Re: [TCML] 10 amp ballast

[SusaX2 X2 <susax2@xxxxxxxxx>]

Hi Scott,

I'm not really an expert on ballasting, but I do have some experience which
I'll share.
First, parallelling ballast is asking for troubles unless they're identical
and if they are variable, you'll have to get them exactly the same. Seems
to me it's a better idea to use 1 big one with a wide varable range to
prevent one will process more current than the other. Everyone, feel free
to correct me if I'm wrong.

The first decent ballast I had was made of an old cheap mig-mag welder. I
removed the secondary low voltage windings leaving the primary winding. It
had about 330 windings, so it just wouldn't saturate the core if plugged in
directly to mains. I split the core and milled the surfaces smooth. then I
made some brackets to clamp both halves, leaving a variable gap between
them which has to be filled with some plastic shims. In principle this
ballast is comparable with the ones you can see on Richie Burnett's site.

I did some testing with various gaps and it proved to be quite effective,
with no gap at all short circuit current was under 2A. A gap up to 4mm
limited current to 16A.
The down side, it's winding had 3 Ohm DC resistance if I remember
correctly, so 250V in dropped to 200V out.

If you decide to go with shorted MOT's a ballast, you'll find that the
shorted windings will become very hot in a short time and cooling is
needed. And this is not variable.


If you want to find out how many turns are needed compared to the core's
cross section, I found this site to be very helpful. It has an excell sheet
along the page to do the calculations.
http://ludens.cl/Electron/trafos/trafos.html


Mark






2012/8/5 Scott Bogard <sdbogard@xxxxxxxxx>

> Greetings all,
>      Wondering if anyone has any "instructions" of sorts for a good 10 amp
> 240V ballast that will last long runs.  I know 10 amp seems kind of small
> for a power supply needing ballasting, but my idea is to stack four of them
> in parallel to A. dissipate heat better, and B. to allow for some variable
> power in the stead of a variac...  I was thinking the welding rod approach,
> maybe a 1.5 inch PVC pipe, 2 feet long wrapped with x turns of 14 AWG...
>  Just not sure ballpark how many turns to use, of how much heat that will
> generate, hence what kind of cooling I will need for say 10 minute runs.
>  Input is appreciated!
>
> Scott Bogard.
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