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

In a message dated 4/28/00 10:45:25 PM Pacific Daylight Time, 
tesla-at-pupman-dot-com writes:

> 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.

Hi Ed,

OK, so the welder was infinitely variable, and had a wide inductance 
range.  Did you ever use the welder with the .05uF cap, or only with
the .025uF set up?  I'm thinking maybe that made the difference....
the cap size?  I'm still having trouble seeing what the difference would
be between a welder and a variac if they both have the same inductance
(other than saturation issues that is).  Maybe the welder inductance
did not go low enough?  I'm wondering if the improvement you're seeing
is due to the larger caps, not due to the use of the variac.  Although it
is possible that when you added the larger caps, you no longer had
enough inductance range in the welder.  A different sized cap, requires
a different amount of inductance.  Also, for a given total power and 
spark length, a larger cap will not need to charge up to as high a
voltage assuming the break rate is still the same, so this in itself
would keep the cap voltage lower, etc.

I think the variac has a lot of inductance for its size because the
toroidal core shape really does a good job of containing the 
magnetic flux.

Cheers,
John Freau

>  
>  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
>