Electrical Motor arcing!


Old 08-14-07, 04:11 PM
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Join Date: Aug 2007
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Electrical Motor arcing!

My electric chain saw (4 hp) motor dropped to about half speed and began to display substantial arcing at the carbon brushes actually looks like flames.

I took the motor apart, cleaned up the brushes and commutator. Still lots of arcing.

Any ideas on what else might cause the arcing?

Thanks for any help
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Old 08-14-07, 04:14 PM
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IMO, if it's not the brushes and you are certain the brushes are in there ( and you did not simply observe the housing for the brushes), and springs with good tension, to push brushes to commutator are good, then I'm afraid the motor is shot, - something in the wires.
Old 08-14-07, 04:37 PM
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Join Date: Aug 2007
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Electric Motor

Yep brushes are present - took them out of housing and cleaned them with fine sandpaper. Spring wire holding the brushes in are fine.

If motor is shot, any guess as to what would cause the arcing? Doesn't seem right.

I thought maybe something loading the motor down might cause this. I'm going to disassemble once more and check for ease of turning. This motor is in an electric chain saw so it has a braking device that seems to be operating correctly but we'll see.

Thanks for your help
Old 08-14-07, 04:48 PM
Join Date: Sep 2002
Location: welland ontario
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Commutator probably is damaged. You would need to remove the rotor and turnthe comutator on a lathe to get round again. Then you need to clean the insulator material between the contacts so that is it slightly lower than the contacts.
Old 08-14-07, 05:05 PM
Join Date: Oct 2005
Location: USA
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just my guess

but an electric chain saw motor has got to be one of the more abused motors out there. Lots of variable loads, controlled by an operator. Obviously just a guess, but i'm thinking wire heating finally caused a short in the windings, making the device a throwaway..
Old 08-16-07, 07:39 AM
Join Date: Mar 2007
Posts: 1,341
If the motor has seen a lot of service try replacing the brushes before scrapping the saw. They may be worn to the point that they no longer make solid contact.

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