terryS wrote:
On Jul 11, 10:18 pm, Fred Cameron
wrote:

I am looking for a 220 volt variac.

Does anyone have such a beast?

Thanks!

Fred
WA4PAV


On the basis that a transformer, In this case a variable tap auto-
transformer, is an electromagnetic device:
Question: Could one not input the variac with say 230 volts instead of
115 volts.
Then at, say, 20% dial setting the output would be 46 volts and at
100% it would be 230 volts. Etc.
As long as the current and total power transformed are within the
ratings of the variac, would it matter?
After all transformers, either those with separate input and output
windings, tapped or untapped, or auto-transformers can be used to step
voltage up/down and so forth.


The basic transformer design equation is:

E = 1.4*f*N*B*A,

E = primary voltage
f = frequency
B = Flux Density [typically 80% of Bmax]
A = Cross sectional area of core.

B is a non linear response of the magnetic material. It become 'flat' as the
core saturates and the current increases DRAMATICALLY.

Since f, Bmax and A are fixed for a 120 VAC design, applying 240 VAC to the
primary will 'fry' the variac and your hand, and pop the circuit breakers for sure.

Now, a 240 VAC design can be run at 120 Vac, but not vice-versa.