Re: Powerstat Surge

• To: tesla-at-pupman-dot-com
• Subject: Re: Powerstat Surge
• From: Jim Fosse <jim.fosse-at-bdt-dot-com>
• Date: Wed, 29 May 1996 06:02:39 GMT

On Tue, 28 May 1996 22:29:37 -0600, Tesla List
<tesla-at-poodle.pupman-dot-com>, you wrote:

>> Subject: Re: Powerstat Surge

>  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,
	By Jove, I think you've got it! to paraphrase an old song from
pigmaleon (sp).

The biggest surge occurs when you disconnect the variac at the peak of
one half cycle and leave the core magnetized, then connect the variac
to the mains on the opposite half cycle. In effect, you have just
applied 2 times the voltage to the core of the variac and large
currents flow until the core catches up.

	jim

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