Cummins/Onan — Generator Voltage Adjust (Detector AC Option)
Adjustments · Voltage regulator / Voltage Adjust R21 potentiometer
From a Cummins/Onan service manual covering: 200 DFP, 250 DFM, 275 DFM, 300 DFM. Check it applies to your exact model before use.
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Before you start
- High voltages in the control present an electrical shock hazard which can cause severe personal injury or death. Proceed with care!
Procedure
- Operate Phase Selector switch to read generator output current and voltage.
- Insert a screwdriver into the Voltage Adjust R21 potentiometer on the front of the control and loosen the locking nut with a wrench.
- While observing the voltmeter, slowly turn the screwdriver clockwise to increase or counterclockwise to decrease voltage; adjust to rated nameplate voltage.
- After setting correct voltage, retighten locking nut without changing the adjustment.
- Operate Phase Selector switch to the Off position.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- adjust to rated nameplate voltage
- generator voltage adjustable within 5% of rated nameplate voltage
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.