Temperature-controlled Freezer

Using Arduino Motors, Mechanics, Power and CNC
1

I am planning of using an Arduino to control the internal temperature of a freezer.

Since I don't want to modify the freezer, I will take the approach of switching its mains supply ON/OFF through a SSR. This has already worked well enough with an off-the-shelf temperature controller, so I am not expecting major problems.

Two questions, though:

  1. Will I need a snubber circuit to protect the SSR? I don't think so, since I will not be driving the compressor directly, but I'm far from being an expert in electronics, so I'm not sure.

  2. I was originally planning of writing the controlling algorithm myself, but then I found out about the PID library: would you recommend its use?

Thanks!

2
  1. I was originally planning of writing the controlling algorithm myself, but then I found out about the PID library: would you recommend its use?

Since you can't expect the refrigerator to run well if you turn the power on and off frequently you probably won't have much use for PID.

Is there some goal to the electronic control that can't be achieved with the normal mechanical thermostat?

3

Of course :). The original thermostat does not allow precise temperature control (i.e.: 4°C), it only has vague "levels of cold" (i.e.: 1 ... 5). Since I need to maintain some precise temperature, I have to resort to a different solution.

As mentioned, I've already done it with an off-the-shelf temperature controller, but now I want to be able to monitor (and control, to a certain degree, i.e.: bypass) the situation remotely, so I need to build my own web-enabled temperature controller.

Thanks for the hint!