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| Onan - No AC output - Help! [message #170873] |
Sat, 26 May 2012 09:35  |
Jon payne
Messages: 495
Registered: May 2008
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Guys,
End of last year after I got the Onan finally running nicely and then the Gen decided to give me more troubles but stopping AC output. Understanding that the Bridge Rectifier is the most likely cause I got one and just replaced it this morning. No luck, still no AC output. I took a look at Gene's website and read the post about no AC output and there it is mentioned to check the Flywheel Alternator AC output between terminals 8 & 11 on the Onan board. Voltage should be between 28 and 30 VAC. I checked and I read 22 VAC. Per the post it says "When the Voltage Regulator fails, it can load down this signal to less than 20 volts AC & the control Board will not function".
Could this be the problem? I didn't think the Onan board controlled the GEN output but it is mentioned as a cause for no AC voltage output.
Any suggestions? It's hot one here in INDY and we are planning a day trip tomorrow and would be nice to have the roof air working!
Jon
Jon Payne
76 Palm Beach
Westfield,IN
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| Re: Onan - No AC output - Help! [message #170874 is a reply to message #170873] |
Sat, 26 May 2012 09:39  |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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NO. AS far as I know the board is engine control only.
Whole different zip code is the generator. Test the primary side of the 30A breaker before you insist the generator is bad. Breaker could be bad. Brush could be stuck. dirty flag terminal somewhere not causing output. Worst case field is open, but unlikely as you didn't burn it out sitting.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: [GMCnet] Onan - No AC output - Help! [message #170876 is a reply to message #170873] |
Sat, 26 May 2012 10:15 |
emerystora
Messages: 4442
Registered: January 2004
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Here is something that I first posted back in 2001. It is possible that when you were working on the rectifier you might have loosened the wires that go into the plastic insulating tubes.
Emery Stora
> 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
On May 26, 2012, at 8:35 AM, Jon Payne wrote:
>
>
> Guys,
>
> End of last year after I got the Onan finally running nicely and then the Gen decided to give me more troubles but stopping AC output. Understanding that the Bridge Rectifier is the most likely cause I got one and just replaced it this morning. No luck, still no AC output. I took a look at Gene's website and read the post about no AC output and there it is mentioned to check the Flywheel Alternator AC output between terminals 8 & 11 on the Onan board. Voltage should be between 28 and 30 VAC. I checked and I read 22 VAC. Per the post it says "When the Voltage Regulator fails, it can load down this signal to less than 20 volts AC & the control Board will not function".
>
> Could this be the problem? I didn't think the Onan board controlled the GEN output but it is mentioned as a cause for no AC voltage output.
>
> Any suggestions? It's hot one here in INDY and we are planning a day trip tomorrow and would be nice to have the roof air working!
>
> Jon
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| Re: [GMCnet] Onan - No AC output - Help! [message #170878 is a reply to message #170874] |
Sat, 26 May 2012 10:25 |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
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Which model coach do you have?
The Coachman had some hidden breakers,
On Sat, May 26, 2012 at 7:39 AM, John R. Lebetski <gransport@aol.com> wrote:
>
>
> NO. AS far as I know the board is engine control only.
> Whole different zip code is the generator. Test the primary side of the 30A breaker before you insist the generator is bad. Breaker could be bad. Brush could be stuck. dirty flag terminal somewhere not causing output. Worst case field is open, but unlikely as you didn't burn it out sitting.
> --
> John Lebetski
> Chicago, IL
> 77 Eleganza II
> Source America First
> _______________________________________________
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Jim Kanomata
Applied/GMC, Fremont,CA
jimk@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502
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| Re: Onan - No AC output - Help! [message #170881 is a reply to message #170873] |
Sat, 26 May 2012 10:48 |
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mike miller
Messages: 3576
Registered: February 2004
Location: Hillsboro, Oregon
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| Jon Payne wrote on Sat, 26 May 2012 07:35 |
... I took a look at Gene's website and read the post about no AC output and there it is mentioned to check the Flywheel Alternator AC output between terminals 8 & 11 on the Onan board. Voltage should be between 28 and 30 VAC. I checked and I read 22 VAC. Per the post it says "When the Voltage Regulator fails, it can load down this signal to less than 20 volts AC & the control Board will not function".
