Re: Variac setting (Was Rd: Rotaty popping)

> Original Poster: Esondrmn-at-aol-dot-com
> Bart,
> I measured my ballast variac last night.  It is made by Luxtrol, says
> Control on it, max 41.6 amps (says to fuse it at 50 amps).  It also says
> taper wound - which is odd, I don't see any taper to the core or the
> windings.  It is however very non-linear.  The maximum inductance is 54
> The point where I had it set was only 5 mh.  Now I find it really odd that
> trying different settings (probably over a range of 3 mh to 30 mh)
> to show no difference in coil performance.  There is something to learn
> but it isn't real obvious to me.  It seems that some inductance is
> but the actual amount used is not critical - and why do welders seem to
> problems that variacs don't?  I even measured the inductance of the welder
> that I originally used and remember it to be in this range.
> Ed Sonderman

Ed, all,

Let me throw in my 2 cents:
Today I checked the inductance of my welder, (old Sears 185A model). This
welder is a infinitely variable type with  front panel  high and low range

With low range selected minimum inductance measures 18.8mH, (moveable core
out). [Best performance].
With low range selected maximum inductance measures 40.8mH, (moveable core
With high range selected minimum inductance measures 11.1mH, (moveable core
With high range selected maximum inductance measures 20.9mH, (moveable core

My coil, (14400V, 5kVA pig, 120bps srsg and 0.058uF tank cap), runs best
with the welder set on low range, minimum inductance, (18.8mH), and no
series or parallel resistance added. If I select high range and adjust the
variable core to 18.8mH, (the moveable core is about 80% in), I would expect
the coil's performance to be the same, but it isn't. The coil performs
worse. It takes a higher input voltage to achieve breakout, and the sparks
are just not as powerful. I am pretty sure that when the welder is on high
range with the moveable core in I'm not getting as much "kick" out of the
welder ballast even though the inductance is the same as on low range. I
would say that my coil is more "lively", or "springy" with the moveable core

The above and other comments in this thread makes me wonder if somehow the
amount, (or mass),  of steel in the ballast core is causing our coils to
perform differently depending upon our use of  different makes of welders
and/or variacs for current limiting? Wouldn't a more massive core change the
natural frequency of the inductor?  Or could the mass of the core affect the
"damping", (is the correct term hysteresis), of the inductor? I know that on
my system when the welders moveable core is in it gets quite hot, so it must
be sucking up some power. When variacs are used as current limiters do they
get hot? Probably with a variac it would be difficult to determine if the
wire or the core was getting hot.


Jon Rosenstiel