From: "Michael A. Terrell"
Subject: Re: Is it possible to run a shaded pole AC motor at half speed?
Date: Thu, 12 Sep 2002 14:23:39 -0400
Organization: I'm trying!
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"N. Thornton" wrote:
> John's got the right approach here. A series inductor or capacitor
> would be the best solution. But DONT use a capacitor until youve
> calculated it _carefully_. Motors are RL loads, mainly L, so the
> wrong size cap will result in fast destruction of both cap and motor.
> Calculate it! Also calculate the V required too, the cap will need to
> be rated at more than your mains voltage.
> I run a shaded pole motor in series with an inductr, and it runs
> cooler as well as slower.
> Oh, dont try putting a diode in series wih it!
> Regards, NT
> John Larkin wrote in message news:...
> > On Wed, 11 Sep 2002 16:28:23 +0000 (UTC), email@example.com (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
> > >controls.
> > >
> > >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?
> > Yes, but too much work.
> > >
> > >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?
> > Should be OK.
> > >
> > >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?
> > DON'T try that. Toast city.
> > >
> > >Any comments would be welcome, thanks.
> > >
> > >Best wishes, Wayne
> > >
> > >P.S. How do three-speed ceiling fans do their speed control?
> > If you reduce the applied voltage, it will certainly slow down and get
> > quieter. I sometimes run 240 volt muffin fans at 120 to get a gentle
> > air flow and near dead silence.
> > Try a series resistor; wild guess 50-200 ohms, wirewound power
> > resistor. It will get hot! A series capacitor would work and not get
> > hot; maybe 10 (??) microfarads, 200 volt mylar or other nonpolarized
> > film cap.
> > A stepdown transformer or autotransformer would work too. I bet 3/4 of
> > full line voltage would be a lot quieter. A 24-volt bell-type
> > transformer could be used as a buck-type stepdown autotransformer.
> > John
Why not just buy a ceiling fan controller? Three speeds, no
problems. You can even buy them mounted on a wall plate to replace the
existing wall switch.
An old fart since August 5th, 2002!
Michael A. Terrell
Check out my web site and tell me what you think.
I'm up to 160 pages, and still working on it.