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From: Darcy Roberts
Subject: Re: Is it possible to run a shaded pole AC motor at half speed?
Date: Wed, 11 Sep 2002 15:06:06 -0400
Organization: Agricultural Instruments Canada Ltd.
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Why not just try a diode in series with the motor? say 1A 400v ?
The worst that could happen is it will overheat. These things
should have a thermal fuse in with the winding anyway to protect
against real overheating. In any case, run it with the diode
outside of the housing long enough to ascertain it won't
get too hot.
Another possibility is to try to insert a duct booster fan into the
duct and not use the squirrel cage fan at all. You might even be
able to put the new fan right at the exhaust port. It should be much
quieter in the bathroom.
Wayne Whitney wrote:
> My bathroom fan is too loud, and I can't change it because I rent. So
> I was wondering if there is some way to provide the option of running
> it at half speed. The fan motor is a shaded pole AC motor, and the
> specifications on the fan say "not for use with solid state fan
> controls". I assume that rules out the readily available fan
> I understand from reading a January, 2002 thread that it is hard to do
> speed control on single-phase motors, so perhaps I am asking the
> impossible. The following possibilities did come to mind, though:
> 1) Change the frequency of the AC supply to 30Hz. Is there any simple
> way to do this other than an AC to DC to AC circuit? Is a shaded
> pole motor designed only for a particular frequency, say as far as
> the location of the shadings, or will it work at half frequency?
> 2) Change the voltage of the AC supply. I believe that a very low end
> motor like this runs with a lot of slip. Is it possible that by
> lowering the voltage I could increase the slip to as much as 50%?
> Would that be bad for the motor?
> 3) Add another tap to the winding in the stator. This might be tricky
> to do, but if I could tap the motor winding in the middle, then
> would running with half the winding halve the magnetic field
> strength and increase the slip? Would that be bad for the motor?
> Any comments would be welcome, thanks.
> Best wishes, Wayne
> P.S. How do three-speed ceiling fans do their speed control?
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