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Pole Pig Ballast
Request for Comment,
Hi,
I just discovered the importance of the current limiting
ballast for a pole pig. It is an integral part of the TC primary
circuit!
For the last several weeks, I've been trying to get my first rotary
gap to work. I've been fighting, vibrating structure - shattering the
electrode supports, wide open spacing, power arcs, no arcs, and
finally very sporadic gap firing. I was ballasting my pig with various
parallel and series combinations of 10 ohms and 2 1kW shunt limited
metal-halide lamp ballasts. At best, I could get 4" sparks from 11kW
input !!!!! My pig is a Westinghouse 10+ ll-65 => 10kW 6.5kV to 220V.
I'm running 220V into the 110V tap to get about 13kV out.
Last night, out of desperation, I wound a 1.2mH air core / 9.2mH iron
core choke as a ballast. I was trying for 12mH air core to limit to
50A. I kept emptying spools of magnet wire. So I stopped at 2 layers
of 12" by 3" on a pvc former. To make up for my lack of inductance I
put 5 ohms of resistance in series: limit about 44A. For the iron
core, I grabbed some Is of a batch of EI cores that I have laying
around.
Boy, did I get a surprised when I fired her up! The input current was
only 10A, the gaps fired smoothly with no power arcing, and I was
getting 2' air discharges with NO tuning!
After playing for an hour, I wanted more power, so I removed half of
the iron core. Zip, nada, nil, nyet, nichts. Higher current, bad gap
firing, power arcing, and NO sparks!
I've concluded that the inductance in the primary circuit flysback as
the spark gap communitates and brings the power supply voltage back up
faster. Measuring the pig primary voltage with my Simpson 760 VOM
shows very little voltage difference. I blew something in my 220V
line filter network before I could scope it. However, I have run my
rotary up to 7000RPM / 1870 BPS (potential, not scoped yet) with no
change in the (visual) sparkgap operation.
Has anyone experienced this? Tried to run their pig with resistive
ballast only? Inductive ballast only? No ballast;)
Quizzically,
jim