Cummins/Onan — Testing Brushless Exciter Stator
Testing & diagnosis
From a Cummins/Onan service manual covering: 15.0YD-3G, 20.0YD-3G, 20.0YD-5DG, 25.0YD-3G, 25.0YD-5DG, 30.0YD-3G, 30.0YD-5DG, 6.0-3CS1, 7.5-3CS1. Check it applies to your exact model before use.
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Procedure
- Disconnect F1+ and F2- exciter field leads from terminal block in generator end bell.
- Measure resistance between field leads (should be 10.98 to 13.42 ohms at 68°F (20°C)).
- Connect ohmmeter between either field lead and exciter stator laminations.
- Reading must be one megohm (1,000,000 ohms) or greater.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Field lead resistance: 10.98 to 13.42 ohms at 68°F (20°C)
- Ground insulation: 1,000,000 ohms or greater
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.