Re: Finished with Isolation Transformer.

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Richard W. by way of Terry Fritz <teslalist-at-qwest-dot-net>" <potluck-at-xmission-dot-com>

Hi Steve,
That idea could work. You'll need a lot of room in the core window for the
insulation needed between secondaries, the more secondaries the more
insulation and less room for wire. Also, to be able to wire the secondaries
in series you'll also need to insulate them from the core they're wound on.
The total voltage may be a lot lower than expected due to the insulation
taking up room necessary for wire.

Unless there is a lot of room in the core window I'd try to stay away from E
and I laminations salvaged from LV high current transformers for homebrew HV
transformers because the core windows are usually too small for HV
applications. Stuffing enough insulation into the pack doesn't leave much
room for wire therefore the output voltage/current may not even come close
to the desired spec making the end product not worth the work involved. And
believe me, it's a LOT of work. And try to leave at least 10 to 15% margin
for room in the window. Winding wire and packing insulation rarely comes out
exactly as it was drawn on paper.

One observation I made that many here probably already know is that a well
designed transformer whose primary and secondary VA are equal will result in
the same weight of wire. If you use 8 pounds of one gauge to wind a primary
then to get the secondary to match VA it will also require 8 pounds of wire
of the gauge necessary to carry the desired current. An imbalance of primary
to secondary VA is simply wasted wire, work and output.

Rick W.
SLC

----- Original Message -----
From: Tesla list <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Wednesday, February 26, 2003 6:02 PM
Subject: Re: Finished with Isolation Transformer.


 > Original poster: "Stephen Conner by way of Terry Fritz
<teslalist-at-qwest-dot-net>" <steve-at-scopeboy-dot-com>
 >
 > At 07:51 25/02/03 -0700, you wrote:
 > >Original poster: "Richard W. by way of Terry Fritz <teslalist-at-qwest-dot-net>"
 > ><potluck-at-xmission-dot-com>
 > >
 > >Steve C,
 > >
 > >I tried that.
 > >
 > >
 > >Lesson learned:
 > >Be sure to wind ROUND coils for homebrew HV transformers. And use
 > >laminations to allow room for round coils.
 > >Square coils should be OK too but the idea is to be sure the forces
applied
 > >to the first few layers aren't unequal and not great enough to deform
them
 > >as more layers are added.
 >
 > Thanks for sharing your hard-earned knowledge. I didn't realise how much
 > more difficult it was to make an HV transformer compared to a LV
 > transformer with HV isolation. I was under the impression that if you were
 > able to do vacuum impregnation, and designed the HV winding to be a short
 > fat pie shape (a la MOT) so that the voltage is distributed over a greater
 > number of layers, and if you were careful to wind the layers evenly, you
 > didn't need insulation between winding layers. I've never built a HV
 > transformer, though.
 >
 > A good plan for a HV winding might be a bunch of pies, each on its own
 > thick insulating bobbin, all connected in series. It would be like four or
 > six MOTs all on the same core. You could use a core from a dead 12/60 NST
 > or something. What do you think?
 >
 > Steve C.
 >
 >
 >
 >
 >