Re: variac survival

To: tesla-at-poodle.pupman-dot-com
Subject: Re: variac survival
From: Tesla List <tesla-at-stic-dot-net>
Date: Wed, 26 Mar 1997 00:01:24 -0600
Approved: tesla-at-stic-dot-net

Subject: 
        Re: variac survival
  Date: 
        Tue, 25 Mar 1997 12:22:30 -0500 (EST)
  From: 
        FutureT-at-aol-dot-com
    To: 
        tesla-at-pupman-dot-com

In a message dated 97-03-25 03:20:31 EST, you write:

 > beasties, but overcurrents can cause plenty of damage.   The free
little
 > booklets are available at electrical supply stores, and give all the
variac
 > specs, and tell how much you can safely over-load them and for how
long.
 >  They seem to handle double their ratings reasonably well for short
 > durations.  It's a matter of heat, and brush roasting.  It all
depends on
how much 
 > you're willing to push the variac and < snip >                 John
Freau
  >>

It is also important to use RF line filters between the variac and the
Tesla
coil, to protect the variac from kickback.  Failure to use filters may
cause
arcing from the winding to the core of the variac, and carbonization of
the
insulation between windings and core.   Another way that variacs get
destroyed is by supplying too much voltage to a transformer causing the
core
to saturate which causes high current spikes.  (Most 120 volt
transformers
cannot tolerate more than about 145 volts input before saturation
becomes too
much of a problem).  This can cause the brushes to "stick", making the
handwheel hard to turn, and particles of copper can get "blasted" out of
the
variac winding where it contacts the brushes. 

Towards optimal coiling,

John Freau