On Mon, 18 Jul 2011 06:31:03 -0700 (PDT), klem kedidelhopper
wrote:

On Jul 18, 9:22*am, klem kedidelhopper
wrote:
On Jul 17, 6:30*am, "Michael A. Terrell"
wrote:



klem kedidelhopper wrote:

On Jul 16, 7:35 pm, "Michael A. Terrell"
wrote:
klem kedidelhopper wrote:

We have a ceiling fan in our bedroom that we sometimes like to run at
very slow speed at night. The fan was purchased as new surplus many
years ago and never came with a speed control. So I have been using a
generic solid state speed controller. With this unit we are able to
take the unit down to complete "crawl" however there has always been a
slight rhythmic buzzing noise whose loudness and duty cycle are both
directly proportional to the motor speed. I know it's related to the
pulse type of control I'm using but short of just using a variac or a
rheostat for that matter, does anyone know of a method to achieve a
very slow speed without the noise?

Also this motor has no brushes and so even though its not labeled as
such I wonder if it could be a "Universal" type of motor that could
run on DC? It wouldn't take much to put a bridge and perhaps even a
filter in the electrical box ahead of the motor. I'm thinking that DC
operation could possibly be quieter. Thanks, Lenny

* *Is the speed controler made for induction motors?

How would a speed controller made for induction motors differ from say
an ordinary lamp dimmer?

* *Lamp dimmers are simple phase controllers. *They aren't designed for
inductive loads. That's why most light dimmers can't be used on
Florescent lights. *They can cause the motor to overheat at some speeds,
and cause it to be noisy or erratic at low speeds.

Leviton makes variable speed fan controls with a slider to set the
speed. You can get them at HD, Lowes or a lot of other building supply
stores.

http://www.leviton.com/OA_HTML/ibeCCtpSctDspRte.jsp?section=10857&min...

http://www.lowes.com/SearchCatalogDisplay?Ntt=speed+control&langId=-1...

http://www.homedepot.com/webapp/wcs/stores/servlet/Search?keyword=spe...
--
It's easy to think outside the box, when you have a cutting torch.

Thanks Michael for sending me those dimmer links. They are pricey
though... Lenny

I did find the Leviton but it may not be a continuously variable unit.
I'll have to go look at them. Lenny

I had a fan that was noisy like that, and stuck a 5-10 uF capacitor
in series with the motor. You can't use the dimmer - so you need a
switch to hook the fan either to the controller or the series cap. It
runs quite slowly, and no buzzing. Make sure the capacitor is designed
for line use ..... 250vac or 600vdc should be OK. If it fails, the fan
will just run at full speed. The only worry would be if it were to get
hot say from internal arcing or something wierd like that. To be one
the safe side use a U/L approved or type Z capacitor.
You can cause the cap and inductance of the fan to resonate....
That will cause voltages greater than the line voltage to appear
across the fan motor, and it go fast, and overheat. Try a few
capacitors, starting at 1uf, and increase until you get the speed you
want.
Some fans have a switch that gives 3-4 speeds, with a series cap,
you can effectively get a much slower range of speeds, and thereby not
need to use a dimmer type speed controller.

Paul G.