Ballast Resistance For Pig Coils (fwd)

["Tesla list" <tesla@xxxxxxxxxx>]

---------- Forwarded message ----------
Date: Fri, 26 Oct 2007 17:41:37 -0700 (PDT)
From: Yurtle Turtle <yurtle_t@xxxxxxxxx>
To: tesla@xxxxxxxxxx
Subject: Ballast Resistance For Pig Coils

What size resistance are you folks using inline with
ytour ballast for their pig powered coils to prevent
"thumping"? I decided to tune up my coil this evening
in preparation for Halloween. I recently started using
two slide inductors instead of my welder. This evening
all was running well, as I slowly cranked up the amps.
As I got to around 25 amps, the actuator motor died on
my Powerstat stack. I replaced the fuse, and it blew
again. I decided to set the voltage, then remove the
fuse, to keep from risking damage to the stepper
controller board. As I continued to run, I heard
several hard thumps from my powerstats. I quickly
turned up the breakrate, which solved the problem.
However, I noticed that the line in to the Powerstat
actuator had flashed over to the chasis. Apparently I
am getting some nasty spikes that I hadn't experienced
with the welder.

I know folks have advocated using resistance in line
with their ballast. Is there a way to calculate what
resistance is effective at certain configurations, or
is it more trial and error?

The reason I'm concerned is I don't want to blow up my
Powerstat actuator or my VFD.

I have EMI filters between my incoming power and my
pig/ballast, but maybe I should consider something for
voltage spikes. While a spark gap for 120/240 sounds
silly, and hard to set, the 120 volt input to my
actuator jumped 1/8" to the grounded chasis. Without
having access to some kind of power monitor, I
wouldn't know if MOV's would last for years or
seconds.

http://www.hot-streamer.com/adam/bigass_coil/schematic.pdf

thanks
Adam

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