Re: Soft transformer turn on without a variac

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

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)
 >
 >
 >
 >
 >
 >
 >