1 Answer

Things You'll Need

120V to 12V transformer

1 extension cord with the receptacle end cut off

1 full wave bridge rectifier

1 wire wound potentiometer

Electrical wire

Wire strippers

Wire cutters

Voltage meter

Instructions

1 Strip 1/2 inch of insulation from the cut end of the extension cord. Connect these two wires to the 120 volt side of the transformer. Connect the two 120 v AC terminals of the bridge rectifier to the two 12 volt terminals of the transformer.

2 Connect the 12 volt negative terminal of the bridge rectifier to the fixed terminal of the variable potentiometer. The fixed terminal of the potentiometer will be the negative output for the power supply. A wire can be run from the fixed terminal to allow easier access to the terminal.

3 Connect a wire to the 12 volt positive terminal of the full wave bridge rectifier. This wire will serve as the positive terminal of the variable power supply.

4 Connect the positive and negative voltage meter probes to the positive and negative wires of the power supply. Set the meter to read DC voltage. Plug in the power supply and note the readings. Verify that the readings change based on the position of the variable terminal of the potentiometer.

Read more: http://www.ehow.com/how_6782658_build-variable-dc-power-supply.html#ixzz2yUl6cxZF