Cummins/Onan — Testing Brushless Exciter Rotor (Armature)
Testing & diagnosis
From a Cummins/Onan service manual covering: JC 15.0, JC15, MDJC 10.0, MDJE 75, MJC15. Check it applies to your exact model before use.
Applies to: Cummins/Onan MDJC, Cummins/Onan MDJE, Cummins/Onan MDJF
Procedure
- Use a Wheatstone Bridge. Disconnect main rotor field leads at F1+ and F2-.
- Disconnect lead wires from diodes CR1, CR2, CR3, CR4, CR5 and CR6.
- Test between exciter lead pairs T1-T2, T2-T3 and T1-T3. Resistance should be 0.5 to 0.6 ohms at 20 C (68 F.).
- Connect leads of ohmmeter between each CR lead and exciter rotor laminations; use RX 100 scale; reading less than infinity indicates defective ground insulation.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- 0.5 to 0.6 ohms at 20 C (68 F.)
Full service-parts list: Cummins/Onan MDJC →, Cummins/Onan MDJE →, Cummins/Onan MDJF →
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.