Caterpillar — Rotating Rectifier - Test (Brushless Exciter)
Testing & diagnosis
From a Caterpillar owner's manual covering: 3306B, 3406, 3406E, 3412C, 3412C Generator Set, 3500 Series. Check it applies to your exact model before use.
Applies to: Caterpillar 3306B, Caterpillar 3406, Caterpillar 3406E, Caterpillar 3412C, Caterpillar 3412C engine
Procedure
- Remove the cover from the exciter.
- Remove the nut securing the rectifier to the heat sink.
- Remove the diode lead and lift the rectifier from the heat sink.
- Connect ohmmeter leads across the rectifier and note reading.
- Reverse the ohmmeter leads and note reading.
- Low resistance one direction and high the other indicates a good rectifier.
- Low resistance both directions indicates shorted rectifier.
- High resistance both directions indicates open rectifier; replace faulty rectifiers.
Tools required
- 6V-7070 Digital Multimeter Amazon
- 9U-7330 Multimeter Amazon
- 146-4080 Digital Multimeter (RS-232) Amazon
- 7X-1710 Multimeter Probe Group Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Full service-parts list: Caterpillar 3406 →, Caterpillar 3406E →, Caterpillar 3412C →, Caterpillar 3412C engine →
Source: Caterpillar owner's manual. Steps and values are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.