N3 Series Brushless Alternators Caterpillar


Rectifier - Test

Usage:

D6D 01Y
The illustrations below show the N3 series alternator (35 amperes).

Negative Diode Check




    Illustration 1g00869032

    (1) stator

    (2) stator leads

  1. Disconnect all stator leads (2) from the rectifier.

  1. Disconnect the lead for the capacitor from the "D+" terminal.

  1. Set the multimeter to the diode scale.



    Illustration 2g00868986

    (3) Frame

    (4) Rectifier terminals

  1. Connect one of the multimeter leads to one of the rectifier terminals (4). Connect the other multimeter lead to the frame (ground).

  1. Record the multimeter reading.

  1. Reverse the multimeter leads.

  1. Record the multimeter reading.

Expected Result: One reading is "0L" and the other reading is .4 to .9 volts.

Results:

OK - One reading is "0L" and the other reading is .4 to .9 volts. The diode is normal. Repeat steps 4 through 7 for the other rectifier terminals (4). STOP.

NOT OK - Both readings are "00". The diode is shorted. Replace the rectifier. STOP.

NOT OK - Both readings are "0L". The diode is open. Replace the rectifier. STOP.

Positive Diode Check




Illustration 3g00868988

Positive diode check (inside view)

(4) rectifier terminals

(5) Connection to the "B+" terminal




Illustration 4g00868990

Positive diode check (outer view)

(4) Connection to the rectifier terminals

(5) "B+" terminal

  1. Stator leads (2) remain disconnected from the rectifier.

  1. The multimeter remains on the diode scale.

  1. Connect the multimeter leads across one of the rectifier terminal (4) and "B+" terminal (5) .

  1. Record the multimeter reading.

  1. Reverse the multimeter leads.

  1. Record the multimeter reading.

    Expected Result: One reading is "0L" and the other reading is .4 to .9 volts.

    Results:

    OK - One reading is "0L" and the other reading is .4 to .9 volts. The diode is normal. Repeat steps 3 through 6 for the other rectifier terminals (4). STOP.

    NOT OK - Both readings are "00". The diode is shorted. Replace the rectifier. STOP.

    NOT OK - Both readings are "0L". The diode is open. Replace the rectifier. STOP.

Exciter Diode Check




Illustration 5g00868991

Test for the Excitation diodes (inner view)

(4) Rectifier terminals

(5) (To the D+ terminal)




Illustration 6g00868994

Test for the excitation diodes (outer view)

(4) Rectifier terminals

(5) (To the D+ terminal)

  1. Stator leads (2) remain disconnected from the rectifier.

  1. The multimeter remains on the diode scale.

  1. Connect the multimeter leads across one of the rectifier terminal (4) and "D+" terminal (6) .

  1. Record the multimeter reading.

  1. Reverse the multimeter leads.

  1. Record the multimeter reading.

    Expected Result: One reading is "0L" and the other reading is .4 to .9 volts.

    Results:

    OK - One reading is "0L" and the other reading is .4 to .9 volts. The diode is normal. Repeat steps 3 through 6 for the other rectifier terminals (4). STOP.

    NOT OK - Both readings are "00". The diode is shorted. Replace the rectifier. STOP.

    NOT OK - Both readings are "0L". The diode is open. Replace the rectifier. STOP.

    Note: The 35 amp alternator has three exciter diodes and three stator leads. The remaining alternators have three exciter diodes and four stator leads. If the alternator has four stator leads, do not test the stator lead with the black mark. The stator with the black mark lacks an exciter diode. Ignore the result for that stator lead. See Systems Operation, "Component Description" for more information on the stator and on the stator leads.

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