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Ballasting ..... the never-ending thread ;-)



G'Day,

At 19:20 2/12/98 -0700, Malcolm Watts wrote re: Off-axis primary inductance:

>I'm intending to take this idea one step further by using a variable 
>reluctance coil. I have constructed two "cores" , both heavily gapped 
>internally by recovering 3C8x ferrite cores from old computer SMPS, 
>smashing them to bits and stuffing the chips into PVC and acrylic 
>piping. The largest of the two is about a foot long, 4.5" diameter 
>and weighs a bundle and has an Al value somewhere around 300nH/turn^2 
>if memory serves. By sliding this core in and out of a modest winding 
>I have a variable inductance. This might also be useful for adjustable
>primary ballasting with a stiff power transformer. The power losses 
>should be considerably less than the gap. I did experimentally check a 
>primary with one of these cores for losses and it looked better on 
>the scope than an equivalent inductance and much larger air wound 
>primary, gap included.

Now this has me somewhat inspired.  I had ballasted my HBP (home-brew pig)
with my neighbours welder plus some series R elements with initial success.

Just bought a new house and am moving end of January, so coilin' takes a
back seat for a while (but it does have a work-shop <big grin>).  Problem
is my new neighbour is very unlikely to have a spare welder ...... so back
to the drawing board :-(

My second-favourite junk shop has *lots* of ferrite rods going cheap.  Lets
say we fill a 4" PVC pipe with these & set the lot in epoxy resin, allowing
a 1cm channel though the middle to take a threaded rod for position
adjustment.

1.  How long will I need to make the core ?

2.  How many turns & what guage wire ?

Given my aims are to limit current over the range 5-35 amps (more likely
10-30A), with primary mains at 240V/50Hz.

Thinking further.  Could we make it whole set-up shorter by using several
winding layers, or would heat dissipation be a problem ?

cheers


Mark

http://www.cobweb-dot-com.au/~dkfinnis