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Posted by Christopher Tidy on February 29, 2008, 4:53 pm
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Brad. wrote:
> Hoping someone can help on a little problem of mine !!
> I have a 2.2KW 3phase extractor fan motor which is bifurcated (inside
> seperate ducting within the flue). The fan motor is controlled by a
> transformer type device rather than an inverter. The motor seems to be
> getting very hot at slower speeds. I am considering extra cooling by
> inserting a 4" axial fan (bathroom extractor fan) into the ducting access
> plate to add extra cooling. Question is, is there an easy way on monitoring
> the motor's temperature? to avoid burning the thing out? I thought about
> one of those digital thermometers with a long probe that you can use when
> cooking turkeys etc. Would this work? What sort of temperature would be
> normal for a fan motor running at low speeds?
> Any help would be greatly appreciated.
> Cheers.
> Brad.
There is a section on measuring motor temperature in one of Jim Cox's
books, I think "Electric Motors in the Home Workshop". He explains that
there is not a lot of point in measuring the temperature of the casing;
you need to measure the temperature of the windings themselves. He
recommends measuring the increase in temperature by measuring the change
in resistance of the windings. Obviously you need to be careful not to
give yourself an electric shock doing this, but it can be done safely.
I've done it in the past and it gives sensible results. I would give you
the parameters required for the calculation, but I seem to have
misplaced my copy of Jim's book. If you think you'll find the
information useful, I might be able to find my copy. But if you use
electric motors often, I'd recommend buying the book. It's very
informative. Jim Cox also sometimes visits rec.crafts.metalworking using
the name Jim Pentagrid.
Best wishes,
Chris
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> I have a 2.2KW 3phase extractor fan motor which is bifurcated (inside
> seperate ducting within the flue). The fan motor is controlled by a
> transformer type device rather than an inverter. The motor seems to be
> getting very hot at slower speeds. I am considering extra cooling by
> inserting a 4" axial fan (bathroom extractor fan) into the ducting access
> plate to add extra cooling. Question is, is there an easy way on monitoring
> the motor's temperature? to avoid burning the thing out? I thought about
> one of those digital thermometers with a long probe that you can use when
> cooking turkeys etc. Would this work? What sort of temperature would be
> normal for a fan motor running at low speeds?
> Any help would be greatly appreciated.
> Cheers.
> Brad.