Home » Public Forums » GMCnet » Next project - onan!
| Next project - onan! [message #73654] |
Fri, 12 February 2010 18:16  |
mini577
Messages: 16
Registered: March 2008
Location: Berryville, AR
Karma: 0
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Okay, here is where I am at with the onan. The control board is toast. No problem. I have applied power to the coil/fuel pump/etc. and then to the starter and after a few cranks it starts and runs like a champ. I am going to be leaving the control board out of the equation. Nearly all of the wiring on my onan is rotting off anyway.
So now that it is running I check my output and get nothing. I try to remove the bridge rectifier and find that the bolt holding it in place is seized, and I break the BR reoving it from it's home. No big deal. The last time I was at Gemrecs I salvaged one from another old onan. I install it - being very careful I think to be sure that it is installed the same as the old one. Still nothing. I measure across the BR and get somewhere in the neighborhood of 5 volts. I get about the same when I measure the AC side. I also checked the circuit breaker on top of the unit and get the same voltage on both sides.. nothing.
Can you guys give me some more hints where to start?
Thanks!!
Drew
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| Re: Next project - onan! [message #73660 is a reply to message #73654] |
Fri, 12 February 2010 20:32  |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Did you check the 'new' bridge out of circuit with a meter? It too could be bad. Adjacent leads should have continuity in only one direction. I guess next check the field ohms and the armature ohms. Then the compounding reactor. I think that's about all there is if the brushes are good and making contact. There was a post just a little while back that leads you to the GMC DVD of how to troubleshoot the Onan from the factory service films. I just don't know how to link you there.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: Next project - onan! [message #73687 is a reply to message #73661] |
Sat, 13 February 2010 03:12 |
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mike miller
Messages: 3576
Registered: February 2004
Location: Hillsboro, Oregon
Karma: 0
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| mini577 wrote on Fri, 12 February 2010 18:49 |
I read in the manual that I should be reading 8 ohms between the leads, but I am not getting that. I AM getting continuity only in one direction on the pins as I would expect though, which makes me think maybe it is all right. I guess I will have to go back to the manual again and check the rest. I was SO hoping this was going to be an easy fix!
Drew
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Another common problem with Onan's is bad spade connections on the wires in/out of the rectifier... I am talking about the plastic covered connectors connecting 3 or four wires. they are shown in this picture: (not my pic, just the 1st I found showing them.)
<http://www.gmcmhphotos.com/photos/showphoto.php?photo=3472&cat=3346>
Mike Miller -- Hillsboro, OR -- on the Black list
(#2)`78 23' Birchaven Rear Bath -- (#3)`77 23' Birchaven Side Bath
More Sidekicks than GMC's and a late model Malibu called 'Boo'
http://m000035.blogspot.com
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| Re: Next project - onan! [message #73689 is a reply to message #73687] |
Sat, 13 February 2010 03:31 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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Isn't there something about flashing it to get it started generating after it has sat stagnant for a long time? I have never done it.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: Next project - onan! [message #73700 is a reply to message #73661] |
Sat, 13 February 2010 07:53 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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| mini577 wrote on Fri, 12 February 2010 21:49 |
I read in the manual that I should be reading 8 ohms between the leads, but I am not getting that. I AM getting continuity only in one direction on the pins as I would expect though, which makes me think maybe it is all right. I guess I will have to go back to the manual again and check the rest. I was SO hoping this was going to be an easy fix!
Drew
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Drew,
You need to be a little more specific. . .
You say you are not getting the 8 ohms between the leads, but you do not say which. If you mean the two leads that go to the field, well guess what you have to find.
That 8 ohms that is not there means that there is no field and without that, you got gotz.
If the wires were rotted off, (again about specifics) you are not clear about whether the insulation has cooked and fallen apart or the copper has corroded and is gone.
In either case, you have to find the field before you can expect much to happen.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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| Re: Next project - onan! [message #73704 is a reply to message #73654] |
Sat, 13 February 2010 08:29 |
bobby5832708
Messages: 237
Registered: November 2006
Location: Winter Springs FL
Karma: 3
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Senior Member |
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Drew,
Here's a cut & paste of my reply to Toby Maki last year when he was having 'fun' with his Onan. Maybe this is your problem?
===========================================================
Toby,
The field coil is polarity sensitive. Try swapping the wires from the field coil that are on the + and - of the bridge. I found this out the hard way a few months ago.
Here's the story:
The onan quit making AC while running in my driveway. Removed the bridge rectifier and, using a multimeter, found one diode open. Removed the wires from the original holder because the generic bridge rectifier I bought had different terminal locations. Connected the wires to the new bridge, started the onan, and 3.(something) volts was the output.
After much swearing and a few more beers I decided to remove the onan from the GMC. Using a Harbor Freight lift table made the job really easy, about 45 minutes and it was on the table and in the garage. I ohmed out the rotor and field, removed and cleaned the brushes, polished the slip rings, ohmed the compounding reactor, checked the wires against the wiring diagram, and everything looked fine. Hooked up a battery and a piece of fuel hose to a gas can, started the onan, and got 3.(something) volts.
