Re: Luxtrol 45A 240V variac as ballast--cutting up core?

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Randy Turner" <toxandale@xxxxxxx>

I've split a couple of 1256 cores using a sawzall (used two or three good
quality blades per core). I fabricated miniture clamps (using 1/2" square
steel tubing and 5/16" all-thread) and placed them on both sides of the
intended cut zone, tightened them up (which kept the core compressed as I cut
through the wound strap used to make up the core). The key to all this was
keeping the core rigid and well supported so that it would not fall apart
(unravel) as the core was cut. When I finished splitting the core, I filled
the gap (about .100") with a high quality epoxy. After the epoxy cured, I
removed the clamps and reinstalled the parts of the framework that was
removed to gain access to the core. I had tried the "doubling stacking"
method in hopes to alleviate the saturation (I tried both parallel and
series), but to no avail. After testing the split core, I was so happy with
the saturation problem being licked, plus the added "modulation" gained as
well, that I went ahead and split a second one for added current capability.

Terry


On Tue, 27 Sep 2005 13:38:21 -0600, Tesla list wrote
> Original poster: "J. Aaron Holmes" <jaholmes@xxxxxxxxxxxxxxxxxx>
>
> Thanks all for the help!  I actually did put the thing
> in series with the resistor last night and was making
> ready to try it when I got called away and didn't end
> up coming back.  I'll try it (hopefully tonight) and
> see how it does as-is.
>
> As for getting an arc welder, I've always had an eye
> out for a good deal.  < $100 would be great! :))
> Getting a new one at Home Depot is not in the cards,
> I'm afraid.  Not, at least, if used purely as a
> ballast :)  Although, if used in series with a
> resistor, one of these newer Lincoln units with taps
> (that you can't change while it's running) would be
> ok, since you'd just be using the welder to establish
> the maximum current, and the resistor for soft
> starts/stops.
>
> Using a contactor to short across the resistor when
> it's at its lowest resistance setting is also a good
> idea.  I'll probably give that a shot, too (not that a
> little warm water is bad :))
>
> Thanks again,
> Aaron
>
> --- Tesla list <tesla@xxxxxxxxxx> wrote:
>
>  > Original poster: "Barton B. Anderson"
>  > <bartb@xxxxxxxxxxxxxxxx>
>  >
>  > Hi Aaron,
>  >
>  > Congrats on the variac! But, if it's a 45A variac, I
>  > wouldn't
>  > recommend cutting the core unless you actually begin
>  > to run into
>  > saturation (and then I'd recommend a double stack).
>  > I did cut the
>  > core in my variac, but only because it is a single
>  > 28A variac
>  > ballast. I did this early on, not realizing that I
>  > should have just
>  > picked up the other 2 variacs (which were only $45
>  > ea). Yep, live and
>  > learn. If I had it to do again, I wouldn't. You may
>  > want to sell it
>  > someday and it would be best to sell it without a
>  > slit core.
>  >
>  > Take care,
>  > Bart
>  >
>  > Tesla list wrote:
>  >
>  > >Original poster: "J. Aaron Holmes"
>  > <jaholmes@xxxxxxxxxxxxxxxxxx>
>  > >
>  > >Hey folks!  I recently acquired a Luxtrol 45A 240V
>  > >variac.  I'd like to make it a ballast for a pole
>  > >transformer, and I'm wondering if somebody could
>  > share
>  > >an experience:  How shall I go about putting a gap
>  > in
>  > >the core?  About how wide should the gap be?  I'm
>  > >thinking of trying to coerce a machinist friend
>  > into
>  > >helping me, since I'd like to avoid hours of hack
>  > >sawing by hand! :)
>  > >
>  > >And one related question:  I recently built a water
>  > >resistor (20 gallon garbage can full of doped water
>  > >with copper rods immersed about 1/8th inch apart,
>  > >sliding PVC sheath over one rod to control
>  > resistance)
>  > >and have used this to create some nice 20+kW
>  > Jacob's
>  > >ladders.  It's obviously quite lossy, but the nice
>  > >thing is that I can ramp the current down to near
>  > zero
>  > >before cutting the power, thereby avoiding big
>  > >inductive spikes.  To avoid forfeiting this
>  > "feature"
>  > >of the resistor while deliberately forfeiting most
>  > of
>  > >the losses, I thought perhaps that I'd put the
>  > water
>  > >resistor in between the modified variac and the
>  > pig.
>  > >The resistance can then be slowly brought down
>  > until
>  > >the majority of the limiting is being done by the
>  > >variac (resistor varies down to about one ohm).
>  > This
>  > >would seem to offer the low losses of an inductive
>  > >ballast while simultaneously allowing nice soft
>  > stops
>  > >and starts.  The variac would just be preset to the
>  > >desired operating current and then left alone.
>  > >
>  > >Thoughts on this?
>  > >
>  > >Aaron
>  > >
>  > >
>  > >
>  > >
>  > >
>  >
>  >