# Re: Powerstat Surge

```Tesla List wrote:
>
> >From Esondrmn-at-aol-dot-comSat May 25 11:50:30 1996
> Date: Fri, 24 May 1996 16:49:56 -0400
> From: Esondrmn-at-aol-dot-com
> To: tesla-at-pupman-dot-com
> Subject: Re: Powerstat Surge
>
> In a message dated 96-05-24 00:10:29 EDT, you write:
>
> >
> >[ I wonder if it matters what order things are in.  I have the variacs
> first,
> >and the arc welder between them and the pole pig. -- Chip ]
> >
> >
> >
> Chip,

In a series circuit, such as the primary power circuit, the order in
which a component is in in a circuit is of no consequence.  I use a 5 ohm
200 watt resistor in seires with my variacs and place a 120 VAC relay
across the variac input terminals as well.  The normally open contacts
(should be rated the full load of the variac) are placed across the
resistor.  After the inrush current is over, and the voltage across the
variac rises, the relay pulls in and shunts the resistor out of the
circuit.

Richard Hull, TCBOR

[ Just a quick question appended 'cause it's easier for me...

The primary power circuit that I use is not quite a pure series circuit
in my eyes.  The power comes in through the plug and energizes the variac.
The power from the variac then goes to the pole pig off one side, and to
the welder from the other.  From the welder, the power goes to the pig.
If we could take the pig and welder out of the circuit, we would still
measure a small amount of current that is used to energize the variac.
Now, if the variac had no impedance for some reason, I believe that the
breaker would trip.  From what I have been hearing, and what I believe about
inductors and AC, there is a period of time where the core of a
transformer has to magnetize.  I believe that this time period (1/120th
sec. or so) is when a large surge of current can flow.

A______
3
3
3<------------------ Pole Pig -|
B______3_________ Welder _____________|
|            |
|/\/\/\/\/\/\|
oven element

A and B are the inputs to the variac.

I believe that the best way to limit the current at startup would be to have
a resistor at A or B that was cut out after energizing the variac as
mentioned.
So, the question is "Is my understanding about the primary power circuit
correct?"

---- Chip]

```