Mosfet controller kills the hevac hum

The triac-based speed controllers traditionally used to control fan and pump motors in heating and ventilation installations have a weakness - their non-sinusoidal output creates complex magnetic field patterns in the motor windings, resulting in an irritating hum.

Now a Salisbury company specialising in this market has developed an electronic speed controller for single-phase motors which, it claims, produces a sinusoidal output, thus eliminating the noise problem.

Stock Electronics (SEL) adds that its Mosfet-based controller also boosts efficiency because without the triac switching harmonics, the motor runs cooler. SEL says that its QMC controller provides stable voltage settings, unaffected by motor load conditions, even for two-pole machines that cannot be used with triac controllers.

It can be used with motors with operating currents up to 1.5A. SEL says that the controller is smaller and lighter than the transformer controls usually used to tackle the noise problem, and is cheaper than conventional PWM (pulse width modulation) speed controls.