Monday, December 19, 2011

Alternator testing?

The detail to test alternator is as follows :---



  1. Check drive belt(s) for wear and tension. Check wiring for obvious damage.
  2. Go to Step 7 for vehicles without a charge indicator lamp.
  3. With the ignition switch ON and the engine stopped, the lamp should be ON. If not, detach the wiring harness at the generator and ground the "L'' terminal lead.
  4. If the lamp illuminates, replace the alternator. If the lamp does not illuminate, locate the open circuit between the grounding lead and the ignition switch. Check the lamp, it may be open.
  5. With the ignition switch ON and the engine running at moderate speed, the lamp should be OFF. If not, stop the engine, then turn the switch ON and detach the wiring harness at the alternator.

See Figure 1

Fig. Fig. 1: Proper connections for alternator testing
  1. If the lamp goes out, replace the alternator. If the lamp stays ON, check for a grounded "L'' terminal wire in the harness.
  2. Determine if the battery is undercharged or overcharged.

    An undercharged battery is evidenced by slow cranking or a dark hydrometer.
    An overcharged battery is evidenced by excessive spewing of electrolyte from the vents.
  3. Detach the wiring harness connector from the alternator.
  4. With the ignition switch ON , and the engine not running, connect a voltmeter from ground to the "L'' terminal in the wiring harness, and to the "I'' terminal, if used.
  5. A zero reading indicates an open circuit between the terminal and the battery. Repair the circuit as necessary.
  6. Attach the harness connector to the alternator and run the engine at moderate speed with accessories OFF.
  7. Measure the voltage across the battery. If above 16 volts, replace the alternator.
  8. Connect an ammeter at the alternator output terminal, run the engine at moderate speed, turn ON all the accessories and load the battery with a carbon pile to obtain maximum amperage. Maintain voltage at 13 volts or above.
  9. If the output is within 15 amps of the rated output of the alternator (stamped on the alternator case), the alternator is good. If the output is not within 15 amps, replace the alternator.



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