While I was looking for a variac....someone gave me an idea....to make it to 240 volts...now I want to know if it will actually work or not....

but heres an idea....I would get a 140 volt max variac
then use a 120 to 240 step up transformer plugged in to the variac and I would lower the variac....would it lower the 240 volts step up to...maybe for example to 180 volts or so??? will that work???

let me know...thanks

-Jace

Yes, you could connect the 0-140v out from variac to the 120v input of the 120/240v transformer. However, if you cranked it all the way to 140v, it might cause something to overheat and the transformer would put out 280 volts.
It's a 1:2 ratio for voltage. If the variac is set for 90 volts, then the transformer will put out 180. Give or take a few.

The current will have to be monitored carefully though. If the load is drawing 2 amps from the transformer...then the variac has to put out 4 amps. At least double. Plus, add 10 to 15% for transformer losses.