Re: ballasting problems

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Mark Broker by way of Terry Fritz <twftesla-at-uswest-dot-net>" <broker-at-uwplatt.edu>


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> Hi Mark....
> 
> sounds like your inductor either saturated or the H is too small ... 

Doubt it saturated....  6 turns on a 18" sq core carrying 40A of juice (fuse
was rated for 40A). 


>
> you should be looking for around 6 ohms of "resistance" from the inductor
> to get 40A -at- 240V 

That's what my calcs show, too.


>
> do you have a variac of substantial size ???  ( 30+ amp rating??) 

Will tomorrow!  Two, in fact!  (pretty sure they're rated for 240V.....)


>
> hook up the variac as normal, place the inductor across the outputs of the
> variac. Slowly apply
> voltage and record at 10 volt intervals the voltage out of the variac AND
> the current running thru
> one of the wires feeding the inductor  ( clamp on amp meter is great here) . 

Didn't think of that method...  duh!  We don't have a clamp-on ammeter, though
one should definately be purchased (only $40, too)


>
> what I have found in my playing around with scrapped cores is that with
> 180- 200 winds of #10THHN
> on various core sizes have resulted in about 2.5 amps per square inch of
> area ( center leg
> measurements) before saturation begins to become a problem. 

Umm....  I had 6 turns of 6AWG, PVC coated wire on an E-I core measuring about
3"x6".  According to my handy-dandy speardsheet, that's about 1.8kVA worth of
ballast.  I guess Chris rewound it with "a lot of turns" (would guestimate 30
or so).  I don't know if he's tried it yet or not....  By my calcs, that's
around 700VA....

Even assuming poor quality steel with a mu of 1000 (the books I've seen say
3000-5000 for transformer silicon steel), 6 turns still gives me 8kVA.  At 500,
we start getting into problems (15kVA-ish.).  And we weren't just slightly
over-current...  that breaker POPPED!

Thanks

Mark



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> Scot D
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