I was planning to mature both meat and cheese within my fridge. However, as their temperature requirements differ significantly and the original thermostat in my Beko has a significant tolerance, I decided to upgrade my fridge with an electric temperature controller.
The plan to upgrade my fridge with an electric temperature controller.
I was initially planning to build an Arduino or a Raspi based controller, but then a good friend said, that the application I’m trying to build, is probably one of the most used in industrial applications, there’s bound to be tons of ready made gizmos at reasonable prices. And oh boy there were.
I ended up choosing an STC-1000 (I should’ve ordered from Amazon, probably would’ve gotten what I ordered), that is really widely used in strange home applications from brewing beer to upgrading fridges.
In addition to the temperature controller, I ordered some digital hygrometers, so I can see the humidity inside the fridge and get rid of my Xikar cigar hygrometer. I ordered the stuff and started waiting.
The reality – wirings
Well, first of all, the cheap STC-1000 I ordered turned out to be an even cheaper MH1210. In my setup, it luckily doesn’t matter, but I was a bit surprised. Neverthelss, I started stripping wires.
I built an easy setup to test the controller, where the load was a lightbulb, so that I could see the relay working. It did, I used the original wiring diagram as my guide and it worked like a charm. I bought a pack of wago connectors to ease the installation and they worked like a charm as well.
The next step was to look inside the fridge and see how I could connect the controller to control just the compressor, not the fan nor the light. I’ve read a post, where they just connected the mains socket of the fridge to the controller, but that would prevent the fan from operating as well, when the target temperature is reached. In addition, as the original thermostat was quite sloppy, I’d still be stuck with it, even though I could crank it to max cold.
So I pulled the fridge from the wall and tried peek into how the wiring is arranged. I finally realized, that the old thermostat must control the compressor and thus should be easier to examine. An so it was. I opened the thermostat casing and found four wires; a ground, a live and a black and a white wire. I was trying to google around the Ranco K54 thermostat to find the pinout diagram but I didn’t. So enter the trusted multimeter.
I identified the black wire to be the fan and the white to be the compressor. As I wanted the fan to be constantly on and the compressor to turn on when needed, I attached the fan to the live wire and attached the compressor to the relay in my controller.
The stragest thing was, that without the compressor in the controller, the fan turned on. But as soon as I attached the compressor to the controller, the fan stopped working. So I did a hack where I fed the controller power from a different mains cord than the fridge’s own. That made the whole setup work.
I justified this to myself, as I plan to install another of these controllers to heat a thermal box in the fridge to a nice 10°C for my cheeses to ripen. That controller can then be attached to the same mains as the one I now used to upgrade my fridge with an electric temperature controller.
The mechanical setup
I drilled a hole to the back of the fridge. having read a bunch of stories, where the drill had hit a coolant pipe, I really carefully probed with a screwdriver first through the insulation and then lightly drilled through. When I hit something hard, I knocked on it with a nail, to confirm it was plastic, i.e. the back wall of the inside of the fridge. So I pushed through.
For the hygrometer, I realized that it works with Lithium batteries. That I don’t have. So I just stripped the sensor from its casing, so I could fit it through the hole I drilled. In the end, I taped the wire to the inside wall of the fridge.
Once both wires were through, I placed some duct tape on top of the drilled hole to reduce the airflow to and from the fridge.
The verdict
So far so good. I think this will increase my electricity consumption, as the compressor is more often on. I may have to adjust the controller to give the fridge some more tolerance (now it is 1,5°C) as long as it is better than the previous (somewhere around 5°C).
I will need to build a case for the temperature controller and the hygrometer. I think I’ll setup the cheese cave mod first and then plan the case. There’s a great guide to follow, with three different setups (I chose option 2).