Motor Question?

staffwalker · Post by **staffwalker** » Wed Jan 21, 2009 7:25 pm

I have a GE 1/2hp motor I bought at a charity auction. It had been donated by a close friend who said it was almost new and came from an attic fan. He had bought the fan and replaced the motor with a bigger and faster rpm motor. This one runs at 1075 and is the perfect wax buffer. The question, it is thermally controlled. When I buff a pipe the motor will overheat and shut down after 15-20 minutes. As soon as it cools off it will come back on. On the plate it says Time Rating: Continuous Air Over. Does this mean I need to mount an external fan? I suppose in its original configuration the attic fan provided cooling for the motor. Or could it be a motor problem?

bob gilbert

Sasquatch · Post by **Sasquatch** » Wed Jan 21, 2009 9:01 pm

Could be a problem with the motor... Is there any place on the shaft for a fan to mount? A lot of motors have a shaft sticking out of both ends of the armature, one takes the belt or whatever, and one takes a fan (usually in some kind of shroud). If that fan is missing, a motor will overheat surprisingly fast.

staffwalker · Post by **staffwalker** » Wed Jan 21, 2009 10:41 pm

No, there is no place to mount a fan it's only a single short shaft. I am assuming if the motor was designed to be air cooled it was cooled by the attic fan. This motor came out of a large 48" attic fan. Fans I have seen have the motor mounted in the housing. The fan running would have pulled air over the motor.

I'll have to get a fan and run some tests. Just thought some of you 'motor' folks might know if certain motors were designed to only work with air cooling. Thanks for the answer.

bob gilbert

Frank · Post by **Frank** » Thu Jan 22, 2009 3:29 am

The only thing that occurs to me is that, without the fan blades attached to assist motor cooling, the motor is not continuous rated.

Post by **KurtHuhn** » Thu Jan 22, 2009 11:47 am

Yes - that rating is a standard in motors. Most electric motors carry a duty rating, some carry a duty with qualifications. Continuous Air Over is one such qualification - it is rated as continuous, but only so long as there is constant air movement through the windings. Most electric motors in use on equipment or as buffers are rated based on the internal (or externally attached) fan. This where things like TEFC (Totally Enclosed Fan Cooled) enclosures come in.

For a motor designed to drive a fan, there is no internal fan to cool the windings - it would be extraneous since the fan would provide more than enough cooling air movement. Using that motor for something else, with no attached fan, would almost certainly trip the thermal protection. My guess is that the enclosure type is "Totally Enclosed, Air Over", or TEAO - these are very, very common in HVAC and ventilation uses.

It may be possible to modify the motor with a small external fan housing on the back.

Frank · Post by **Frank** » Thu Jan 22, 2009 3:06 pm

It would be less hassle and much more convenient to get a used TEFC motor with twin shafts, rather than trying to figure out how to cool that motor.

FredS · Post by **FredS** » Thu Jan 22, 2009 5:10 pm

Frank - Some of us have a condition known as cobbleritis. That's when a guy will spend six hours in the shop and make two trips to the hardware store to spend $53 buying bushings, all-thread, hose clamps, angle iron & rubber washers in order to convert a free motor into a buffer he could have bought for $60. It's most prevalent in people from Arkansas.

Frank · Post by **Frank** » Thu Jan 22, 2009 5:43 pm

FredS wrote:Frank - Some of us have a condition known as cobbleritis.

I know that only too well. I used to make electronic gizmos at home, then install them in homemade wooden boxes, rather than buy metal or plastic boxes. Some of my junk were right old Heath-Robinson affairs.

staffwalker · Post by **staffwalker** » Tue Jan 27, 2009 12:29 am

Thanks for the help. When it gets warmer I will move a pedestal fan into the shop and direct it over the motor to see if it will continue running. At the moment my shop is a little chilly so don't think a fan would feel too good.

bob gilbert