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No tachometer speed regulation for small motors

2016-09-02 16:46  
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A power factor control system for use with AC induction motors which samples line voltage and current through the motor and decreases power input to the motor proportional to the detected phase displacement between current and voltage to thereby provide less power to the motor, as it is less loaded.Motor speed controller circuit is designed for controlling the speed of small household motors like drill machines.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 provides bidirectional speed regulation for small motors and requires no tachometer. The voltage that summing amplifier  IC1A  applies to the motor`s windings equals: where Vc is the command voltage and IM is the motor current. If you set the motor`s winding resistance and brush resistance (RM) equal to: the command voltage will be proportional to the motor winding`s counter emf. CI provides compensation. Set Rl`s value so that it equals 5 to 10% of RM`s value. You can generally find RM`s value in a motor`s spec sheet.

Tachometerless Motor Speed Control