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Onion Omega as a fridge controller?

  • Hello there,

    as I have this fridge whose parts are incredibly difficult to find, incompatible, etc, I thought about using an Onion Omega to replace the existing board whose specifications are frustratingly unknown, and where no manual is available.

    Keeping the absorbing coil free of ice appears to be the most difficult part of the project: the air inlet at the bottom of the coils is tiny, and easily clogged by frost. As such, only 4 days of normal use are necessary to build enough ice the fan can't push enough cold air toward the fridge. (Conversely, when the coil is completely free of ice, it takes only 20 minutes of runtime to have it turn off for 25 to 45 minutes)

    A still-unresolved question is: how does so-called "adaptative defrost" work?

    Would such a project be feasible for someone who doesn't have a degree in refrigeration engineering or electronic engineering?
    Is the Onion Omega the right platform for this project?

    Existing inputs:
    Temperature sensor in the freezer (likely broken, maybe reuse wiring?)
    Temperature sensor in the fresh food section (likely analog)
    Control panel inside to adjust temperature

    Features would be:
    Keep fresh food section at standard fridge temperature (4C or less)
    Keep coil ice-free

    Optional but nicer: make a LAN-accessible graph of compartment's temperature over time

    In any case, just laying the idea here…

  • @Patrick-Nou I can't really answer most of your questions, but if the temperature sensors are analog you'll need to either replace them or use something to convert their output into digital for use with the Omega. There are a billion different ways to go about converting the values to digital, but then there's the fact that you'd also need to calibrate any code related to them to match the specifics of the sensor itself -- they may not have a linear response curve for temperature, for example. Might be easiest to just replace them with good, digital ones instead.

    I don't know what would be the best way to keep the air inlet of yours ice-free. Enlargen it? Maybe a PTC-heating element that's turned on every couple of days for ~5min or something to melt any ice on it? That would be easy, but I don't know if it's a good idea or not.

  • @WereCatf Indeed turning it on every few hours was the classical way to deal with ice build-up for 10 to 15 min at a time, only. However, this is inefficient and to save electricity, modern fridges use adaptative defrost.

    I don't have any data on the current sensors, they are just enclosed in white, unmarked tubes.

    I thought about enlarging the openings, but I also understood air needs to be pulled through the maximum number of loops possible for proper cooling.

  • Adaptive defrost is a field of research in itself. You can use what you have right now, no need for any external blower to mess with your results, but you'll have to adapt your strategy over time. Your fridge is a functioning balanced environment in itself. You just need to learn how to power it efficiently. Keep in mind that Temperature Regulation is a VERY SLOW process. First, you need the temperature inside your fridge at all time, that you can study at any time, maybe a sample every 10 sec. would be manageable? Try it to find out. You need to note the actions that the fridge performs (compressor on, compressor off), and mix with that your visual observations on the coil (amount of frost, thickness). The result doesn't need to be perfect the first try, but you need to try different strategies (power duration and rest duration) to find out which strategy work best for YOUR fridge.

    Well, that's how I would do it! Good luck! Keep us informed about your progress. It's always fun and motivating to see good results out there.

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