RE: The "second pig" ballast: Questions.

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "J. Aaron Holmes" <jaholmes@xxxxxxxxxxxxxxxxxx>


I'm sure I've got more than enough cross-sectional
area, since this thing comes from a 15kVA transformer.
 I'm mainly wondering why the LV winding pulls only an
amp with 30 or so turns...?  That makes me think 150
would be *way* too many turns, since I want the thing
to pass around 20A at 120V.  To be clear:  It is *not*
an "EI" core, but rather two "spools" of steel sitting
side-by-side.  It looks like an "EI" core only in that
it has two "windows", where many modern pole
transformers only have one.  This one comes from a
Westinghouse 14.7kV 15kVA transformer dated 1963.
It's an oldie.  Does this sort of core have a much
greater permeability than a core made of discrete E's
and I's?

It just doesn't add up (to me), which probably means
it's time for bed :-)

Aaron

--- Tesla list <tesla@xxxxxxxxxx> wrote:

> Original poster: "david baehr" <dfb25@xxxxxxxxxxx>
>
>
> I have a book on how to make your own arc
> welder,.....it states you should
> have 2.5 sq. in. of core for every 1000 watts . I
> made my own ballast on an
> E I core with a 8 sq. in. center leg area, with 150
> turns of #12 high temp
> mag wire. I run up to 3kva, works good,..could go
> higher I think.Its got a
> range of about 6amps and up.........adjusting the
> air gap bettween the Es
> and Is
>
>  >From: "Tesla list" <tesla@xxxxxxxxxx>
>  >To: tesla@xxxxxxxxxx
>  >Subject: The "second pig" ballast: Questions.
>  >Date: Sun, 06 Feb 2005 16:41:31 -0700
>  >
>  >Original poster: "J. Aaron Holmes"
> <jaholmes@xxxxxxxxxxxxxxxxxx>
>  >2)  If using the old LV windings sounds like a bad
>  >idea, about how many turns will I need to rewind
> the
>  >core to about 15mH?
>  >
>  >Curiously, I see some old posts where people have
>  >suggested using 200+ turns of wire on an ?EI? core
>  >with a 16-inch-square center leg.  That seems like
> an
>  >awful lot of turns, considering that the LV
> windings
>  >on my transformer (with a 24-inch square core)
> consist
>  >of only a *few dozen* turns each.  On top of that,
>  >when I drop 120V across one of the LV windings on
> an
>  >almost identical transformer (with the HV side
> open),
>  >it only wants about an amp.  So the ?200? figure
> would
>  >seem to be off by an order of magnitude?I must be
>  >missing something, but what is it?
>  >
>  >Many thanks,
>  >Aaron
>  >
>  >
>
>
>