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Delco 27SI Testing and Adjusting – Regulator – Test

The regulator test determines problems in the following components: the regulator, the field winding, the rectifier and the diode assembly. The regulator test does not cover all failures.

  1. Connect a variable power supply (VPS) and two multimeters to the alternator. The alternator is completely assembled for this test. Set one multimeter as a voltmeter (V). Set the other multimeter as an ammeter (A). The setup is shown in Illustration 1.

 

  1. Set the variable power supply to 0 volts. Slowly raise the power supply until the ammeter indicates a current draw.

 

  1. Measure the voltage. Record the result as the “Turn On” voltage.Expected Results:
    3T-6352 Alternator Gp … 27.4 ± 0.6 volts
    5N-5692 Alternator Gp … 27.4 ± 0.6 volts
    7G-7889 Alternator Gp … 14.0 ± 0.3 volts

    Results:

    OK – The voltage is within tolerance. Go on to Step 4.

    NOT OK – The voltage is not within tolerance. The regulator has failed. Replace the regulator. STOP.

 

  1. The regulator remains on. Measure the current. Record the result as the field current.Expected Results:
    3T-6352 Alternator Gp … 3.3 to 3.8 amperes
    5N-5692 Alternator Gp … 2.5 to 2.8 amperes
    7G-7889 Alternator Gp … 5.7 to 7.1 amperes

     

    Results:

    OK – The current is within tolerance. Go on to Step 5.

    NOT OK – The current is below tolerance or the current is 0 amperes. The field winding, the rectifier, or the regulator is open. Refer to Testing and Adjusting, “Field Winding – Test” and Testing and Adjusting, “Rectifier – Test”. If the field winding is open, replace the field winding. If the rectifier is open, replace the rectifier. If the field winding and the rectifier are normal, the regulator is open. Replace the regulator. STOP.

    NOT OK – The current is above tolerance. The field winding has a short circuit. Replace the field winding. Go on to Step 5.

 

  1. Divide the “Turn On” voltage by the rotor field winding resistance. Refer to Specifications, “Alternator” for the rotor field winding resistance. Record the result as the field current. Compare the current that was calculated above with the current that was measured in Step 4. The values should agree.

 

  1. The power supply remains at the “Turn On” voltage. Slowly raise the voltage until the ammeter reads 0 amperes. Record the result as the “Turn Off” voltage.Note: The ammeter should drop quickly to 0 amperes. If the ammeter drops slowly, the regulator has failed.

 

  1. Subtract the “Turn On” voltage from the “Turn Off” voltage.Expected Result: The difference is 0.3 volts or less.

    Results:

    OK – The difference is 0.3 volts or less. The regulator is normal. STOP.

    NOT OK – The difference is greater than 0.3 volts. The regulator has failed. Replace the regulator. STOP.

 

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