Electrical Circuits and Meters –– Study Guide Course Objectives
Contents
1. Capacitors are rated in microfarads A capacitor s rating is determined by three factors e The area of the plates To find the value of capacitors e The distance between the plates placed in parallel simply add the e The dielectric material values of the indradual capacitors Capacitors in Parallel lf two or more capacitors are placed in parallel in a circuit figure 3 16 the total capacitance is determined by adding the individual capacitor values as shown by the equation C C1 C2 Parallel Therefore two 1000 uF capacitors in parallel have a total of 2000 uF capacitance Keep in mind that combining capacitors does not increase the working voltage Any C 2 C C number of capacitors in parallel will have the same working voltage as the capacitor with the lowest working voltage rating Figure 3 16 Capacitors in parallel Note It is always a good idea to discharge any capacitor by touching the leads together before connecting it to a circuit or meter Applying Capacitors for Noise If a noise or pop occurs in the audio system when a switch or contact is deactivated capacitors can be used to filter out the noise Referring to the diagram below the first 47uF capacitor will be placed across the switch contact 1 to absorb any surge current at deactivation If the pop is gone you re finished If not place a second capacitor leaving the first from the positive side of the switch contact to ground 2 and test again T2. The red lead is inserted here for volts ohms and diode testing Rotary dial set to a position other than mA A or LA This DVOM is also equipped with an alert feature that serves two purposes It will emit a constant chirp if a lead is inserted into either the A or mA uA terminal input and the rotary dial is not turned to the mA A or uA position It is designed to prevent damage to the fuses and meter by accidentally using the meter in an incorrect configuration The alert also lets you check the fuses by putting the rotary dial in a non amperage position V or Q and inserting a lead into each of the amperage inputs to listen for chirp If a fuse is blown the alert will not sound Make sure you check both inputs since there are two fuses and ensure that the lead isn t connected to anything else before inserting into the terminal as damage may occur 5 Rotary Dial The rotary dial has eight positions for selecting the desired measurement Starting from the Off position and moving clockwise they are e Off No power is applied to the meter e V AC Volts e DC Volts e mV Millivolts up to 400 mV DC 0 Q zm Continuity Ohms Capacitance e bi Diode test e mA A AC and DC Milliamps Amps e uA AC and DC Microamps Pushbuttons Eight pushbuttons are used on this DVOM to change display readouts and some rotary dial functions Beginning with the round yellow button and moving clockwise they are 6 Yellow Button Displ
3. 2004 Melior Inc Electrical Circuits and Meters Study Guide 12 Rel A Relative Delta The Delta triangle is a mathematical symbol for change The Rel A button is used when the meter is making very small resistance measurements Touching the leads together and pressing Rel A will zero out any resistance there may be in the leads themselves and allow for a very precise resistance measurement 13 Hz Frequency Counter and Duty Cycle When the Hz button is pressed the meter changes to measure cycles per second while a second press will read duty cycle percentages Duty cycle percentages can also be used to determine dwell readings Digital Display 14 The display is a digital and analog LCD readout screen for all meter functions Turning the meter on while holding any button will allow the user to see all of the possible display segments on the screen Each screen function is self tested for one second when the meter is turned on and to save battery power the meter will also turn itself off if not used for a certain amount of time The following explanations of the meter s features will show each of the segments and its application 15 Analog Display Located along the bottom of the screen the Analog Display is a 32 segment pointer that updates 40 times a second and is most useful for rapidly changing values It is also useful in determining the value of capacitors This feature does not operate in Frequency Counter or Peak Min Max modes
4. we will look at electrical fundamentals and how they determine the construction and application of all automotive circuits Let s begin first with a question What is Electricity m Em Electricity may be defined as The movement of electrons through Defuution of Electricity a conductor having the ability to do work Where does Electricity come from The movement of electrons An easy answer might be batteries generators a wall outlet etc though a conductor having the But let s take a closer look at the origin of electricity ability to do work Atoms The atom figure 1 1 is composed of a nucleus including Protons positive charge and Neutrons no charge with revolving Electrons negative charge Each atom has a different number of electrons around its perimeter figure 1 2 The movement of these electrons makes up electricity 2004 Melior Inc Electrical Circuits and Meters Study Guide UN MA 7 Neutrons J gt Protons Electrons Atoms are made up of protons amp neutrons in the nucleus and electrons in orbit around the nucleus Figure 1 1 The Atom Figure 1 2 Atomic Structure Let s look at one specific example of an atom that FREE ELECTRON M we re familiar with copper The copper atom figure 1 3 has 29 electrons around its nucleus located in different layers or shells around the nucleus two in the first shell eight in the second and 18 in the third shell for a
5. 16 Analog Display Scale Used in conjunction with the Analog Display from number 15 the Analog Display Scale applies values to varying signals that are easier to read than those on a continuously changing digital readout It has a O to 10 display that scans up to four times for any given test value Each scan is of the maximum range value 17 Analog Display Polarity Located to the left of the Analog Display it indicates whether the signal has a or polarity 18 Input Range The Input Range in the lower right of the display will show the range of scale currently being used by the meter This number shows the largest value that can be measured in that range such as 4V 40V 400V 4000V etc Turning the dial to the mV scale will also display the mV display segment Note that when the dial is set to mV the display range can not be changed from 400 mV 19 OL Out of Limits Also referred to as Overload an OL display indicates that the range is too low for the input being tested For instance if a 12 volt circuit is checked with the meter in a 4V range the display will read OL It tells the technician that a larger scale is needed 40V to read the signal Too often technicians interpret OL to mean that the system is malfunctioning rather than requiring a simple meter change 20 AUTO Autorange Located in the upper left corner the AUTO feature will select the best range to use for a given measurement The meter starts in AUTO mode e
6. There are two different ways to look at current flow in a complete circuit one is called Electron Flow and the other is Conventional Flow An understanding of the difference will help the technician in the use of electrical diagrams The Electron flow theory says that since electrons do the work in a circuit and since electrons have a negative charge then current must flow from the negative battery terminal through the circuit and into the positive terminal This is used mostly by electrical engineers Conventional flow theory says that since positive is greater than negative then current must travel from to Conventional flow is used by the automotive industry and as such all of our electrical diagrams will be written in that format DC and AC The current in any circuit will be one of two types Direct Current DC or Alternating Current AC 2004 Melior Inc Electrical Circuits and Meters Study Guide Direct current always flows in the same direction in a circuit whereas Alternating current flows in one direction then reverses itself and moves in the opposite direction Batteries and other steady state devices produce DC figure 1 6 We will also see what is referred to as Pulsating DC Pulsating DC is often incorrectly called AC although it is merely DC with a varying voltage Technicians will find that the vast majority of automotive circuits operate on DC Alternators and wheel speed sensors produce AC figure
