Re: Ballast inductor.

[FutureT-at-aol-dot-com (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

In a message dated 10/2/00 6:12:15 PM Pacific Daylight Time, tesla-at-pupman-dot-com 
writes:

> Original poster: "M Fabs" <the_machin_shin-at-hotmail-dot-com> 
>  
>  I just wound 100 feet of #10 romex THHN wire onto a 2" dia pvc conduit.  I 
>  also poly'ed a bunch of welding rods together to fit inside.  I am hoping 
to 
> 
>  use this as a variac substitute, a variable inductor. I measured the 
>  inductance with the rods in the coil and with them out of the coil, and 
the 
>  numbers I found are 1.72millihenries with the rods fully inserted, and 
about 
> 
>  330microhenries with them not inside. (That last one might be off a bit, I 
>  was paying more attention to the full insertion number.)  60Hz 120Vac 
>  standard wall outlet is my power source.  I forgot the formula for 
inductive 
> 
>  reactance.  Anybody willing to crunch the numbers for me and tell me what 
>  current range this will allow me?  Another option is to arrange a brush 
deal 
> 
>  to use like a true variac.  Just looking for some idea as to how useful 
this 
> 
>  will be, or what changes I ought to make. Thanks folks.
>  
>  MPF

MPF,

I have a homemade ballast, but I didn't build it.  I think it has 300 turns
of #12 wire, with a bunch of taps.  Originally it was filled with welding
rods and threaded rods, but I replaced that with transformer "I's" from
NST's.  Max inductance  is about 26mH, minimum is about 1mH.
This gives the range that I need.  The range that you need will
depend on the coil specs and voltage input.  The form for the
ballast is 3" by 19" pvc.  A large selector switch selects the
8 taps as needed.

John Freau