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RE: Soft transformer turn on without a variac



Original poster: "Ian McLean" <ianmm-at-optusnet-dot-com.au> 

Hi Bill,

Is this really a problem with the Variac, or with the inrush current of the
NST's ?  I too had breaker problems with a bank of two 15kV/60mA NST's until
I put power factor correction caps on the NST's, which reduces inrush
current significantly.

This solution may have already been discussed previously, but I am new to
this list and have not had a chance to read all the list archives yet.
Apologies if I am off the mark.

BTW, hello all from a new list member and avid coiler from down under !

Rgs
Ian

-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Wednesday, 29 October 2003 6:43 am
To: tesla-at-pupman-dot-com
Subject: Re: Soft transformer turn on without a variac


Original poster: Bill Vanyo <vanyo-at-echoes-dot-net>

Hi All,

	Anyone remember this discussion?  Basically, the problem I want to
solve, and that was discussed previously, was how to turn on power to a
variac without tripping breakers.  For my own setup, I have a variac
rated 50 amps 240 volts fed from a 30 amp 240 household line (electric
clothes dryer).  I set the variac at half way to step down to 120.  I'm
using 3 (soon 4) unmodified 15/60 Franceformers.

	What I'm looking for, if anyone can help me with this, is a cut and
dried plan using readily available parts (part numbers & sources would
be ideal), a la Terry's NST Protection filter - just something so I can
turn on power to the variac (turned down to the low end) without
tripping the house breakers.  Right now I'm using a big old knife
switch, which more often than not trips the breaker.

	I suspect many other novice coilers could benefit from a solution to
this too.

	Thanks,
	Bill V.

Tesla list wrote:
  >
  > Original poster: "Rick W by way of Terry Fritz <teslalist-at-qwest-dot-net>"
<potluck-at-xmission-dot-com>
  >
  > Hi Peter,
  >
  > I had that problem also with a stack of 2 variacs for 120 volts and a
stack
  > of 6 variacs for 240 volts. The scheme I'm currently using is shown in
the
  > link. For 240 volts I'm using an 18 ohm resistor. I believe the wattages
can
  > be less but that's what I had in the resistance range I wanted. This
works
  > really well. I don't add load (ramp up the variacs) until both contactors
  > are pulled in.
  >
  > http://xmission-dot-com/pub/users/p/potluck/pics/rampup.jpg
  >
  > I see Scot D. is using an inductor. I tried that and found the same
problem.
  > The current draw feeding six 240 volt paralleled variacs is rather low
after
  > the intitial small spike. Much lower than I had expected so these worked
  > very well.
  >
  > Also, the post about Negative Temperature Coefficient Thermistors in
power
  > supplies is very interesting. Very interesting indeed. I too will be
looking
  > into that.
  >
  > Rick W.
  > Salt Lake
  > ----- Original Message -----
  > From: Tesla list <tesla-at-pupman-dot-com>
  > To: <tesla-at-pupman-dot-com>
  > Sent: Wednesday, July 23, 2003 6:53 PM
  > Subject: Soft transformer turn on without a variac
  >
  >  > Original poster: "Peter Terren by way of Terry Fritz
  > <teslalist-at-qwest-dot-net>" <pterren-at-iinet-dot-net.au>
  >  >
  >  > Hi all.
  >  > For my 5 kW museum
  >  > coil,
  >  >
  >
<http://members.iinet-dot-net.au/~pterren/Scitech.htm>http://members.iinet-dot-net.a
  > u/~pterren/Scitech.htm
  >  > ,   I need to have a single switch for turn on preferably without a
variac
  >  > to keep things simple for the staff.  The present system has solid
state
  >  > relays but is complicated and unreliable. I need to turn on the motor
  > first
  >  > then a couple of seconds later soft turn on the power to the
transformer.
  >  > Even switching  on power to a normal variac gives a spike that will
trip
  > my
  >  > lower current breakers. The whole system will have to be electrically
  >  > quiet.  Does anyone have experience with inrush limiters or have other
  >  > suggestions?
  >  >
  >  > Cheers
  >  > Peter (Tesla Downunder)
  >  >
  >  >
  >  >
  >  >
  >  >
  >  >
  >  >