I noticed that the wires from the field coil are the same color and length and it was possible I put them on the wrong terminals of the bridge, hey I THOUGHT I transferred the wires to the new bridge properly. With nothing to lose I swapped the field wires on the bridge, started the onan, and had 122 volts output. Who woulda thought the field coil on an AC generator was polarity-sensitive? Now I know.
Put the onan back into the GMC and it has run flawlessly since. What should have been about a half-hour repair turned into an all-day event. I came really close to getting rid of the onan. That's the problem -- whenever the onan acts up it only costs a few bucks to fix it. When something expensive breaks on it then it's gone, but until then I guess I will put up with it.
Good luck!
Bob Heller
2017 Winnebago 29VE
Winter Springs FL
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| Re: Next project - onan! [message #73712 is a reply to message #73689] |
Sat, 13 February 2010 11:04 |
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mike miller
Messages: 3576
Registered: February 2004
Location: Hillsboro, Oregon
Karma: 0
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| Ken Burton wrote on Sat, 13 February 2010 01:31 |
Isn't there something about flashing it to get it started generating after it has sat stagnant for a long time? I have never done it.
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Yes.
I have never done it either.
In relatively non-technical terms, this is how I understand it works: (Engineers might laugh, but I am a tech... this is how it works inside my head!)
You need a magnetic field to generate electricity. Big permanent magnets are not suitable for portable generators for many reasons so an electromagnet is used. A small amount of the OUTPUT of the generator is used to power this magnet. The compounding reactor is what taps this power. It sends an AC voltage to the Bridge Rectifier where it gets converted into a DC voltage. This DC voltage is applied to the field windings to create the electromagnetic field.
The thyrector in the compounding reactor works as a voltage regulator varying the strength of the magnetic field by varying the power being sent to the field windings. (It is my understanding thyrectors "never" go bad.)
I am sure you noticed that we are using the output to make something that we need to make the output!
Normally there should be enough residual magnetism to get the generator started putting out a low voltage to "feed back" into the field.
I am not sure of all the reasons why some generators loose this residual magnetism -- but if your genny looses it, you will need to "Feed the Baby." (Field to Battery) I have heard you run a wire from the positive side of the battery to the positive side of the field coil to power the electromagnet enough to get back "some" magnetism. I know it shouldn't take much....
BE SURE the wiring is good and not shorted before trying this...
It would also be good to get instructions from someone WHO HAS ACTUALLY DONE THIS! (Not just from me....)
Mike Miller -- Hillsboro, OR -- on the Black list
(#2)`78 23' Birchaven Rear Bath -- (#3)`77 23' Birchaven Side Bath
More Sidekicks than GMC's and a late model Malibu called 'Boo'
http://m000035.blogspot.com
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| Re: [GMCnet] Next project - onan! [message #73717 is a reply to message #73687] |
Sat, 13 February 2010 12:10 |
emerystora
Messages: 4442
Registered: January 2004
Karma: 13
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Senior Member |
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On Feb 13, 2010, at 2:12 AM, Mike Miller wrote:
>
>
> mini577 wrote on Fri, 12 February 2010 18:49
>> I read in the manual that I should be reading 8 ohms between the
>> leads, but I am not getting that. I AM getting continuity only in
>> one direction on the pins as I would expect though, which makes me
>> think maybe it is all right. I guess I will have to go back to the
>> manual again and check the rest. I was SO hoping this was going to
>> be an easy fix!
>>
>> Drew
>
> Another common problem with Onan's is bad spade connections on the
> wires in/out of the rectifier... I am talking about the plastic
> covered connectors connecting 3 or four wires. they are shown in
> this picture: (not my pic, just the 1st I found showing them.)
>
> <http://www.gmcmhphotos.com/photos/showphoto.php?photo=3472&cat=3346>
> --
> Mike Miller
I was just about to suggest the same thing.
Here is something that I had posted to the GMCnet about nine years ago
on April 6, 2001.
> On the trip to Palm Desert, my Onan was not putting out much voltage
> when a load was applied. When I had the water heater and the coffee
> pot going at the same time (under 3000 watts) the voltage would drop
> to about 100v. I tried adjusting the carb, the governor speed and
> sensitivity and got the voltage to finally hold at 110v with this
> load. However, I didn't go back and check the no load voltage.
> Unfortunately, I later discovered that my no load voltage was in
> excess of 150 volts (thats as high as my plug in voltmeter would
> display) and the result was that I fried my Statpower charger when I
> started up the Onan the next morning.
>
> The manual shows that if a high or low voltage occurs when there is
> no load at 1800 rpm but the loaded condition has the proper voltage
> it is probably a bad "compounding reactor". So, I started working
> on the Onan with this as the premise. I quickly discovered that I
> would have to remove the whole brush end of the Onan to get at this
> part so I decided to see if I could test it while in place.
