Warm disc grinder motor (3 PH, AC)

PIndelicato

PIndelicato

Joined
Sep 16, 2002
Messages
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I recently (finally!) put together a variable speed disc grinder with a new/used Craigslist motor that I picked up at a reasonable price. After about an hour of steady use last night, I noticed that the body of the motor was quite warm to the touch. Is this normal, or an indication of a problem?

I've never noticed my VS belt grinder motor getting warm, but I'm not sure that I've ever touched it after use either...
 
Motors are rated for "rise over ambient" the temperature of the motor should stay below ambient temp + the rise. (usually listed on the motor plate)

VFD's can and do over a range of varrying conditions add to motor heat.
 
The speed you run at, combined with the load you put on the motor, will affect temperature.

With a TEFC motor, the amount of cooling airflow varies with the speed.

However, the heat input varies with the current, which varies with the torque.

If you lean on the grinder at low speed, Heat input is high and cooling airflow is low, so it will tend to get hotter than normal.

As the speed goes down, motors on VFDs should be derated. In most cases, it's no big deal, as "we" tend to work most grinders less hard at low speed quite naturally.

The most common motor insulation seems to be class F, which is good to 155 degC (311 degF) at the windings. Obviously the outside of the motor casing will be a fair bit cooler than the windings, but "quite warm to the touch" sounds like you are quite a long way from a problem
 
Thanks guys, that's about what I thought but better safe than sorry I guess. I'm sure the load is quite low on a disc grinder, but I am running it pretty slowly and that probably doesn't help matters.
 
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