| No VAC Output From Onan [message #143083] |
Mon, 12 September 2011 12:00  |
Jon payne
Messages: 495
Registered: May 2008
Karma: 1
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Senior Member |
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Guys,
All of a sudden the Onan stopped outputting AC voltage. Just before going to Goshen I was getting the GMC ready. I cranked up the Onan and when to turn on the roof AC and nothing happened. I checked the CBs and of course made sure it was plugged in. I started to troubleshoot per the MM and it is asking to check the brushes for contact on the collector ring. Can anyone point me to where on the Onan the brushes are located? Also any additional troubleshooting suggestions would be greatly appreciated.
Now, regarding the low charge rate to the house battery, I have noticed that the voltage was very low going to the battery. After running for 5 minutes or so I checked the voltage at the battery with a VOM and found ~12.7 VDC (The batt voltage with Onan off was around 12.5 VDC). Troubleshooting per the MM I checked the resistance between the AC terminal on the VR and the BAT term of the start solenoid and was in the indicated range. Then checked for proper voltage at the same points with the Onan running and found to be the correct voltage (30VAC).
So it seems that the VR is a little weak and I'm wondering if I should replace or not. Also, where can I get one if it should be replaced?
Jon
Jon Payne
76 Palm Beach
Westfield,IN
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| Re: [GMCnet] No VAC Output From Onan [message #143085 is a reply to message #143083] |
Mon, 12 September 2011 12:09  |
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ljdavick
Messages: 3548
Registered: March 2007
Location: Fremont, CA
Karma: -3
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Senior Member |
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As for your lack of a/c from the Onan I had a similar circumstance that turned out to be the bridge rectifier.
My first reaction was "what's that?". In my case the answer was - it's the thing that's broken.
They're cheap. They're easy to replace. Why not start there. <http://appliedgmc.com/prod.itml/icOid/974>
Larry Davick
On Sep 12, 2011, at 10:00 AM, Jon Payne <embrep@sbcglobal.net> wrote:
>
>
> Guys,
>
> All of a sudden the Onan stopped outputting AC voltage. Just before going to Goshen I was getting the GMC ready. I cranked up the Onan and when to turn on the roof AC and nothing happened. I checked the CBs and of course made sure it was plugged in. I started to troubleshoot per the MM and it is asking to check the brushes for contact on the collector ring. Can anyone point me to where on the Onan the brushes are located? Also any additional troubleshooting suggestions would be greatly appreciated.
>
> Now, regarding the low charge rate to the house battery, I have noticed that the voltage was very low going to the battery. After running for 5 minutes or so I checked the voltage at the battery with a VOM and found ~12.7 VDC (The batt voltage with Onan off was around 12.5 VDC). Troubleshooting per the MM I checked the resistance between the AC terminal on the VR and the BAT term of the start solenoid and was in the indicated range. Then checked for proper voltage at the same points with the Onan running and found to be the correct voltage (30VAC).
>
> So it seems that the VR is a little weak and I'm wondering if I should replace or not. Also, where can I get one if it should be replaced?
>
> Jon
> --
> Jon Payne
> 76 Palm Beach
> Westfield,IN
> _______________________________________________
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Larry Davick
A Mystery Machine
1976(ish) Palm Beach
Fremont, Ca
Howell EFI + EBL + Electronic Dizzy
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| Re: No VAC Output From Onan [message #143086 is a reply to message #143083] |
Mon, 12 September 2011 12:15 |
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mike miller
Messages: 3576
Registered: February 2004
Location: Hillsboro, Oregon
Karma: 0
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| Jon Payne wrote on Mon, 12 September 2011 10:00 |
Guys,
All of a sudden the Onan stopped outputting AC voltage. ...
....
Now, regarding the low charge rate to the house battery, ...
|
the 120vac issue sounds like a Bridge Rectifier
<http://gmcmotorhome.info/generator.html#noac>
With a 1976 coach the Onan charging system isn't used. As built at the factory, the Onan starts from the house battery and it is recharged by the converter... no ac, no converter, no recharging of the battery.
Lots of good info on the Onan found here:<http://gmcmotorhome.info/list.html#GEN>
There is a section on disconnecting the Voltage Regulator (Charger) from your Onan.
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] No VAC Output From Onan [message #143090 is a reply to message #143085] |
Mon, 12 September 2011 12:45 |
George DV
Messages: 132
Registered: August 2004
Karma: 0
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Senior Member |
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And Ken Henderson here in Goshen has a box full sale for cheap.
George DV
1976 Glenbrook
On 9/12/2011 10:09 AM, Larry Davick wrote:
> As for your lack of a/c from the Onan I had a similar circumstance that turned out to be the bridge rectifier.
>
> My first reaction was "what's that?". In my case the answer was - it's the thing that's broken.
>
> They're cheap. They're easy to replace. Why not start there.<http://appliedgmc.com/prod.itml/icOid/974>
>
> Larry Davick
>
> On Sep 12, 2011, at 10:00 AM, Jon Payne<embrep@sbcglobal.net> wrote:
>
>>
>> Guys,
>>
>> All of a sudden the Onan stopped outputting AC voltage. Just before going to Goshen I was getting the GMC ready. I cranked up the Onan and when to turn on the roof AC and nothing happened. I checked the CBs and of course made sure it was plugged in. I started to troubleshoot per the MM and it is asking to check the brushes for contact on the collector ring. Can anyone point me to where on the Onan the brushes are located? Also any additional troubleshooting suggestions would be greatly appreciated.
