Shorted Stator windings (melted)

[Cowinthfog]

Hello, I have a 1991 Bounder with an Onan 7NHMFA26105B Generator with shorted stator windings. I have been troubleshooting and decided to just pull the generator out to see better and identify the different parts, since it is still new to me (a little over a year). Needless to say, I would love it if the generator worked, and could be repaired, not replaced. So, upon removal, I took the cover off the brush access hole, looked in and saw dreaded blackness and burnt things....I have removed that end of the generator and now have it on my workbench. I have the parts, service, and Flight Systems troubleshooting manuals. Before I dig further, what are my options with the stator assembly and what may have caused it? I want to make darn sure once it is fixed, that there isn't another failure in the system that would burn it up again. These things are spendy!  I did notice the control board has the number 300-3764 D...what does the D represent? Does it matter? Before pulling it, and being sure to check plugs, fuel, carb condition, basic settings and such, not knowing there was a problem with the stator, it would crank fine from the panel at the unit or in the coach, and would try to catch but never quite start. This would end as soon as I let go of the button. I assume now this is because of the stator issue. What else should I check while it's out and partially disassembled? Thanks for any help, Josh

[DaveVA78Chieftain]

I take it you have all the Onan manuals for this unit (Operators, Parts, Service, etc.)?  If not, than as member of the site, you have access to them in the members area.  The service manual goes through operation and checkout of all the components.  You have a 7NHM Spec B generator.

[Cowinthfog]

Yes, I have all the manuals. My big question, is, so I don't overlook something, how does one component affect the others. Specifically here, when the stator went, was it likely to have been by itself? Or did something cause it, and what may have fried because of it? I need to learn the systems better anyway, and am happy to go through the testing procedures, I simply am not sure where to start. Does one thing point to another? If it were yours, how would you begin? Thanks for the reply, Josh

[DaveVA78Chieftain]

You will most likely have to replace the stator which may be expensive.  Could have been caused by heat, a short, manufacturer defect, or over current.  You simply have to replace/repair the defective components then perform all the checks in the manual to ensure all is well.

[Cowinthfog]

I think I would like to try repairing the stator myself. I have discovered by testing the the coils for the B1, B2 and T3 sections cooked. They are all grouped in one section together, that is, inner, middle and outer loops. I have an electrical shop where I can get supplies, and I have counted wraps and know it is 16 gauge wire. What I don't know is exactly which wires are connected through the stator from one loop to the next, because some of them were melted when it went. So, does anyone have, or know where I can get a wiring diagram of the internal wiring of the stator? I believe the B1 and B2 were all alone in their loop, but the other consists of two wires which jump to the neighboring group of loops. I just need to know which way the wiries go.


Thanks, Josh

[Cowinthfog]

I decided to give repairing it myself a shot. I looked around at several sites for supplies, forums for exactly (sort of) what to do, and went for it. I counted the turns, marked the wire size, which wire connections went where, tore out the old wire, cleaned the grooves in the frame and rewound it. I took way more wire than I anticipated, and a lot of varnish to get it all sealed up. I did tie everything off nice and neat before hand, lined the frame with the proper nomex paper and lo and behold......she lives!!! all other parts tested good and it now runs like a champ, except for a minor starting issue, which I believe is the float set a bit low. I cleaned that up too. I didn't think to get many pictures, but if anyone want more info, it's in my brain forever. on the side, I only had to rewing the battery charge loop and one of the four quad windings. Did I mention it works?     

[87Itasca]

I'm impressed. Job well done.

[tmsnyder]

Very cool!  Congrats!

That would make for an excellent 'Project' article on this website.  Maybe you could recollect the process and borrow photos from other sources to recreate what you did?