Hi I have some questions regarding modifying a domestic fridge (Party Cooler) with an external temperature controller and wondering if there is anyone here with experience in such areas?
I’m trying to convert a small fridge I have for use as a fermentation chamber for beer brewing and wanted to check if doing so would be problematic at all. The aim is to be able to keep the fridge at a stable temperature of my choice - between 18° and 23° (the general range of temperature for ale yeasts) For lagers, where I would want to ferment at 12° I can use the inbuilt fridge controller (which has a max setting of 16°). My ambient temperature is 24°/25° - as I don’t want to add a heating pad, I am limited by the ambient temperature.
I’ve bought a temperature controller from KegLand in Australia ( RAPT Wi-Fi Temperature Controller Box | KegLand ) (the European model, of course with the correct plugs!) which as far as I can tell uses a temperature sensor to just cut and activate the main power to the fridge (it does have a secondary outlet for a heating pad, but I will not be using that). In the image below, the fridge plugs into blue; the heating pad to red.
The controller has a lot of options and configuration settings - which can be seen here: Menus | KegLand RAPT Portal Help - in summary (and of most interest)
- it can use the inbuilt sensor shown in the image above, or can attach to a remote bluetooth sensor
- Cooling Hysteresis: Sets the cooling hysteresis (range 0.0°C-10°C, default 1°C)
- Heating Hysteresis: Sets the heating hysteresis (range 0.0°C-10°C, default 1°C)
- Compressor Cooldown: Sets the minimum compressor delay (Range 0-10 minutes, default 5 minutes)
- Allowed Sensor Diff.: This sets the allowed temperature differential between the built in probe and the current setpoint when using a Bluetooth device for temperature control (range 1°C-50°C, default 5°C)
You can set profiles that will automatically adjust the set-temperature based on fermentation conditions (if you know, you know!) … so pretty cool! But at its heart it just appears to be enabling/disabling the mains to the fridge in response to the set temperature point vs current temperature sensor.
I have seen these (and others like Inkbirds) used on “standard” fridges (and freezers) however in my case, the fridge has some extra electronics (like most modern fridges I guess) and wondering if that’s going to be any issue? The fridge is one of those round party cooler types
(the actual product page if that helps is here: Andersson PartyCooler PYC 3.3 | NetOnNet )
The fridge has a max set temperature of 16° but the display knows that the temperature is higher - turning on after vacation it will show 24° for example which is ambient in my apartment. My speculation is they factor a lowest likely ambient of 16°; to “cool” to a higher value might not be possible (if ambient < requested temp) otherwise it appears they could just allow you to set a higher value!
Looking around on the internet, I haven’t found the exact schematic, but the following appears to be pretty close (and what I would expect)
(the above schematic is from this Party Cooler manual: https://img.karkkainen.com/kayttoohjeet/Kayttoohje_6438014380728_6438014380735_Cooltron_50L_75L_kylmasailio_FI_SV_EN.pdf - as you can see, they look slightly different, but same idea. It has the same 0-16° settable temperature range)
I’ve had it plugged into an energy monitoring smart meter, and collected the below screenshot
From the above, it appears the idle draw is 8W (when the compressor is off), and 17.3W when the compressor is on (is this right? Idle seems too high..?)
As mentioned above, the aim is to have a stable temperature from 18° up to ambient (25°). But looking at the above, in addition to the better temperature control. i can imagine power savings to be had as the fridge will be switched off completely, not drawing 8W idle! Additionally I had a situation where the internal temperature sensor got very confused (not sure why) and it was reading 25° even though the fridge contents were ice cold and there was ice on the walls. The compressor would turn on, run for a bit. Turn off, then immediately turn on again. I have only experienced this once, but an added bonus would be an external temperature sensor could prevent that from happening.
Given the above I am guessing that the MCU in the fridge is doing some computation on when to switch on/off the compressor. It’s not a mechanical thermistor that is controlling it - there is some hysterisis etc - it does a good job of maintaining 8° (which is my setting when I have it as a drinks fridge) - but I want fermentation temperatures.
When I plug the fridge back in (after being away on vacation for example) the compressor doesn’t start immediately. It also doesn’t run continuously until the desired temp is reach - it cycles. Which is likely a good thing to cool off the compressor etc. But this is also going to be under the control of the MCU, which is going to have its power removed/returned continuously (by the external controller)
SO! essentially, given the above - is there anything bad that could happen by using my external temperature controller which is going to be cutting the power to the fridge semi-regularly. Since the set temperature is going to be much closer to ambient than when running as a normal fridge, it should be cycling less - but still, it is ripping the mains power out from under the fridges feet! Will this cause problems with the fridges MCU magic? Anything I should be concerned about? I know I will need to dial in the hysteris, compressor cooling etc (any tips there would be appreciated!)
when not needing to be warmer than 16° is it beneficial to move back to the internal controller?
thanks! (I know this is not about DIY electronics, but I wasn’t sure where else i would find any experts in the topics… maybe the above is useful for building …. an environmental test chamber for electrical products!)
