Re: Variac vs. Fan speed control

Subject:  Re: Variac vs. Fan speed control
  Date:   Mon, 21 Apr 1997 09:29:22 -0600 (MDT)
  From:   Chip Atkinson <chip-at-XiG-dot-com>
    To:   Tesla List <tesla-at-pupman-dot-com>

On Sun, 20 Apr 1997, Tesla List wrote:
> >for
> >answers from anybody who's already explored this area. 
> >
> >              Aaron Datesman
> >
> >
> Aaron, these types of "speed controls" work by controlling the duty
> cycle or the "on time" during the ac sinewave using a threshold
> bidirectional trigger diode (diac) which in a controlable manner gates
> a bidirectional SCR called a triac. 

> They are totally unsuitable for 
> voltage control, could be use to vary the speed of a SMALL ac motor
> running a rotary gap but not the low side of a drive transformer.

Not quite true.  They are totally unsuitable for the rotary gap too.  I
tried this a long time ago.  The controller was an actual motor
(not a light dimmer) that I got at an electric motor place.  The problem
is that once the coil starts firing, the controller loses its mind and
motor goes full speed.  Turn off the coil and the motor controller
to normal.


First Corollary of Taber's Second Law:
        Machines that perturb people often get murdered.
               -- Pat Taber