>
> It has a lead going to the bridge rectifier which is easy to get at
> by just pulling off the plastic cover under the lower rear part of
> the brush housing. While under the Onan I accidentally discovered
> that another lead going to the rectifier was very loose at a
> connection and would not hold together. There are two male/female
> spade connectors going from the field windings to the + and -
> terminals of the rectifier. Each set is in its own approximately 2"
> plastic insulating tube. They are made of brass and I found that
> there was very poor contact as the brass female connector had lost
> its tension. I attempted to squeeze it with some needle nose pliers
> and it immediately cracked. I then soldered in a new steel female
> connector, coated it with dielectric grease and plugged in back to
> the male connector in the tube. I checked the other connector and
> found that it also was making very poor connection and was also
> loose in the tube. I replaced that connector as well.
>
> I next started the Onan and found that I had much higher voltage
> than before. I used a mechanical tach through the front flywheel
> cover hole and set the no load to 1800 rpm which corresponds exactly
> to 126 volts. I went through the various adjustments with the carb,
> the governor speed and the sensitivity and was able to get 126 volts
> at no load but it would still drop to about 110 with 3000 watts.
> That's about where is used to be and I figured that I would have to
> live with that and just turn the water heater off when I wanted to
> use the microwave as we had been doing for the last few years. I
> then noticed the paragraph in the maintenance manual about the
> linkage adjustment (from the carb throttle to the ball on the
> governor arm). I had never adjusted that so I decided to check it.
> Following the instructions, with the Onan off, I popped it off the
> ball joint and held the carb wide open against its stop and checked
> the end against the ball joint. I found the linkage to be about
> 1/4" too long. I rotated the end until it just fit over the ball
> stud. I then restarted the Onan and readjusted the carb and
> governor until I again had 126 volts at no load. I then started to
> turn on electrical equipment and found that the voltage never
> dropped below 120 volts. I started with the water heater, added the
> coffee pot, the air conditioner heat strip and even the microwave
> and it would still hold at 120 volts. I calculate that I had about
> a full load of 6000 watts on the Onan. It has never done this
> before in the 20+ years that I've had the GMC.
>
> I had never thought to adjust the linkage arm before. In fact, the
> factory paint was still on the threads when I turned the end to
> shorten it. It apparently had never been set properly by the factory.
>
> I also noticed that there are two more of the connectors in the same
> type sleeves on the left top of the Onan in the wires going to the
> fuel pump and to the solenoid. I checked these but they were tight.
> Apparently the heat from the engine and generator caused the lower
> brass field wire connectors to loose their temper and thus cause a
> loose connection.
>
> I would suggest that everyone check these two connectors and the
> carb linkage on their Onan. There was nothing wrong with the
> compounding reactor. I believe that my initial problem was
> occurring because of intermittent contact on the field windings.
Emery Stora
77 Kingsley
Santa Fe, NM
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| Re: [GMCnet] Next project - onan! [message #74124 is a reply to message #74111] |
Wed, 17 February 2010 05:06 |
Mr ERFisher
Messages: 7117
Registered: August 2005
Karma: 2
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Senior Member |
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remember,it is no longer necessary to rewire the diode bridge. Do the trick
Bobdk showed us here
http://gmcmotorhome.info/generator.html#bridge
gene
On Tue, Feb 16, 2010 at 9:48 PM, Drew Wood <drew@usa650.com> wrote:
>
>
> Thanks to everyone for all the advice.
>
> I visited Gemrecs today and tested the field windings on several backends
> and found one that looked good, removed it, and brought it home. A few hours
> of reassembly and reinstall and finally the big test! Nothing. ugh. I was
> seeing a slightly higher voltage than before though (about 10 volts), so I
> shut it down and reversed my wires on the rectifier and tried again.
> Success!
>
> Actually I was a little concerned because I was reading about 165 volts
> when I first fired it up. I had not installed the muffler or air filter yet,
> though, so I did those and tried it again. 120 volts! The backpressure
> apparently is pretty important!
>
> Apart from a minor oil drip it is all ready to go in case I need it. When I
> have the time I will pull it out again and get into the gaskets and cosmetic
> problems. :)
>
> Best Regards,
>
> Drew
>
> _______________________________________________
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--
Gene Fisher -- 74-23,77PB/ore/ca
“Give a man a fish; you have fed him for today --- give him a URL and
-------
http://gmcmotorhome.info/
Alternator Protection Cable
http://gmcmotorhome.info/APC.html
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| Re: Next project - onan! [message #74151 is a reply to message #73654] |
Wed, 17 February 2010 11:59 |
mini577
Messages: 16
Registered: March 2008
Location: Berryville, AR
Karma: 0
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Junior Member |
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Yes, I found that the easiest way was to simply pop the spade connectors out of the plastic fitting that they are in and attach them directly. I think I will go back and put a little shrink wrap on them though to make sure they can never touch each other..
Best Regards,
Drew
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