Re: Variac vs. Fan speed control (fwd)

Subject:   Re: Variac vs. Fan speed control (fwd)
  Date:   Sun, 20 Apr 1997 21:21:00 -0600 (MDT)
  From:   List owner <listown-at-poodle.pupman-dot-com>
    To:   tesla-at-poodle.pupman-dot-com

> I received some advice recently which didn't work at first try, but I'm
> curious what the list wisdom has to offer.  I was shopping for a Variac
> (don't know where to find a new one) when I was told to use a fan speed
> control instead - it would do the same thing.  The one I bought,
> however, I
> burned two neons with - when I finally thought to check it, it turns out
> that
> my dimmer-type switch moves immediately from "OFF" to "120 Volts".  So
> it
> isn't surprising that I burned out the two Xformers.
>    Obviously the switch I bought doesn't control the fan speed by
> varying the
> voltage input to the fan.  1) How does it work?  2) Is there a variety
> of fan
> speed control which would work in this application (replacing a
> Variac)?  If
> so, it would certainly be cheaper and more easily available.  :)  Thanks
> for
> answers from anybody who's already explored this area.
>               Aaron Datesman

The usual fan speed control with which I am familiar uses
a diac or r-c time delay to trigger a triac to determine 
how much of the AC sine wave is transmitted to the load. 
This means that instead of the load receiving the entire
sine wave, the first quarter wave or half wave might be 
blocked, reducing the effective rms power delivered to
the load. This type of speed control is not at all suited
to TC work, as it does not limit instantaneous power at all,
and can't handle the power requirements of the smallest TC coil.
In other words, *mucho smoke* and we all know that electronic
circuits run on smoke! ;)

Be very careful in trying to use a system in this manner; in fact,
don't! The danger is extreme, not only of fire, but exploding parts!

Be safe; be happy!

     Rick Holland

     The Answer is 42.