Cummins/Onan — Testing Exciter Rotating Rectifiers
Testing & diagnosis
From a Cummins/Onan service manual — check it applies to your exact model before use.
Browse Cummins/Onan generators & specs →
Before you start
- Layers of dust can cause diodes to overheat and fail. Brush dust off regularly.
Procedure
- Disconnect all leads from assembly to be tested.
- Connect one test lead to F1+ stud and other lead to CR1, CR2, and CR3 in turn; record resistance value of each rectifier.
- Connect one lead to F2- stud and other lead to CR4, CR5 and CR6 in turn; record resistance value of each rectifier.
- Reverse ohmmeter leads and repeat steps 2 and 3.
- All three resistance readings should be high in one test and low in the other test. If any reading is high or low in both tests, rectifier assembly is defective.
- Replace defective rectifier assembly with new, identical part.
Tools required
- accurate ohmmeter Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Use 24 lbs-in. (2.7 N·m) torque when tightening nuts on F1+ and F2- and CR1 through CR6.
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.