Re: Request for math (ballasting) (fwd)

---------- Forwarded message ----------
Date: Fri, 17 Jul 1998 16:43:50 -0700
From: Ed Phillips <evp-at-pacbell-dot-net>
Reply-To: ed-at-alumni.caltech.edu
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: Request for math (ballasting) (fwd)

"If I understand your explanation correctly that is why people cut a
variac and use it as a variable inductor (it's then a c shaped core).  I
was going to ask if a modified 400hz variac would work as an inductor
but It would probably saturate at 60 hz."

	It is hard for me to see why anyone would ruin a good variac that way. 
Cutting that core is a bitch and, since the air gap won't change the
saturation of the iron, the resultant variable inductor will be usable
over only a limited range of inductance.  I have an adjustable ballast
choke for some kind of lamp which is rated at 2.5 or 5 amps, depending
on series or parallel connection of the windings, and is just a big E-I
core with wire wound on it and the I mounted on threaded rods so it can
be moved closer to the E or farther from it in order to vary the
inductance.  Would seem to me exactly the same principal could be
applied to a device intended to carry much more current.  Of course, the
number of turns would have to be sufficient to avoid saturation at the
maximum operating voltage.  Perhaps any big old transformer which can be
disassembled would do the trick.