Re: variac ballasts

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

Original poster: "BunnyKiller by way of Terry Fritz <twftesla-at-uswest-dot-net>" <bigfoo39-at-telocity-dot-com>

Tesla list wrote:

> Original poster: "Oxandale, Terry by way of Terry Fritz
<twftesla-at-uswest-dot-net>" <Toxandale-at-SPP-dot-org>
>
> I've tried to follow any strings about the variacs being used as
> ballasts, and have a thought I'd like to throw out to you guys. My
> interpretation of the data so far is that my 1256's have a core too
> small to be used effectively as a ballast (or too few turns?)for a
> 240vac supply. I only use about 40% of the windings in the single variac
> ballast mode. I reasoned that with 2 in parallel, they would work better
> because more of the winding would be used on each variac (half the
> impeadance so more winding needs to be used, leaving less turns on the
> open end), but the improvement was insignificant. It still appears the
> cores are saturating. I am currently using a 14.4kv pig set up for
> 240vac input. If I was to re-wire the pig (parallel the two separate
> primary windings) primary for 120vac in, 14.4kv out, then use only
> 120vac on the ballast variacs, would this not be a "step" in the right
> direction toward eliminating my core saturation problem? My thoughts are
> that the open end of the variac will see a much lower voltage (closer to
> the 280vac specs for the 1256) and thus I may avoid the perceived
> problem of turns/volt (is this correct?) for this small cross section of
> the variac core. If I am correct in reading these strings that high
> voltage is a culprit in saturation for a given size of core, would my
> reasoning be flawed here? Thanks.
>
> (Un)Terry

Hi UnTerry...

to start  if you were to rewire the innards of the pig for 120V operation
then you would see only
7200V out, AND still need to feed the pig double the amps ( minimum but
most likely 4X) to see the
same "action" you were previously seeing.

when using variacs as current limiters one must be careful not to bring the
"wiper" down too close to
the input wire. ( this is like turning the rheostat resistance to zero,
thus lotsa amp flow and fried
variac.)

cores saturate thru the effects of VA...  you can run a lower voltage,
true, but the needed increase
of amperage will reintroduce the saturation.

Scot D