i have a variac which is 8 amp 220 v. is there any reason it wouldn't work on 120 v.? i can't see why it wouldn't instead of 2 110 v. lines there would be 1 120 v. line and a neutral but then with the 220 there would be no neutral i've never tried it as i don't have room on my workbench.butch

Butch,
I believe that Variac is a trade name, and its really called an auto transformer, and as I recall has both step up and step down capability. The individual specs may differ from one unit to another, but are basically the same. Unless it has separate "line in" terminals for 110/220 use, it may not provide a full 120v, when stepping up using standard 120 volt house current. Another option is to purchase an inexpensive travel transformer that converts 220v (Europe) to 110v (USA) Provided it has sufficient current capability, (hair dryer comes to mind) you simply reverse the connections by attaching a std USA plug to the 110v side, and a standard 220v/15A receptacle to the 220v side. Keep in mind that under these circumstances, the knob rotated to the approx. halfway point ONLY will provide required 110-120v output for domestic appliances, and DON"T try loading to its full 8 amp capability.
marv

:i have a variac which is 8 amp 220 v. is there any reason it wouldn't work on 120 v.? i can't see why it wouldn't instead of 2 110 v. lines there would be 1 120 v. line and a neutral but then with the 220 there would be no neutral i've never tried it as i don't have room on my workbench.butch

Butch, I can't think of why it wouldn't work as you propose.

Marv's idea should be OK, too, but I'd worry about turning the knob past the half-way point, and frying something.

This variac must be one heck of a beast -- 1.76 kVA. Gosh, there are some houses that you could nearly power the whole she-bang with.

Hi

Don't need to worry about getting too high of a voltage. With 230 volts you would get up to this or 10% higher depending on wiring. With 115 input the knob would adjust 0-115 volts or a liitle higher depending on wiring.

Norm

:Butch, I can't think of why it wouldn't work as you propose.
:
:Marv's idea should be OK, too, but I'd worry about turning the knob past the half-way point, and frying something.
:
:This variac must be one heck of a beast -- 1.76 kVA. Gosh, there are some houses that you could nearly power the whole she-bang with.

:i have a variac which is 8 amp 220 v. is there any reason it wouldn't work on 120 v.? i can't see why it wouldn't instead of 2 110 v. lines there would be 1 120 v. line and a neutral but then with the 220 there would be no neutral i've never tried it as i don't have room on my workbench.butch

I have a variac that is rated for 220volts also and use it on a 120 volt line it works fine

Tom

Norm is correct. Remember, everybody, how a transformer works. A Variac is a transformer. It has a main coil that is put across the line and then an additional section of coil after this main coil for adding additional voltage to the voltage at hand. The ratio of turns in this additional coil will raise the available 115 volts up the same percentage as would be possible with 220 volts. That is, if it raises the 220 volts up 5% more, then it will also raise the 115 volts up 5% more. The 220 volt coil simply has a higher impedance allowing it to operate at 220 volts. In some cases you may find trouble using a larger transformer in a smaller voltage situation. That would be if the impedance of the coil was very high for what you were using the coil for, you may find a low spot somewhere in the middle of the coil due to the resistance of the coil being higher than what it should be for what you are using it for. Since the 220 volt Variac is made to handle high amperage, however, I doubt that the wire used in winding it will create too much resistance for 115 volt work.

Simply try the Variac out first with a meter and get an idea as to what it will do. You may make an index card with voltages that correspond to those marked on the device. Then load the Variac up to almost full potential and test the voltages available again. They may or may not shift.

Thomas