7. an Ohms value resistors also have a wattage value Recall from module 2 that wattage Power is the product of Voltage and Current given by PzIxE As such resistors are not rated in either voltage or current but rather in watts to limit their heat exposure For example if a resistor is rated at 10 Watts and is used in a 12 Volt circuit then the maximum allowable amperage is 833 Amps I P E If we decrease the voltage by half to 6 volts then the current can double without damaging the resistor P IxE or P 1 66 amps x 6 volts or P210 watts Most often the wattage rating of a resistor is determined by its size Some of the most common sizes are shown in figure 3 13 1 10 WATT i 1 4 WATT sm 1 2 WATT Hlil 7 1 WATT J 2 WATTS Figure 3 13 Resistor sizes by watts _ STEERING WHEEL CONTROLS RETURN STEERING WHEEL CONTROLS INPUT Figure 3 15 Steering Wheel Controls 31 2004 Melior Inc Electrical Circuits and Meters Study Guide Variable Resistors A variable resistor is one whose value can be changed either manually by turning a knob or sliding a lever or automatically by Variable resistors can be used altering the temperature The range of values for any variable resistor is determined by the material used in its construction or by the size and number of turns in wire wound units Some v
8. because it will give false readings Figure 1 18 Resistance Measurement 4 2004 Melior Inc Electrical Circuits and Meters Study Guide Module 2 Overview In Module 1 of this series we introduced the concepts of voltage voltage drops current and resistance as well as digital multi meter usage In this module we expand on the applications of those concepts as well as adding Power Ohm s Law and Magnetism General Electrical Rules Applications of voltage current and resistance follow some general electrical rules If the Resistance remains the same e As voltage increases current increases e As voltage decreases current decreases If the Voltage remains the same e As resistance increases current decreases e As resistance decreases current increases Ohm s Law In electrical circuitry if any one of the three variables V A Q changes it will affect at least one of the other two An equation allows us to determine the effect of that change called Ohm s Law Ohm s Law is expressed as follows Ohm s Law Formulas Voltage E IxE E IxR or V AXQ Current ER Resistance E ET In this equation e E Electromotive Force Voltage e Intensity Amperage e R Resistance Ohms Simply by rearranging the variables we can calculate a value for any one if we know the other two Variations The primary formula for Ohm s Law is E x R or Volts Amps x Ohms This tells us t
9. e Potential Difference e Electromotive Force or EMF or E For the purposes of this course we will use the term Voltage and either the V or the E designation Also remember that voltage is merely a pushing force and does not perform the real work in an electrical circuit Current Current is the movement of electrons in a circuit Like our voltage and water pressure analogy from Current is the movement of electrons through a conductor before current would be compared to the actual water moving through the hose It is current rather than voltage or power which causes the lights to shine the motors to turn and the fuses to blow Conventional Current Flow is positive to Unlike voltage which is the presence of electrons negative Electron Current Flow is negative to current is the movement of electrons through some T sort of conductor The greater the number of pos electrons past a certain point the greater the current or Amperage Automotive systems vary from very high to very low current For instance the starter system typically is high current being in excess of 100 Amps whereas spark plug current is very low many confuse high voltage with high current in ignition coils at much less than one amp Current is generally referred to in one of two terms e Amperes Amperage Amps or A e Intensity or I For our purposes A and will be used interchangeably Conventional Current Flow vs Electron Current Flow
10. high flux density is strong whereas a weak magnet has few flux lines or low flux density Students may be familiar with instances where magnets have become weak and caused operational problems such as a Crank Position Sensor that causes the engine to cut out at higher rpm s or an ABS sensor that drops to zero while the The stronger a magnet is the vehicle is still moving These problems are most often caused by a greater its flux density drop in the flux density of the magnet itself but will not be seen in a resistance check of the wire winding Magnetic Force As electric current is passed through a wire it creates magnetic lines of force around the wire If that wire is wound into a coil it creates North and South Poles much like a permanent magnet except that it can be turned on and off and made stronger or weaker figure 2 6 Because many metals are good magnetic conductors a core is often used in the center of the coil to enhance the strength of the electromagnet Most often the core is part of the design like the plunger in a starter solenoid or the pintle in a fuel injector If a number of different magnetic devices were cut open it would be apparent that the size of the 18 02004 Melior Inc wire and the number of turns around the core are not the same For various applications designers will change the wire size the number of turns the diameter of the coil the length of the coil and the applied current to get ju
11. to solve Amps 6 Circuit current is now known to be 6 Amps In figure 2 4 the resistance is unknown The given source voltage is 12 volts and the current flow is 6 amps Find the resistance by using Ohms Volts Amps R E I Our known values yield Ohms 12 Volts 6 Amps After dividing we find Ohms 2 This circuit has a total resistance of 2 Ohms 16 Electrical Circuits and Meters Study Guide 20 TOTAL CURRENT 6 amps TOTAL RESISTANCE 2 ohms SOURCE VOLTAGE volts 6A Figure 2 2 Calculate voltage using Ohm s law 20 SOURCE VOLTAGE 12 volts TOTAL RESISTANCE 2 ohms TOTAL CURRENT amps 2A Figure 2 3 Calculate current using Ohm s law 20 GA SOURCE VOLTAGE 12 volts TOTAL CURRENT 6 amps TOTAL RESISTANCE ohms Figure 2 4 Calculate resistance using Ohm s law 2004 Melior Inc Electrical Circuits and Meters Study Guide Power Unlike Voltage Current and Resistance Power is not a direct measurement for an electrical property Power is the output or rate of work performed by a machine As with gasoline and diesel engines motors are rated as to the number of horsepower they produce However many other electrical The formula for measuring power is P IxE devices eg light bulbs are rated by the amount of power they consume rather than by output Power symbol P is expressed in Watts but can be converted to horsepower using this equation Power is rated i
12. total of 28 That leaves just one electron in the outer shell or Valence shell and this single electron is the one that does all of the electrical work Atoms that have one or two electrons in the valence shell are called conductors They include copper gold silver aluminum nickel zinc and others That is why they are used to make wire Figure 1 3 Free Electron from Copper Atom Atoms with a large number of electrons in the outer shell are Atoms with or 4 Valence electrons are conductors called insulators and include e Atoms with 3 4 or 5 valence electrons are semiconductors rubber plastics etc Those atoms that have around four electrons in the valence shell are called semiconductors Semiconductors are used to make electronic components such as transistors which will be discussed later e Atoms with 6 7 or amp valence electrons are insulators Electrical Energy When a sufficient electrical force Voltage is applied to a wire the one free electron figure 1 3 in the outer shell can Electrical force is applied to valence no longer hold on to the atom It then begins to carry its electrons which causes them to move negative charge down the wire much like feeding Ping Pong balls into a paper towel roll The higher the applied voltage the more electrons are moved Those moving electrons operate the lights horns computers and every other electrical device on your car or truck If a substance has a large numbe
