Report Speed control of cooling fan in Vision & Samba PLC + HMI Controllers & VisiLogic Software Posted yesterday at 01:39 AM I'll try to fantasize a little on this topic. You have an AC fan. There are two points in such devices. The first - the fan is guaranteed to start only after reaching a certain supply voltage. Second - by slowing down the fan you can go to a voltage lower than the starting voltage and the fan will still rotate. Therefore, I recommend determining the PWM at which the fan will start if you gradually add voltage. Conversely, determine the PWM when it stops when the voltage drops. I think that's all you need to know. By setting the adjustment within (minimum starting voltage + some margin) up to 100% PWM - you will have everything your fan can. However, in general, it is said that it is illogical to apply a voltage below 40% of the nominal voltage to the fan - because the fan no longer creates an air flow.