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The "second pig" ballast: Questions.

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

I recently began the despicable chore of unwinding a
15-kVA pole transformer so the I can put its core to
use in a ballast.  The high voltage coils are all gone
and only half of the low voltage coils remain.  The
core consists of two separate ?spools? of steel (not
E?s and I?s, although the whole core has two ?windows?
like an ?EI? core), and won?t come apart in any way
which might make winding easy.  Bummer.  So before I
cut the last of the LV coils off, I have a few

1)  Can I simply tap the remaining coils and use them
instead of rewinding the thing with insulated wire?
The coils are made of copper strap painted with
insulating varnish.  I was hoping that, with the HV
coils gone, I could run this without oil.  Can I?
What do people think?  Is the varnish going to be good

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,