Hello,

New Guy looking for an education! My field is HVAC; every day is something new. I have a problem I am Trying to solve and need some input. I have a 277 volt P.S.C. motor with a solid state speed control, used for a blower motor. I am wondering how the speed control lowers the voltage but maintains the amperage, understanding ,and any guidance, or info would be appreciated.

 

Pulse Width Modulation, or a variation of same.

For AC, Triacs are used to chop the turn on time of the sinewave in both directions. Such as in a light dimmer. More advanced circuits do full PWM on the sinewave.

The most common circuits pulse DC at full voltage/current several thousand times per second at different duty cycles (time on vs. time off) to vary the speed.

Essentially, the voltage and current are never changed. It simply turns the power on and off quickly to keep the motor turning at the desired speed.

Hope that makes sense.