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How to regulate fan speed with AC induction motors?

Motor and fan related questions

An AC voltage controllable motor is an AC induction motor that can be controlled by varying the motor voltage. Sentera offers different types of fan speed controllers for these types of motors, based on different technologies:

Technologies that regulate the motor speed by reducing the motor voltage:
Transformer fan speed controllers feature a 5-step speed control for AC voltage controllable motors. These fan speed controllers with autotransformers provide a simple, yet robust solution to control the fan speed by adjusting the voltage of the AC voltage controllable motor in steps. In some cases, the fan speed controller can produce a humming noise due to the autotransformer technology, but the motor will be very quiet. Available for single or three phase voltage controllable motors up to 20 A.
Electronic fan speed controllers feature an infinitely variable speed control for AC voltage controllable motors. These fan speed controllers use Phase angle control (TRIAC technology) to adjust the motor voltage and to control the fan speed. Thanks to this technology, the fan speed controller will be very quiet. Depending on the motor type, the motor can cause a humming noise at lower speeds. Available for single or three phase voltage controllable motors up to 10 A.
AC choppers feature an infinitely variable speed control for single phase AC voltage controllable motors. These fan speed controllers adjust the motor voltage via PWM (Pulse Width Modulating) technology using IGBT's (Insulated Gate Bipolar Transistors). Compared to Electronic fan speed controllers, AC choppers generate an almost perfect sinusoidal motor voltage. Both motor and fan speed controller will be very silent. Available for single phase AC motors up to 2,5 A.

For those AC induction motors that cannot be controlled by varying the motor voltage, a frequency inverter or Variable Speed Drive (VSD) is required. 
Frequency inverters generate an almost perfect sinusoidal motor voltage via PWM (Pulse Width Modulating) technology using IGBTs (Insulated Gate Bipolar Transistors). The ratio of voltage to frequency is kept constant, resulting in an optimal motor control and very silent operation of both motor and frequency inverter. Available for single or three phase motors up to 46 A.

In all of these scenarios, the desired motor speed can be adjusted manually via a knob (local or remote control) or in function of CO2, air quality or another parameter (demand based). In this second scenario, an HVAC sensor is connected to the fan speed controller to calculate the optimal fan speed. More information can be found on the Sentera solutions page.