Could this be the problem? I didn't think the Onan board controlled the GEN output but ...
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The flywheel alternator AC power doesn't have any electrical connection to the generator (AC) power output.
While the flywheel alternator DOES create AC voltage it is used for two proposes. 1. it is fed through the voltage regulator to rectified into DC to charge the starting battery. Most 1975 and newer GMC's do not have a starting battery so some have disconnected the regulator. But the second use is more important... it is an "engine running" signal to the control board. Loss of this signal is to remove power to the fuel pump and ignition system. It is a safety thing.
As far as no generator AC power, what are you measuring it with? I thought I had a no-AC power problem. ie: No lights on my little LED tester. I didn't even think to measure it with a meter. I messed with it from time to time on our last trip.
Turns out the voltage was a little low and just needed adjustment to above what the LEDs wanted to see. (The rest of my stuff wasn't happy with the low voltage either...)
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] Onan - No AC output - Help! [message #170883 is a reply to message #170882] |
Sat, 26 May 2012 11:14 |
Jon payne
Messages: 495
Registered: May 2008
Karma: 1
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Okay I checked both sides of the breaker using different grounding points, gen frame/slide and only would get 5.3 VAC on either side of the breaker.
Also checked the terminals as Emery suggested and did not find them loose. So....does this mean my generator is toast?
Jon Payne
76 Palm Beach
Westfield,IN
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| Re: Onan - No AC output - Help! [message #170886 is a reply to message #170873] |
Sat, 26 May 2012 12:07 |
Jon payne
Messages: 495
Registered: May 2008
Karma: 1
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Update - Looks like the field windings are bad. I removed the field wires at the splices and measured resistance between F1 & F2 and found 2000+ Ohms! Should be 38 Ohms. Started the Gen and then measured the voltage between F1 & F2 for the heck of and found zero volts. Should be 50 VDC.
Looks like no Gen for this weekend or our big trip out east in June. Damn!
So, is it possible to find a replacement field windings? I doubt new but maybe used? Maybe I need to check with Jim Bounds.
Jon
Jon Payne
76 Palm Beach
Westfield,IN
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| Re: Onan - No AC output - Help! [message #170911 is a reply to message #170886] |
Sat, 26 May 2012 19:42 |
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mike miller
Messages: 3576
Registered: February 2004
Location: Hillsboro, Oregon
Karma: 0
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| Jon Payne wrote on Sat, 26 May 2012 10:07 |
Update - Looks like the field windings are bad. I removed the field wires at the splices and measured resistance between F1 & F2 and found 2000+ Ohms! Should be 38 Ohms. Started the Gen and then measured the voltage between F1 & F2 for the heck of and found zero volts. Should be 50 VDC.
Looks like no Gen for this weekend or our big trip out east in June. Damn!
So, is it possible to find a replacement field windings? I doubt new but maybe used? Maybe I need to check with Jim Bounds.
|
Seems odd that the winding would just go bad. It would normally take some kind of physical damage. Without actual damage, I would suspect the connectors more than the windings.
If the field wiring is really bad, the following will not help. But I will include it for others... including lurkers.
| Quote: |
The Onan uses a electro-magnet rather than a permanent magnet. It varies the power of this magnet to regulate the output of the generator. The power to run this magnet, that is used to create power, comes from the generator itself.
I am sure a few of you are thinking "what?" or "how?"
The Onan relies on "residual magnetism" to start a small output that is fed back to power the field. It powers up pretty quick. (The bridge rectifier is what takes the AC feedback voltage and makes it DC voltage to apply to the field.)
Rarely, under odd circumstances, the magnet loses the residual magnetism. To get it back you can "Feed The Baby." IE: Flash the Field To Battery. Jump the positive field connection to the positive side of the battery to power the magnet with 12v. It only takes a bit... that is why it is referred to as FLASHING.
