VARIAC for Idiots :)

[sdumper]

I know nothing about Variacs will this work?

HEW W5M VARIAC INPUT IS 120VAC OUTPUT 0-140VAC 5AMPS

Or will that limit me to only 140 watts of load?

Im looking to power this with it http://www.xtremesystems.org/forums/showpost.php?p=3593816&postcount=36

[[XC] gomeler]

Output is 0 to 140 volts, alternating current. Maximum current of 5 amps, so 0w to 700w of power can be transformed by the device.

[sdumper]

Awesome thanks Chris!!

You can fill a lot of libraries with what I don't know ....

[[XC] gomeler]

I think anyone can say that :up: Ask me what I know on International Policy and I'd say "carry a bigger stick" and that's about it :D

[sjg0]

Ok so I dont remember if I ever figured this out, but will that variac for example provide a maximum amp draw of 5A regardless of the volts?

So if I set it to 10V it will still have max of 5A but
If I set it to 140V then the max amps will be 5A?

[[XC] gomeler]

Yes. Size your resistors for an operating voltage around 100v to 120v with the variac, giving yourself ample room upwards just in case. Use Ohm's law to figure out the resistance necessary with your resistors. Resistors in series add in resistance while resistors in parallel are (1/R) = (1/R_1) + (1/R_2) + (1/ R_n). Cartridge heaters and wirebound resistors make great dummyloads.

[sjg0]

gomeler;3594356']Yes. Size your resistors for an operating voltage around 100v to 120v with the variac, giving yourself ample room upwards just in case. Use Ohm's law to figure out the resistance necessary with your resistors. Resistors in series add in resistance while resistors in parallel are (1/R) = (1/R_1) + (1/R_2) + (1/ R_n). Cartridge heaters and wirebound resistors make great dummyloads.

Thanks gomeler. In your opinion, is a cartridge heater better or a resistor?

Rather than worry about getting multiple resistors/heaters I was just going to get a single 350W heater and regulate voltage down to the desired heat load. :)

[[XC] gomeler]

A cartridge heater can be fully inserted, with ease, into a block of copper and fully disperse it's heat into the copper. I have wirebound resistor dummy-load that is attached to the backside of my dummyload. With this arrangement on single-stages with a heavy load, the dummyload may radiate some of it's heat away from the copper as it's surface temperature rises above ambient. You can insulate against this but it isn't the most efficient method. So in short, cartridge heater inserted in copper would be easiest and potentially most effective.

[DetroitAC]

Ok so I dont remember if I ever figured this out, but will that variac for example provide a maximum amp draw of 5A regardless of the volts?

So if I set it to 10V it will still have max of 5A but
If I set it to 140V then the max amps will be 5A?

The maximum current you can pass through the variac would be 5A

BUT the variac does not regulate this! If you hook up heaters that draw more than 5A (plus a little margin) you will blow the fuse in the variac. If you were to install a larger fuse or bypass the fuse you'll get the variac wires too hot, the insulation will fail and it'll short out.

[[XC] gomeler]

Hrm, guess I was taking that as a given. Using Ohm's law you need to choose appropriate resistors that don't exceed the current limitations of your variac.

[sdumper]

DetroitAC sent you a PM :)

[sdumper]

Heres the one I ended up with $41.00...

THIS AUCTION IS FOR ONE HEW W5M VARIAC INPUT IS 120VAC OUTPUT 0-140VAC 5AMPS

THE CORNER A SMALL DENT BUT SHOULD NOT AFFECT OPERATION YOU CAN SEE IN THE PHOTO

[sjg0]

The maximum current you can pass through the variac would be 5A

BUT the variac does not regulate this! If you hook up heaters that draw more than 5A (plus a little margin) you will blow the fuse in the variac. If you were to install a larger fuse or bypass the fuse you'll get the variac wires too hot, the insulation will fail and it'll short out.

Gotcha so the internal wiring of the variac is only made for a max of 5 amps. :up:

Is there such thing as a Variable Transformer ACtoDC and also ACtoAC? Preferably 40A+ and somewhat reasonable in price?

[DetroitAC]

Gotcha so the internal wiring of the variac is only made for a max of 5 amps. :up:

Is there such thing as a Variable Transformer ACtoDC and also ACtoAC? Preferably 40A+ and somewhat reasonable in price?

AC to DC is called a power supply, variable power supplies are quite common.

AC to AC is a transformer, a variable AC transformer is called a variac. They come in many different sizes, I was just using sdumper's specific variac as an example.

There are also many other devices that convert/regulate/refine electrical power, enough to fill several tons of textbooks :up: