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

[bartb <bartb@xxxxxxxxxxxxxxxx>]

Hi Jeremy,

There are welders, variacs, and homemade pipe ballasts used for 
inductive current limiting in general. Some have also used MOT's or 
other iron core transformers. I use a variac. I would like to change 
over to an air gap ballast some day based on what Richie Burnett has 
done. It's just something to consider if you happen upon a nice core 
someday. May even spark other ideas.

Mechanically, it's a ballast with with the turns wrapped around the 
center core. The top of the core is adjustable and this is where Richie 
sets the air gap for current control. He used high density polystyrene 
to fill the gap preventing the magnetic field from collapsing the air 
gap. This is probably the best ballast idea I've seen. Anyway, you can 
see pics and read about it here. In my opinion, this is really an ideal 
ballast as it can be set for any TC transformer current (small to 
large), it's compact, and it's efficient.
http://www.richieburnett.co.uk/parts2.html#ballast

Richie was going to put together a program way back when for inductive 
ballast design, but I don't think that actually transpired. Regardless, 
Richie does have a procedure in the TCML archives which helps shed light 
on this subject.
http://www.pupman.com/listarchives/2001/June/msg00744.html

Richie Burnett's web pages in my opinion are the most informative on the 
internet.
http://www.richieburnett.co.uk/tesla.shtml

Take care,
Bart


Jeremy Scott wrote:
> 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
> heat-dissipation user-friendly adjustable version
> 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
> the current instead. Perhaps both.
>
> 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. :)
>
> Thanks in advance! -Jeremy
>
>
>       
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