13. 1 7 In order for a current to be AC the current flow in a circuit must actually change direction e Direct Current always flows m the same direction e Alternating Current must change direction Volts 12 Volts DC 10 Time TIME Figure 1 6 Direct Current or DC Figure 1 7 Alternating Current or AC Resistance Resistance is anything that opposes the flow of electrons As the resistance in a circuit is decreased the amount of current increases and as the resistance increases the current decreases Comparing this once again to our water hose analogy we find that if we use a larger diameter hose less resistance we will carry more water more current Conversely a smaller hose higher resistance carries less water lower current Some resistance is necessary in any electrical application as it is used to convert electrical energy to other forms such as heat defogger grids or light and to limit circuit current Materials with low resistances such as copper wire we use as conductors while materials with high resistances rubber for instance we use as insulators What determines a substance s resistance Several things including e he number of free electrons in the outer shell of the atom e Length of the conductor A longer wire will have a higher resistance e Cross Sectional Area The larger the circumference of a conductor is the less its resistance Example A 1 0 mm wire 16 Ga has less resistance than a 3
14. 5 mm wire 22 Ga e Temperature generally as a substance is heated its resistance increases exceptions to this rule will be seen later Other factors also affect the resistance in a circuit such as loose connections corrosion broken wire strands etc In contrast to the useful applications of resistance mentioned before these will cause a circuit to operate inadequately or not at all We will also become familiar with devices called Resistors whose function is to limit the current or voltage to another Eesistance is measured m Ohms and is part of a circuit and thus control its operation even the Greek letter omega 2 2004 Melior Inc Electrical Circuits and Meters Study Guide The standard unit of measure for resistance is known as the OHM and is given the Greek symbol Omega Q An Ohm is defined as the amount of resistance that when applied to a one volt circuit will limit the current to one Amp Thus one volt through one Ohm equals one Amp Students may choose to use either the Ohm symbol or a capital R to signify resistance Source Voltage Source voltage is a term used to refer to the amount of voltage available to move electrons through a circuit For Source voltage is the voltage applied most automotive applications source voltage should be in the 12 14 Volt range However many of today s sensors operate on a 5V supply while some actuators will use 7 8 or 10 volts Electronic computer components m
15. ECIMAL POINT TO AND FROM BASE UNITS 3 3 3 3 4 4 M K m Li MEGA KILO BASE UNITS MILLI MICRO Figure 1 10 Prefix Chart Each of the prefixes is a factor of 1000 as compared to the next and converting is a simple matter of moving the decimal point three positions three zeros to the left or right figure 1 11 For example 3 500 ohms is a base unit ohms and if we need to know how many KQ that would be we simply move the decimal point three places to the left since Kilo is to the left of Base on our chart Likewise if we have 1 2 amps and want to convert to mA then we move three places to the right to get 1 200 mA Figure 1 11 Mega M 1 000 000 1M 1 0 0 0 0 0 0 base units Decimal Point 6 places right Kilo K 1k 1 0 0 0 base units Decimal Point 3 places right Milli mK 11000 gt 1m Decimal Point 3 places LEFT 1 1 000 000 0 0 0 0 0 1 base units Decimal Point 6 places LEFT Micro 1u X hy ee In order to add values they must be in the same units It is not possible to directly add 9 volts and 340 mv one or the other must be converted first Only eight of the above values are typically used They are KV V mV A mA MQ KO and Ohms 2004 Melior Inc Electrical Circuits and Meters Study Guide Scaling If a technician is trying to measure 10 000 000 ohms with the meter set on a 400 Q range the display will read OL since the maximum Always use the corr
16. Electrical Circuits and Meters Study Guide 02004 Melior Inc Course Objectives Upon completion of this course technicians should understand and be able to apply their knowledge of Electrical properties atomic structure voltage current resistance AC and DC Digital Volt Ohm Meters setup usage and procedures Making measurements on circuits Electrical principles and variables Ohm s Law Power magnetism Series parallel and series parallel circuitry characteristics measurement methods and applications Reading and interpreting schematics Components and applications fuses relays solenoids fixed and variable resistors capacitors and others Using the Job Sheets As you proceed through the online modules on some pages you will find links that will open a window with a printable procedure or job sheet containing hands on lab activities based on the NATEF standards related to the content you are studying When you come upon a procedure or job sheet link click on it and print the job sheet for completion in the shop See your instructor for guidance in completing the job sheets Some jobs sheets will require supplemental materials such as a vehicle service manual equipment manual or other references Module 1 Overview In order to properly diagnose and repair automotive electrical systems the technician must first have an understanding of the basics underlying how those systems operate In this section
17. Induction We have already seen that we can create a magnetic field with an applied current but now we will find that we can also produce a current from a magnetic field The process is called electromagnetic induction When a magnetic hae field and a wire are moved near each other a voltage is a current in a second windmg produced in the wire that causes a current to flow This is called an Induced Voltage As long as the movement continues the current will continue but if the motion stops the current will stop Electromagnetic induction occurs when a varying magnetic field creates Applications of electromagnetic induction are typically in generators or alternators and in transformers or ignition coils Generators and alternators are designed similarly to motors in that they have a field winding and an armature winding How they differ in terms of their induction is this generators have a coil that turns and a magnetic field that is stationary whereas alternators have a magnetic field turning inside of a stationary coil The amount of induced voltage and therefore current depends on several factors e Strength of the magnetic field e Speed of motion between the coil and the magnetic field e Number of conductors in the coil Transformers Transformers are another type of device that works by electromagnetic induction A transformer is constructed with two separate windings a primary and a secondary wrapped around a common meta
18. S IRA There are two different mathematical formulas used far calculating Applying our values we have resistance 1 RT 1 05 033 1 RT 183 RT 1 183 RT 5 460 The Windows calculator on your computer can be used to make these calculations You can open the Windows calculator by clicking on Start and then Run Type the word calc without the quotes in the space provided and then click the OK button Try both of these methods using our example numbers of 10 20 and 300 If your calculator has a 1 x inverse key the formula can be entered by pressing the calculator keys shown in parentheses in order as follows R1 1 x R2 1 x R3 1 x 1 x answer If no inverse key is available then figure the resistances by pressing the calculator keys shown in parentheses in order as follows 1 R1 M 1 R2 M 1 R3 M 1 MRC or MR 2 answer 1 x is the inverse key is the addition key M is the Memory Add key MRC or MR is the Memory Recall key is the Division key and 7 is the Equals key Parallel Circuit Current Unlike series circuits where current is always the same parallel circuits can have a different amperage value for each branch in the circuit You will recall that the voltage drop is the same for parallel branches but if each branch has a different resistance then Ohm s Law can be used to determine that the branches have different currents The total circuit cu