>>
>> Now, regarding the low charge rate to the house battery, I have noticed that the voltage was very low going to the battery. After running for 5 minutes or so I checked the voltage at the battery with a VOM and found ~12.7 VDC (The batt voltage with Onan off was around 12.5 VDC). Troubleshooting per the MM I checked the resistance between the AC terminal on the VR and the BAT term of the start solenoid and was in the indicated range. Then checked for proper voltage at the same points with the Onan running and found to be the correct voltage (30VAC).
>>
>> So it seems that the VR is a little weak and I'm wondering if I should replace or not. Also, where can I get one if it should be replaced?
>>
>> Jon
>> --
>> Jon Payne
>> 76 Palm Beach
>> Westfield,IN
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
> _______________________________________________
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| Re: [GMCnet] No VAC Output From Onan [message #143152 is a reply to message #143083] |
Mon, 12 September 2011 20:27 |
emerystora
Messages: 4442
Registered: January 2004
Karma: 13
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On Sep 12, 2011, at 1:00 PM, Jon Payne wrote:
>
>
> Guys,
>
> All of a sudden the Onan stopped outputting AC voltage. Just before going to Goshen I was getting the GMC ready. I cranked up the Onan and when to turn on the roof AC and nothing happened. I checked the CBs and of course made sure it was plugged in. I started to troubleshoot per the MM and it is asking to check the brushes for contact on the collector ring. Can anyone point me to where on the Onan the brushes are located? Also any additional troubleshooting suggestions would be greatly appreciated.
>
It is likely one of two possible things. There is a 120 volt circuit breaker on top of the Onan. Try resetting it. If that does not give you AC voltage then take the cover from the box and, with the Onan running use a voltmeter to check the voltage on each side of the breaker (to ground). It the breaker is reset and you have 120 volts on only one side of the breaker then the breaker is bad and needs replacing. If you have no voltage on either side then the problem is likely the bridge rectifier.
If you need any help or instructions on how to replace it let me know.
> Now, regarding the low charge rate to the house battery, I have noticed that the voltage was very low going to the battery. After running for 5 minutes or so I checked the voltage at the battery with a VOM and found ~12.7 VDC (The batt voltage with Onan off was around 12.5 VDC). Troubleshooting per the MM I checked the resistance between the AC terminal on the VR and the BAT term of the start solenoid and was in the indicated range. Then checked for proper voltage at the same points with the Onan running and found to be the correct voltage (30VAC).
With a 76 GMC I doubt that your Onan is hooked up to charge the battery with that little battery charger. That was only used when they had a battery that was only to used to start the Onan. Now they use the house battery to start the Onan and it is charge by your converter (battery charger) that is plugged into their 120 volt receptacle inside the GMC.
GM still had the voltage regulator on the Onans but most of us have removed it. If you do this leave the two wires that go to one terminal connected and tape them and then remove the other wire (the B+ wire) and leave it unconnected but tape off the end of it.
Emery Stora
77 Kingsley
Santa Fe, NM
>
> So it seems that the VR is a little weak and I'm wondering if I should replace or not. Also, where can I get one if it should be replaced?
>
> Jon
> --
> Jon Payne
> 76 Palm Beach
> Westfield,IN
> _______________________________________________
> GMCyeanet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
Emery Stora
77 Kingsley
Santa Fe, NM
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| Re: [GMCnet] No VAC Output From Onan [message #143320 is a reply to message #143152] |
Wed, 14 September 2011 11:11 |
Jon payne
Messages: 495
Registered: May 2008
Karma: 1
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Senior Member |
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Thanks Emery! And yes I do need some help on replacing the bridge rectifier as I'm not sure where it is even located. I see that JimK sells one on his website but there is a note saying it is not a direct fit and some modification is needed. Any help you could provide would be greatly appreciated!
Jon
Jon Payne
76 Palm Beach
Westfield,IN
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| Re: [GMCnet] No VAC Output From Onan [message #143476 is a reply to message #143320] |
Thu, 15 September 2011 08:21 |
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mike miller
Messages: 3576
Registered: February 2004
Location: Hillsboro, Oregon
Karma: 0
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| Jon Payne wrote on Wed, 14 September 2011 09:11 |
Thanks Emery! And yes I do need some help on replacing the bridge rectifier as I'm not sure where it is even located. ...
|
I am not Emery, but I understand he is busy...
So... start here:
<http://www.gmcmhphotos.com/photos/showphoto.php?photo=3473&cat=3346>
New Bridge Rectifiers are avalable (cheaply) that have a MUCH higher rating than the stock Onan part. (Last time I needed one it was cheaper to buy four or five off ebay than one in the store.) But there is a catch... the pins are indexed wrong. (Even JimK's.)
To plug directly into the oem socket, three of the pins on the new bridge rectifier need to be rotated 90 degrees. (I have never had much luck with this... but I had a few extras!)
Another method is to remove the connectors from the plug, drill out places where these connectors where and run the wires through the resulting holes turning the connectors as needed to plug into your new bridge rectifier. The drilled out plug serves as a nut to hold the rectifier to the case and protects the connetors from being bumped. (I have done this method twice.)
I have also seen the plug removed, the bridge bolted to the case and the wires connected individually.
There was a series of pictures on the photo site showing both the drilling out of the connector and the twisting of the pins... I haven't been able to find 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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