Cummins/Onan 3100 series — Testing the Rotating Rectifier Assembly Diodes
Testing & diagnosis · Rotating Rectifier Assembly (exciter rectifier bridge)
For the Cummins/Onan 3100 series, from the Cummins/Onan service manual.
Applies to: Cummins/Onan DGBB, Cummins/Onan DGBC, Cummins/Onan DGCA, Cummins/Onan DGCB, Cummins/Onan DGCC, Cummins/Onan DGDA, Cummins/Onan DGDB, Cummins/Onan DGDK, Cummins/Onan DGEA, Cummins/Onan DGFA, Cummins/Onan DGFC
Before you start
- Layers of dust can cause diodes to overheat and fail. Brush dust off regularly.
Procedure
- Disconnect the diode pigtails from the terminal posts.
- Measure electrical resistance between each diode pigtail and the plate on which the diode is mounted.
- Reverse the meter test probes and repeat the tests.
- Replace the diode if resistance is high or low in both directions.
Tools required
- Ohmmeter Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Diodes torqued to 36 to 42 in-lbs (4 to 4.8 Nm)
- Pigtail terminals torqued to 24 in-lbs (2.7 Nm)
- Surge suppresser terminals torqued to 24 in-lbs (2.7 Nm)
Full service-parts list: Cummins/Onan DGBB →, Cummins/Onan DGBC →, Cummins/Onan DGCA →, Cummins/Onan DGCB →, Cummins/Onan DGCC →, Cummins/Onan DGDA →, Cummins/Onan DGDB →, Cummins/Onan DGEA →, Cummins/Onan DGFA →, Cummins/Onan DGFC →
Source: Cummins/Onan service 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.