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