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big "variacs" for sale cheap
Hi Everyone,
Does anyone know the technical name for a "variac" (General Radio) /
"powerstat" (Superior Electric) / "volt-pac" (GE)? It is an
autotransformer, but an autotransformer does not necessarily have
a wiper to vary the tap point. In any case, I found a source for
GE's brand at a good price. They are used in good condition. The
ratings are
Input: 520 Volts, 50/60 Hz
Output: 0 - 520 Volts
Current: 30 Amps
Duty Cycle: 67%
These units have 3 sections ganged on a common shaft (probably
originally intended to be used with 3-phase power), and the shaft
is driven by a 24 VDC motor. There is also a limit switch at
each end of travel for the wiper and a potentiometer connected
to the free end of the shaft at the bottom. The motors will begin
to turn the shaft at around 5 VDC, and at 24 V, the full rotation
takes about a second. I am not sure if the duty cycle refers to
the transformers themselves or the driving motors, and some do not
have a duty cycle listed on the unit. If it is referring to the
transformers, that should work out to a continuous rating of around
25 Amps using
P = I1*I1*R*duty_cycle1 = I2*I2*R*duty_cycle2 ->
I2 = sqrt(duty_cycle1/duty_cycle2)*I1
There are 9 tap points on the winding, including one for the wiper.
In terms of size, they are about 1 foot square by 2 feet high up to
the motor, and the motor adds about another foot to the height.
Weight is around 200 lbs. Cost? $150 each, and shipping is not too
bad anywhere in the USA. The seller is Ctr Surplus in Ohio, phone
number 419-683-3535, M-F 9 AM to 4 PM Eastern Time. They have around
50 of them. Ask for Brian Mead.
Jim Monte