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Charging System Service

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Presentation on theme: "Charging System Service"— Presentation transcript:

1 Charging System Service
Chapter 31

2 Objectives Measure and interpret voltage drops on the positive side of the charging circuit Measure and interpret voltage drops on the ground side of the charging circuit Test and repair an alternating current (AC) generator Diagnose voltage regulator problems

3 Introduction This chapter discusses testing and repair of common charging system problems Principles of operation and electrical fundamentals are useful Diagnosis of failures before replacing parts is important Most parts stores will not accept returns of electrical items

4 Charging System Service
Common charging system complaints Dead battery Battery water low Indicator light glows Noises Perform complete charging system diagnosis Before replacing parts Check battery charge At least 80%: perform 15-second load test Fails load test: might be sulfated

5 Testing the Charging System
Perform visual inspection Corroded or broken wire connections Indicator lights and gauges functioning correctly Listen for noises Loose or damaged alternator drive belt Loose drive belt causes two problems: Low charge rate Rotor shaft overheating can cause drive end bearing failure

6 Testing the Charging System (cont'd.)
Connect volt-amp tester to battery Set meter range to highest scales during starting Adjust to lower ranges as needed Four charging tests Charging system output test Regulator voltage AC generator full-field test Charging circuit resistance tests


8 Charging System Output Test
Procedure Start the engine Raise idle speed to 2,000 rpm while lowering battery voltage Read amount of current put into battery Maximum output will be more than gauge shows Move amp probe to B+ wire More accurate estimate of output Testing using an amp clamp Place it around all of wires from battery terminal

9 Regulator Voltage Check
Regulator must be able to: Full-field an alternator immediately Keep the system at predetermined voltage With engine running, meter should show gradual decrease in charging amperage Voltage should remain within normal operating limits

10 Full-Field Test Low output of AC generator
Could be due to generator or regulator Full-fielding the alternator eliminates the regulator from the circuit Energizes the rotor fully Causes the alternator to produce full output Full-field test results If alternator puts out more at same voltage with regulator bypassed: regulator is faulty When current output remains low: bad alternator or drive belt are probable causes


12 Full-Field Test (cont’d.)
PCM controlled voltage regulation service Warning message may or may not be displayed on the instrument panel for the driver If warning light does not come on when the key is first turned on, look for a problem in that circuit If the warning message comes on and stays on as the engine runs, check for diagnostic trouble codes

13 Diode Tests Leaking diodes decrease alternator output Diodes:
Rectify AC output to DC Prevent AC from leaving in the B+ output wire Are defective if more than 0.5 AC volt in B+ output With engine off, there should be less than 0.5 milliamp of current flow in B+ output wire

14 Diode Tests (cont’d.) Testing diodes with a power probe Scope testing
Peak-to-peak mode: tester measures differences between positive and negative peak voltage levels Scope testing Lab scope can be used to look at AC generator patterns Diode noises When the sound is loud enough for a customer complaint, a bad diode is probably the cause

15 Charging System Voltage Drops
Check voltage drops as preventive maintenance Combined voltage should be less than 0.5 volts Positive circuit with 10 amps flowing: no connection should have more than 0.3-volt drop System with an ammeter: 0.7-volt drop limit Small amount of voltage drop through the fuse link is normal

16 AC Generator Service and Repair
Most shops do not repair AC generators Easy to disassemble Remove the bolts Separate the rotor from its housing Brushes may be serviced without disassembling Stator is discarded if it has signs of burned or overheated insulation Test the continuity of the rotor winding for opens, shorts, or grounds Resistance is checked with ohmmeter

17 Diode Service Diodes must be tested under load Good diode
Diode tester Ohmmeter Good diode Shows high resistance in one direction Low resistance in the other Shorted diode Low readings in both directions Open diode High resistance in both directions

18 Alternator Reassembly
Reassembling the alternator is not difficult Brushes inside the frame must be raised against their springs Slip rings positioned under them Brushes mount from outside are compressed against springs as holding bracket is installed

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