Re: controlling motors with dimmers

["Jim Lux" <jimlux-at-xxxxxxxxxxxxx> (by way of Terry Fritz <twftesla-at-xxxxxxxxxx>)]

A firm I used to work for builds fans that use PSC (split capacitor) motors
and they control quite nicely with off the shelf $5 Lutron ceiling fan
controllers.  Lutron is probably the market leader in inexpensive Triac
dimmers.   Here are the caveats:  You have to start it fast and slow down
(enforced in the dimmer by having the OFF position next to full on). The
motor gets kind of noisy at low speeds due to the waveform distortion, and
the torque gets pretty low, which isn't a problem for things where air drag
is dominant (i.e. fans and RSGs) because the HP requirement drops off
pretty fast as the speed drops.

Tesla list wrote:
> 
> Original poster: Tesla729-at-cs-dot-com
> 
> In a message dated 11/13/00 5:33:16 PM Pacific Standard Time,
> tesla-at-pupman-dot-com writes:
> 
> << Original poster: "Lau, Gary" <Gary.Lau-at-compaq-dot-com  stated :
> 
> If the motor is a brushless induction type, the dimmer won't
> work. >>
> 
> Hi Gary, all,
> 
> Although I agree that you won't have a full range of RPM conrol of a
> brushless induction motor with a dimmer, I disagree that it won't work
> at all. I use a dimmer for a limited control of my asynch RSG, and I
> can probably vary the the RPMs by at least 50%. No, it's not as good
> control as a variac, but it still works good enough for finding a sweet
> spot in the phase. And though the motor does tend to get quite warm
> after extended run time, I never run my 10 kVA system for more than a
> few minutes at a time.
> 
> Keeping 'em Sparkin' in Memphis,
> David Rieben