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current limiting and 220



	I wanted to thank everyone for their help with current limiting questions!
 I also wanted to offer up my own experiences in case anyone needs
information.  Oh yeah, and I have another question of my own!
	I obtained a free welder transformer from a local welding supply company
(if you ask for old, used welders they sometimes have some available, and
apparently, the transformers don't usually go bad, it's often the fan or
some other part you don't even need for current limiting).  I first shorted
out the output leads from the welder transformer.  I then hooked up the
primary to the wall (like plugging in a neon sign transformer and shorting
out the secondary) in series with a current shunt (basically a resistor)
that reads 100 mV across it when 50 amps are running through it.  I hooked
up my voltmeter, screwed in the core as far as it would go (I got a
transformer with a variable depth core) and plugged it in.  I then flipped
the circuit breaker while my friend watched the voltmeter.  It worked, and
the current turned out to be about 12.5 amps.  Since I was plugged into 220
I calculate my power to be about 2.75 KVA.  Next, I hooked up my pole pig
in series with the welder and set up a Jacob's ladder.  Very impressive!
I'll probably pull out the core a little more and use about 3-3.5 KVA for
my coil.
	Unfortunately we ran into a problem.  We were working on hooking our
variacs up to the 220 and it is not working so well.  We are trying to run
our coil off of 220.  The lab where I work has 3-phase power and we are
hooked up to two legs of the three phase.  We tried to hook up the 220 from
the three phase into our Variacs (we put two in parallel to cut down the
current running through each one).  When we turned on the power, they
started buzzing and the fuse blew.  I know that three phase power is
basically three 120 lines running 120 deg. out of phase with each other.
As far as I can tell, a single 220 (like for our dryer at the apartment)
and 220 from a three phase are about the same thing.  When I hook up across
the 220 at home it reads 220 on the Voltmeter, when I hook across the
neutral and either of the 220 leads I read 110, same for the neutral of the
three phase and any of the other legs.  Anyway, I would like some
information on transforming 220 using variacs.  We have checked out some
books from the engineering library, but there's nothing like some first
hand information from real coilers!  Any help you can provide would be
really appreciated, especially since Engineering open house is a month
away!  (F.Y.I. Engineering open house is an event at the U of I where all
the engineers on campus show off cool research, projects, and basically let
the public see how cool science, physics, and engineering can be.)  The
Society of Inventors is working on the coil and we're trying to get done by
March.  Wish us luck!

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   _/_/  _/_/
  _/  _/  _/ _ _|_ _|_ |_  _            matthew wenger
 _/      _/ (_| |   |  | |(/_ |_|_|     m-wenger-at-uiuc.edu
_/      _/    '