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I plan to use a fridge as a temperature-controlled fermenting chamber, and I'd like to use some spare electronics to DIY a temperature controller that works by turning on and off a relay that sits between the wall outlet and the fridge's plug, so basically pulling the plug and plugging it back in depending on temperature. The fridge won't be moved or tilted between cycles.

My question is, since I am concerned about the well-being of the compressor, how long should I wait between turning it off and turning it back on, assuming this will be done multiple times per day ? I'm seeing all kinds of advice for when you move or tilt the fridge and how bad it is to restart a compressor too quickly, but no actual time for this particular use case.

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  • How about the make and model of your fridge.
    – JACK
    Jul 4, 2022 at 14:45
  • Fermenting for me usually means a higher(~75F) temperature than what a fridge maintains. Imagine you are in a place that is way above room temperature and need the cooling instead of heating function. A fridge should maintain temp for sometime(a few hours) without needing the compressor.
    – crip659
    Jul 4, 2022 at 14:59
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    @crip659 you get different flavor profiles at different temperatures, and there are a large number of common beer yeasts that work better for the desired flavor at temperatures ranging from 33-60 °F so if you don't have a handy cold cave, you need a cooler (most people use chest freezers, as they are more efficient both electrically, and how many fermenters you can cram into them.)
    – Ecnerwal
    Jul 4, 2022 at 15:51
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    I agree with Ecnerwal I haven’t used a cooler but used to have a basement “root cellar” that made a nice cool room great for aging mead also.
    – Ed Beal
    Jul 4, 2022 at 16:11
  • @crip659 Yep, the issue is that my yeast calls for a relatively low temperature (15°C/60°F) that needs to be relatively constant over a few days, so I need an automated solution. Furthermore current room temp over here is most of the time over 85°F which is too high for most yeasts, it makes stuff ferment too fast and you get off flavors.
    – anto418
    Jul 4, 2022 at 23:56

2 Answers 2

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Most ac systems have a short cycle controller that is usually adjusted for as short as 3 minutes and as long as 7.

One way to find out if your refrigerator has a short cycle timer is to turn it to the coldest temperature open the door and unplug. Wait a minute and plug back in, time how long it takes to start the compressor. I have seen as short as 1.5 minutes to 3 on small systems, repeat the test and if the delay is the same you have the manufacturer time delay (some do not have short cycle timers).

The short cycle timer prevents the system from trying to start while the pressure in the system is at its peak.

Another thing to consider is controlling the internal fan the coils will radiate cold but also stopping the fan from cycling the air over the coils can help.

It probably will depend on the temperature you are trying to regulate to if the additional fan control would be helpful.

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  • If you are willing to set up for and do a little datalogging you could also see what the fridge does when plugged in normally.
    – Ecnerwal
    Jul 4, 2022 at 15:55
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One thing that you should consider is the use of a zero-crossing SSR device if you expect frequent power cycling on the refrigerator. This may help extend the life of the compressor. I used these devices in a circuit to improve my pool pump's life. I had the SSR controlled by a timer with up to 12 cycles per day. See this for more info:

https://www.celduc-relais.com/en-us/zero-cross-or-random-relay-what-are-the-differences/

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  • I guess this is already present in the fridge's relay ? I don't plan to bypass the fridge's circuitry so it should be handled down the line from my controller, but I'll check it if I can get my hands on a scope, thanks for the reminder :)
    – anto418
    Jul 6, 2022 at 12:17
  • I highly doubt this is present in the fridge. They are expected to be plugged in once or twice in their useful life....
    – peinal
    Jul 6, 2022 at 14:33

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