Re: Good Deal? SURE !!

To: tesla-at-pupman-dot-com
Subject: Re: Good Deal? SURE !!
From: NickandSim-at-aol-dot-com (by way of Terry Fritz <twf-at-verinet-dot-com>)
Date: Wed, 10 Mar 1999 12:41:49 -0700
Approved: twf-at-verinet-dot-com

To All,
          No way is that a liniac supply (the current is too high and the
voltage too low.  If it was intended to drive a voltage multiplier it would
have an ac output).   If I were you I'd just strip out the variacs and put the
transformer in a warm dry place until I found a buyer for it.  If you want to
use it remember that your local powerco will only give you a 3 phase supply if
you register as an industrial user.  If you're really unlucky you might have
to pay for your own substation.  Also the transformer will not be shunt wound
like a neon so you will need an old welder transformer or one hell of a big
saturable inductor to limit the current.
If you are very smart you could come up with a system which double rectifies
the output from a mains isolation transfomer then re-modulates it to give you
the 3 phases -at- 380-440V.(Warm MOSFETs)  There are some comercial inverter kits
available in the uk (maplin part no. VF62s) which you may be able to modify to
do the job.  You will need to put some linear mos driver chips in to take the
gate current  and a lot of big  and very expensive MOSFETs (I'd recommend
BUZ61s $3 each) in a push pull configuration off +200 -200 supply rails.  For
a highly inductive load such as transformer you will also need all the
smoothing and snubbing netwroks you can get your hands on.  Some zeners to
protect the FETs would be a good idea as well.
The hard part will be getting the 3 sine wave signals 120 degrees out of
phase.  The easy but expensive way to do this is to program 3 eproms with an
8bit sine wave then scan throught the addresses with scaled decade counters
120 degrees out of phase and feed the outputs to 3 8bit D/As.


Nick Field