Re: Ballast

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Esondrmn-at-aol-dot-com>

In a message dated 2/15/02 2:36:28 PM Pacific Standard Time, tesla-at-pupman-dot-com
writes:

I have to reply to my own post here.  Robert is correct.  I thought these cores
were powdered or sintered ferrite.  This one is not.  It is made as Robert
describes, one piece of thin steel wound tightly over itself until it is 1.1"
thick with a 1.8" diameter hole in the center.
Ed Sonderman

>
> I have used old variac cores just as you intend with no cutting. I think you
> should have room for 80T if you overlap your turns. I never throw those
> cores away. They are to good. They are made of wound iron strapping not
> ceramic solid so I dont think you want to be cutting them.
>    Robert  H
>
> > From: "Tesla list" <tesla-at-pupman-dot-com>
> > Date: Fri, 15 Feb 2002 13:10:39 -0700
> > To: tesla-at-pupman-dot-com
> > Subject: Ballast
> > Resent-From: tesla-at-pupman-dot-com
> > Resent-Date: Fri, 15 Feb 2002 13:14:22 -0700
> > 
> > Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> > <Esondrmn-at-aol-dot-com>
> > 
> > I currently use a 5,000 watt variac for ballast for my coil using a 5 kva
> > 14,400 v transformer, normally running at about 30 amps.  I can hear this
> > variac groan sometimes and suspect I might be into saturation - and I don't
> > want to cut the core.
> > 
> > I recently came across a 7.5 amp Powerstat variac that has burned windings.
> > I stripped them all off and am considering slicing .25" out of the core (
> to
> > allow ease of winding and prevent saturation) and winding it with insulated
> > #8 house wire.  If I have enough room to overlap the inside windings, like
> > the variac manufacturers do, I could get about 68 turns of #8 wire on
> there.
> > Reality might be 40 to 50 turns.
> > The core weight about 6.5 lbs.  It is 3.0" tall, 4.0" wide with a 1.8"
> > diameter hole through the center - i.e. the sides are about 1.1" thick.
> > After winding I would epoxy a .25" thick piece of phenolic back into the
> core
> > to give structural integrity again.
> > 
> > Does anyone think this might work as a 30 amp ballast?  What might the
> > inductance be?  I see where Jim Lux supplied a formula of L = k * N
> squared.
> > Is k permeability?  If so, what is the k of this material likely to be?  I
> > would think that we would need to account for the core area and the
> > permeability of the material.  The core is 1.1 x 3.0 which would be 3.3
> > square inches times maybe a 10.0" winding length would be 33 cubic inches.
> > 
> > I do need some help here.
> > 
> > Thanks, Ed Sonderman