GILLIG LOW FLOOR, Service Manual

Page: 368 / 506

Electrical System
368
Figure 9-13, Testing Alternator Output Under Load
BATTERY
OFF LOAD
CARBON PILE LOAD
(VARIABLE RESISTANCE)
CLIP ON D.C.
AMMETER
VOLTMETER
BATTERY
F1 F2
POS R
ALTERNATOR
20-800-54
Testing the alternator using the “full fielding” method can cause severe
electrical damage to the electrical system of the vehicle!
Testing Alternator Output Under Load:
If the alternator is operating but indications are that it is not producing adequate current when under
heavy load, perform the following checks:
1. Check the alternator drive belt tension. If belt is loose, it may slip under heavy load.
2. Connect a carbon pile, 24 volt load tester across the batteries (Figure 9- 13).
3. Connect an induction type ammeter over the positive cable at the alternator.
4. Connect a voltmeter to the alternator positive cable and ground.
5. Check the Specifications for the output ratings at specific rpms.
6. Start the engine and activate the “Fast Idle” feature.
7. Check the voltage reading; it must be 28+/–0.1 volts*. If not, adjust voltage at the regulator.
8. Increase rpm and gradually apply load on the carbon pile. Observe the voltmeter and ammeter at
the specified rpms and loads.
9. The voltage output should read 28+/–0.1 volts.*
10. The current output should be within 10% of the rated output at a specific rpm; if not, the alterna -
tor is defective and must be replaced.
* This reading may vary depending upon battery type and original customer specifications.