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Multi Purpose Rotary Machine - Mulling, Welding, Pottery, Photography Turntable

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Step 19: Motor Control #5 - Triac Triggering, Snubber Circuit and Transients

Picture of Motor Control #5 - Triac Triggering, Snubber Circuit and Transients

To trigger the power triac (the BTA16) we use an MOC3023M optocoupler connected to pin A3 of the Arduino. The optocoupler isolates the relatively fragile 5V Arduino microcontroller, from the mains voltage triac.

Transients are basically voltage spikes cause by inductive loads like motors. They can play havoc and cause unwanted triggering of the triac - essentially leading to choppy unpredictable motor running.

The snubber circuit 'snubs' the transients. It consists of resistor R14 and capacitor C4. I also added a 400V varistor in parallel with R14 and C4 (not shown in schematic).

A varistor is a device that will block current unless a certain high voltage is reached, at which point it will all of a sudden conduce. It is useful for redirecting voltage spikes if and when they occur.