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| Onan help [message #298673] |
Tue, 05 April 2016 11:32  |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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I need a bit of help with Jason's Onan 6KW. I think I may be chasing my tail. Mechanically no problem, the set cranks and runs like a top. But. No A/C. P.O. states he replaced the rectifier. Inspection showed one broken tab on the new rectifier, and one loose crimp on it... P.O. had extended the wires from the original connector 'cos the new rectifier tabs are oriented differently. Replaced the poor crimps, fired it up sans rectifier, and there's ~~35V AC on the wires going to the rectifier. Connect + and -, the output is like 1.5VDC. AC winding drops to near zero. Meassuring the + and - shows a ground somewhere along the line, - is grounded, + nearly so. Looking at the schematic, it appears that the DC out of the rectifier goes only through a thyrector and the winding.... I see no ground on the schematic. Is this correct? If so, we've a short someplace in that circuit, if not I've misread it. Reversing the DC makes no difference.
Ideas, anybody? If the winding isn't supposed to be grounded, we'll have to pull the set and go looking. Jason is on the forum, I told him to watch for suggestions. I'm off to a show and then Dothan. If it has to come out, we're go after it Friday week or whenever he's available.
Thanks!
--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: Onan help [message #298674 is a reply to message #298673] |
Tue, 05 April 2016 11:35  |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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I said 'winding' I meant the reactor in series with the DC side of the rectifier. AC side also has a ground on it, but it appears that's correct.
--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: Onan help [message #298678 is a reply to message #298673] |
Tue, 05 April 2016 11:58 |
A Hamilto
Messages: 4508
Registered: April 2011
Karma: 39
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Senior Member |
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Johnny Bridges wrote on Tue, 05 April 2016 11:32I need a bit of help with Jason's Onan 6KW. I think I may be chasing my tail. Mechanically no problem, the set cranks and runs like a top. But. No A/C. P.O. states he replaced the rectifier. Inspection showed one broken tab on the new rectifier, and one loose crimp on it... P.O. had extended the wires from the original connector 'cos the new rectifier tabs are oriented differently. Replaced the poor crimps, fired it up sans rectifier, and there's ~~35V AC on the wires going to the rectifier. Connect + and -, the output is like 1.5VDC. AC winding drops to near zero. Meassuring the + and - shows a ground somewhere along the line, - is grounded, + nearly so. Looking at the schematic, it appears that the DC out of the rectifier goes only through a thyrector and the winding.... I see no ground on the schematic. Is this correct? If so, we've a short someplace in that circuit, if not I've misread it. Reversing the DC makes no difference.
Ideas, anybody? If the winding isn't supposed to be grounded, we'll have to pull the set and go looking. Jason is on the forum, I told him to watch for suggestions. I'm off to a show and then Dothan. If it has to come out, we're go after it Friday week or whenever he's available.
Thanks!
--johnny If it is connected like this picture shows, I hope all you have is a bad BR. I think if you have 35VAC on the wires going to the BR, that is correct, but have to defer to Jim Miller on that. The ACs don't matter, but minus has to go to F2 and plus has to go to F1. If that is how you have it wired, do you have another, known good, BR that you can try?
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| Re: Onan help [message #298686 is a reply to message #298673] |
Tue, 05 April 2016 15:19 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Senior Member |
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Me and the manual disagree - I'll use an ohmmeter first. Or borrow a megger.
-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
[Updated on: Tue, 05 April 2016 15:19] Report message to a moderator |
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| Re: Onan help [message #298687 is a reply to message #298673] |
Tue, 05 April 2016 15:25 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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We got a sack full of rectifiers, I think the one we're using is good. I think the problem is, we haven't gotten the wires quite right yet. I'm going to see if I can get a service mirror back there to trace without taking the set out of the coach. Otherwise I'll have to haul my stinger lift over to Jason's place to get it out. It's on hold till after Dothan.
--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: Onan help [message #298717 is a reply to message #298673] |
Tue, 05 April 2016 20:27 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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I was commenting on the FB side. I assume it quit making AC so you assume it's the bridge. Test the old bridge on bench. If it's good, problem is elsewhere. That sack of bridges won't help.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: [GMCnet] Onan help [message #298723 is a reply to message #298678] |
Tue, 05 April 2016 21:13 |
Jim Miller
Messages: 501
Registered: March 2008
Karma: 10
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On Apr 5, 2016, at 12:58 PM, A. wrote:
> If it is connected like this picture shows, I hope all you have is a bad BR. I think if you have 35VAC on the wires going to the BR, that is correct,
> but have to defer to Jim Miller on that. The ACs don't matter, but minus has to go to F2 and plus has to go to F1. If that is how you have it wired,
> do you have another, known good, BR that you can try?
There is no intentional path to the chassis on either the F1 or F2 leads. Neither a megger or a conventional VOM should indicate such a path.
The resistance of the field as measured between F1 and F2 should be around 38 ohms and the measurement should be done with the VOM on Rx1 scale. Any reading in the hundreds of ohms or greater is indicative of a bad field assembly. All resistance measurements of the field must be done with F1 and F2 disconnected from the bridge rectifier.
An easy experiment is to use a battery (NOT an electronic power supply) to apply 12V to F1(+) and F2(-) with the unit running. This does two things - 1) refreshes the magnetic field that lives permanently in the field assembly and 2) should produce a couple tens of volts of AC output from the machine IF and ONLY IF the field coils are in good shape. If you get only a volt or two AC output during this test then you have a bad field.
If you use an electronic power supply to do this test then you do so at your own risk - the magnetic field present in an energized field assembly is tremendous and when you pull the leads off the power supply the flyback pulse of the collapsing field can be many hundreds of volts and can cook your power supply. It’ll also shock the crap out of you if you happen to be holding the disconnected leads with your hands (ask me how I know).
Note: On a functional unit the field excitation voltage is between 120VDC and 150VDC depending on output AC load. Applying 12VDC with a battery as I’ve described will not hurt the field in any way.
—Jim Miller
1977 Eleganza
1977 Royale
Hamilton, OH
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Jim Miller
1977 Eleganza II
1977 Royale
Hamilton, OH
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| Re: Onan help [message #298733 is a reply to message #298673] |
Wed, 06 April 2016 07:53 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Senior Member |
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Jim -
That's the test I was looking for. I have insulated clips, I hate the inductive kickback out of anything resembling a coil. Thanks!
For those who wondered, Jason just got the coach, and the PO noted he'd replaced the rectifier but hadn't seen AC out of the set before or since. Given the low time appearance of the engine and its smooth running, >if< the field coil ends up toast, this one is a good candidate for a replacement field. Post Dothan we'll figure it out.
--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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