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Onan Generators

What Have You Done to Your Onan Generator Today?


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  #3671  
Old 01-12-2018, 05:58:27 PM
len k len k is online now
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Default Re: What Have You Done to Your Onan Generator Today?

Can you measure ohms and MFD of cap at room temp, then repeat after cold soak in freezer.

Would be interesting to measure ohms again after cap comes out of freezer , and a fine sweat condenses over it .


I didn't have a cap meter so I once measured current when it was connected to 120 VAC utility outlet, 60 hz. Turned out utility line resistance and inductance were negligible as cap measured as printed on it. Think I was measuring a motor cap for A/C unit, ~ 6-8 k BTU unit.


Freezer of my refrigerator can fairly easily get down to -10 deg F, and when thermostat was stuck would get down to ~ -20 or -25 degs after ~ 1/2 day of continuous running.

Last edited by len k; 01-12-2018 at 06:52:45 PM.
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  #3672  
Old 01-12-2018, 08:25:45 PM
Leon N. Leon N. is offline
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Default Re: What Have You Done to Your Onan Generator Today?

I cold soaked a new JB ignition condenser at -2 F. And there was no change in the resistance reading of > 20 megohms.
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  #3673  
Old 01-12-2018, 09:16:55 PM
len k len k is online now
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Default Re: What Have You Done to Your Onan Generator Today?

Wasn't expecting basic cap resistance to change.
However now take it out and measure ohms while it sweats up outside in the ~ 100% humidity. This is similar to the conditions your JB was under when cap sparked.

We had to test our gyros to full mil specs of temperature and humidity. We had many cycling environmental chambers in house for that proof testing. Stuff like bare connections to electronics had to either be potted or conformal coated to continue to preform to specs while environment was condensing humidity.

That cover over points area should go a long ways to keeping humid air out of the cap area.

Last edited by len k; 01-12-2018 at 09:33:07 PM.
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  #3674  
Old 01-12-2018, 09:34:20 PM
Leon N. Leon N. is offline
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Default Re: What Have You Done to Your Onan Generator Today?

Len no I am not going to do that. I suspect it was a combination of dirt and condensation that precipitated the arc over. I will try to get a Meg ohm reading off the installed condenser tomorrow. Of course I will have to disconnect the condenser lead to make the measurement. If the installed condenser is shorting out to ground t hat is not a good situation.
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Old 01-12-2018, 10:09:45 PM
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Default Re: What Have You Done to Your Onan Generator Today?

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Originally Posted by Leon N. View Post
I have a new 312A116 Onan JB condenser on my desk. It measures around 15-20 meg ohms. Just not looking forward to changing it out for two reasons. Once the JB gets going everything seems fine and I hate to mess around in that area and possibly upset the timing. Although I think the condenser can be changed without messing with the points. Just a pain to get down on my knees. Everything is now dried out and toasty warm. Not suppose to get cold until tomorrow evening.

I just was very surprised to see the condenser arc over. Wow!
Leon, changing just the condenser will not upset the timing. Very worst case scenario is you may accidently upset the point gap if you accidently loosen the wrong screw. This is unless your JB is of a different design than mine. I think there is a several decade difference between mine and your JB.

JohnnyC
New Jersey

p.s. - ignore the paint chipping and scratches in my JB's pictures above. These pics were taken as I was tearing down my JB prior to a refurb & new paint job.
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  #3676  
Old 01-12-2018, 11:10:13 PM
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Jim McIntyre Jim McIntyre is offline
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Default Re: What Have You Done to Your Onan Generator Today?

Quote:
Originally Posted by Leon N. View Post
I suspect it was a combination of dirt and condensation that precipitated the arc over...
Me too. If it bothers you, get a toothbrush and some alcohol and clean it up. When the points open, there's several hundred volts developed, even with a good condensor...
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Old 01-12-2018, 11:22:33 PM
len k len k is online now
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Default Re: What Have You Done to Your Onan Generator Today?

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Originally Posted by Leon N. View Post
I suspect it was a combination of dirt and condensation that precipitated the arc over.
I agree dirt helped, but I suspect key ingredient was condensation. It reduced the creepage distance for arc.
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Old 01-12-2018, 11:53:11 PM
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Default Re: What Have You Done to Your Onan Generator Today?

Well, now that it's been arcing, it's moot because it's likely there's some carbon there...
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Old 01-13-2018, 12:34:26 AM
JohnnyC JohnnyC is online now
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Default Re: What Have You Done to Your Onan Generator Today?

Simple solution. Replace it. Leon already stated hew has a new condenser. It should take no more than 10 minutes to replace it and be done with it!

JohnnyC
New Jersey
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  #3680  
Old 01-13-2018, 12:50:42 AM
len k len k is online now
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Default Re: What Have You Done to Your Onan Generator Today?

I gave it some more thought, dirt or contamination is likely needed.

When condensation starts to occur it likely is many microspheres of pure semi-distilled water on the surface ( 18 megohm water). Dirt makes the spheres more conductive. So now the spheres have some conductivity, so the creepage distance is now lower, since conductive spheres dot the insulative surface. And sparks can occur easier between spheres. At least that's my current theory......
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