Re: Homemade Trasformer

To: tesla-at-pupman-dot-com
Subject: Re: Homemade Trasformer
From: "Ed Phillips" <evp-at-pacbell-dot-net> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
Date: Mon, 21 Feb 2000 19:22:03 -0700
Approved: twftesla-at-uswest-dot-net
Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme

Tesla List wrote:
> 
> Original Poster: "ross andrews" <sflourine-at-home-dot-com>
> 
>         Nick,
> 
>         Thanks, I understand now -- What I plan on doing is building my own
> 24kVA tranny (I couldn't leave the 240V, 100A service feeder in the
> garage alone :P).  I came up with 14^2 in. when I calculated the
> magnetizing current.  If my primary has 120 turns at 240v/60Hz, this
> gives the flux density as 7.5E+05 lines - since the maximum flux density
> of steel is, conservatively, 55 kilolines/in^2, this gives the core size
> at 13.6, or 14^2.  I don't know how to calculate the maximum current
> this tranny is capable of, only  that dad said i'd blow every breaker
> from here to Cancun before i saturate a core like this.  [All this seems
> to say that you actually can't build a 240v tranny with a smaller core
> unless you use more turns on the primary -- is this right?]  For the
> secondary, I plan on 6,000 turns -  for the core I'm planning on many
> pieces of 1/4" barstock each covered with formvar or something suitable
> and then wrapping the primary around a suitably sized bundle of these,
> and the secondary over the primary.  Though I seem to recall posts to
> the contrary, I, myself, see no problem in using a cylindrical core as
> opposed to a toroidal or square core -- is there?
> 
>         <<sorry for the long post>>
> 
>         Any comments appreciated,
> 
>         Ross

Ross:

	That's a mighty big core; wonder where you are going to get it.  You're
correct in that the required number of turns per volt varies inversely
as the area of the core.  Another point is that steel bar stock won't be
any good at all due to excessive losses; you need a good laminated
electrical steel core.  Finally it sounds as if you mean to build an
"open-core" transformer without a return magnetic path.  If you do that
you'll probably have enormous magnetizing current, as the transformer
inductance will be pretty low.

Ed