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Re: Soft transformer turn on without a variac
Original poster: Bill Vanyo <vanyo-at-echoes-dot-net>
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
Tesla list wrote:
> Original poster: "Rick W by way of Terry Fritz <teslalist-at-qwest-dot-net>"
> 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.
> 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,
> > , I need to have a single switch for turn on preferably without a
> > 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
> > 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
> > 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)