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Old 05-09-2011, 09:41 AM   #1
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Trouble shoot this one!

I have the below rig in my sig with the Onan 4.0kW MicroQuiet Generator. The genset wouldn't run when a load was applied. The fault code I received was an over-voltage fault, code # 12 I believe it was.

Took the rig to the dealer a month ago. They took it to Cummins and Cummins claims the genset works just fine when they power it up isolated from the motorhome. So, now it is back to the dealer. Cummins thinks it must be the converter or something else.

The converter? A converter converts AC to DC. When the rig is plugged into AC power, everything works just fine. Something sounds a bit fishy about this.

1. The rig's electrical system works fine when plugged in
2. The genset will not run when a load is applied.
3. The genset's built in self diagnostic code reveals an over-voltage code.

What else could be the problem if the genset is working properly????
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Old 05-09-2011, 12:53 PM   #2
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Hi jtroop,
I do not know your coach. Based on the information in the OP, consider looking at the transfer switch. Make sure it is passing power within spec. Next I'd check the voltage at the generator (both lines).

Is there a specific load the generator does not like (HWH, A/C, micro wave, etc.)? If that is the case, something in that circuit may be the cause of pulling too much power.
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Old 05-09-2011, 01:01 PM   #3
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I'm not that familiar with your coach, but do you even have a converter...I don't.
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Old 05-09-2011, 02:05 PM   #4
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What load do you apply when it faults out? Don't forget that you are converting AC to DC to charge your coach batteries. That said try turning off the main breaker in the coach, fire up the genset and see what happens. Have you turned off the breaker at the genset, to make sure the genset itself is not the problem?
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Old 05-09-2011, 02:58 PM   #5
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I think the Cummins dealer meant Inverter rather than Converter. The inverter changes DC battery current to AC current to power AC devices like the TV and microwave when dry camping. Most energy managment systems do not monitor the house battery charger or the inverter (they can be seperate units but in many cases one unit does both).

Since these units are not monitored they cold be drwaing more current than the generator is able to provide. The generator will shut down with an over voltage code rather than burn itself up trying to meet the demand.

Another thing that could be causing a massive current draw is a short in the wiring harness that connects the generator to the coach. It could be that a wire has rubbed against a frame or body component and is shorted to ground. Or it could be that a mouse, chipmunk or other furry critter has had a snack on some of the wiring. For some reason rodents seem to be attracted to wiring harnesses.
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Old 05-09-2011, 03:32 PM   #6
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Similar to what other's have mentioned: Turn off ALL breakers including genset, then start the gen. Then turn on the gen breakers, if no shut-down then your main breaker and then one by one your single breakers. Then let us know what happens.
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Old 05-09-2011, 03:48 PM   #7
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You say that cummins tested the genset isolated form the MH. Did they apply a load to it? That is where your having the problem. I'm not familiar with your coach but I'm assuming it is a gas genset. If you have an over-voltage fault I would suspect the voltage regulator.
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Old 05-09-2011, 04:48 PM   #8
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Quote:
Originally Posted by RJay View Post
You say that cummins tested the genset isolated form the MH. Did they apply a load to it? That is where your having the problem. I'm not familiar with your coach but I'm assuming it is a gas genset. If you have an over-voltage fault I would suspect the voltage regulator.
I don't believe anything newer than the early 1990's uses a separate voltage regulator. They now use printed circuit control module that isn't servicable. The module controls just about every function including regulating output voltage. It also generates the fault codes displayed. If you follow the diagnostic tree in the service manual (for almost every fault code) it's an orderly process of eliminating all potential reasons for the error code. The last thing in each of the diagnostic trees is the control module. When all other possible physical contributors have been eliminated the last thing left is the conrtol module.
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Old 05-09-2011, 11:27 PM   #9
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Thanks for all the replies everyone. I've been at work all day so let me try to answer some of the questions.

My rig does not have an automatic transfer switch. The dealer picked it up from cummins and is trying to figure out what is wrong. When the genset went out, we were running the AC and the microwave. When you turn off the genset breaker, it will run. Turn the breaker on and it shuts down. It shuts down with nothing powered on in the rv. Of course the converter would be drawing some power.

I do not have an inverter. I'm thinking hikerdogs is correct, it is a short in the wiring harness. Cummins says the genset is fine when isolated from the rv. It shouldn't be the converter or I'd have a problem when plugged into shore power, right? I don't know why the dealer is having a hard time finding the problem. I hope they find the problem soon. We are suppose to go camping this weekend.
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Old 05-10-2011, 12:02 AM   #10
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Believe me I speak from experience, too much to get into here. I had similar issues with my genset. Breaker on, no joy. Breaker off it would run all day. I ended up disconnecting the coach wires at the genset terminal after the breaker, no joy. Problem was in the genset. Maybe you should check this as well it might save you a lot of headaches and it is pretty simple and quick.
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Old 05-10-2011, 05:20 PM   #11
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Originally Posted by Buford B View Post
Believe me I speak from experience, too much to get into here. I had similar issues with my genset. Breaker on, no joy. Breaker off it would run all day. I ended up disconnecting the coach wires at the genset terminal after the breaker, no joy. Problem was in the genset. Maybe you should check this as well it might save you a lot of headaches and it is pretty simple and quick.
Yes, well...Cummins already ruled out the genset. The dealer is still trying to figure it out. I had to cancel our camping this weekend. They said it wouldn't be ready in time.
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Old 05-10-2011, 06:35 PM   #12
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Hi jtroop,
I vote for doing another isolation from the coach. Tell the RV tech to remove the wires (at the generator) that connect the generator to the coach. Only then do we know the proper isolation was done by Cummins. If the generator runs when truly isolated from the coach, the dealer tech should be able to find the hard failure quite quickly.

If possible, try to determine if the tech working on your coach is a Certified RV tech in the area of the failure.
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Old 05-11-2011, 04:00 AM   #13
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If you do not have a transfer switch, then you have a receptacle you plug the coach into that is feed by the generator. May certain that the wiring in the receptacle box is not shorting out when the cord is connected.
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Old 05-14-2011, 04:53 AM   #14
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*UPDATE* Stopped by the dealer. They are sending the rig back to Cummins! They brought in a technician who isolated the genset from the rv. The genset would shutdown when a load was applied. Cummins was wrong. The service rep said on top of that, when they pulled the cover off the genset, Cummins didn't completely reassemble the genset!

Service rep talked to a foreman at Cummins and they said to bring it back monday. What the heck Cummins!!
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