Generator 3D wiring model
Onan / Cummins QG
An Onan generator is a 12 V control circuit: the start switch and a 5 A control fuse feed the board, which drives the starter, the fuel pump and the ignition, then watches oil pressure and AC output.
Parts in this model
- 5 a control fuse: Onan: the 5 A control fuse on the board. No crank with a good battery points here first.
- Start switch: Onan: hold START at the center position; prime is at the bottom. The switch LED flashes two-digit fault codes.
- Starter
- Fuel pump
- Ignition
- Low oil switch: Most gensets shut down on low oil to protect the engine. A bad low-oil-pressure switch is a common Onan failure.
- Ac output: The control watches AC output within seconds of start. No output = shutdown. Check the output breaker on the generator itself first.
The sequence
- Off. The start switch is open. The board waits.
- Prime. Hold the switch to PRIME and the fuel pump runs to fill the carburetor.
- Crank. Hold START. The board closes the starter solenoid and the engine cranks.
- Starts. The engine fires. The board watches oil pressure and AC output.
- Running on load. The output breaker feeds the coach. The board keeps watching oil and output.
Faults you can find with the meter
- 5 A control fuse blown
- Weak battery (10.8 V)
- Fuel pump failed
- Low oil shutdown
- No AC output
- Start switch open
- Starter clicks, won't crank
- No spark
Numbers
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