Cummins/Onan — Adjusting Voltage Regulator
Adjustments · Automatic voltage regulator (AVR)
From a Cummins/Onan service manual covering: 4BT3.9-GC1, 4BT3.9-GC2, 6BT5.9-GC1, 6BT5.9-GC2, 6CT8.3-GS/GC1, 6CTA8.3-GS/GC1, 6CTA8.3-GS/GC2. Check it applies to your exact model before use.
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Before you start
- Sealed voltage regulator potentiometers are factory calibrated.
Procedure
- Adjust voltage control rheostat R21 to mid position.
- Open control panel doors to access voltage regulator.
- With generator set operating, adjust Volts potentiometer to desired voltage.
- Perform fine voltage adjustment (+3 percent) with rheostat R21; retighten locking nut.
- Stop and restart generator set to confirm operation.
- If adjustment not possible, check wiring and connections; replace regulator if faulty.
Tools required
- screwdriver Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- +3 percent adjustment via R21
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.