RE: Soft transformer turn on without a variac

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

Original poster: Thomas <tom-at-pwrcom-dot-com.au> 

Another option may be a solid state or mechanical zero crossing switch so
that power is only applied to the variac when the mains voltage is 0V.

http://www.phenixcontrols-dot-com/Services/Engineering/Zero_Crossing_Mechanical/
Zero_Crossing_Mechanical.htm

http://www.celduc-relais-dot-com/uk/relais.asp

 > 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://membe
rs.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)
  >  >
  >  >
  >  >
  >  >
  >  >
  >  >
  >  >