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Onan: 15 k onan genset with no power output

Ruffus_71

Registered
I was brought an Onan 15kw generator that is not putting out AC power they said they were welding with it ran it out of gas got it restarted and it seems that somebody grabbed the governor and over rev the engine now it won't put out ac voltage I don't usually work on generators I work on engines can anybody help me where to start. thank you. Ruffus.
Numbers I found. onan 15.ojc/8388aa. O and its not charging the starting battery if that means anything 20200325_162346.jpg6066027791.jpg
 

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Max Thompson

Sponsor
Last Subscription Date
09/03/2019
Looks like yours has a push button "field breaker" above the amp gauge, be sure it is not tripped. You can download the service manual for your set here http://www.twinslan.net/~n0nas/manuals/onan/
#900-0184 is the YD generator service manual and will have test procedures.

Flight Systems no longer tests the VR boards, but they do sell a good replacement. Last I knew they were north of $200. There is a $35 alternative in the chinese clone SX460 regulators that many of us have used with good results. There is a thread linked below that has all the info on the clones.
https://www.smokstak.com/forum/threads/sx460-voltage-regulator-for-old-onan-generators.139868/

That is a real nice looking JC. Welcome to The Stak.
 

BigBlockChev

Subscriber
Last Subscription Date
07/06/2019
With a YD generator end as in the JC there is about a 95% chance it is the voltage regulator, 3% the exciter coil, 1% the rotating diodes and 1% everything else , all of this is based on my personal experience. Step one is to test the field exciter coil resistance, if you get around 11.5 ohms try exciting it with 12V Dc with the engine running if that gives you maybe 60+ V AC output then it is pretty much given that the voltage regulator is toast. If it does not give you output then your problem is one of the more esoteric issues. Cheers Dan
 

Motorhead

Subscriber
Age
67
Last Subscription Date
07/09/2019
I second BBC diagnosis. I don't know the procedure but there is a way to put a certain amount of voltage to the field to bypass the voltage regulator. PLEASE DON'T experiment yourself until one of the smarter guys posts how to do it. 1) Don't want you to get electrocuted and 2) Don't want you to fry anything else that could be more expensive than just a voltage regulator. It looks like a nice clean set!
 

Ruffus_71

Registered
With a YD generator end as in the JC there is about a 95% chance it is the voltage regulator, 3% the exciter coil, 1% the rotating diodes and 1% everything else , all of this is based on my personal experience. Step one is to test the field exciter coil resistance, if you get around 11.5 ohms try exciting it with 12V Dc with the engine running if that gives you maybe 60+ V AC output then it is pretty much given that the voltage regulator is toast. If it does not give you output then your problem is one of the more esoteric issues. Cheers Dan
I believe that is one and two on the field exciter and in have very low resistance. like .4ohms. And i just found out that the field breaker did pop and wont reset. I bypassed it and still nothing. So does that mean the field excited is bad?
 
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