AC Motor Speed Controller Circuit

Posted on Feb 5, 2014

This triac-based 220V AC motor speed controller circuit is designed for controlling the speed of small household motors like drill machines. The speed of the motor can be controlled by changing the setting of P1. The setting of P1 determines the phase of the trigger pulse that fires the triac. The circuit incorporates a self-stabilizing technique

AC Motor Speed Controller Circuit
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that maintains the speed of the motor even when it is loaded. For example, when the motor of the drill machine is slowed down by the resistance of the drilled object, the counter-EMF of the motor also decreases. This results to a voltage increase in R2-P1 and C3 causing the triac to be triggered earlier and the speed increases accordingly. Actually the circuit has errors. The layout of the board does not match the circuit (C1 should not be connected to the gate of the triac according to the diagram). Also, the group R1 C1 C2 does not seem to have any role, probably the node C1 C2 has to be connected somewhere else in the circuit. I might use this circuit in my wife`s vacuum cleaner. Its speed control is drastically varying. The regulator uses a uC chip ST62T00C and a BTB16 600v triac. Nothing looks cooked` nor o/c nor s/c. The motor runs fines too. I`m about to try a BTB24 (24A) replacement. Maybe that`ll work. Using the circuit for a 1 amp 100 watt 1/8 HP universal motor I had to reduce C4 to. 022uF to get any sensible action. Then I dropped R3 to 33K, scrapped R2 and changed P1 to a value of 150K (well, I put a 470K in parallel with the original 220K var). This is a non-critical component, but 200uH seem unreasonably high. What I would do is to make a 50uH air core inductor by winding 54turns solid wire around a 1 ³ dowel. Select wire size for load current. However I can say from my experience that there is no way it can...

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