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Old 03-09-2013, 02:26 AM   #9 (permalink)
Ryland
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Join Date: Jan 2008
Location: Western Wisconsin
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honda cb125 - '74 Honda CB 125 S1
90 day: 79.71 mpg (US)

green wedge - '81 Commuter Vehicles Inc. Commuti-Car

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Quote:
Originally Posted by mechman600 View Post
What dies when the heat gets too high? Is it an "over time" thing, where too many amps over a period of time cause something to degrade quicker than normal, or is it something that happens quickly?
This is a brushless motor, so it's pretty much down to the varnish on the motor windings and the other insulation and glues that hold it all together and keep everything from shorting out, each grade of varnish has a heat rating where that varnish should last for 10,000 hours or more at or below the rated temp, as you go higher the life is cut back, I think I read every 10 degrees above rated temp cuts the motor life in half, class H motor insulation is good for 180c while class A is only good for 105c if I remember right.

On motors with brushes, the brushes and commutator are the weak points, brushes break down with heat and the commutator has insulation and glue that break down with heat.

So yes, it's both time and heat, more heat and insulation doesn't last as long so the motor doesn't last as long or "burns up" in the case of a saw that I was using at work, blue flames shoot out when the last of the insulation burned off, but I could also see the heat damage on the brushes and commutator and could clearly see that it was under a lot of stress, cheap motor tho and that tool we run till it burns out so I kept running it and it burned out.
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