I've been reading about a few projects where people controlled refrigerator temperature by replacing the fridge's board with an arduino. No one (that I've seen or read about) has been very specific about how they actually rig up the hardware, usually there is talk of relays and controlling the compressor, but as someone who hasn't tinkered with refrigerators I don't know how they're doing it. Are they hooking up to a pre-existing relay that controls the compressor? Are they putting in a relay between the refrigerator's main power cable and the home power outlet?
What other hindrances are there controlling a refrigerator with an arduino? I've heard that the defrost cycle can be an issue, if so, how is it usually taken care of?
Seems like a very interesting idea that I'd like to give a try if I can.
I don't know how people doing this sort of thing usually tackle it, but a typical bimetallic 'otter switch' style thermostat is a simple make/break switch which can be replaced by a plain old relay.
Seems like a very interesting idea that I'd like to give a try if I can.
If you want a reliable refrigerator, repair/replace the parts that were made for it. Why do you want to change the way the refrigerator currently works (with just a little maintaince, they often work for decades)? I repaired my refrigerator sometime back and learned a lot.
I agree, controlling a refrigerator via an Arduino is kind of a what for situation. However if there is a valid need one should start out with a good electrical drawing or service manual to see how it presently works and what components it uses. Also improper compressor cycling can cause damage to a compressor so be sure you understand proper refrigeration fundamentals. I would suggest trying a project that doesn't involve household AC or large size motors because as the old saying goes, if you have to ask you probably shouldn't be fooling with it.
Most cheap refrigerators controllers are purely mechanical, they simply close a switch when the sensor gets warm(ish) and open the switch when the sensor gets cold(ish). This is done by long aluminium pipe filled with liquid that expands when it warms, causing the switch to flick over, then when it cools down, it contracts, causing the switch to flick the other way. The most common causes of failure on these controllers is the aluminium pipe leaking so the liquid can't expand enough to flick the switch or the contacts on the switch wear out. This type usually has adjustment screws but if you have to move them the controller is about to fail completely. I've also seen the switch simply stuck in one position. You can also have bimetal spring that flicks the switch over.
The more difference you set between warm and cold, the fewer times the compressor starts (each day) and the longer it runs each time it starts. Since it's aircooled you don't want it to run for too long and you also don't want it to be constantly switching on and off.
The cheapest defrost methods are simply a clock that keeps the compressor off for some time, allowing the temperature in the freezer to rise and melt the ice from the coils. The most complicated use all sorts of electronically controlled valves and pipes to actually run the system backwards so that the cooler becomes heater but it's only run for long enough to melt the ice from the coils, then it resumes normal operation.
Just for info, below is the schematic for my refidgerator. Newer ones have door opening counters and such to modify defrost cycles and such. Never heard of a consumer level refrigerator with gas reversing valves like in a heat pump (but then I haven't been looking).
