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Re: Motor driven variac

Subject: 
            Re: Motor driven variac (
       Date: 
            Mon, 24 Mar 1997 06:35:16 GMT
       From: 
            robert.michaels-at-online.sme-dot-org (Robert Michaels)
Organization: 
            Society of Manufacturing Engineers
         To: 
            tesla-at-pupman-dot-com


T>  From:
T>        "Jason Edward Pecor" <pecorjas-at-pilot.msu.edu>
T>    To:
T>        tesla-at-pupman-dot-com (Tesla List)


T>What exactly does a Variac do?  Is it some sort of Spark Gap?

        It =exactly= allows the 120-v ac line power to be varied
        typically from 0 to 140-v ac.  It's a variable transformer.
        It plugs into the wall (in the smaller sizes).  A large
        knob on the top sets the desired voltage which is then
        available from an electrical outlet built into the Variac
        (as said, in the smaller sizes).

        "Variac" is a proprietary name for variable transformers
        made by General Radio Company and invented by them
        circa 1940.  "Variac" has now almost become a generic
        term.  Similar products are made by Superior Electric Co.
        and called (by them) "Powerstats".  Several second and third
        rate manufacturers now make functionally-equivalent products.

        "Variacs" are important in Tesla work because it is highly in-
        advisable to instantly apply full line voltage to a Tesla
        system. The input voltage is best brought up gradually.
        Also, for test and tune-up purposes it is very useful to
        be able to run at less than full voltage.

        "Variacs" have faded in importance in the solid-state era
        as various semiconductor devices can be employed to do similar
        work in a great many applications tho such are not desirable
        Tesla-wise.

                                         More power to you,


                                        Robert Michaels - Detroit, USA