Both electronic fan speed controllers and transformer fan speed controllers offer reliable speed regulation for AC voltage controllable motors. Electronic fan speed controllers allow you to regulate the rotational speed of AC fans manually or demand based. Phase angle control, achieved with triac technology, is used to adjust the motor voltage and to control the fan speed. On the other hand, fan speed controllers with autotransformers provide a simple, yet robust solution to control the speed of AC voltage controllable motors in steps. The AC motor can be controlled in 5 steps, manually or demand based. There are solutions available for single phase 230 VAC or three phase 400 VAC voltage controllable motors.