Cummins/Onan — UFRO (Under Frequency Roll Off) Adjustment
Adjustments · Voltage Regulator VR21
From a Cummins/Onan service manual — check it applies to your exact model before use.
Applies to: Cummins/Onan DGBB, Cummins/Onan DGBC, Cummins/Onan DGCA, Cummins/Onan DGCB, Cummins/Onan DGDA, Cummins/Onan DGDB, Cummins/Onan DGEA, Cummins/Onan DGFA, Cummins/Onan DGFB, Cummins/Onan 4B3.9 engine
Before you start
- High voltage - use insulating protection
Procedure
- Note the red LED on the board lights when frequency dips below threshold.
- Turn the UFRO pot clockwise to raise the threshold frequency.
- Turn the UFRO pot counterclockwise to lower the threshold frequency.
- Determine threshold frequency by lowering generator frequency until the LED lights.
Specs & values
- Typically 59 Hz for 60 Hz applications and 49 Hz for 50 Hz applications
- Dip and Dwell adjustments are related
Full service-parts list: Cummins/Onan DGBB →, Cummins/Onan DGBC →, Cummins/Onan DGCA →, Cummins/Onan DGCB →, Cummins/Onan DGDA →, Cummins/Onan DGDB →, Cummins/Onan DGEA →, Cummins/Onan DGFA →, Cummins/Onan DGFB →
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.