[TCML] Taming the Beast: Inductive Ballast vs. Variac, PFC

Jeremy Scott supertux1 at yahoo.com
Sun May 25 22:12:52 MDT 2008

```Hello Coilers!

I'm getting back into the 'hobby' after a few years of
being out. A little rusty on my theory and math. I've
accumulated some stuff since then and would like to
build another coil using some parts from my old coils.

At the heart of my system is a 3KVA GE Potential
Transformer.

Most of the things I'm confused about is how to build
the proper controls to tame this thing without blowing
breakers.

INDUCTIVE BALLAST:

In the past I've used a 500 foot 12 gauge wire spool a
la Home Depot. The problem with this is that the heat
it generates almost melts the spool it's on. I think
this is because there is no cooling for all but the
outer layer of wire.

I'd like to build a more robust and controllable
ballast.

My idea is to wrap the 500ft of wire around a PVC pipe
of a diameter that is the average (half) of the
spool's diameter and then slide a chunk of metal in
and out of the pipe to control current. That half
diameter thing is just a guess. I have no idea what
the reactance
of the spool is or how to recreate it in a more
using common parts.

I'm also scared of turning my coil on full blast
instantly. In the past I've used an expensive variac
to dial the voltage up and look for problems, unwanted
arcs etc, but I think it would be better to control

I guess I'm looking for something that will limit up
to 20A, so I can get all that the outlet will give
without tripping a breaker.

POWER FACTOR CORRECTION CAPS:

Making the most of what I can get from the wall, I've
got 6 oil filled 'can' capacitors wired in parallel
across the primary. Each is 100uF @ 370VAC. I'm not
sure if this is correct, I don't know the reactance of
the transformer's primary to apply a formula. I did 6
by trial and error, monitoring the current pulled from
the outlet for the lowest value. It's probably
completely wrong but it doesn't blow the breaker. :)