Re: Variac question...

At 01:33 AM 11/30/98 -0700, you wrote:
>Original Poster: "Ross W. Overstreet" <ross-o-at-mindspring-dot-com> 
>I didn't want to send this to the TC mailing list b/c it is pretty simple.
>If you
>have time...
>I picked up a variac at the swap meet for $10.  It is an old, but
>unused, Powerstat rated at 1.3 Max KVA and 9.0 Max Amps.  My 12/60 NST
>requires 6.35 amps with the secondary shorted.  With 2 of these I will
>be at 1.53 KVA and 12.7 amps.  Clearly this is over the label value but
>hopefully under the true design value (without safety factor).  What
>kills Variacs?  I assume that it is heat, if that is the problem I will
>fan cool.  Do you think that this variac will make it???  Any
>suggestions, other than look for bigger variacs :-)
   What kills variacs and other transformers if you over power them is that
the core will saturate.  Once this happens the winding look like they now
have no core, just the mue of air and inductance the value of that in air.
Now you have a very low impedance from hot to neutral and draws even more
power and you can see where this lead to.  A runaway burn up.

hope this will help,