PID DC fan control using ssr or 4-20ma

Thread Starter


Joined Sep 12, 2013

I want to control the temperature of a charcoal bbq by controlling a fan speed. I did built it using a PID controller. The actual fan (120v) speed is controlled using an ssr. Work great, but.... it is overkill. Two much air, i need a smaller fan. A 12v oc fan should be fine

To my understanding, my pid controller output is either pulsed output for an ssr relay or 4-20ma. The ssr won't work to control a dc fan. How can I create or use to control a dc fan (0.5W) using either 4-20ma or input from the ssr (the output of my PID controller)

Hope I'clear. English is not my first language and my electronics experience us getting old.


Joined Dec 2, 2013
When your controller (PID) is two wire active you need a simple transistor circuit (current amplifier ).
Make sure that the first 4mA are under the conducting threshold.

fan 0,5 W I assume 12V max current 0,5/12 amp 40mA approx nearly any transistor will do.