| Onan [message #350470] |
Tue, 03 December 2019 19:01  |
Melbo
Messages: 144
Registered: August 2018
Location: Albuquerque NM
Karma: 0
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I am fairly knowledgeable about electric systems. My onan runs fine. Just put a new board and pertronix ignition in. Had it running and plugged in the electric supply for the panel inside the coach. Went in and turned on the breakers. The ac started and was playing with the controls and everything quit. Now I only get 7 volts at the outlet and about the same at the breaker on top of the onan when I test it to ground. My guess is the bridge rectifier but I thought that I would draw on the knowledge base here to see what the consensus is. Any thoughts or other things that should be checked would be greatly appreciated.
Thanks in advance
Melbo
Albuquerque NM Bus Conversion 1978 MCI 1973 GMC
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| Re: Onan [message #350471 is a reply to message #350470] |
Tue, 03 December 2019 23:00  |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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That definitely the first to look. The board has nothing to do with generating power so leave it and the Pertronix alone.
If the full wave bridge rectifier is not bad, them you need to ohm meter the (non-rotating) field. The value is in the manual. I forgot what it is suppose to be. Get one locally. They are cheap for a 1000 volt one.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Onan [message #350473 is a reply to message #350472] |
Tue, 03 December 2019 23:27 |
mghamms
Messages: 466
Registered: March 2016
Location: Ware, Massachusetts
Karma: 2
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I had the same symptoms as you.
I bought one of the new RB's and bent the pins to match the plug.
First shot did't work.
Rotated 180 deg and all is good.
1977 Kingsley 455 as stock as it gets except lots of Ragusa parts
[Updated on: Tue, 03 December 2019 23:28] Report message to a moderator |
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| Re: [GMCnet] Onan [message #350558 is a reply to message #350474] |
Sat, 07 December 2019 16:10 |
Melbo
Messages: 144
Registered: August 2018
Location: Albuquerque NM
Karma: 0
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Thanks for the help with this. I got a bridge rectifier locally and got it installed. I did it wrong a couple of times but finally figured it out and now it is working fine.
Melbo
Albuquerque NM Bus Conversion 1978 MCI 1973 GMC
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| Re: [GMCnet] Onan [message #350560 is a reply to message #350558] |
Sat, 07 December 2019 20:58 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Super!!
I have been told that shutting down the generator under load can cause this failure. I do not know this from my own experience, but I always turn off everything that is high load like the AC or water heater BEFORE shutting down the generator.
Someone tell me I am wrong and why. I'm listening.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Onan [message #350562 is a reply to message #350560] |
Sat, 07 December 2019 23:10 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Bob, I believe, as did Dwayne Simmons and several others, that you are 100%
correct. Turning off ALL loads on the generator before shutting it down, is
the correct way to do it.
Jim Hupy
Salem, Oregon
On Sat, Dec 7, 2019, 6:59 PM Ken Burton via Gmclist
wrote:
> Super!!
>
> I have been told that shutting down the generator under load can cause
> this failure. I do not know this from my own experience, but I always turn
> off
> everything that is high load like the AC or water heater BEFORE shutting
> down the generator.
>
> Someone tell me I am wrong and why. I'm listening.
> --
> Ken Burton - N9KB
> 76 Palm Beach
> Hebron, Indiana
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
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| Re: Onan [message #350566 is a reply to message #350470] |
Sun, 08 December 2019 09:23 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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The under load shutoff failure appears with the OEM rectifiers, which had questionable revers voltage ability, and questionable current capacity. As the engine slows at shutoff, if there's a load it will draw enough current to increase the voltage on the compounding reactor that it may spike beyond the reverse voltage rating of the rectifier which then shorts and almost instantly burns open... At least that's my take on it - the symptom is the rectifier goes Dixie all at once. 1KV 30 Amp or so rectifier bridges are cheap on eBay and the overkill in spec doesn't hurt a thing.
Shutting down under load may do dirt to some of the things turned on but shouldn't bother a higher rated bridge.
There are 16 discrete ways to connect the thing, only 1 will work. Note which wire goes where >before< you remove it because the blades on the new one are not oriented the same. I make 4 male to female jumpers a half inch or so long and plug the females on the new bridge, males in the existing [plug.
--johnny
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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| Re: [GMCnet] Onan [message #350568 is a reply to message #350560] |
Sun, 08 December 2019 11:41 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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Ken Burton wrote on Sat, 07 December 2019 21:58Super!!
I have been told that shutting down the generator under load can cause this failure. I do not know this from my own experience, but I always turn off everything that is high load like the AC or water heater BEFORE shutting down the generator.
Someone tell me I am wrong and why. I'm listening.
Ken,
After mine blew out at an inconvenient time because the control board failed a solder joint, I though to figure out why and how to prevent it.
(Short aside note: A BF (4Kw) unit in a 23 cannot be pulled out far enough to access the bridge.... BTDT)
Being a hair-ball engineer, I got out a package of software that was copied from the inventory of a former employer and modeled the system as best I could with no real measured values except what I could infer from the test setup in the Onan manaul.
I modeled the rotating armature as half a transformer because I couldn't figure out how to spin the computer. I made the shutdown by just opening the supply to the primary. For a simple system, it sure does go berserk.
After several runs as various settings, I got the system to spike to about 300 volts to the field winding. For a system designed with a field voltage of about 50 Volts and in the day, higher PIVs cost more money, I bet that the rating of the bridge is not all that high. This was all with just a resistive load and a little inductive to make a PF of 0.8.
If I knew where to get a hold of a curve tracer and an original part, it would be fun to know.
I am not completely sure why I bothered, but I know the higher PIV bridge that I put in has never had any problem.
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 [message #350569 is a reply to message #350568] |
Sun, 08 December 2019 13:18 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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Hi Matt,
I have never needed to replace mine but I have carried a couple of spares for years and installed a few on other peoples Onans. I also never turn mine off under load and Laurie knows that she is in deep dodo if she does it wrong.
Now that I said that, it will probably blow the next time I use it.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: Onan [message #350570 is a reply to message #350470] |
Sun, 08 December 2019 15:01 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Mine failed when the main tank level dropped too far with both roof air on. Yes as RPM drops the output voltage drops so the bridge and reactor try to compensate by sending more to the field. This would happen during start under load as well. I always start Onan no load, let it warm at least 30 seconds before applying load On shut down I remove load and run at least 60 seconds to let Onan dissipate working heat before shut down. Longer if very hot out. Some have been ok Not doing this but I don't think it's good practice. Same as with a horse, you warm up, work, cool down, put away.
John Lebetski
Woodstock, IL
77 Eleganza II
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