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26-SI ALTERNATOR
1G/287 4/96
PAGE
ALTERNATOR BENCH TEST
TEST EQUIPMENT NEEDED:
• Alternator Test Stand (5000 rpm capability at least
5 HP)
• Battery or Battery Set (fully charged)
• Variable Carbon Pile Load Test
• Ammeter (current capability at least 15 amps higher
than alternator rating)
• Voltmeter
• Ohmmeter
The bench test procedure will verify alternator
performance prior to installation on the vehicle. This test
checks the alternator output in the same manner as the
Rated Output Check covered earlier. If bench test
equipment is not available, install the alternator on the
engine according to manufacturer’s instructions and repeat
the Rated Output Check to verify alternator operation. If
bench test equipment is available, proceed as follows:
1. Mount alternator in test stand according to test stand
manufacturer’s instructions.
2. IMPORTANT: Battery or battery set must be
fully charged for test results to be valid.
NOTICE: When a 12-volt carbon pile load test is used
to diagnose a 24-volt system, attach load test only to 12-
volt potential in battery set. Attaching a 12-volt load
test to a 24-volt potential will damage the carbon pile.
With carbon pile load turned off and with battery or
battery set fully charged, make electrical connections
as shown in Fig. 47. Battery voltage and ground
polarity must be same as system in which alternator is
used. Check and record battery or battery set voltage
before proceeding with test.
3. With carbon pile load “off,” start test stand and slowly
increase alternator speed to highest rpm shown under
Cold Output specifications in 26-SI Alternator
Specifications at the end of this manual. Observe
voltmeter.
- If voltage does not increase but remains at or below
previous reading (Step 2), there is no alternator output.
Turn carbon pile load off and stop test stand. Residual
magnetism in rotor may have been lost. Skip to Step 5.
23
Figure 47. Alternator Bench Test
CLAMP-ON
AMMETER
CARBON PILE
E9
ALTERNATOR
E6,E8
V
BATTERY
VOLTMETER
26-5046