19. ach time it is turned on and the RANGE button must be used to manually switch scales Caution must be used with Autorange as it automatically changes the scale in the lower right of the screen and the display can be easily misread 21 Low Battery This symbol alerts the user that the battery is low and readings may be affected Replace 9V battery before continuing 22 Negative Polarity When shown to the left of the digital numbers the minus sign signifies a negative polarity reading usually just reversed leads This symbol is for the display numbers only and should not be confused with the symbol for the analog scale 23 This beeper symbol notifies the user that the continuity audio alert is active for the scale 24 Relative Mode The A Delta symbol displays to let the user know the leads have been zeroed for making precise measurements Pressing the REL A button turns this feature on and off 25 100 ms Normal Speed for Min Max Mode When in Min Max mode this symbol indicates that the recording function is operating in 100ms increments The Peak Min Max beeper button will change the record time to 1 ms increments for greater accuracy and usefulness in tracing intermittents 26 Record This identifier informs the user that the meter is currently recording the signal being probed 2004 Melior Inc Electrical Circuits and Meters Study Guide 27 Max Pressing the Min Max button once while in record mode will dis
20. ariable resistors change at the same rate throughout their range linear while others will change more quickly at first then taper off later non linear either to control voltage output or to irut current Rheostats A rheostat is a mechanically operated variable resistor with two connections It is used to change the current in a circuit based on its position Dash light dimmers some fuel gauge sender units and wiper delays are all applications of rheostats Potentiometers Potentiometers are also mechanically operated but unlike rheostats they act as voltage dividers rather than as current limiters Pots have three connections and are commonly used as sensors to send varying voltage signals to a vehicle s computers Some examples of potentiometers are Throttle Position sensors EGR Position sensors Accelerator Pedal Position sensors and transistorized Dimming Control Thermistors Thermistors are solid state variable resistors that operate based on the amount of heat applied There are two types of thermistors Positive Temperature Coefficient PTC and Negative Temperature Coefficient NTC A PTC will increase its resistance as the temperature increases whereas NTCs will have a decreased resistance from increased temperature PTCs are commonly used to protect circuits from excessive current and are found in applications such as window motors and door locks NTCs however are most often used for sensing temperature and to input vol
21. ay Back Light Pressing the yellow button turns on the display light for easier viewing in dark places The light automatically turns off after 68 seconds to preserve battery power 7 Blue Button AC DC Resistance Capacitance The blue button will switch the display between AC and DC readouts when the rotary dial is in an amperage position If the dial is in the Q position it changes from resistance ohms to capacitance F 8 Min Max The Min Max button is part of a recording function that will catch and save the highest max lowest min and average values of Volts Amps or Ohms being tested It is most useful for finding intermittent glitches 9 Range Manual ranging allows the user to change the display scale such as from 4V to 40V to 400V and so on When a meter is first turned on it will come up in AUTO mode which will select the necessary range for the test being performed 10 Hold Sometimes it isn t possible to take a measurement and read the display at the same time If the Hold button is pressed whatever measurement is taken will remain on the display after the leads have been removed That readout will remain until a different measurement is made 11 Continuity Beeper Peak Min Max When the rotary dial is in the Q position if a measured resistance is close to zero continuity the meter will beep Pressing the button will disable the beep function Peak Min Max function will be shown later as part of the Display features
22. ay use less than one volt It is most important for the electrical technician to be aware of the amount of voltage that should be applied to a circuit to insure that misdiagnosis does not occur to a circuit when there is no current flow Voltage Drop Voltage drop is very important in the diagnosis of HIGH LOW electrical circuits To explain voltage drop let s return PRESSURE PRESSURE to our water hose analogy once again At one time or oS another we ve all folded a hose in half to stop the ded a c ig water flow When that happens the water pressure i e remains the same between the kink in the hose and the faucet while the pressure on the other side of the ORIFICE kink is zero or almost zero This difference is called the pressure drop and it is principally the same as in electrical applications Voltage drop is then defined as HIGHER LOWER the difference between the voltage on the inlet side of VOLTAGE VOLTAGE a device compared to the voltage on the outlet side figure 1 8 Comparing that value to a written specification will assist the technician in determining the fault with the system VOLTAGE DROP Voltage drop 1s the difference 1n electrical pressure between the two sides of a device Figure 1 8 Voltage Drop Digital Multi Meters In order for a technician to diagnose an electrical problem he must first test the system to determine which part is malfunctioning Part A good digital multi meter must of system te
23. c Electrical Circuits and Meters Study Guide Motors Electric motors also work on the principles of electromagnetism but unlike relays or solenoids their function is to produce rotary spinning motion Motors have two primary components an Armature or rotating element that produce rotating motion and a stationary Field Coil Motors can have permanent magnet armatures with wound field coils permanent magnet field coils with wound armatures or have both the armatures and field coils wound Permanent magnet armature motors are used in Alternating Current applications and are not common in automotive applications Motors are electromagnetic devices In a DC electric motor voltage is applied to the armature winding through a pair of carbon brushes and a split ring called a commutator The commutator has the effect of alternately changing the poles of the armature coil from north to south and back again for each half revolution of the armature For example let s assume that a point on the outer Field Coil has a north orientation The half of the armature that has a south polarity would be attracted to that point and would cause the unit to rotate as they pulled closer However just as the two points align the commutator switches the armature polarity and the new south point is now on the opposite side of the armature winding which causes it to attract the north point on the field coil and the rotation continues Electromagnetic
24. ctrical Charges on capacitor plates 3 2004 Melior Inc Electrical Circuits and Meters Study Guide When a capacitor is connected to a voltage source as in figure 3 15 there is a brief period of current flow in the circuit while it charges As a capacitor charges electrons flow from the power source to the negative plate until the voltage across the capacitor is equal to the source voltage Current flow stops when the voltages equalize If the source voltage increases the capacitor will charge to the higher value but if the source voltage decreases the capacitor will discharge until the voltages are equal once again Once a capacitor is charged it can maintain that charge for an extended amount of time sometimes for years if the ends are not allowed to come into contact Some of the charge however may be lost internally through the dielectric material This loss is called leakage Units Capacitors are rated in terms of their storage capacity called Farads as well as their working voltage The Farad F is a measure of the number of electrons a capacitor can store and mt or nanofarads nt and worlang is very large Most applications will be rated in microfarads volts DC Ganrdc uF or nanofarads nF A microfarad is one millionth of a farad and a nanofarad is one billionth of a farad When selecting a capacitor for a given application make sure the working voltage rating is higher than the source voltage to prevent damage
