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Re: Welders vs. Variac ballasts, was Rotaty popping, (Was Re: comm

In a message dated 4/28/00 4:13:35 AM Pacific Daylight Time, tesla@pupman.com 
writes:

<< 
 Why should the variac stop the unwanted resonances?  Was your welder
 the infinitely variable type, or the stepped adjustment type.  If you had the
 stepped type, then I can understand that you may not have been able to
 obtain exactly the right amount of L.  But with the infinitely variable type
 you would have ..... unless .... maybe the welder did not have enough of
 a range of inductance ??   Maybe you would have needed to use 2
 welders in series?   Or maybe the L of the welder did not go low enough?
 Many questions.
 
 >  My original configuration with the welder and using 
 >  about 1.5 ohms of series resistance also seemed to run better at lower 
 > welder 
 >  settings, which would be with higher inductance.  I haven't measured the 
 >  inductance of the variac, but I would guess from looking at it that it 
 would 
 > 
 >  be considerably less than the welder.
 
 I think that variacs have a surprising amount of inductance, more than
 one would think by looking at it.  Another question....  Does the TC still
 draw the same total current now compared with the original set up using
 the welder... for the same spark lengths?
 
 Cheers,
 John Freau >>

John,

The welder that I was using was a Miller Thunderbolt with the crank on the 
top - infinitley variable.  It is rated at 240 volts 45 amps.  The secondary 
is rated at 230 amps.  I can't find where I recorded the inductance of this 
welder, but I seem to recall others have measured them to be somewhere in the 
range of 10 to 50 mh - very similar to the range we are measuring for the 
variacs.  I agree, you would not guess the inductance from the variac would 
be as high as it is, must be a good core in those things - and a lot of turns 
on them.

The primary current draw is still the same, in the 30 to 35 amp range.  It 
does swing up and down.  The spark length comparison is not easy to make 
since I am now using twice the primary capacitance (.05 uf total) as the 
original configuration.  Also, the original configuration was not very 
stable, current fluctuated more than today, the welder growled a lot and as I 
have stated, the primary voltage was way too high due to the resonance 
problem - very hard on caps.  It is possible the spark length, with the same 
.025 uf cap, was about the same.

Ed Sonderman