Starting/Charging Test Procedures

 To quickly check Alternator Diodes we recommend the following:

ALTERNATOR - Ripple Voltage Test

Using a DMM

The Alternator produces AC voltage and current. The battery requires DC voltage and current to charge properly.  Diodes located within the alternator change (rectify) the AC to DC.  However, a small amount of AC can still be present and no harm is done.  Problems can develop when alternator diode faults permit unacceptable amounts of AC to pass into the vehicle electrical system. 

1. Set the meter to read “AC” Volts (lowest range) .

2. Connect the black COM lead probe tip to the battery negative post.

3. Connect the red Volts lead probe tip to the battery positive post.

4. Run the engine at 1500 RPM.

5. Turn ON the high blower and high beam lights.

6. Your meter reading should not exceed .09 volts (90 mV) AC.

High ripple voltage readings imply faulty diode(s) which can cause:

· Undercharged battery.

· Stalling.

· Rough idle.


NOTE:  If your meter reading exceeds 90 mV AC, use an  ADL7100 labscope or equivalent to verify that ripple voltage spikes do not exceed one volt peak to peak.