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Generators & Electric Motors General Discussion Antique Generators and Old Electric Motors: Questions and answers about restoring and showing old power generation systems.

Generators & Electric Motors General Discussion

Would you trust this?


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  #1  
Old 10-25-2018, 03:17:40 AM
cjjmw cjjmw is offline
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Default Would you trust this?

Hi all,

So I finally pulled apart a generator I've been working on that currently has no output. The windings test good, and it's been assumed the caps just need to be flashed but I pulled it all apart because I wanted to see the physical condition of the genhead.

This apparently was at a beach house for most of it's life and it also looks like a mouse was living in it.


Would you trust this? The color of a few windings concerns me as does a green spot on one. Does this mean the insulation is compromised?
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  #2  
Old 10-25-2018, 05:22:49 AM
armandh armandh is offline
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Default Re: Would you trust this?

exactly what tests?

you need to first test the windings for resistance to ground
https://www.google.com/search?q=mege...nt=firefox-b-1
if you can't borrow a "megger"
a high voltage source and a FET front end volt meter will do

Probably could not find it among all the junk but I had a low current KV supply
3v bat, osc, xf, doubler rectifier out of one of these
https://www.google.com/search?q=elec...nt=firefox-b-1

if leaky to gnd probably not worth the effort unless you can get one similar with a bad engine

if it is a typical pacific rim junkerator it probably was not trust worthy when new, less so now.
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  #3  
Old 10-25-2018, 07:20:14 AM
cjjmw cjjmw is offline
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Default Re: Would you trust this?

Quote:
Originally Posted by armandh View Post
exactly what tests?

you need to first test the windings for resistance to ground
https://www.google.com/search?q=mege...nt=firefox-b-1
if you can't borrow a "megger"
a high voltage source and a FET front end volt meter will do

Probably could not find it among all the junk but I had a low current KV supply
3v bat, osc, xf, doubler rectifier out of one of these
https://www.google.com/search?q=elec...nt=firefox-b-1

if leaky to gnd probably not worth the effort unless you can get one similar with a bad engine

if it is a typical pacific rim junkerator it probably was not trust worthy when new, less so now.
The only tests I could do using a typical ohm meter. Best I can tell nothing is shorted to ground, at least not at a few volts.

Don't own a megger and have no where to borrow one from.
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Old 10-25-2018, 01:04:40 PM
Vanman Vanman is offline
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Default Re: Would you trust this?

I think the green spot is disconcerting. It may not give trouble, for a while, so long as it is always dry (no condensation) when run. Might try to carefully clean it and apply some varnish.

Not knowing the design, I am guessing that the few darker colored turns may be a different winding. If they are shorted turns, it wouldn't run long at all like that.

Being two pole (high speed) I would agree that it's likely not worth doing a whole lot to it, if it turns out to need something major.
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Old 10-25-2018, 01:16:19 PM
akirkland akirkland is offline
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Default Re: Would you trust this?

3600 rpm gensets that have been living at the beach are always 1 start away from being toast. No, I would not trust it.
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Old 10-25-2018, 01:24:34 PM
cjjmw cjjmw is offline
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Default Re: Would you trust this?

I wish I could find a decent 2 pole 8-10K genhead somewhere close by.
I've got the perfect engine to go with it.
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Old 10-25-2018, 01:26:52 PM
georgineer georgineer is offline
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Default Re: Would you trust this?

I can't see anything there which would come to any harm if it got wet, so if it were mine, I would give it a thorough wash in fresh water to remove all the muck, sea salt and murine urine. Possibly rinse it with distilled water if I was feeling fussy.

Then I would put it in a warm - not hot - place for days or weeks to dry out thoroughly. I would use an ordinary £5 multimeter to measure the resistance between the windings and the metal frame (which I presume has a ground/earth terminal on it somewhere. If not, scrape a little patch until bare metal shows.)

I would be looking for a resistance of at least 1 megohm, which is the minimum acceptable insulation resistance under UK portable appliance testing rules. US rules may be different. If it is less than 1 meg, stick it back in the warm place for a few days and see if it improves. Repeat until the reading levels out, at which point you can assume it is thoroughly dry.

Obviously the multimeter test is at a very low voltage, but if the resistance won't come up to at least 1 meg then you know the thing is done for and you can throw it away. If it does show over 1 meg, you can choose whether to get a test done at working voltage or above, or reassemble it and give it a try. (Following safe practices, whatever happens isn't my fault, and other necessary disclaimers.)

George

P.S. Incidentally, with motors it is often successful to leave them running on no-load for a few hours to dry the windings out. I recently improved a 1920s motor which had been in storage for years from 300 kilohms to 5 megohms - something like a 15 times improvement.
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Old 10-25-2018, 01:34:46 PM
cjjmw cjjmw is offline
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Default Re: Would you trust this?

Quote:
Originally Posted by georgineer View Post
I can't see anything there which would come to any harm if it got wet, so if it were mine, I would give it a thorough wash in fresh water to remove all the muck, sea salt and murine urine. Possibly rinse it with distilled water if I was feeling fussy.

Then I would put it in a warm - not hot - place for days or weeks to dry out thoroughly. I would use an ordinary £5 multimeter to measure the resistance between the windings and the metal frame (which I presume has a ground/earth terminal on it somewhere. If not, scrape a little patch until bare metal shows.)

I would be looking for a resistance of at least 1 megohm, which is the minimum acceptable insulation resistance under UK portable appliance testing rules. US rules may be different. If it is less than 1 meg, stick it back in the warm place for a few days and see if it improves. Repeat until the reading levels out, at which point you can assume it is thoroughly dry.

Obviously the multimeter test is at a very low voltage, but if the resistance won't come up to at least 1 meg then you know the thing is done for and you can throw it away. If it does show over 1 meg, you can choose whether to get a test done at working voltage or above, or reassemble it and give it a try. (Following safe practices, whatever happens isn't my fault, and other necessary disclaimers.)

George

P.S. Incidentally, with motors it is often successful to leave them running on no-load for a few hours to dry the windings out. I recently improved a 1920s motor which had been in storage for years from 300 kilohms to 5 megohms - something like a 15 times improvement.
I was actually wondering if I could use brake cleaner on it. I believe it leaves very little residue behind. But I was concerned about it attacking the varnish.

Using a Fluke DMM I was unable to measure anything between windings or to ground. I'm fairly confident they're good, right now, with the tools I have at hand.
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  #9  
Old 10-25-2018, 02:08:42 PM
Andrew Mackey Andrew Mackey is offline
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Default Re: Would you trust this?

I would not use brake cleaner on it. Use electrical contact cleaner. Works just as good, won't attack insulation and dries with no residue.
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Old 10-25-2018, 08:13:54 PM
cjjmw cjjmw is offline
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Default Re: Would you trust this?

So, what about rusty laminations. The stator and rotor cores?

Does surface rust cause issues?
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