Alternator: Testing and Inspection

Fig. 4 Alternator Test Connections:

To check alternator in a test stand, proceed as follows:
1. Connect alternator as shown in Fig. 4, except leave carbon pile disconnected. The ground polarity of the alternator and the battery must be the same. The battery must be fully charged. Use a 30-500 ohm resistor between battery and ``L'' terminal.
2. Slowly increase alternator speed and observe voltage.
3. If the voltage is uncontrolled and increases above 16.0 volts, the rotor field is shorted or grounded or the regulator is defective, or both. A defective rotor field coil can cause the regulator to become defective. The battery must be fully charged when making this test.
4. If voltage is below 16.0 volts, increase speed and adjust carbon pile to obtain maximum amperes output. Maintain voltage above 13.0 volts.
5. If output is within 15 amperes of rated output the alternator is good.
6. If output is not within 15 amperes of rated output, alternator is defective and requires replacement.