25. dy Guide current stops and return to its original shape which closes the circuit to current flow once again A mechanical turn signal flasher works this way also A non cycling type of breaker will open from excessive current as well but must be manually reset Another type of circuit breaker is the solid state device called a PTC Positive Temperature Coefficient PTCs have no moving parts and are commonly used in window motors and door lock actuators to protect the circuit from damage should a control switch become stuck or in case a limit switch fails They can also be used as end of travel stops without a limit switch figure 3 9 l i DOWN CURRENT INPUT POWER SENSE INPUT UP STOP INPUT RELAY CONTROL M SOLID STATE Figure 3 9 Power Window schematic with PTC s A PTC is a thermistor that works by greatly increasing its resistance when too much current generates excessive heat in the device As the resistance increases the current in the circuit is reduced which protects the wiring from damage Fusible Links Like fuses fusible links are single use devices that melt internally from heat caused by too much current figure 3 10 Although they Fusitle links should be 4 sizes look like typical wires fusible links have an insulation designed to withstand a greater amount of heat than regular wire insulation This prevents inadvertent shorting to ground during a failure caused by exce
26. e incorrect readings to be displayed To prevent this loading look for a meter with high Input Impedance generally the higher the better This becomes even more critical when measuring electronic components as some low impedance meters can actually cause damage to those circuits Our digital meter has an input impedance of 10 000 000 Ohms 10MQ Typical Meter Functions This meter has four major areas They are e Input Terminals four ports for input leads e Rotary Dial with eight positions for different measurements e Pushbuttons eight buttons for making changes in the display e Digital Display gives information on values scales ranges etc Refer to the illustrations in figure 1 9 as we discuss each of the areas in more detail Figure 1 9 Fluke 87 DVOM MINMAX RANGE HOLDE u RELA Hz PEAK MIN MAX mAuA COM VO _spoma MAX FUSED TIEI MAX 3 2 4 5 PNIS 2004 Melior Inc Electrical Circuits and Meters Study Guide Input Terminals There are four input terminals at the bottom of the meter for inserting test probes From the left they are 1 A Amps The red meter lead goes here for making current measurements up to a 10A maximum Rotary dial is set to mA A 2 mA pA Milliamp microamp The red meter lead goes here for making current measurements up to a 400mA maximum Rotary dial must be set to either mA A or LA 3 COM Common ground The black lead is inserted here for all measurements 4 VQ Volts Ohms
27. e the most common circuit protectors in automotive use and are rated from 5 A to 80 A They are one use devices with a HA metal strip inside that melts from the heat caused by exceeding ii the current rating of the strip The most common fuse types are the Auto Fuse Mini Fuse and Maxi Fuse figure 3 7 As shown in the graph on the next page figure 3 8 different colors are used to identify the amperage values of the various fuses Current Rating in Amperes Fuse Color Fuse Element Auto Fuse Mini Fuse z Gray 3 Violet 5 Tan 7 5 Brown 10 Hed 15 Blue Yellow Minifuse 25 White or Natural 30 Green Maxi Fuse Figure 3 7 Assorted automotive 20 Yellow fuses 3 Light Green 40 Orange or Amber 50 Red 60 Blue Figure 3 8 Fuse Colors Circuit Breakers Unlike fuses circuit breakers can be reset either mE manually or automatically and reused Circuit Circuit breakers can be either cycling or non cycling breakers are either cycling or non cycling A circuit breaker is made with a bi metallic strip that operates much like the thermostat in many homes As current passes through the strip it creates heat which causes the two metals to expand but at different rates When one expands faster than the other the strip bends and opens a contact which stops current flow through the circuit In a cycling type of breaker the bi metallic strip will cool after the _27 2004 Melior Inc Electrical Circuits and Meters Stu
28. ect range readable value is 400 ohms After switching the meter to the 40 MQ to prevent reading errors range the display will show 10 00 Do not confuse this with 10 ohms That is why it is so important to be aware of the scale currently being used especially if Auto Ranging is active figure 1 12 10 000 00 000 Value too Meter ranged large to to display display Megaohms Figure 1 12 Very Large Values The opposite condition can also be confusing in dealing with small values Imagine you are trying to measure 25 mA on a 40 A scale The meter would basically display zero 00 03 However by switching to a 4A 4000mA scale the readout now shows 0025 mA which is accurate figure 1 13 Value too Meter ranged small to to display measure milliamps Figure 1 13 Very Small Values A technician who is careful to use the correct unit setting Volt Amp Ohm and the right scale can consistently rely on the meter information to assist in proper diagnosis 12 2004 Melior Inc Electrical Circuits and Meters Study Guide DVOM Measurements Voltage Measurement To properly configure a meter for voltage measurements follow these steps and refer to figure 1 14 Insert the meter leads into the COM and VQ inputs Turn the rotary dial to the AC or DC Volt position Place the leads across the component to be tested voltage drop Apply power to the circuit Figure 1 14 Voltage Measurement Current Measurement To mea
29. ent magnets in Crank Position Sensors distributor and distributorless types Cam Position Sensors ABS sensors some fuel pumps Vehicle Speed sensors and new style starters Electromagnets Electromagnetism occurs when an electrical current is passed through a conductor and creates a surrounding magnetic field Electromagnets An electromagnet is created usually consist of a wire wound around a metal core and powered by when a current is run through an electrical source Some students may have done an experiment in school where a wire was wrapped around a nail with both wire ends attached to a battery to form an electromagnet The device could then be used to pick up paper clips Examples of electromagnetic automotive applications include starter solenoids and fuel injectors as mentioned earlier as well as some EGR valves relay contacts transmission shift and pressure control solenoids numerous vacuum control valves blower motors cooling fans wiper motors fuel pumps generators and of course old style starter motors a wound Wire Magnetic Fields All magnets whether permanent or electromagnet have two poles North and South Like poles N N or S S repel and unlike poles N S attract Automotive applications all operate by magnetic attraction rather than magnetic repulsion Between these two poles are invisible lines of force called the flux lines which make up the magnetic field figure 2 5 A magnet with many flux lines or
30. erent units Voltage Current Resistance and Power Most students have no doubt used these terms and probably measured for them but often they are used interchangeably even though they are in fact all different To ensure that we are all talking about the same thing a brief description of each is in order Voltage Voltage can be described as electrical pressure A comparison to a household water hose will be useful in discussing voltage If you have a Voltage is defined as water hose with a closed nozzle on the end and the spigot has been electrical pressure opened there is water pressure in the hose even though no water is able to escape through the nozzle 2004 Melior Inc Electrical Circuits and Meters Study Guide What actually causes voltage can be understood by recalling the earlier discussion about free electrons When there are more free electrons in one place as compared to another such as between the positive and negative plates of a car battery there is said to be a Difference of Potential or Voltage The greater the difference between the number of electrons on one battery plate and the number on the other plate the higher the voltage A dead battery has the same number of electrons on the positive plates as on the negative plates As we deal with electricity we will see that this electrical pressure has a number of different names that all mean the same They are e Voltage or V e Electrical Potential
