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Hank F.
Hank F., Technician
Category: Small Engine
Satisfied Customers: 14893
Experience:  Certified on Onan and Generac generators
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I'm having an issue with an older Onan genreator. It's a

Customer Question

I'm having an issue with an older Onan genreator. It's a 6.5NH3CR/23001P unit. The other day it was running and we smelled battery acid. It's in a car trailer so we went inside and the battery had acid boiling out of it and the unit would not shut down until we disconnected the battery ground. We cleaned up the mess and tried anotehr battery and as soon as the negative terminal was attached, the Generator tried starting on it own. I'm being told there is a circuit board under the start/stop button on the unit itself that could be bad and cause the problem but I don't want to start replacing parts to see if that's the problem.
Any help would be greatly appreciated as far as testing and troubleshooting and/or part number for a replacement
Submitted: 1 year ago.
Category: Small Engine
Expert:  Rico_Soma replied 1 year ago.

Sorry there was a glitch and your question appeared where it shouldn't have

Expert:  Rico_Soma replied 1 year ago.

So, I'm going to open this backup to my colleagues so one of them can help. Please don't respond (even to acknowledge this post)until you get a response from us. If you respond first it will only delay your answer.

Expert:  Hank F. replied 1 year ago.

Hello, my name is ***** ***** I am going to assist you with this.

I need to know one thing before we start here - do you have a remote start switch connected to this genset, or do you have to physically go to the genset to start and stop it?

Customer: replied 1 year ago.
Hi Hank,
This unit has a remote start/stop switch by the door to the car trailer. I removed that panel and there is no printed circuit board behind that switch. The only circuit board is on the generator itself in a box under the start/stop switch. It has about 8 spade terminals on it as well. I contacted a local dealer and I was told I would have to look online for an aftermarket supplier as cummins/Onan no longer produces that part. I was given a part number of(###) ###-####and I did find one online but the photo doesn't look like the board on my unit. Before I purchase anything I want to make sure that board is indeed the cause of my problem. Any help would be greatly appreciated. By the way, the vendor I contacted sent me a parts listing with that part number on it but I noticed the parts list a drawing he sent me was for a "spec K" and my unit is a spec "P"
Expert:  Hank F. replied 1 year ago.

Battery charging is not accomplished through the control board. If the genset is starting and running, the board is good.

Battery charging on this unit is done through a resistor and a diode - they are what usually fail.

But before even thinking about changing any parts at all, you need to measure the voltage and frequency output of the unit, with no load on it. The genset may simply be producing too much voltage.

Connect a meter to the AC output leads, and start it up.

What voltage reading do you get?

What frequency reading do you get?

Customer: replied 1 year ago.
Happy Thanksgiving Hank,
This problem started while the generator was running. The only way we could shut the generator down was to disconnect the negative terminal from the battery. It would shut down holding the "stop" side of the start/stop switch but as soon as we let go of the stop button, the generator tried starting all but itself without touching the start/stop switch at all. That's why we had to disconnect the negative cable from the battery. When we try to reconnect the negative battery cable, the terminal sparks the generator tries to start. Any suggestions?
Expert:  Hank F. replied 1 year ago.

Unplug the remote switches from the genset.

Does that allow the genset to operate properly?