3-31. ALTERNATOR AMPERAGE OUTPUT TEST.
Conduct this test at shop temperature (See Figure 3-10).
Connect
1. Carbon pile across the vehicle batteries hooked
in parallel.
2. Induction ammeter, clamped around alternator
output wire.
NOTICE
If more than one wire is connected to the
alternator output terminal, clamp around
ALL these wires.
Test
NOTICE
In following test,
alternator should be
turning at approximate rated speed. Most
heavy-duty alternators are rated at 5000
rpm.
Check manufacturer’s specifications
for specific alternator being tested.
1. If off, start engine and make sure all vehicle
electrical loads are turned off. Speed up engine. Turn
on and adjust carbon pile until ammeter reads its
highest value. Record this reading.
2. Turn off carbon pile and engine.
3. If reading is zero (no output), magnetize the
rotor with the alternator hooked up normally.
Momentarily connect a jumper lead from the battery
positive (+) to the alternator relay (R) or indicator (I)
terminal. This procedure applies to both negative and
positive ground systems, and will restore the normal
residual magnetism.
4. Repeat steps 1 and 2. If output is still zero,
replace the alternator.
3-32.
ALTERNATOR REPLACEMENT.
Replace
alternator if either of the following conditions exist:
1. Alternator output voltage exceeds 15.5 volts
(paragraph 3-30). If alternator has separate regulator,
use the appropriate regulator service bulletin to isolate
the defect.
2. Alternator output current is not within 10% of
alternator rated output (stamped on alternator case).
Examples: 30-SI - 105 amps, 26-SI - 85 amps, 21-SI -
100 amps.
3-33. COMPLETION OF ALL TESTS
Make sure that all test instruments have been removed
from the vehicle and that the vehicle wiring, if altered,
has been returned to the operational state.
3-9
Figure 3-10. Amperage Output Test
DP-1028
CARBON PILE
new diagnostic manual 4/5/05 9:48 AM Page 3-9
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