Variac substitute

To: tesla-at-pupman-dot-com
Subject: Variac substitute
From: "J. B. Weazle McCreath" <weazle-at-hurontel.on.ca> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
Date: Sun, 13 Feb 2000 15:21:43 -0700
Approved: twftesla-at-uswest-dot-net
Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme


Hello coilers:

     Here is a novel hookup that will allow you to control a load which
     draws more current than your variac is rated for.  It doesn't give
     the full range of adjustment that a conventional hookup does, but
     it does allow you to raise or lower the full line voltage quite a
     signifigant amount if you don't have or can't afford a big variac.

     Three items are required, a variac, a transformer, and a S.P.D.T.
     switch.  The secondary winding of the transformer should be able
     to carry the full current of your load, and the voltage should
     be the amount that you wish to raise or lower the line voltage.

     Connect the hot and neutral input leads to the variac as in the
     normal configuration and also connect them to the N.O. and N.C.
     terminals of the S.P.D.T. switch.  Connect one primary lead of
     the transformer to the remaining switch terminal and the other
     primary lead to the wiper terminal of the variac.  Connect the
     secondary of the transformer in series with the hot lead going
     to the load.  This can either come off the hot terminal of the
     variac, or another source entirely.

     Put a voltmeter across the hot and neutral output leads and apply
     power to the circuit.  Turn the variac up while watching the meter
     and if the voltage goes up you've got it right.  If the voltage
     goes down instead of up, reverse the transformer primary leads
     and try again.

     I used a transformer with a 24 volt, 25 amp secondary, which gave
     me an adjustment range of 48 volts.  One switch position gives a
     low range of 96 to 120 volts, while the other position allows an
     adjustment from 120 to 144 volts, assuming a 120 volt input.


73, Weazle, VE3EAR/VE3WZL

Listening: 147.030+ and 442.075+
E-mail:    weazle-at-hurontel.on.ca
           or ve3ear-at-rac.ca
Web site:  www.hurontel.on.ca/~weazle