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Jon,
Yes, if you need "new" field windings, I would call JimB or any (or all) our GMC maintenance facilities. The might have an old Onan that the generator section could be pulled from. JimB had an Onan graveyard... at least when I stopped by there about 7 years ago.
It looks like you will be pulling the unit at least to open the bell-end. I hope you can find the problem... It would be sad to pull and scrap something that runs.
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: Onan - No AC output - Help! [message #170918 is a reply to message #170873] |
Sat, 26 May 2012 21:19 |
bobby5832708
Messages: 237
Registered: November 2006
Location: Winter Springs FL
Karma: 3
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Senior Member |
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Jon,
Here's a 'cut & paste' from a reply I made to a similar post back in 2009. As of last weekend (the last time I used it) it still runs great.
===================================================
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.
I 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.
================================================
Bob Heller
2017 Winnebago 29VE
Winter Springs FL
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| Re: Onan - No AC output - Help! [message #170929 is a reply to message #170873] |
Sat, 26 May 2012 22:49 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Senior Member |
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It's possible the bridge was bad and the new one not installed exactly correctly as they are not clocked the same. Also what about where strange event the unit looses residual magnetism and needs to be battery zapped for an instant to re electromagnet the metal magnetizm "memory" Lasty are you sure your mere is good on Ohms and giving you accurate readings. Even good meters can give bad data due to oxidized connections on what is being tested etc. Also waht about Ohming out the compound reactor coil? Easier to replace than the field.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: [GMCnet] Onan - No AC output - Help! [message #170948 is a reply to message #170927] |
Sun, 27 May 2012 08:56 |
Jim Miller
Messages: 501
Registered: March 2008
Karma: 10
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On May 26, 2012, at 11:39 PM, Matt Colie wrote:
> This is one of two that I know of. The first I ran into is a local non-member owner that even went so far as to buy a replacement bridge from Cinnabar. Then I got in and found the field winding open.
My Eleganza had a 6kW Onan that produced no AC at the time I bought the coach. It had an open field. Took it apart and found that some pebbles had gotten in and bounced around and nicked the varnish on the windings in a couple places. Once moisture came in contact with the aluminum wire at the nicked location, the wire turned to powder. One location was right where the winding turn went into the frame - too close to even attempt a repair.
The solution in my case was to buy a field off a donor unit and pay $150 to have it shipped halfway across the US. I'm now very careful to make sure the plastic screen covers on the generator section are always in place.
By the way, a regional GMC vendor let me go through his pile of onans (which had been replaced by generacs and hondas in customer coaches) and out of three 6kW units all three had open fields. I checked a couple 4kWs in the same pile just for fun and they were all intact.
And yes, I said my field was wound with ALUMINUM wire. I could not believe it when I saw it. I guess the corner-cutting bean-counters were just as active in the 70s as they are today.
--Jim Miller
Hamilton, OH
1977 Eleganza II
1977 Royale
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Jim Miller
1977 Eleganza II
1977 Royale
Hamilton, OH
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| Re: [GMCnet] Onan - No AC output - Help! [message #170950 is a reply to message #170948] |
Sun, 27 May 2012 09:11 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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If someone near me has a 6kW field that's failed, it would be interesting
to get a rewinding estimate from my friend who runs a small one-man
electric motor shop. No question he can do it, but I have no idea of the
cost.
Ken H.
Americus, GA
'76 X-Birchaven w/Cad500/Howell EFI+ & EBL
www.gmcwipersetc.com
On Sun, May 27, 2012 at 9:56 AM, Jim Miller wrote:
> ...
> By the way, a regional GMC vendor let me go through his pile of onans
> (which had been replaced by generacs and hondas in customer coaches) and
> out of three 6kW units all three had open fields. I checked a couple 4kWs
> in the same pile just for fun and they were all intact.
>
>
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Ken Henderson
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Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] Onan - No AC output - Help! [message #170951 is a reply to message #170948] |
Sun, 27 May 2012 09:21 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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| Jim Miller wrote on Sun, 27 May 2012 09:56 |
On May 26, 2012, at 11:39 PM, Matt Colie wrote:
> This is one of two that I know of. The first I ran into is a local non-member owner that even went so far as to buy a replacement bridge from Cinnabar. Then I got in and found the field winding open.
