Re: The "second pig" ballast: Questions.

["Tesla list" <tesla@xxxxxxxxxx>]

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

Correcting one thing:  I've said "inch square" when I
meant "square inch" (cross-sectional area) :)  No, I
don't have anything quite as large as the original
mail suggests!! :)

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

> 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
> questions:
>
> 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
> enough?
>
> 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
>
>
>