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Tool Talk Discussion Forum

Generator loses magnetism ????

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jCarroll

11-26-2004 05:43:42




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I have little experience with backup/emergency generators - just borrowed 'em. Talking single phase, 120/240v units. Now I'm kicking the tires, and reading the posts. Every once in a while, someone mentions generators losing their residual magnetism. Give me a lesson on this:

Is this a "real" problem?
Does it affect every kind of generator?
What do you do to prevent it?
Other advice?

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Bob M

11-28-2004 16:21:40




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 Re: Generator loses magnetism ???? in reply to jCarroll, 11-26-2004 05:43:42  
My experience is it depends on the generator. I've got a Coleman 4 KW unit that has sat as long as 30 months. But it always self excites immediately upon startup. But I also have an ancient US Electric 1.5 KW unit that must have the fields "flashed" if it sits idle for more than a few weeks.



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Bob

11-26-2004 09:41:24




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 Re: Generator loses magnetism ???? in reply to jCarroll, 11-26-2004 05:43:42  
John and Coloken,

I work on small engines, and I can assure you the problem of losing residual magnetism comes up quite often with the newer gas-powered generators.



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Coloken

11-26-2004 13:20:40




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 Re: Generator loses magnetism ???? in reply to Bob, 11-26-2004 09:41:24  
Thanks Bob I guess your never too old to learn. Hadn't run into it. Yet..... ..



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John *.?-!.* cub owner

11-26-2004 09:37:01




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 Re: Generator loses magnetism ???? in reply to jCarroll, 11-26-2004 05:43:42  
With the very old generators it was sometimes a problem if they sat for several months. I've never heard of it needing to be done with the modern ones.



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buickanddeere

11-26-2004 09:56:22




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 Re: Generator loses magnetism ???? in reply to John *.?-!.* cub owner, 11-26-2004 09:37:01  
The Coleman 5000 I got rid off would need the field flashed after three months if it wasn't used.



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Coloken

11-26-2004 06:40:48




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 Re: Generator loses magnetism ???? in reply to jCarroll, 11-26-2004 05:43:42  
Don't worry about it. Most posts are about "polarizing" generators, 6 or 12 volt so they will charge the right way. Plus or minus. Kinda needed with a brand new one. If a piece of metal has once been magnetized it is all most imposible to completly "demagnitize" it unless you want to. Like a watch.



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Bob

11-26-2004 06:37:51




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 Re: Generator loses magnetism ???? in reply to jCarroll, 11-26-2004 05:43:42  
In my experience some do, and some don't. The longer a unit sits without being used, or even started, the greater the chance of this happening.

There's an easy way to "flash" a generator, and get it working again, though:



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Rockin' Farmer

11-27-2004 05:49:47




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 Re: Generator loses magnetism ???? in reply to Bob, 11-26-2004 06:37:51  
Well I'll be! A while back I fired up my Coleman 2500W plant that had been sitting for over a year, plugged in a trouble light to test the generator, and got nothing. Thinking the bulb was burned out, I grabbed my drill and plugged it in. Nothing. Gave the drill a spin with my hand, out of desperation, and it started running! Plugged the trouble light back in, and it worked! Been scratching my head about that one for quite a while. Now I know what I did!

All this time, I've been blaming "Evil Spirits".

Thanks for the tip!

Rockin' Farmer

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John *.?-!.* cub owner

11-26-2004 09:38:50




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 Re: Generator loses magnetism ???? in reply to Bob, 11-26-2004 06:37:51  
Bob, that's a good tip. wish I'd know about it when I used to own a 60 year old Sears light plant that I used for standby power.



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Dusty

11-26-2004 08:28:27




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 Re: Generator loses magnetism ???? in reply to Bob, 11-26-2004 06:37:51  
That's a great way, I've never heard that method. The other way is to use a 1.5 to 6 volt battery, momentary connecting to the brushes, the generator must be turning/running while doing this. Polarity matters. I extended a wire from each brush, red on one and black the other, out to where I could get to them. Even a AAA battery will work.

Dusty



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Stickler

11-27-2004 00:01:43




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 Re: Generator loses magnetism ???? in reply to Dusty, 11-26-2004 08:28:27  
I operate Hydro power stations for a living. Yes, all genreators are prone to this. We "flash" ours with a 8D battery to build it back up if it's been sitting for a long time.....a year or more.



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