Test
1. Turn on and adjust carbon pile to alternator
rated amperage output.
2. Read voltmeter and record voltage (V25) which
is negative circuit voltage loss. Immediately turn off
carbon pile.
3. Add positive circuit loss (V24) and negative
circuit loss (V25) to get total system loss (V23). This
loss (V23) shall not exceed:
• 12 volt system - 0.500 volt maximum
voltage loss
• 24 volt system - 1.000 volt maximum
voltage loss
4. Replace cables or repair circuits with excessive
voltage loss.
3-28. TEST COMPLETION.
Remove carbon pile and
voltmeter. For 12 volt systems proceed with Alternator
Replacement Determination. For 24 volt systems, proceed
as follows:
1. Reconnect temporary 12 volt system back to
24 volt system.
2. If Magnetic Switch Circuit Test was delayed,
conduct at this time.
3. After completing Magnetic Switch Circuit Test,
be sure to reconnect lead to “S” starter solenoid
terminal. Then proceed with Alternator Replacement
Determination.
3-29. ALTERNATOR REPLACEMENT
DETERMINATION
If the alternator wiring circuits are OK, conduct the
following tests to determine if the alternator must be
replaced.
NOTICE
Make sure that alternator mounting
hardware is secure and that belts are OK
before testing alternator.
NOTICE
Batteries shall have been satisfactorily load
tested and must be near full charge with
more than 12.4 Volts no load voltage.
3-30. ALTERNATOR VOLTAGE OUTPUT TEST.
Conduct this test at shop temperature (See Figure
3-9).
Connect
1. Digital voltmeter from positive alternator
terminal to alternator ground.
Test
1. Start engine and make sure all vehicle
electrical loads are turned off. Fast idle engine until
voltage stabilizes (does not increase) for two minutes.
2. Check that alternator output voltage does not
exceed 15.5 volts (31 volts for 24 volt system). Remove
voltmeter.
3-8
CARBON
PILE
NEGATIVE
CIRCUIT
LOSS
(25)
POSITIVE
CIRCUIT
LOSS (24)
Figure 3-8. Alternator Wiring Test - Typical
12Volt System
DP-1026
CARBON
PILE
NEGATIVE
CIRCUIT
LOSS
(25)
POSITIVE
CIRCUIT
LOSS (24)
Figure 3-8. Alternator Wiring Test - Typical
12Volt System
DP-1026
new diagnostic manual 4/5/05 9:48 AM Page 3-8
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