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A variac is a type of transformer that is used to provide voltage adjusting of AC electricity. The variac is usually a plug in device that has a knob that is used to control it.  The output range on the variac is from 0 volts AC to about 140 VAC.  This control range depends on how the winding if connected. The variac does not provide isolation from the wall unit as a true transformer does. Therefore, they aren't particularly good for powering low voltage devices. The variac is often used with tube audio for powering experimental circuits along with testing and repair. It is not used as a permanent source of voltage shifted power.

Variacs are used in several different applications such as electronic service departments will use them when they check out equipment that have low and high voltages. Engineering departments will also use the variac when they are checking their designs to assure that their new products will operate with the correct input power variations. The engineering and industrial market uses the variac for high current generator control along with quality control testing, such as testing electronic equipment for burn-in and life tests.

The variac is often described as being a tapped inductor. When we speak of the tap, we are referring to a conductive slider.  It moves along the length of the inductor. The inductors is shaped like a doughnut that has wire that is wrapped radially through the center of the whole on the doughnut shape and then wrapped around the doughnut.  The variac has a single winding that is used for both the input and output source. The inductive slider is an arm that is equipped with a carbon contact.  This contact rotates on an axle through the doughnut hole. The winding wire has enamel insulation that is removed when the carbon contact touches the winding. This in turn means that the contact forms a circuit through part of the winding.

The voltage in a variac is divided into two parts by dividing the impedance that is between the inputs. The divided input impedance that is connected to the output will determine the output voltage. The variac uses an inductance rather than a resistance as the divided impedance. The variac gets much higher efficiency using the inductance as it eliminates the power that is lost in heating the resistance. When you use a variac, virtually all the power is consumed when delivered to the load that is connected to the output. Some heating is experienced using the variac due to the resistance of the winding wire but overall it is much more efficient that a resistive voltage divider.

If you find this confusing, than you should call a TEMCo variac specialist to help explain and educate you on a wide range of variac applications. This company has been in business for 40 years and can assist you in choosing a make and model of a variac to fit your needs. TEMCO has the experience and understanding of a wide range of variacs. Give them a call at 1-510-490-2187 and they will assist you with any questions you may have regarding any of their electrical products. They guarantee you will be a satisfied customer.



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