| Onan Rectifier Replacement - Broken Screw [message #277763] |
Wed, 13 May 2015 09:02  |
westlanddave78
Messages: 27
Registered: March 2006
Location: Westland, MI
Karma: 0
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Hi all,
My 6k Onan appears to need a bridge rectifier R&R as the engine runs great but there's no AC output. (I did check the breaker, etc.) Unfortunately, while I was trying to undo the old rectifier, I twisted the head off the screw that holds it in place. As anyone who's done this job knows, the quarters are pretty close...too tight to get an EZ-OUT to work. Does anyone have a good way to install the new rectifier without pulling the genset from the motorhome and disassembling the housing? Thanks.
Dave P.
Westland, MI
75 Palm Beach
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| Re: Onan Rectifier Replacement - Broken Screw [message #277769 is a reply to message #277763] |
Wed, 13 May 2015 11:28  |
skip2
Messages: 544
Registered: September 2011
Location: Winter Haven,FL (center o...
Karma: 3
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Senior Member |
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What about mounting elsewhere possibly hang with tyraps
And hooking an auxiliary ground wire to the hole in it with a bolt and nut. Should work might have to extend the 4 leads though. Just a thought.
Skip Hartline
74 Canyon Lands, FiTech,
3.7 FD LSD, Manny Tranny,
Springfield Distributor,
2001 Chevy Tracker Ragtop Towd
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| Re: Onan Rectifier Replacement - Broken Screw [message #277822 is a reply to message #277763] |
Thu, 14 May 2015 08:49 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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Senior Member |
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Dave,
I hate to suggest this, but I just have to.
Before you expend any more energy, measure the resistance of the field.
A significant number of our Onans have died of a broken field.
If it is still in the 38ohm region, then go and do what ever you need to do to hold that bridge close to where it should be.
Can you drill through from the outside? I only have BF to look at.
I kind of hope Jim Miller will hop in here. Here knows that end of the machine very well.
Matt
westlanddave78 wrote on Wed, 13 May 2015 10:02Hi all,
My 6k Onan appears to need a bridge rectifier R&R as the engine runs great but there's no AC output. (I did check the breaker, etc.) Unfortunately, while I was trying to undo the old rectifier, I twisted the head off the screw that holds it in place. As anyone who's done this job knows, the quarters are pretty close...too tight to get an EZ-OUT to work. Does anyone have a good way to install the new rectifier without pulling the genset from the motorhome and disassembling the housing? Thanks.
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 Rectifier Replacement - Broken Screw [message #277825 is a reply to message #277822] |
Thu, 14 May 2015 09:13 |
Jim Miller
Messages: 501
Registered: March 2008
Karma: 10
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Senior Member |
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> On May 14, 2015, at 9:49 AM, Matt Colie wrote:
>
> Before you expend any more energy, measure the resistance of the field.
Matt’s suggestions are spot-on.
I am well aware that a lot of bridge rectifiers have failed in the past however at this point in time I suspect the majority of no-AC-output failures are caused by failed field windings. There is also the possibility that the machine in question has sat so long (read: “years”) that the residual magnetic field has decreased to the point that it cannot start the self-excitation process.
This would be my diagnostic approach:
First step is to measure resistance between the F1 and F2 leads using the Rx1 scale of an ohmmeter, it should be in the near vicinity of 38 ohms.
If that was successful then:
Start the machine and use a car or lawnmower battery (but NOT a bench-type power supply!!) to apply 12V to the F1 and F2 leads. F1 is + and F2 is -. Measure the AC output of the Onan and see if you have 50VAc or so. This step not only serves to “re-flash” the fields but it also proves the armature is OK.
If that was successful then replace the bridge.
If there is still no output then there is likely a failed reactor (although I have never seen this happen in any Onan I’ve worked on).
One of these days I’ll work all this into a troubleshooting flowchart!
Also: someone mentioned running a ground wire to the bridge mounting screw…this is not necessary. The body of the bridge is an insulating material and grounding the mounting screw serves no electrical purpose.
--Jim "saving the lives of Onans...one unit at a time" Miller
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: Onan Rectifier Replacement - Broken Screw [message #278096 is a reply to message #277763] |
Wed, 20 May 2015 20:14 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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westlanddave78 wrote on Wed, 13 May 2015 08:02Hi all,
My 6k Onan appears to need a bridge rectifier R&R as the engine runs great but there's no AC output. (I did check the breaker, etc.) Unfortunately, while I was trying to undo the old rectifier, I twisted the head off the screw that holds it in place. As anyone who's done this job knows, the quarters are pretty close...too tight to get an EZ-OUT to work. Does anyone have a good way to install the new rectifier without pulling the genset from the motorhome and disassembling the housing? Thanks.
I would leave the old one in place and just tie wrap the new one so it doesn't get caught in the machinery. These things run a couple of bucks so it is worth a try:
http://www.gmcmhphotos.com/photos/onan/p17103.html
http://www.gmcmhphotos.com/photos/onan/p17103.html
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: Onan Rectifier Replacement - Broken Screw [message #278145 is a reply to message #277763] |
Thu, 21 May 2015 10:55 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Senior Member |
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Has anyone ever measured current in the bridge? I wonder if the rectifier needs a heat sink if you outboard it.
--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 Rectifier Replacement - Broken Screw [message #278148 is a reply to message #278145] |
Thu, 21 May 2015 11:16 |
Jim Miller
Messages: 501
Registered: March 2008
Karma: 10
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Senior Member |
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On May 21, 2015, at 11:55 AM, Johnny Bridges wrote:
>
> Has anyone ever measured current in the bridge? I wonder if the rectifier needs a heat sink if you outboard it.
At 5500W of output load the DC excitation current supplied by the bridge is around 4.1 amps.
Using P=IE and considering 1.4V of voltage drop across the bridge I come up with ~6 watts of dissipated power. I don’t think any heat sink is necessary.
--Jim "saving the lives of Onans...one unit at a time" Miller
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: Onan Rectifier Replacement - Broken Screw [message #278150 is a reply to message #277763] |
Thu, 21 May 2015 11:23 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Senior Member |
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You're right, it's got enough metal sink it's potted in. Tie it to something and go.
--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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