Re: Powerstat Surge

In a message dated 96-05-29 21:24:11 EDT, you write:

>Assuming that you have the variac turned all the way down when power is 
>applied, (the normal case) you still have a series circuit.  With the 
>variac turned down at power up, all the AC line sees is the variac core 
>only.  The other stuff is invisible.  The resistor should go is series 
>with the core of the variac at point A or B, it doesn't matter.  For the 
>sake of the drawing let us assume A.  A set of normally open contacts 
>from a relay are placed across the resistor.  The relay's coil is placed 
>directly across the variac's windings A to B.
>By the way, you should never just throw a switch and have the system just 
>blast on!  This is a big no-no! With little neon circuits under 500 
>Watts, this might be OK, but not with pole pigs.  I am assuming you never 
>do this and use the variac to slowly bring up the power.  In this case 
>the line sees only the variac core at powerup.
>Richard Hull, TCBOR


I still believe placing the current limiting inductor along with its parallel
or series resistors (welder in my case with oven elements in parallel) in
series with the line to the variac provides enough current limiting when the
power is applied to prevent the surge that I hear people talking about that
wipes out fuses and breakers.

The current limit device for the pole pig can be placed anywhere in its power
supply path - either after the variac or before.  It seems to me, placing it
between the variac and the line eliminates the need for a separate resistor
and relay to limit the surge to the variac when the mains are powered up.

Ed Sonderman