2 Charging Systems Primary purpose is to recharge battery Changes mechanical energy into electrical energyVoltage is induced into a wire as it passes through a magnetic fieldThe voltage has positive and negative pulses
3 AC Generator Construction Rotor assemblyRotating magnetic field4 .0 to 6.5 amps pass through coilOne pole piece assumes north and the other south polarity
5 Slip Rings and BrushesRegulated current supplied to rotor coil via slip rings and brushes
6 StatorMost AC generators use three stator windings
7 Stator (Cont.)Each stator conductor produces a single phase of AC currentThe phases are staggered 120° apart
8 End Frame Assembly Contains rotor shaft bearings and air ducts Rectifier diodes attached to end frameHeat passes from diodes to airCooling fans pull air through generatorMay have external or internal fans
9 Diodes with cooling fins Rear driveshaft bearing
10 Liquid Cooled Generators Water or coolant used to keep diode temperature downEliminates fans and reduces noiseHoses connect generator to engine cooling systemAllows for increased output and longer generator life
11 AC Generator Operation Produce alternating currentThe AC must be converted, or rectified, into direct current, DCThe AC passes through diodes
15 Knowledge Check Describe how diodes are used to change AC into DC. Diodes allow current to flow in one direction so by placing them with either a positive or a negative bias, the diodes can be used to block unwanted AC.
16 Factors Controlling Generator Output Rotational speed of the rotorNumber of windings in the rotorCurrent flow through rotorNumber of windings in the stator
17 Voltage RegulationOutput is controlled by varying current through the rotorResistance in series with the field coilSensing voltage allows the regulator to monitor system voltageTemperature also monitored
18 Types of Field Circuits “A” typeHas the regulator on the ground side of the field coil“B” typeHas the regulator on the positive side of the field coilIsolated fieldThe regulator can be on either the ground or the positive side
21 Types of Voltage Regulators Electronic regulatorCan be internally or externally mountedUses a zener diode or pulse width modulation to control field currentIntegrated circuit voltage regulatorsInternally or externally mountedControls field current through a diode trio
22 Types of Voltage Regulators (Cont.) Computer-controlled regulationIs used on many late-model vehiclesThe computer (PCM) uses battery voltage and temperature to determine voltage needsMost systems use pulse width modulation to control field current
24 Motor/GeneratorsUsing electronic controls, a generator can work as a motorCan be mounted external to the engine or mounted directlyCapable of high charging outputsCan crank engine at high speeds
25 Motor/Generators (Cont.) Capable of stop-start operationRegenerative brakingElectrical assist
26 Regenerative Braking Braking energy used to recharge batteries Motor/generator converts kinetic energy into electrical energyA combination of conventional and regenerative braking usedFound on all hybrid vehicles
28 Knowledge Check Explain how the PCM controls generator output. The PCM can pulse the voltage regulator very quickly on and off. This is called pulse-width modulation.
29 Preliminary Charging System Checks Safety PrecautionsDisconnect negative terminalAvoid contact with generator output terminalOnly apply pressure to front of generator housing when applying belt tensionObserve correct polarity of battery cablesKeep carbon pile tester off at all timesUse caution around moving parts
30 Charging Indicators Indicator (charge) lamp Meters Operates on the principle of opposing voltagesMetersVoltmeter or ammeter display on dashElectronic voltage monitorIs used to monitor voltage and control a lamp or warning message
35 Noise Diagnosis Noise can be mechanical or electrical Some electrical noise is normalBelts and bearings can produce noiseCheck mounting, wiring, cooling and A/C hoses and lines for misroutingGenerator pulley should spin freely with belt removed
36 Regulator TestsExcessive charging most likely caused by voltage regulatorCan also cause no outputSome systems can bypass regulator for full-field testsAlways follow manufacturer’s procedures
38 Voltage Output Test Measure battery open circuit voltage Run engine at fast idle (1500 rpm)No load voltage should be about 2 volts higher than open circuit voltageIf low, increase speed to 2000 rpm and turn on accessoriesVoltage should be about 0.5 volts above open circuit voltage
39 Current Output Test Run engine around 2500 rpm Adjust carbon pile to maximum current outputShould be within 10 amps of rated output
40 AC Leakage TestConnect DMM in series to charging output terminal with engine offReading should be no more than 0.5 mA
42 Knowledge CheckA generator rated for 120 amp only produces 75 amps. Technician A says the voltage regulator may be faulty. Technician B says the diodes may be faulty. Who is correct?Both Technician A and B
43 Circuit and Ground Resistance Check voltage drop of charging output connection and ground circuit.Test between battery positive and generator output terminal.Test between battery negative and generator case.Test under at least 20 amps output.
45 Replacing a Generator Disconnect the battery negative connection. Remove generator wiring and drive belt.Remove the generator.Compare new and old generator.Install and torque fasteners.Test the new generator.