31. hat if we multiply the current in amps times the resistance in ohms we can find the applied voltage or voltage drop To find an unknown current we use E R or A V O Divide the voltage by the resistance to find the current Resistance is found with R E I or Q V A Divide the voltage by the current to find resistance Ohm s Law Solving Circle The solving circle in figure 2 1 can be used to determine which formula to use Cover the letter for the value you don t know and the formula to use will be shown by the remaining two For example if you want to know the voltage drop in a circuit just cover the letter E which will leave IxR Covering the I will give E R and if R is covered then E I remains Figure 2 1 OHM s Law Solving Circle 15 02004 Melior Inc In the circuit shown in figure 2 2 the source voltage is unknown The resistance of the load shown as a resistor is 2 ohms and the current flow is 6 amps To solve for the missing voltage we apply Volts Amps x Ohms E xR Inserting the known values Volts 6 Amps x 2 Ohms Then multiply and we have Volts 12 Therefore source voltage in the circuit is 12 volts In figure 2 3 the current is unknown The load resistance is given as 2 ohms and the source voltage is known to be 12 volts To solve for the current we use Amps Volts Ohms I E R Inserting the known values Amps 12 Volts 2 Ohms Perform the division
32. he input voltage is 12 Volts and the output voltage is 12 000 Volts then the step up ratio is 1000 1 12 000 12 while at the same time the current will drop by the same ratio from 6A to 006 Amps 6 1000 A Step down transformer will likewise increase the output current by the same ratio that the voltage was decreased It s also interesting to note that the input power and the output power for a transformer are basically identical Ignition coils 1 The primary coil resistance will typically measure between 5Q and 1 0Q and the secondary will have a resistance of around 5KQ to 15KQ 2 Distributor type coils are sometimes called autotransformers because the primary and secondary coils are physically connected at the terminal 2 2004 Melior Inc Electrical Circuits and Meters Study Guide Module 3 In Module 2 of this series we looked at the applications of Voltage vom Current Resistance Power and Magnetism Now we will apply these as well as Ohm s Law to electrical circuits Protection Electrical circuits are divided into three categories known as Series Parallel and Series Parallel Although there are differences in the three which will be seen later we will examine some fundamental similarities that exist in all electrical applications both automotive and non automotive Control Ground Figure 3 1 Circuit elements Source The first requirement for any circuit is a source of power Automotive appl
33. her simply by moving the decimal point to the left or right In the automotive field we will use five primary unit sizes including base units and four prefix units which are defined below Mega Mega is the metric term for one million and uses the upper case symbol M If a measurement reads 1 MO it is equivalent to 1 000 000 Ohms likewise 6 000 000 Ohms is given as 6MQ Kilo Kilo is the prefix for one thousand and uses the capital letter K One KQ is equal to 1000 Ohms and an ignition coil secondary winding with 4000 ohms resistance would be shown as 4 00KQ Base Units Base or root units are the most commonly used and most familiar to the technician They include Volts V Amps A Ohms Q and Watts W Watts are a unit of Power to be covered later Milli Milli corresponds to one thousandth of a base unit and has the lower case symbol m One thousand millivolts equals one volt and 12 volts equals 12 000 mV Many relays operate in the 600 mA range and wheel speed sensors typically produce around 150 mV Micro Micro is the smallest unit used in the automotive field and is given the Greek symbol mp A microamp for instance is one millionth of an amp Measurements in the micro ranges tend to be in electronic 10 02004 Melior Inc Electrical Circuits and Meters Study Guide circuits For a better understanding of how these units correspond to one another refer to this table and figure 1 10 MOVEMENT OF D
34. his capacitor will filter out noise on the power side If a problem still exists insert the third capacitor between the switch and load to ground 3 This capacitor will filter out noise on the load side of the switch oS 2004 Melior Inc Electrical Circuits and Meters Study Guide 12V 12V ATUF le Direct Switch Activated Device Relay Activated Device Figure 3 19 Adding capacitors to eliminate popping noises Portions of materials contained herein have been reprinted with permission of General Motors Corporation Service Operations License Agreement 110410610 234
35. ications generally have two primary power sources the battery and the generator Protection A fuse circuit breaker or fusible link is needed to prevent wiring damage from excessive circuit current Control A control device can either turn a load on and off or it can vary if a changing output is required Loads such as headlights or fan motors will be either on or off and will use switches or relays as controlling devices However applications such as instrument panel dimming fuel injection and transmission valves have variable outputs and will be controlled by potentiometers transistors and Pulse Width Modulation computer signals Load A load is any part or component in a circuit that causes resistance to the current flow in the circuit All circuit loads will have a corresponding voltage drop Loads can be devices such as bulbs motors and actuators as well as unintentional items including bad connections and corrosion Ground All circuits must have a complete path to operate Automotive applications all terminate at ground or battery negative A ground return can be either hard wired to the battery negative or chassis grounded through the metal pieces of the vehicle Case grounded components have an internal connection to their metal casing and become chassis grounded when installed in the vehicle 2095 2004 Melior Inc Electrical Circuits and Meters Study Guide Series Circuit A Series circuit is the most basic type
36. l core figure 2 10 When alternating current or pulsating DC current is applied to the applied voltage or current primary winding a voltage is created or induced into the secondary winding lranstormers use electromagnetic induction to mcrease or decrease an 20 2004 Melior Inc Electrical Circuits and Meters Study Guide IGNITION CONTROL MODULE IGNITION COILS SPARK PLUGS AMPLIFIER Figure 2 10 Transformers Transformers are classified as either Step up or Step down A Step up transformer will create a higher voltage in the secondary winding while a Step down will cause a lower voltage Your local electrical sub station has a series of Step down transformers to reduce the voltage before it enters your house The Step up or Step down ratio is determined by the number of turns of the wire used in both the primary and secondary windings One other thing to keep in mind is that the primary and secondary currents will also change except they go up as voltages drop and decrease as voltages increase As an example let s use the most common transformer in automotive use the ignition coil In a typical ignition coil the ignition module will apply 12 Volts pulsating DC with a current of between 4 10 Amps We ll use 6A as an example The voltage that comes from the secondary to fire the spark plugs is typically between 5 000 Volts and 20 000 Volts some can go as high as 80 000 Volts Our example will use 12 000 V If t
37. n watts and 12 a measurement of work output 1 Horsepower 746 Watts Power Formula As mentioned earlier Power is not a direct measurement but rather the product of the Voltage and Current applied to a device To calculate the power consumed use P IxE or Watts Amps x Volts From this formula we can see that one Watt is equal to one Volt multiplied by one Amp We can also see that if either the voltage or current is increased then the power wattage also increases Likewise a decrease in either voltage or current causes a corresponding reduction in power As an example let s assume we have a device with 120 Volts applied and a Current of 10 Amps Using the formula we obtain P IxE P 10A x 120V P 1200 Watts The Power formula can then be applied to any circuit or device where both the voltage and current are known If either or E is unknown the Power formula can be expanded and calculated with other Alternate formulas for calculatng power are quantities that are known For instance we given by know that E IxR and if a substitution is made 2 2 MONS P I xRandP E R P Ix IxR or P I xR which allows us to use and R to calculate Power instead of and E Likewise since I E R then P E R xE or P E7 R if is unknown As a general rule those things that are rated in watts consumed have a different form of output For instance light bulbs are rated in watts but have an output in lumens Audio speakers have an o
