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What Have You Done to Your Onan Generator Today?


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  #3661  
Old 01-10-2018, 04:51:00 PM
PopsGarage PopsGarage is offline
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Photo Re: What Have You Done to Your Onan Generator Today?

well nothing did not even remove the snow from the cover, but I did pick up a new oil filter and four quarts of rotella synthetic 5w30 ready for a change when the weather warms up. dose anyone see any problems changing from rotella 10w40 standard oil to the synthetic? the generator is a 1966 MDJB with unknown hours right now cold oil pressure is 45 psig+ and hot is 30 psig (180 degf) any thoughts
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Old 01-10-2018, 07:33:06 PM
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Default Re: What Have You Done to Your Onan Generator Today?

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...does anyone see any problems changing from rotella 10w40 standard oil to the synthetic...
I think it is a non-issue. Go for it.
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  #3663  
Old 01-12-2018, 01:17:23 PM
Leon N. Leon N. is offline
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Default Re: What Have You Done to Your Onan Generator Today?

What did I do for my JB today? Well wait till you read the following. It has me very very curious because it may be an indication of TR ahead.

Today, Jan 11, it is now 50+ degrees outside, very humid. Inside my JB shed it must be well below freezing and I wanted to warm up the JB to perhaps dry out any the condensation.

I have previously left the JB ignition points cover off so I could look for any sparking at the points. Well here is what I observed today. During the cold start cranking I noticed sparking between the ignition condenser center conductor and the condenser case! Once the JB started and came up to speed no more arcing/sparking from the condenser hot terminal to the case. The JB started normally and warmed up nicely and no sparking at the points.

What do you think all this means? Should I be concerned. I have never observed this behavior before.
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Old 01-12-2018, 02:03:12 PM
len k len k is offline
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Default Re: What Have You Done to Your Onan Generator Today?

Sounds like inductive voltage spike from spark coil is arcing over condensation on top of condenser, when points open. Either that or condenser capacitance is low and it's not doing it's job, however no spark when warm implies that might not be the problem.

I do know that caps change value with temp, I've been bitten by that at work (sensor design). But guessing it's not enough to be an issue here.

Engine cold soaked at very low temps, now "warm" moist humid air wafting in thru your open shed vents = condensation over every cold engine part. Today here fog is everywhere, NOAA says 55 degs and humidity is 95- 100%

Here it usually happens for 2 weeks in spring so bad that large sweat drops are all over car engines, but now the conditions are right for it.

IF cover was left on it likely would have reduced infiltration of moist air to area of points/condenser.

Good thing you replaced spark wires with sealed boots or you'ld likely see sparking over the plugs too.

Last edited by len k; 01-12-2018 at 03:16:59 PM.
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Old 01-12-2018, 02:30:59 PM
Leon N. Leon N. is offline
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Default Re: What Have You Done to Your Onan Generator Today?

I think you are correct. That is, the condenser is not performing its job, perhaps due to low capacitance at low temperatures. I did observe some sparking at the points also until the machine reached normal RPM. After it ran for a couple of minutes, the random points sparking stopped. Will have to R & R that condenser. I have a new spare, will measure resistance and compare with the suspect condenser.
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  #3666  
Old 01-12-2018, 02:40:59 PM
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Default Re: What Have You Done to Your Onan Generator Today?

Leon,
It would be very interesting to have the exact same conditions and you try to start it with the new condenser to see what it does!
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  #3667  
Old 01-12-2018, 02:41:23 PM
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Default Re: What Have You Done to Your Onan Generator Today?

Leon, You got to keep that JB running well. It will go to the Smithsonian Museum some day..... and probably be used as back up power for the Museum!
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Old 01-12-2018, 02:59:56 PM
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Default Re: What Have You Done to Your Onan Generator Today?

You'ld have to look it up but I suspect cap valve shift with temp is 10-25% MAX, over aircraft mill spec temp range.

Problem I ran into is I was using a spreadsheet model for a differential transformer design that PHd had just wrote the electrical part for. Customer wanted high sensitivity so turns out I selected cap valve that gave good numbers, but I didn't notice it was at LRC electrical resonance. As cap changed value a little, circuit natural frequency changed and output slid down quickly. Turned out program didn't model capacitance change with temperature. Had to find special caps that didn't change with temp.

Quote:
Originally Posted by nothingbutdarts View Post
It would be very interesting to have the exact same conditions and you try to start it with the new condenser to see what it does!
Easy enough to do. It'll be cold again soon. A hot steam vaporizor aimed towards points area should easily recreate the surface condensation. Maybe hold it 3 ft away so it steam won't warm metal much.

Last edited by len k; 01-12-2018 at 06:47:00 PM.
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  #3669  
Old 01-12-2018, 04:26:00 PM
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Default Re: What Have You Done to Your Onan Generator Today?

Started up my JB 7.5 and warmed it up good just in case we loose power do to the threat of an ice storm on its way Hunter i guess the screamers calls this storm so bring it on my Jb is chopping at the bit ready to kick Hunters Arse
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Old 01-12-2018, 05:17:06 PM
Leon N. Leon N. is offline
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Default Re: What Have You Done to Your Onan Generator Today?

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!
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Old 01-12-2018, 05:58:27 PM
len k len k is offline
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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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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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Old 01-12-2018, 09:16:55 PM
len k len k is offline
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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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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?

Quote:
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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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 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.
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 offline
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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
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Old 01-13-2018, 12:50:42 AM
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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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