I have seen a bit of banter back and forth about various
transformers for Tesla coils. Neons, ganged microwave,...
and my all time favorite, THE POLE PIG!
I am a pig coiler, but I have fired Tesla coils and Jacob's
Ladders with just about every combination of jury lashed high
voltage power supply that you can think of.
And do you know what? After running a pole pig for the very first
time, I knew I would never go back. Not for serious lab coiling
anyway. There are so many advantages to pole pig power supplies,
that after a couple of years of running them I have accumulated
several of these commerical, oil submerged, power distribution
transformers; and I have let my neon banks rust. Pole pig xfmrs
offer what I am looking for: economy, reliability, safety, and
the ability to operate at varying power levels.
Now if you are a tabletop coiler you could have stopped reading
after "OK, everybody...", but if you fire, or plan to fire, six
inch diameter coils or larger, and you plan to peak these systems
out, then hear me out on this. I know what I am talking about.
First let's talk about economy, where I put the pole pig at the
top of the list. The shell wound cores on these transformers are
designed and constructed with commercial efficiency in mind, and
nearly every watt put in comes out. In normal operation, and as
Tesla power supplies, they do not get hot (they stay cold when I
use them), and they do not saturate. In addition to the economy
of operation, they are cheap to purchase; the local neon whole-
saler here in my town prices a 15,000 volt 60 miliamp neon, new
out of the box, at over $200.00 (US). Yet I have never paid over
$220.00 for a new 10 KVA pole pig; that is including shipping on
a surplus, never connected xfmr. Call my friend Larry J. Rebman
at the Transformer Bank and get a quoted price (including the
shipping!) faxed to you, and you'll see what I mean.
> Larry J. Rebman
> The Transformer Bank, Inc.
> University Technology Center
> 1313 Fifth St. SE
> Minneapolis, MN 55415
> Tel: (612) 379-3958, Fax: (612) 379-5962
What about the time in wiring up banks of smaller transformers?
In an enviroment where spare time is tight, a pole pig connects
and disconnects in seconds.
Next let's talk about reliability. Pole pigs, quite simply, are
virtually indestructable. The windings typically don't: short
out, break, melt, or carbon track. You can run them three times
over the plate rated output with duty cycles up to 20% and they
STILL don't get hot. They are highly impervious to RF and kick-
back from the Tesla tank circuit. Or, to put it another way, you
can't find a more reliable transformer to power your Tesla coil.
Next on the list is safety. Pole pigs safe? You bet! First and
foremost people respect the pole pig because these transformers
just look mean. The appearance alone intimidates many coilers
from even thinking about using one, and the tendency for those
who do use them is to check things twice before they throw the
switch. In my opinion, respect is the first line of safety. But
the pole pig promotes safety in another way as well: they are
easy to wire and built with plenty of reserve insulation on both
the low and high voltage sides of the windings. These trans-
formers are equipped with heavy, plated bronze, bolt terminals.
There is no need to "jerry-lash" several different transformers
together to work up the proper voltage and amperage. One or two
pigs can be connected up with heavy cable that is well separated
and securely clamped to commerical grade insulated terminals.
They make an unsafe "lashing-up" with crossed or grounded wires
difficult to accomplish.
There is not really a whole lot I need to say about the ability
of the pole pig to boost power levels. These transformers do
require current limiting and actively quenched gaps, but once
you assemble these essential componets "the sky is the limit"
on your power levels.
Then I hear people crying in the back of the room.
"I don't need 15 foot sparks!"
Then you simply limit down. If you put a 1000 watt toaster in
series with your pole pig's 240 volt winding, you are not going
to pull down the entire neighborhood through your breaker box;
and you are not going to get more than a few feet of spark off
the coil discharge terminal either. But when you want to really
peak out that 6" inch coil, or you just get done winding a brand
new 8" coil... All you have to do is head down to the appliance
junk yard to salvage six or eight Magic Chef oven elements.
Or do what I did, and place a variable shunt electric arc welder
in series with the pole pig primary when running larger coils,
and run a few (paralleled) oven elements in series with the pig
primary on the smaller (6") coils.
So you have decided to maybe look at a pole pig? There are
thousands of configurations to choose from, and custom units can
be made to your specs, but basicly look for: Two high voltage
bushings, no taps, 120/240 "secondary", and a minimum of 14kV on
the "primary". Err on the side of higher voltage rather than
lower. My first pig was rated for 22890 volts across the two high
voltage bushings, a little high for most, even after the current
limiting reduced the maximum obtainable voltage to right around
20kV. But then again I knew I needed 20kV, whereas most people
will do fine with between 12-16 kV rms into the Tesla Tank
circuit. I would recommend you choose no less than a 14kV plate
rating across the two high voltage bushings for Tesla work.
Oh, and a few parting thoughts after reading about ganged
microwave xfmrs dimming the house lights...
Before I set a high voltage power supply up on a coil, I always
jury-lash up a Jacob's Ladder to test the power supply perform-
ance and reliability. If I cannot control a smooth arc of high-
voltage between the rails on a Jacob's Ladder... then I would
forget even attempting to use the power supply on a Tesla coil.
One of my most useful tools in de-bugging power supplies is a
power cabinet with voltage controlling variac(s). The cabinets I
wire have an ammeter and two voltmeters (one before the variac &
one after) to monitor the line voltage and transformer draw. I
always make sure that the line draw is in accordance with the
rated (and expected) output of the 60 cycle step up transformer
in testing before I connect it to an oscillator tank circuit.
Nuff said for now?
... If all else fails... Throw another megavolt across it!