Re: Variac vs. Fan speed control

Subject:  Re: Variac vs. Fan speed control
  Date:   Wed, 30 Apr 1997 15:57:28 +0500
  From:   "Alfred A. Skrocki" <alfred.skrocki-at-cybernetworking-dot-com>
    To:    Tesla List <tesla-at-pupman-dot-com>

On Fri, 25 Apr 1997 12:25:29 -0600 (MDT) Chip Atkinson
<chip-at-XiG-dot-com> wrote;

> > 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 continuous 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,
> and 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.

Variacs are always nice if you've got em! There is some lag inherent 
to triac phase shift controls. Like a Tesla coil they need a voltage 
avalanche device to run this used to be a diac which would conduct 
at a few volts, some companies substituted a neon -2 lamp which 
would conduct at something between 75 to 85 volts (really bad - you 
get half on to full on) now a lot of units use two silicon diodes in 
parallel each conducting in the opposite direction, these will start 
conducting at a few volts! So they've improved over the years and 
they are a lot cheaper now too! It used to cost over $5.00 just for a 
200 V 10 amp triac let alone the potentiometer , resistors, mylar 
capacitor and diac (you can't even bye a diac any more!)to build the 
whole unit! Now you can get a whole working unit for close to $5.00 
at your nearest K-Mart's.


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