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Re: More Tuning/Debugging


Richard Quick said:

> To bring the "bumping" and
> "spiking" under control with resistance means giving up the
> 14,400 volts output, the whole purpose of running with the
> overvoltage in the first place.
> 
> This is perhaps compounded by the huge amount of inductance in
> the system. Locally, if you start with the 50KVA pad mount
> transformer that supplies my house (and a few neighbors), then
> add in the arc welder, 60 amps worth of 240 volt Powerstats, and
> 25KVA worth of pig, we are talking about some serious inductance.
> The actual delay as measured on a stop watch exceeds 1.5 seconds
> from the time the welder is opened up to the time spark leaves
> the discharger on a coil. We are talking real horsepower tied up
> (hopefully tied up) in magnetic field flux throughout this power
> supply. 
> 
> Just the right amount of resistance can get things working pretty
> well, but the balance is precarious at best. Any substanial
> altering of the system inductance, either in the current limter
> or voltage setting on the variac, throws everything out of wack.
> This is rather frustrating because not only do I love smooth
> systems, but I have too much invested in my power control/supply
> to want things welded up into a useless mass. This would also
> appear to be a handy way to lose a few line filters.
> 
Ed:
>Good discussion.  I am convinced I am experiencing somewhat the same problem.
> I don't know if I am saturating the pig or not, but my system is certainly
>shaky right now and I don't like it.  I like things to be well ordered and
>predictable.  Right now, sometimes my coil will run and sometimes it won't.  
>
>I have noticed the welder really growls now that I am operating with no
>resistance in the system.  The pig is a few feet farther away but I think it
>is also making noise.

For a neon based system I can show that bumping is a beat frequency
between the resonant frequency of the neon's leakage inductance and
the TC's primary capacitance with the line frequency. I would expect
that this result in current surges in the variac but I have not taken
my spice simulations that far.

With an externally ballasted system, this effect is between the
ballast inductor and the primary capacitance and probably between the
PFC and the ballast also.

However, given Richards 1.5 second delay factor, I would look for an
interaction between the PFC caps and the ballast and variac also.
Try removing most of your PFC caps and see if there is a significant
change in the time constant or behavior of the system. Don't remove
all of the PFCs because they prevent the voltage spikes from the
ballast from blowing your RFI filters and home electronics.


Another thought: try running with just resistive ballasting. This will
eliminate the major resonance producer in the mains circuit and its
voltage boosting effect. I would guess that you will have little or no
firing of you spark gaps. If so, You are relying on the flyback
voltage boost from your ballast as a major voltage booster in the
system. While this effect produces spectacular results when it is
tuned, it can be quite sensitive to system changes. Ed appears to have
lost this tune just by rerouting his TC primary wiring. 

Just resistive ballasting will also show the effects the ballast
inductor plays in quenching the spark gap. I can throw arcs completely
around my 8" rotary gap using this method.


	Regards,

	jim