Re: Transformer core

To: tesla-at-pupman-dot-com
Subject: Re: Transformer core
From: Finn Hammer <f-hammer-at-post5.tele.dk> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
Date: Wed, 06 Oct 1999 07:58:34 -0600
Approved: twftesla-at-uswest-dot-net
Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme

Not that I am a transformer "expert", but I have done this, so here
goes:

The size of the core suggests, that 1 turn per volt would be suitable.
So choose a wire that will fill the window out, with as many turns as
you have voltage across terminals. 

This will produce a choke that has as much inductance as the primary of
your pig, when it is unloaded. Put it in series with the pig, and when
you try to draw power from it, the voltage will shift from the pig`s
primary to the choke.

Stack the E`s together, and the I`s together, and insert spacers btwn
the them  to create an airgap. This reduces the inductance of the choke,
and allows current to flow after all.

  +--------------------------------+
  |                                |
  |                                |
  |                                |
  +--------------------------------+
                                      <---  Spacer
  +-----+ooooo+-------+ooooo+------+
  |     |ooooo|       |ooooo|      |
  |     |ooooo|       |ooooo|      |
  |     |ooooo|       |ooooo|      |
  |     |ooooo|       |ooooo|      |
  |     |ooooo|       |ooooo|      |
  |     |ooooo|       |ooooo|      |
  |     +-----+       +-----+      |
  |                                |
  |                                |
  |                                |
  +--------------------------------+

With a choke designed like this, you will be able to controll the
current very well: No spacer and you have a neon equivalent, thick
spacers and you have as much current as the pig can deliver.

A little experimenting is required to determine the desired thickness of
the spacer, but that is all.

Hope this helps.

Cheers, Finn Hammer

Tesla List wrote:
> 
> Original Poster: "Matt Behrend" <electronxlc-at-earthlink-dot-net>
> 
> Hi all,
> 
> I have a large transformer core that I want to wind for my inductive
> ballast - 13mH.  It must handle 3kVA without saturating, so could
> some of the transformer experts tell me if my core is large enough,
> and minimum number of turns required?
> 
> Overall dimensions are 7.5" x 6.25" x 2.5"
> cross sectional area 1.25" x 2.5" on perimeter sides and 2.5" x
> 2.5" in center leg of the El  shape.
> 
> This is from a 1kVA Topaz isolation transformer, but the size of the
> core seems like it can take much more power.
> 
> Matt Behrend