Help modifying a variac?

From:  D.C. Cox [SMTP:DR.RESONANCE-at-next-wave-dot-net]
Sent:  Sunday, April 12, 1998 10:50 AM
To:  Tesla List
Subject:  Re: Help modifying a variac?

to: Bart

Clamp it as tight as possible and put gobs of epoxy with a 1/2 inch overlap
all around.  The tighter you clamp the core ends to the mylar spacer
(usually 0.0625 to 0.100 inch) and keep the void very tight the less 60 Hz
humming you will get.  It works great -- we used a lot of them wound with
10 AWG wire -- the peak instataneous currents will quickly overheat the
windings if using 12 AWG with a 10 kva xmfr.  Use 8 or 10 AWG and a small
blower if running longer than 60 seconds per blast.


> From: Tesla List <tesla-at-pupman-dot-com>
> To: 'Tesla List' <tesla-at-pupman-dot-com>
> Subject: Help modifying a variac?
> Date: Saturday, April 11, 1998 7:42 PM
> ----------
> 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?
> Brian,
> 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
> story).
> 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
> saturating.
> 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,
> |_Bart_|
> 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
> > core) as a current limiter?  Also, what size variac would be needed for
> > a 2kva potential transformer.
> >
> > Thanks,
> > Brian B.