VARIAC VARIABLE VOLTAGE AC POWER SUPPLY

P. Wokoun, Sr. (10/2008)

 

 

Front panel view of variac power supply.

 

 

 

This is the front panel view of my variac power supply. What makes this supply unique is that it makes available both output ranges that can be selected from the variac taps. Normally you only see variacs wired one way or the other.

It uses a General Radio type W5 variac rated at 7.8 amps 0-120 VAC output and 6 amps 0-140 VAC output.

With 120 Volt AC input the output can be set to either 0 to 120 Volts AC or 0 to 140 Volts AC, depending on how you move the ON/OFF switch.

It was built into an old General Radio case.

 

 

 

 

 

 

ON/OFF SWITCH.

 

 

 

 

The output range is selected from the ON/OFF switch: UP for 0 to 140 Volts AC output and DOWN for 0 to 120 Volts AC output. The switch center position is OFF.

A power-on indicator light is also included.

 

 

 

 

 

 

 

 

 

 

Voltage adjust knob.

 

 

 

 

The voltage adjust knob is marked off in PERCENTAGE of the full scale range selected. For example, with the knob at 100%, on the 0-120 VAC range the output will be 120 volts, on the 0-140 VAC range the output will be 140 volts. To avoid having to calculate the output voltage, the output voltage can be read directly on the meter.

 

 

 

 

 

 

 

 

 

 

 

 

 

Output voltage meter.

 

 

 

 

The output voltage can be read directly off the meter scale when using either voltage output range.

 

 

 

 

 

 

 

 

 

 

 

 

variac power supply schematic

 

 

Schematic of the variac power supply.

 

Click HERE for schematic in .pdf format.