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8.10
Section 8
Electrical System and Components
Troubleshooting Guide
15/20/25 amp Battery Charging Systems
If it is difficult to keep the battery charged, or the battery overcharges, the problem is usually with the charging
system or the battery.
NOTE: Always zero ohmmeter on each scale before testing to ensure accurate readings. Voltage tests
should be made with the engine running at 3600 RPM - no load. The battery must be fully charged.
Problem
No
Charge
to
Battery
Battery
Continuously
Charges at
High Rate
Test
1. Trace B+ lead from rectifier-regulator to key
switch, or other accessible connection.
Disconnect it from switch or connection.
Connect an ammeter from loose end of B+
lead to positive terminal of battery. Connect
DC voltmeter from loose end of B+ lead to
negative terminal of battery. See Figure 8-11.
With engine running at 3600 RPM, read
voltage on voltmeter.
If voltage is 13.8 volts or more, place a
minimum load of 5 amps* on battery to reduce
voltage. Observe ammeter.
*NOTE: Turn on lights (if 60 watts or more) or
place a 2.5 ohm, 100 watt resistor
across battery terminals.
2. Remove connector from rectifier-regulator.
With engine running at 3600 RPM, measure
AC voltage across stator leads using an AC
voltmeter.
3a. With engine stopped, measure the resistance
across stator leads using an ohmmeter.
3b. With the engine stopped, measure the
resistance from each stator lead to ground
using an ohmmeter.
1. Perform same test as step 1 above.
Conclusion
1. If voltage is 13.8-14.7 and charge rate
increases when load is applied, the charging
system is OK and battery was fully charged.
If voltage is less than 13.8, or charge rate does
not increase when load is applied, test stator
(Tests 2 and 3).
2. If voltage is 28 volts or more, stator is OK.
Rectifier-regulator is faulty. Replace the
rectifier-regulator.
If voltage is less than 28 volts, stator is
probably faulty and should be replaced. Test
stator further using an ohmmeter (Test 3).
3a. If resistance is 0.064/0.2 ohms, the stator is OK.
If the resistance is infinity ohms, stator is open.
Replace stator.
3b. If the resistance is infinity ohms (no continuity),
the stator is OK (not shorted to ground).
If resistance (or continuity) is measured, the
stator leads are shorted to ground. Replace
stator.
1. If the voltage is 14.7 volts or less the charging
system is OK. The battery is unable to hold a
charge. Service battery or replace as
necessary.
If voltage is more than 14.7 volts, the rectifier-
regulator is faulty. Replace rectifier-regulator.