RE: variac amperage control??

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Oxandale, Terry by way of Terry Fritz <twftesla-at-uswest-dot-net>" <Toxandale-at-SPP-dot-org>

Bill

Rather that using the variac "across" the source (both legs) to control
voltage, you instead use the variac in "series" with only one leg. To
connect, you only use two wires (vs 4 wires for voltage control). Your
source (wall) wire will go to one side of the winding (1 or 5, I
believe) for current "in", and the other wire to your load goes to the
brush (3, I believe) for current "out" of your variac (thus only two
wires are connected to the variac) and into the xfmr. Then the current
goes through your transformer and returns back to the source
(wall)directly. Depending on which side of the winding you connect the
souce to, will determine whether the current increases from nothing to
fry, or decreases from fry to nothing with the same movement of the
control knob. This should be verified and tested with some resistance
and/or fuse (or even a variac across the circuit to keep voltage to a
minimum) in the circuit to make sure your working the knob the correct
way. Otherwise you could smoke something real quick when you flip the
switch to energize the circuit. Also, the reactance in not linear, so
the last 10%-20% of current rise will ramp up very very quickly, so be
deliberate with the adjustments.

(un)Terry

-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Saturday, February 10, 2001 4:20 PM
To: tesla-at-pupman-dot-com
Subject: variac amperage control??


Original poster: "Bill Trumpet by way of Terry Fritz
<twftesla-at-uswest-dot-net>" <billtrumpet-at-hotmail-dot-com>

Hello TCML,

I'm a little confused as how to use variacs for current limiting for
XFMRs.  
I know how to use them for voltage control and am wondering how to
connect 
them for current control for a pig or PT.

Thanks,

Bill Trumpet


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