38. of circuit and has the following characteristics e he individual voltage drops add up to the applied voltage e Current is the same at any point and flows in only one path e The total resistance is the sum of the individual resistances loads Figure 3 2 Series Circuit Parallel Circuit A parallel circuit is defined as one that has more than one path to make a complete circuit Parallel circuits have the following traits e Each branch has the same voltage applied and the same voltage drop e There is more than one branch or path for current to flow and the total current is the sum of the individual branch currents e he total resistance is always less than the smallest branch resistance Figure 3 3 Parallel Circuit Parallel Circuit Resistance To calculate total resistance in a series circuit we can simply add the values of the individual resistances In a parallel circuit it is a little more involved For example in a circuit with three branches having 10 20 and 30 ohms respectively we know the total resistance must be less than 10 ohms the value of the smallest branch rather than the 60 ohms we would have in a series circuit Parallel circuit total resistance must be less than the resistance of the smallest branch resistance Figure 3 4 Parallel circuit resistance 2253 2004 Melior Inc Electrical Circuits and Meters Study Guide The sum of the reciprocals can also be expressed as URT AIRAMIR24AIR
39. oltage or current in a circuit They can be either fixed or variable and will be rated both in terms of value ohms and power watts The value of a fixed resistor can be read from its color bands Each resistor has several color bands that should be offset to one end Hold the resistor so that the color bands are on your left note the colors and compare them to the chart in figure 3 12 29 02004 Melior Inc 15T BAND 2ND BAND 3RD BAND 4TH BAND WLLLLLLLLLL CLLLLLLLLLA y A Transfers directly into s Translates directly into s Places decimal point of zeroes after 2nd digit If GOLD divide by 10 if SILVER divide by 100 Designates tolerance in Electrical Circuits and Meters Study Guide 4TH BAND TOLERANCE IN 3JRD BAND OF ZEROES 2ND BAND 2ND DIGIT 18T BAND 15T DIGIT BANDS 1 2 3 4TH BAND BLACK BROWN RED ORANGE YELLOW GREEN BLUE VIOLET GRAY WHITE EXAMPLES RED RED BRN GLD 220 2 5 RED RED GLD 2 2 N 20 Figure 3 12 Resistor color coding Some resistors such as those found in blower motor circuits are wire wound and have no color bands figure 3 14 Resistive values for those should be printed in service manuals F oem m m Blower Mater EN ENE UNE GEO NND mM 12 V Figure 3 14 Blower Motor Resistors 30 2004 Melior Inc Electrical Circuits and Meters Study Guide Just as they have
40. play the maximum value input during this record session 28 Min A second press of the Min Max button will show the minimum reading taken in the current record memory 29 Avg On a third press of the Min Max button in 100ms mode only an average of all readings taken in the record cycle will appear 30 H Hold This lets the user know the meter is operating in Hold mode and will keep the most current value on the display until a different reading is taken Various other displays are shown on the screen to inform the user of the active measurement scale These symbols are mostly found on the right side of the screen They include AC Alternating current or voltage DC Direct current or voltage V Voltage mV Millivolts A Amperage mA Milliamps uA Microamps nS Nanosiemens Percentage Q Ohms or Resistance kO Kilohms MQ Megohms Hz Hertz cycles per second KHz Kilohertz uF Microfarad capacitance nF Nanofarad Digital Display Functions The DVOM display is a digital and analog LCD readout screen for all meter functions Turning the meter on while holding any button will allow the user to see all of the possible display segments on the screen Each screen function is self tested for one second when the meter is turned on and to save battery power the meter will also turn itself off if not used for a certain amount of time Reading the Meter As mentioned before our DVOM makes it possible to change from one scale to anot
41. r of outer shell electrons such as rubber they don t let go as easily and as such we use them as insulators through wires 2004 Melior Inc Electrical Circuits and Meters Study Guide Magnetism Another electrical characteristic is Magnetism Magnetism or Electromagnetism is also caused by the movement of electrons in a wire and is the property that makes generators starters blower motors EGR valves and many other actuators work Electrostatic Forces Free electrons also create electrostatic forces but the forces are caused by a collection of charges in one place rather than by a movement of electrons Recall that opposite charges Protons and Electrons attract each An electrostatic force is a collection of electrons in one place that de not other and like charges Proton Proton or Electron move through wires Electron repel each other These attractive and repulsive forces are called Electrostatics and can be seen in figures 1 4 and 1 5 Opposite charges attract Wk we AMET VA TNA IN CWNLOQOS e MESS Like charges repel RSE N GF gt WM Cpo gt o UNZ Mea aM ANFIN SS PM Figure 1 4 Electrostatic Fields Figure 1 5 Electrostatic Forces From this we can now see how the basic structure of atoms is used to produce electricity and is applied to operating automotive systems Electrical Properties In our study of Electricity we will apply measure and calculate four diff
42. rrent can then be found simply by adding the branch currents amps The sum ofthe branch currents raroni adds up to the total current 2 amps 1 2 amp Jl e Figure 3 5 Parallel circuit current 24 2004 Melior Inc Electrical Circuits and Meters Study Guide Given the circuit from the previous page what is the total current We know that since the two bulbs are in parallel their voltages are equal at 12V each The bulb on the left has a resistance of 6Q and applying Ohm s Law we have L E R or l 12V 6Q so h 2 Amps Similarly the 24 Q right bulb has a current given by l E R or b 12V 24Q so l 5Amps Total current is therefore Ir 214 l 22A 5A 2 5Amps Now calculate the total current if the left bulb is 2Q and the right bulb is 120 Series Parallel Circuits Sometimes it is necessary to reduce the amount of voltage drop across the branches of a parallel circuit to less than source voltage To accomplish this we use a circuit called Series Parallel A Series Parallel circuit works by inserting a resistor in series with a parallel network The series resistor will cause a voltage drop that leaves less voltage available to the branch loads and therefore reduces their currents How would you calculate the total resistance of a Series Parallel circuit Calculate the parallel portion of the series parallel circuit just as you would for any parallel network and then add the series resistance
43. ssive current Fusible links are being used less in modern applications as fuses with higher amperage ratings have become available smaller than the wire they protect 28 2004 Melior Inc Electrical Circuits and Meters Study Guide Figure 3 10 Fusible Link When replacing an open fusible link never exceed nine inches in length and use a link that is four sizes smaller than the circuit wire For example a 14 gauge wire would be protected with an 18 gauge fusible link This will ensure that the link burns before the circuit wire An open fuse link can also be verified by pulling its ends to see if it stretches which shows failure Switches Switches are simply on off devices used to open or close an electrical circuit There are various types of switches that are categorized by the number of positions they have as well as the number of circuits they control Some of the most common types are given below Single Pole Single Throw SPST Controls one circuit with two positions ON OFF Single Pole Double Throw SPDT One circuit with three positions two on positions with a center off position Double Pole Single Throw DPST Two circuits with two positions Double Pole Double Throw DPDT Two circuits with three positions owitches are rated by the amount of current the contacts can carry obl DPST Figure 3 11 Switch type examples Resistors Resistors are devices made of carbon or ceramic which are used to limit the v
