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Re: Staco variac inrush (fwd)



---------- Forwarded message ----------
Date: Tue, 30 Oct 2007 11:36:26 -0400
From: Skip Malley <skip@xxxxxxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: Staco variac inrush (fwd)

I do not know about the specific variacs, but I do know there is a 
wide variation in sensitivity of the breakers to short term current 
surges.  I have a sound system that would trip the breaker in one 
club when I turned on the 1000 Watt amp.  I had to leave the amp 
turned on and go flip it a few times until the power supply caps 
charged up.  I think they were Square-D breakers.

A company called Ketema makes inrush surge suppressing 
thermistors.  They start out with a high resistance and then heat up 
with the incoming current and reduce in resistance.  When running, 
they lose less than a volt.  Another option would be to place a 
resistor of a few ohms in series with the input of the variac.  Then 
place a relay on the other side of the resistor with contacts that 
close shorting out the resistor after the reduced inrush.  Just make 
sure you start with the variac turned down.  You could use a couple 
hundred watt light bulb as the resistor.

Skip

At 09:52 AM 10/30/2007, you wrote:

>---------- Forwarded message ----------
>Date: Tue, 30 Oct 2007 13:05:27 +0000
>From: David Rieben <drieben@xxxxxxxxxxx>
>To: tesla@xxxxxxxxxx
>Cc: drieben@xxxxxxxxxxx
>Subject: Staco variac inrush
>
>Hi all,
>
>I was wondering if anyone else has noticed that Staco brand variac
>seem to have more of an inrush current issue than other major brand
>names of variable transformers (namely Powerstat)? For example, I
>have a 22 amp, 120/140 volt Staco that will trip the 20 amp service
>breaker probably 90% of the time at power up, unless I plug it in a
>good ways "downstream" from the breaker box - i.e. plug it in at the
>far end of the house from the breaker box or at the end of a 100 ft.
>extension cord. Also, I once had a triple stack 28 amp, 240/280
>volt Staco (total 84 amps rating) that would trip the 100 amp circuit
>breaker almost every time at power up yet I now have a 4-stack
>1256D Powerstat (28 amps at 240/280 volts x 4) that virtually
>NEVER trips the same 100 amp breaker at power up. Anyone
>else have any other similar experiences to share?
>
>--
>David Rieben