Electronic – use a DC SSR that is switched by a PID controller to control the speed of a 12 V DC fan

dcmotorpid controllersolid-state-relaytemperature

This is my first post here. Let me start by saying that I do not have an engineering background. I tinker with electronics in my spare time (Arduino, solid state low-power guitar amps, etc.), but I do not have a classical engineering education. Please forgive (and feel free to correct) any incorrect terminology that I use.

I would like to use a PID controller (CD101) that will switch a DC SSR that controls the speed of a 12 V low-power DC fan. The desired application is controlling the amount of air that enters into a BBQ smoker grill. I want the PID to hold the temperature inside the grill at a constant level.

I've done a lot of google-research, and I haven't found a lot of people who have taken this approach with motor control. I'm all for learning lessons the hard way, but I wanted to see if anyone in this forum thinks this is a simple approach, or if there are glaring issues with this idea.

Best Answer

If you want to use the PID controller you linked to, you will need to work within the constraints of that device. Like many heat/cool industrial PID controllers, it provides two outputs - one for heating and one for cooling.

Relay output: contact capacity 250V AC 3A (resistive load) (Refrigeration)

Voltage pulse output: 0/12V (suitable for solid state relay SSR) (Heating-up, a 12V relay needed)

In your use case, using a fan to cool your smoker, you'll be using the PID controller in cool mode (refrigeration). As a result, you're stuck with a relay output. Typically, these outputs are made to work with chillers, which require long on-off cycles. Heater outputs are more often time-proportioned (it's basically PWM with a total period measured in seconds--fine for heater control). Some PID controllers can be configured to be reverse acting, which would allow you to use the heater output to control a cooling fan. In looking at the manual, it did not appear that this particular model supports such functionality.

You can add a small pilot relay with contact ratings that compatible with your fan, and simply live with on-off fan control. A quick perusal through the controller manual didn't suggest that there was a lot to this unit that could be configured, so if you really want a variable speed fan, you should look for PID controllers that can support other output options for cooling (or generic) outputs.