Help modifying a variac?

From:  Barton B. Anderson [SMTP:mopar-at-mn.uswest-dot-net]
Sent:  Sunday, April 12, 1998 3:14 AM
To:  Tesla List
Subject:  Re: Help modifying a variac?


I did this for the second time today and just got
through testing it about
10 minutes ago. Dr. Resonance posted that an old variac
core can be sliced
though and about 150 or so turns of #10 wire wound in
place of the old
winding. Then a piece of mylar or whatever is glued into
the gap. The wire
can then be tapped at different points to vary the
inductance. Seemed like a
heck of a lot better than spending the cash for a welder
(even though I'd
love to have one!).

I took this a step further and decided to cut a good
variac and convert it
to a limiter since I picked it up pretty cheap. I
removed the core and set
it in a gravity band saw. I sawed a gap right in the
center of that 2 inch
gap between winding ends holding the connection plate
out of the way. It
took quite some time to saw through the core. I then
superglued a piece of
mylar into the gap and reassembled the variac. I hooked
it up to a jacobs
ladder and tested it. It worked GREAT! This was a 20A
variac. Unfortunately
I goofed and shorted it while running my coil (another

Today, I picked up a big 30A variac for $35.00. I did
the same modification
to it today. This variacs core was different than the
first. The first was a
solid core. This core was made of several layers of flat
bands (interesting
approach). Tonight I hooked it up and it ran GREAT!.

These are kind of nice. Hook up is simple. It's placed
in series with your
input. The reason to cut a gap in the core is to prevent
the core from

As far as size for 2kva, I would probably go with a 20A.
I'm using the 30A
on my 10kva. Whatever you do, don't go to low on the
inductance setting.
zap! You'll know it when you hear that groaning 60Hz
hum. Amazing how loud
that can be! I hear it's a good idea to throw some
resistance in series with
it and something I plan to add. This may also help
prevent the failure that
I obtained on my 20A.

Hope this helps,

Tesla List wrote:

> ----------
> From:  Basura, Brian [SMTP:brian.basura-at-unistudios-dot-com]
> Sent:  Thursday, April 09, 1998 1:28 PM
> To:  'Tesla List'
> Subject:  Help modifying a variac?
> Hello,
> Does anyone have directions on modifying and using a variac (cutting the
> core) as a current limiter?  Also, what size variac would be needed for
> a 2kva potential transformer.
> Thanks,
> Brian B.