I have a couple of Variac cores less the mechanical wipers. I was
thinking of using the Variac as the primary winding and winding the
secondary transformer over it.. I have my own ideas about how I would
procede with this starting with given the old coil a new insulting
coating, maybe Krylon HV coating . Secondary would either be wound for
540VAC or twice that. The transformer this is replacing was a 540vac
transformer feeding a voltage doubler. Any ideas and suggestions would
be greatly appreciated.

You can calculate the voltage drop of the wire in
your secondary with
the heap of a wire table.http://www.powerstream.com/Wire_Size.htm


Hey OM:

That link to that table is ok. I learned building my own transformers.
Heat is the killer of any design.

What those tables don't tell you is the resistance increase caused by
heat which turns out to be run away in cases. It's like the resistance
goes up because of heat and this creates more heat increasing the
resistance further.

Leave a fudge factor in there, use the largest size wire possible

73 OM
de n8zu.

On Apr 30, 9:02*pm, raypsi wrote:
*You can calculate the voltage drop of the wire in

your secondary with
the heap of a wire table.http://www.powerstream.com/Wire_Size.htm

Hey OM:

That link to that table is ok. I learned building my own transformers.
Heat is the killer of any design.

What those tables don't tell you is the resistance increase caused by
heat which turns out to be run away in cases. It's like the resistance
goes up because of heat and this creates more heat increasing the
resistance further.

Leave a fudge factor in there, use the largest size wire possible

73 OM
de n8zu.

Im thinking 20 gauge enameled wire mostly because I think I have a
1000 ft roll in the attic. Not at all sure how well that is going to
fit on the core. I really want to get away from the voltage doubler in
favor of a bridge rectifier so I want to wind it for 1100 volts.

Jimmie

JIMMIE wrote:
On Apr 30, 9:02 pm, raypsi wrote:
You can calculate the voltage drop of the wire in

your secondary with
the heap of a wire table.http://www.powerstream.com/Wire_Size.htm

Hey OM:

That link to that table is ok. I learned building my own
transformers. Heat is the killer of any design.

What those tables don't tell you is the resistance increase caused by
heat which turns out to be run away in cases. It's like the
resistance goes up because of heat and this creates more heat
increasing the resistance further.

Leave a fudge factor in there, use the largest size wire possible

73 OM
de n8zu.

Im thinking 20 gauge enameled wire mostly because I think I have a
1000 ft roll in the attic. Not at all sure how well that is going to
fit on the core. I really want to get away from the voltage doubler in
favor of a bridge rectifier so I want to wind it for 1100 volts.

Jimmie

You really need to do some math before you start winding wire onto your
variac core. Read the theory and do some practice exercises from the info
on these web pages:
http://how-to.wikia.com/wiki/How_to_...er_or_inductor and
http://www.howyoubuildit.com/transformer/

You have a finite winding area in the center of your toroid. Wire size will
define how many turns you can get into that winding area. You might find
that AWG 20 is way too big for the secondary voltage you want.

Cheers,
--
David
dgminala at mediacombb dot net