My Eleganza had a 6kW Onan that produced no AC at the time I bought the coach. It had an open field. Took it apart and found that some pebbles had gotten in and bounced around and nicked the varnish on the windings in a couple places. Once moisture came in contact with the aluminum wire at the nicked location, the wire turned to powder. One location was right where the winding turn went into the frame - too close to even attempt a repair.
The solution in my case was to buy a field off a donor unit and pay $150 to have it shipped halfway across the US. I'm now very careful to make sure the plastic screen covers on the generator section are always in place.
By the way, a regional GMC vendor let me go through his pile of onans (which had been replaced by generacs and hondas in customer coaches) and out of three 6kW units all three had open fields. I checked a couple 4kWs in the same pile just for fun and they were all intact.
And yes, I said my field was wound with ALUMINUM wire. I could not believe it when I saw it. I guess the corner-cutting bean-counters were just as active in the 70s as they are today.
--Jim Miller
Hamilton, OH
1977 Eleganza II
1977 Royale
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Jim,
An interesting account. I wonder if a motor rewinder could rebuild the field for near that part plus shipping cost?
This local source, might he have a flywheel that KenB could get? His has been welded and he doesn't like that.
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: [GMCnet] Onan - No AC output - Help! [message #171026 is a reply to message #170951] |
Sun, 27 May 2012 21:27 |
Jim Miller
Messages: 501
Registered: March 2008
Karma: 10
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Senior Member |
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> An interesting account. I wonder if a motor rewinder could rebuild the field for near that part plus shipping cost?
Possible.
I had considered rewinding it myself. The catch is that the rewinding has to be done in situ - the pole pieces do not unbolt and they are structured such that the coil cannot be wound externally and then laid into place.
I have to think that any savings achieved by the bean counters using aluminum wire for the windings would have been negated by the extra manufacturing expense to wind the coils in-situ.
> This local source, might he have a flywheel that KenB could get? His has been welded and he doesn't like that.
I'm sure Ken's checked there already. He's supposed to be at my house this weekend; I'll ask him.
--Jim
1977 Eleganza II
1977 Royale
Hamilton, OH
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Jim Miller
1977 Eleganza II
1977 Royale
Hamilton, OH
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| Re: [GMCnet] Onan - No AC output - Help! [message #171032 is a reply to message #171026] |
Sun, 27 May 2012 22:14 |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
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We have doner units , we can find out the freight to you and charge
$150 for the part as it takes time to pull it apart and put it back.
On Sun, May 27, 2012 at 7:27 PM, Jim Miller <gmcnet@jcmco.com> wrote:
>> An interesting account. I wonder if a motor rewinder could rebuild the field for near that part plus shipping cost?
>
> Possible.
>
> I had considered rewinding it myself. The catch is that the rewinding has to be done in situ - the pole pieces do not unbolt and they are structured such that the coil cannot be wound externally and then laid into place.
>
> I have to think that any savings achieved by the bean counters using aluminum wire for the windings would have been negated by the extra manufacturing expense to wind the coils in-situ.
>
>> This local source, might he have a flywheel that KenB could get? His has been welded and he doesn't like that.
>
> I'm sure Ken's checked there already. He's supposed to be at my house this weekend; I'll ask him.
>
> --Jim
> 1977 Eleganza II
> 1977 Royale
> Hamilton, OH
>
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Jim Kanomata
Applied/GMC, Fremont,CA
jimk@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502
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1-800-752-7502
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| Re: [GMCnet] Onan - No AC output - Help! [message #171044 is a reply to message #171026] |
Mon, 28 May 2012 00:35 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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Ken B. is NOT going to be able to make it next week end.
I have my Blazer front differential torn apart and the Blazer is occupying my friend's 2 post hoist. I need to order a new gear in the engage clutch assembly Tuesday morning. By the time it gets here it will be the week end. I promised him I would free up his hoist by end of day Saturday. I'm running out of time on this as I'm leaving for AK on June 14th.
Sorry Jim.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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