I have an Onan 4KY Spec J generator. It has worked fine since we purchased our trailer used about 3 months ago. This last weekend, it suddenly started tripping the main breaker on the generator. The first time it did it was one morning after I turned on the coffee pot. The generator keeps running, but I finally figured out the breaker was tripped. I reset it and it stayed on about 10 minutes.
Even if I disconnect everything, the circuit breaker will only stay on about 10 minutes and then pop. The circuit breaker is located inside the generator next tot he start and stop switch.
Is it possible the breaker is just old and needs to be replaced? If so, can I just replace the breaker, or it looks like is is part of another unit? Any ideas on replacing the circuit breaker or looking for something else causing the problem?
Thanks
I would go to where the generator wiring interfaces with the rigs wiring- usually a junction box within a couple of feet. Unhook it there, then test again.
I believe the breaker is a separate part and easily replaceable, though.
Hopefully Gunny or Generator Jim will spot this and jump in. They are the resident Onan gurus on this site.
My guess would be that it very well could be a faulty breaker. However, it could also be some faulty wiring that is creating a true overload on the circuit from the genset.
First thing to check is the voltage output. As volts drop, amps go relative to the watts used.
If the voltage is good, I would try to monitor the amp draw on the circuit as close to the genset as possible. If the amp draw is low and the breaker trips, then the breaker is most likely bad. Opposite and the suspect would be bad wiring somewhere.
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With everything disconnected does the sound of the engine change when the breaker trips? If the generator is actually loaded enough to trip the breaker there should be an instant "unloading" and you should hear it in the engine.
I will try measuring the voltage this weekend. I have the trailer at storage right now.
The generator is not under load when the breaker trips. The last time I flipped it back on and then just waited to see what happened. It just make the click sound and tripped after about 7 minutes of being reset. I had no load on it.
I may go ahead and see if I can get a breaker just to have, because we are using the trailer again this weekend. Hopefully it is an easy thing to change, because we are using the trailer each of the next 4 weekends and will need the generator.
Anyone know how to look up a part number? I live in the Dallas/Ft. Worth Area so I may just call United RV in Ft. Worth and see if they can get one.
Lay hands on an ammeter. This device measure the amp load on the genset.
Coming out of the genset, after the breaker will be some heavy wires colored black, white and green. Seperate the black one away from the rest and clamp the ammeter around the black wire only. Start the genset, be sure the breaker is closed and see what the load onit is. Look at the genset data plate and see what the amp rating is. If the reading on the meter is much lower than the rated capacity, it would almost be a sure bet that you have a breaker that has/is failing. Not uncommon for a breaker to die in this manner.
If you are unsure of how to use an ammeter, you might enlist the aid of an electrician.
Yes, the breaker can be purchased seperately and should be relatively inexpensive (for an Onan part that is) I'm going to guess, its been a whle since I purchased one and say maybe $45.00 or so.
If you find it to be the breaker, call Cummns/Onan with the whole model/spec/serial number, tell them ou need the output breaker, have a shipping address and a credit card handy and you should have a new breaker in short order.
It's probably a bad breaker but -- disconnect the output leads from any load and tape them up (separately). Try another test and record the voltage coming out of the unit. If OK, then order Breaker, Circuit, CB1, ONAN part number 0320-1323 and that should fix it.
Good luck with the troubleshooting
JimL
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Thanks Generator Jim. If I have to replace the breaker, is it fairly straight forward? From what I remember, it is inside a small box that has the starter rocker switch just to the right of the circuit board.
I am used to replacing circuit breakers in breaker boxes, such as Square D. those are really simply as they just plug in. I am guessing this one has some type of spade lugs to connect the wiring. I am not too worried about the wiring or electrical issues, I just don't want any surprises if I need to take it apart.
My Spec K model uses the same beaker but mounted in a different place. It is held in with two small capscrews and has two spade connectors on the back side. The plastic gas drip 'tray' on top of the assembly should come off with a couple of screws. The back of the 'tray' goes down a couple of inches as insulation against wires shorting against the generator housing.
Well guys, thanks for all the help, especially Generator Jim. I got it back working on Saturday. I decided to take a chance and hope it was just a faulty breaker., We we were heading out real early Saturday morning and I wouldn't have time to test anything and then get parts.
I called Central Plains Cummins in Fort Worth on Friday and gave them the part number. They had stock, and the price was $27. Ran by and picked it up, figuring I would install it once we got to the race track. It only took about an hour to take out the oil drip shield and then the mounting flange. Lucky I had a set of torx drivers, as I forgot all the screws were torx.
Put everything back together and it ran like a champ. It probably ran about 12 hours total over the weekend without any problems.
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