cells with a gel electrolyte is different to a standard lead acid cell as used in automotive applications 2 The use of a controlled over charge is required to force chemical reactions to occur that lead to maximum battery capacity and life 3 The use of temperature tracking is required as the battery voltage varies with temperature 4 A slow controlled charge gives maximum battery life In my opinion the following are the three biggest factors that cause a dramatic reduction in useful battery life and capacity not in order of preference 1 The failure to use an over charge cycle during the charging process i e under charging the ba
34. ximum operating junction temperature is 150 deg cel However it would be logical to assume that keeping the junction temperature to a maximum of 125 deg cel would result in less stress on the transistor and thus a longer lifetime Similarly your choice in heatsink might be fine at room temperature but what Sealed Lead Acid Battery Charger MkII Manual Rev 1 3 Page 12 about when accidentallv vou sit something on top of the charger or use it in a tin shed where the ambient temperature could reach 50 deg cel on a hot dav Obviously these are extreme circumstances that are not likely to happen But they can so you should always way up the consequences If you can afford it design in the safety margin If you can t be aware of what the limits are The general procedure for calculating heatsink size is as follows 1 Calculate the maximum power dissipation of the pass device a Maximum dissipation occurs at maximum bulk charge current with minimum battery voltage b Connect a temporary heatsink to the pass device and with the charger bulk charging a battery at the maximum rate measure the DC voltage across the main filter capacitor ie 20v input to the pass device c Since the charger will trickle charge a battery with a terminal voltage less than 10v the maximum voltage differential across the pass device will be 20v Input 10v Battery Voltage 10v Differential Thus if P IV then power dissipated by the pass device is 10 Watts 2 De

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