Cummins/Onan — Testing Generator Set Rotor
Testing & diagnosis · Rotor windings
From a Cummins/Onan service manual — check it applies to your exact model before use.
Applies to: Cummins/Onan HDKA
Before you start
- Use a Megger or insulation resistance meter which applies 500 VDC or more to the test leads.
Procedure
- Isolate the rotor windings by disconnecting the two leads to the brush holder.
- For grounds, connect test leads between each ring and the rotor shaft in turn (100,000 ohms or greater).
- Thoroughly dry and retest if less than 100,000 ohms.
- For open/short windings, measure resistance between the F1 and F2 slip rings with a digital ohmmeter.
- Replace a defective rotor with a new identical part.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- 17.2 ohms (single-phase), 19.4 ohms (three-phase), 22.5 ohms (extended-stack three-phase), 25.5 ohms (husky) at 25°C
Full service-parts list: Cummins/Onan HDKA →
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.