44. st the right amount of magnetic force needed for a particular use Relays A relay is an electromagnetic device that operates as an on off switch It uses a small coil current to control a larger contact current Inside a relay there is a coil of wire and one or more sets of contacts Applying a small current to the coil creates a magnetic field which pulls in the contact s and closes the circuit sending the larger controlled current to the load device eg fuel pump ECM etc figure 2 7 Relays are classified as Normally Open N O or Normally Closed N C A relay is an electromagnetic depending on device that uses a small whether the contacts current to control a larger are open or closed ETT with the coil de energized Solenoids A solenoid is an electromagnetic device that uses applied current to produce lateral back and forth motion figure 2 8 Solenoids such as fuel injectors and transmission shift valves have a movable metal core inside the coil As current is applied to a coil the electromagnetic field it produces either pushes or pulls the core and opens or closes a valve or engages a starter drive The terms relay and solenoid are sometimes used 4 solenoid uses electromagnetic force to interchangeably but in produce lateral motion fact they are two different things 19 Electrical Circuits and Meters Study Guide Figure 2 8 Solenoid fuel injector 2004 Melior In
45. sting requires the use of a Digital Volt Ohm Meter par DVOM A DVOM also known as a Digital Multi Meter DMM or have a high input impedance just Multi meter is a versatile tool that allows for the measurement of Voltage Current Resistance Capacitance Frequency Pulse Width and other parameters For our purposes in this course we will use a Fluke 87 to represent a typical DVOM for our measurements DVOM Our DVOM is a multi meter that operates on a base 4 principle Measurement ranges will be 4 40 400 4000 etc For instance on a voltage setting the maximum value that can be measured will be 4V 40V 400V or 4000V depending on the scale selected Some brands of meters are base 2 2 20 200 2000 etc or base 10 1 10 100 1000 etc Either type will work equally well as long as the technician learns to read the meter properly and accurately Meters come with different levels of features quality and prices A technician considering the purchase of a meter should keep two things in mind 1 Does it have all the functions need and 2 What is its input impedance Impedance is the input resistance a meter has It prevents the meter from becoming a 2004 Melior Inc Electrical Circuits and Meters Study Guide component of the circuit and affecting the circuit operation Some lower quality meters have a tendency to load the circuit being tested and thus affect not only the operation of the devices itself but also caus
46. sure current follow this procedure and refer to figure 1 15 1 2 3 4 5 Insert the meter leads into the A and COM inputs Turn the rotary dial to the mA A position Make an open in the circuit Place the meter leads to complete the circuit leads must be inserted so that all current flows through meter Apply power to the circuit Caution To prevent blown fuses check your meter installation thoroughly before applying power Remember in this mode all of the current in the circuit will pass through the meter Caution Never place leads across a component when measuring amperage Figure 1 15 Current Measurement 13 2004 Melior Inc Electrical Circuits and Meters Study Guide When measuring circuit current always begin with the red lead in the A 10 amp input terminal The lead may be moved to the mA input only after you have determined that the current is below the maximum 1A rating for that terminal Resistance measurement Resistance measurements are made according to these steps and the figure in 1 18 Power must be off Insert the meter leads in the COM and VQ inputs Turn the rotary dial to the position Place the leads across the component Do not allow your fingers to touch the ends of the leads since it will change the reading fs 12V Ed ore po Doors NOTE When measuring resistance it is important to make sure the power is off This is done not because it will damage the meter but
47. tages to computers Typical NTC devices include Engine Coolant Temperature Intake Air Temperature Transmission Fluid Temperature Heat and Air Conditioning Temperature etc Capacitors Capacitors are devices that store electrical charges and behave like temporary batteries Technicians may have Capacitors store electrical charges seen them used as filters on alternators or radios to reduce and act like temporary batteries noise or even in older point style distributors as condensers By controlling how quickly they charge and discharge we can also use them as timers Capacitors basically consist of two metallic plates separated by an insulator called a dielectric Dielectrics can be something as simple as a piece of paper A simple capacitor can be made by placing a sheet of paper between two equal sized sheets of aluminum foil Wrap all three sheets around a paper towel roll don t let the aluminum sheets touch and attach a connector wire to each piece of aluminum foil That is the basic construction of a capacitor There are two types of capacitors electrolytic and non electrolytic Electrolytic capacitors have both a positive and negative end while non electrolytics can be inserted in either direction The symbol for an electrolytic capacitor is T and for a non electrolytic Since the plates in a capacitor do not touch it acts like an open in a circuit and will not pass DC current figure 3 15 Figure 3 15 Ele
48. to that total How would you find the total current Use the Ohm s Law formula I E R just as you would for any circuit In this case the voltage is the 12 volt source and the resistance is the series parallel value determined in the last step 25 2004 Melior Inc Electrical Circuits and Meters Study Guide From Head Park lamp switch i us 2E iaa ana ad 8291 T SE em re bom Amm EARS yd ANP peer TP E Ei a ie 24 mem l a202 Figure 3 6 Series Parallel Circuit This illustration of a Dash Light circuit shows how changing the resistance of the rheostat dimmer control varies its voltage drop and in turn changes the voltage available to the dash bulbs which controls their brightness 26 2004 Melior Inc Electrical Circuits and Meters Study Guide Circuit Components With an understanding of Voltage Current and Resistance we can now turn our attention to the devices that determine those values Circuit Protectors Three types of circuit protectors used in modern automotive DEE applications fuses circuit breakers and fusible links The primary Circuit protectors are used to function of these devices is to protect the wiring from damage prevent wiring damage trom should a circuit failure cause excessive current Although circuit excessive current protectors are rated in amps it is actually the heat caused by too much current that causes the device to open the circuit Fuses Fuses ar
49. utput based on how much air they move and resistors also rated in watts put out heat Electric motors as mentioned before are an exception in that they are rated in horsepower output rather than watts consumed 17 2004 Melior Inc Electrical Circuits and Meters Study Guide Magnetism Magnetism is used extensively in automotive applications to convert electrical energy to mechanical energy or conversely to change mechanical energy to electrical energy For to mechanical energy or mechanical energy to instance if we apply electrical current to certain electrical energy devices we can create lateral straight line motion such as in the starter solenoid to engage the starter drive or to open fuel injectors Still other components will use applied electricity to produce rotary spinning motion as is the case with fuel pumps and starter motors Generators however use magnetism to change motion belt driven to electrical output In the automotive field there are two types of magnets used They are Magnetism is used to convert electrical energy e Permanent magnets e Electromagnets Permanent Magnets We are all familiar with permanent magnets those gray colored devices usually made in bar or horseshoe shapes It s likely most of us have a number of permanent magnets attached to our refrigerators holding up out of date notes and drawings done by our children or grandchildren In cars and trucks we will find perman
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