Sciencemadness Discussion Board

Buying a Variac

beastmaster - 7-5-2010 at 17:18

I was searching e-bay looking for a variac to use on a small mantel. I was over whelmed. What do I look for in a variac if I am using small(50ml to 1L)mantels. Are all of them basically the same? What amp. would I need? I prefer 110v. Could I run a PIC temp. controller with it or does the variac do that on its own . Thanks. Beast

The WiZard is In - 7-5-2010 at 17:43

Quote: Originally posted by beastmaster  
I was searching e-bay looking for a variac to use on a small mantel. I was over whelmed. What do I look for in a variac if I am using small(50ml to 1L)mantels. Are all of them basically the same? What amp. would I need? I prefer 110v. Could I run a PIC temp. controller with it or does the variac do that on its own . Thanks. Beast



Why not use up to date — sold state technology? A full range light dimmer.

entropy51 - 7-5-2010 at 17:50

For the mantle you describe, you can't do better than a Staco variac that puts out 120/140 volts at 10 amps. There are other ways of doing it, including a light dimmer from the hardware store. Unless you're doing precision fractional distillations, a variac will serve as well as a fancy controller. Most of this, including PID controllers have been discussed in other threads. Magpie has given his design for a DIY temperature controller. You could search, or you could just get a Staco or equivalent.

not_important - 7-5-2010 at 19:17

Adding on, 110v @ 10 A is good for mantles up to 1 kW. High wattage lamp dimmers work too, but sometimes through out a lot of RFI. Both depend on the human to adjust them to set the power level to what is needed at that time.

Fancier ones, with PID being near the high end, can be set to automatically control the heat input based on input from a temperature sensor. Useful, but probably overkill for smaller scale home lab work.

Almost all variacs do not isolate their output from the mains, so it may be worth investing in a ground current fault interrupter. These monitor the current through both lines of the mains connect and if the current in them isn't equal because some is flowing from the 'hot' line to earth through something, say the experimenter, the device cuts the power connection.