Features and Power Control Circuit

The hardest part of the build was to find and / or design a circuit that could handle the load and still stay with in my budget. This little circuit does both. It varies the power output with one potentiometer (variable resistor) R1. R1 is a panel-mount pot  with a  shaft for a knob. It varies the power by synchronous triggering across the
Features and Power Control Circuit - schematic

triac. On the triac TR1, terminal T1 is input, terminal T2 is output and G is the gate. All the parts were readily available form my local electronic supply store and built on a point to point prototype circuit board. This is a simple but a reliable circuit which will handle 15 Amps but in my unit it only has to about 4 Amps since I am controlling the primary windings of the transformer. On a side note, this circuit can be adapted to numerous other applications where controlling power is a requirement as in a lamp dimmer or putting a variable speed feature on an AC motor like a drill. As soon as SW1 is turned on, L1 and FAN1 come on. I wanted to do all the switching and control on the primary side of T1. Even though the voltage is higher (120VAC), the current would be much lower. The circuit is switching the incoming AC into the power control circuit thru relay RLY1. In turn, RLY1 is being controlled by SW2. The current draw of RLY1 is very small so this allows SW2 to be compact allowing mounting almost anywhere as in my pistol  like soldering gun (carbon rod holder). I mounted SW2 in the trigger position eliminating the need for a foot switch. With my tweezer set up, the floor switch is still employed. L2 comes on with RLY1 and is mounted to the front panel. Voltage is fed from the power control circuit to T1. The highest current draw that the power control circuit with RLY1, FAN1 and T1 at full power is approximately 4...

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