Cummins
Unstable Voltage Regulation
Generator runs but output voltage is unstable or fluctuates
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Failing AVR, Loose voltage sensing connections, Worn brushes or dirty slip rings (if equipped), Rapidly changing load conditions
How to Fix / Troubleshooting
Safety first: Isolate the generator from the building load. Disable automatic start before opening electrical compartments.
- Measure voltage: Use a multimeter to confirm fluctuations at the generator terminals, not just at the building panel.
- Inspect AVR wiring: Tighten all sensing and power connections to the AVR. Look for heat discoloration or damage.
- Brushes/slip rings: On brush-type alternators, inspect and clean slip rings and ensure brushes move freely and have adequate length.
- Load check: Verify that large loads are not cycling rapidly (e.g., large compressors). If they are, consider soft-start solutions.
- Replace AVR: If wiring and load are normal but voltage remains unstable, replace the AVR with the correct Cummins part.
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Repair Difficulty
Hard
4/5
Required Part
Automatic Voltage Regulator (AVR)
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