Exhaust Fan Control - convert AC variable voltage control to DC 0 to 10 volt control

Thread Starter


Joined Dec 23, 2019
Retrofitting an exhaust hood that uses variable voltage AC to control the exterior remote fan motor (attached line diagram - remote blower cable).

I am upgrading the fan motor to an ECM motor that has an RTC FS-1 controller (see attached manual). The controller permits remote control via a 0 to 10 volt dc input.

As the hood and control are already installed and would require significant work to remove, retrofit or replace. How would it be easiest to convert the current variable AC output used by the current motor to a 0 to 10 volt DC output? I plan to run a new, independent power supply to the upgraded fan so as an option the existing power wiring may be used for control when safely isolated from the power side.

Hood wiring diagram.jpg



Joined Feb 22, 2014
Hmm... well there is no nice way of doing it directly, as you would always run the potential risk of something going wring with your circuit (unless you get complicated), and then putting the full 120V into your fan controller. Your best bet would be to get at the wires from the hoods existing speed controller (which is probably just 3 wires from a potentiometer). Disconnect them from the existing circuit and use them on the new controller between gnd control signal and +10v