Re: Variac vs. Fan speed control

Subject:  Re: Variac vs. Fan speed control
  Date:   Fri, 25 Apr 1997 12:25:29 -0600 (MDT)
  From:   Chip Atkinson <chip-at-XiG-dot-com>
    To:   Tesla List <tesla-at-pupman-dot-com>

On Thu, 24 Apr 1997, Tesla List wrote:

> Subject:   Re: Variac vs. Fan speed control
>   Date:    Thu, 24 Apr 1997 15:22:11 +0500
>   From:    "Alfred A. Skrocki" <alfred.skrocki-at-cybernetworking-dot-com>
>     To:    Tesla List <tesla-at-pupman-dot-com>
> On Mon, 21 Apr 1997 09:29:22 -0600 (MDT) Chip Atkinson
> <chip-at-XiG-dot-com> wrote;
> > > 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
> > controller (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 the motor goes full speed.  Turn off the coil and the motor
> > controller returns to normal.
> Hay Chip, ever hear of a Faraday shield? Seriously, Chip I currently 
> use phase shift light dimmers to control my rotory spark gaps {I use 
> universal motors} and I have no problems BUT I totaly enclose the 
> dimmers in a grounded metal box. Apparently what happened in your 
> case is the triac was picking up some of the radiated R.F and being 
> driven into continous conduction, try it again but this time enclose 
> the control in a grounded metal enclosure.

Hmm... That may be.   I believe that the case was non-metal, so that I
guess I could shield it.  However I now have three variacs available,
they go from 0 to full, whereas the fan control only went to about 20
volts or so (just guessing).  I didn't measure it.  It was from my olde
coiling days, before I knew about shielding, etc.