Onan generator problem

Is that an inverter generator or 2 pole alternator.
If an alternator, that situation indicates a problem in the "flash" circuit that excites the alternator to make it generate.
A capacitor or diode fault.
mike

mike39
It is the engine which won't run, if the engine doesn't run then no alternator will generate anything. Best to have engine running first which seems to be the issue.

Sorry I failed to make myself clear.
Some gen's use a wire from the engine coil low tension circuit to flash the alternator into life. An intermittent short in this circuit may allow the engine to start but stop shortly after.

Mike39
Not having seen the wire you mention, which you say apparently exites the alternator, what then disconnects the coil low tension side from the alternator so the coil energy can be delivered to the HT coil of the ignition. Anything connected to the low side will use energy and the level would then be insufficient to porvide enough magnetic flux in the coil. ie, that is what a kill switch does. Kills the low side energy.

The unit I have is a Lincoln welder/generator. 5kva gen. / 180 a. welder.

Not used for some time, it would fire then immediately stop. Tried everything, full fuel cleanout, carb. etc......just fire a few revs. then no more.
New ignition module, same result.

Traced the wire from the start stop switch to the low oil alert, removed it and the engine started and ran immediately.
However, there was no electricity being generated by the alternator.
Replaced and back to no go.

A wire ran from the oil alert to the inside control box of the gen. Removed the cover to see the wire terminating at a capacitor/diode arrangement. Disconnect this wire and the engine runs as normal, but no generation.

With the engine running, touched this wire to its terminal, the engine immediately starts to behave as if it was switched off, quickly remove it, the engine picks up and the generator starts to deliver power.

This is the "flash" circuit, and either the capacitor or diode block have shorted.
I bought a new capacitor and diode assembly from a local electrician, installed and no more problem.

Hope this explains the suggestions I made, some alternators have a permanent magnet exciter which does not require this external electrical impulse.

The circuit diagram of my unit shows it all quite clearly.
mike

To me .....this sounds like a crook ballast resister, does it have one of these on the ignition circuit?

mike39
That is a good explanation of the system. Thank you. I agree the capacitor was likely to be at fault. It would drain a bit of current initially to excite the alternator, then, effectively drop out of the primary circuit after the capacitor charged up, which is pretty quick and wouldn't normally be noticed in normal starting.

Tony H
Although the system is spark ignition, the Onan has a magneto and a system having a ballast resistor is a Kettering system. First has no ign system battery the Kettering does, hence the resistor to keep up coil energy efficiency to make sparks at high revs. Ballast resistor can give similar trouble symptoms on vehicle engines.

Here's another thought....low oil alert.
A dicky sensor there can create this problem, also some gen's. have a wire from there to "flash" the alternator.
Suggest you remove every accessory wire from the engine (other than starting) and see what happens....think most unlikely carb., more like an electrical fault cutting off power to the coil. Have you checked the "on/off" switch, they also can fail.
mike

Certainly that happens to my EU20i with a full to the brim tank. Not so much with some air space in the tank.

Do you not think the OP who has used the generator in his motor home and now has a problem is suddenly unaware of any breather requirements for the fuel tank which he has filled many times?

Honda EU20i handbook says to open the vent in the cap before use and close after use. That is to prevent vacuum lock overcoming the pulsing fuel pumps ability to transfer fuel.

"Do you not think the OP .....etc"

If that was for me, RMD, yes, I do.

I was responding to sweetwill.

The OP clearly has enough knowledge to discount a cap breather issue. Perhaps in my follow-up I should have said something to that effect to save any misunderstanding..

Frank P
That is ok, it is just the cap issue is of concern when they shouldn't block and are hard to find the cause sometimes.
If I forget to close the one on my EU20 it stinks a bit when in the canopy.