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Re: Bumping above 40%

Richard Hull said to ED:

> I have never heard of anyone paralleling the resistance with 
> the inductance! Wow. maybe you have discovered something.  
> Perhaps your welder is enough ballast by itself.  I would tend
> to suggest that the resistance must be in series with the 
> limiter inductance.  Otherwise you are effectively shunting 
> it out.  If your system is working fine, don't try and fix 
> it!!!!

Then Bert:

> I had always put my resistances in series with my inductor as 
> well, but I tried the parallel method as well on a medium size
> coil on a 5 kva pole pig. I used a Lincoln cracker box welder 
> and a 10 kw heater array in parallel with the welder.  I am 
> _very_ pleased with the result.  No "bumping", and my sparkgaps
> have never sang a clearer song!

I third this motion. I have been running resistance in parallel
with the inductor for some time, and I too am very pleased with
the results. The resistance vs. inductance must be balanced off
a bit, but I feel it is much less of a hassle than trying to sort
things out when the resistance is placed in series. The parallel 
method gets the current through without a lot of fiddling around.
I am using about four times the resistance value (in ohms) placed
in parallel with the inductive control reactance when compared to
what Richard Hull is using in series. While any resistance placed
in the control circuits is going to waste some energy as heat, I
don't think I am getting nearly the resistive heat loss that I
get when I place a much lower value resistance (in ohms) in
series with the control reactance. 

With the resistance in parallel, the inductive delay and normal
surging encountered with purely inductive ballasting is virtually
eliminated. The bumping problem I was having when the inductive
ballasting was opened to about 20 amps dissappeared when I placed
the resistance in parallel and reduced the amount of current
flowing through the inductive reactance. Messing around with this
in the last few weeks has led me to believe that there very well
may be some 60 cycle resonance establishing under certian
conditions in my control circuits. 

One inductor that people have consistantly ignored while dis-
cussing this problem is the distribution transformer outside that
is supplying the lab with 120/240. In my case the supply trans-
former is a hefty pad mount puppie with no visible rating plate,
but it looks like it weighs a couple of tons if the hard points
for lifting it are any reliable gauge. I would be curious to know
more about this unit, but it is unrealistic to think I could ever
get it isolated for measurement and diagnostic work. Suffice to
say simply that this inductor is large, and should not be ignored
when considering problems such as bumping in the coil control
circuits. 


Comments welcomed.


Richard Quick


... If all else fails... Throw another megavolt across it!