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Re: Variac vs. Fan speed control
Subject: Re: Variac vs. Fan speed control
Date: Fri, 25 Apr 1997 07:52:23 -0400
From: "Thomas McGahee" <tom_mcgahee-at-sigmais-dot-com>
To: "Tesla List" <tesla-at-pupman-dot-com>
----------
> From: Tesla List <tesla-at-pupman-dot-com>
> To: tesla-at-poodle.pupman-dot-com
> Subject: Re: Variac vs. Fan speed control
> Date: Thursday, April 24, 1997 7:37 PM
>
> 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.
>
>
> Sincerely
> Alfred A. Skrocki
> alfred.skrocki-at-cybernetworking-dot-com
Chip & Alfred,
Just to throw in my two cents worth... Yes, the controller itself should
be
mounted in a metal enclosure used as a Faraday shield. It is important
that
the motor wiring be fully shielded, connected to the motor casing, and
properly AC grounded, otherwise the wiring acts like a glorified antenna
for the RF, and sneak into the Faraday shield. Not all AC controllers
can
take the wild transients that exist around a Tesla coil. A Faraday
shield
will always work as long as the shield completely encloses the entire
circuit. Unfortunately, the power leads themselves can be bringing in
nasty
little spikes, in which case many of the cheaper circuits go totally
bonkers. The nice thing about a variac is that in Tesla use they are
fairly
bullet-proof and survive the environment. Well, most of the time :)
Fr. Tom McGahee