TLDR SUMMARY: I want to power a refrigerator circulation fan from two different power sources: the fridge's original source from its motherboard, and also from an MCU that I control. How do I do this?
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About two years ago I purchased a new Blomberg kitchen refrigerator. It wasn’t long before we noticed that our fresh greens were freezing regularly unless we placed them on the top shelf. They would freeze in the crisper shelf which was at the bottom of the fridge. During that first year we had a repair person come three times to try to fix it. Once he tried replacing the circulation fan and once replacing the fridge’s motherboard. I got to keep the “broken” parts (I tested the 12V fan he pulled out and it worked fine). Anyway, it’s now been two years and I’m not happy with the temperature control. Veggies keep freezing, but not as frequently, and something is definitely not working right, and I’m no longer under warranty and don’t want to pay the high repair bills.
Here’s what I’ve done so far: Using an MCU (an ESP8266 - Wemos D1 mini), I set up 4 calibrated temperature sensors on 4 different shelves in the fridge. I took readings every 3 minutes and sent them to an IoT cloud service. The results were very useful! (see attached graph)
I concluded the following:
My conclusion from all of this is that the circulation fan is just not staying on long enough.
I’m writing you for a review of my design to force the circulation fan to be on for longer periods, which should keep the fridge from having extreme temp differences between the top and lower shelves.
Here are the parameters I have to work with:
Please review the attached schematic. It uses a DPDT relay “controlled” (the coil) by the motherboard that turns on the circulation fan.
Do you think this will work? A simpler plan is to not use a relay and just disconnect the fan from the motherboard completely and power it only from my own source. Don’t know if this is a good idea or not.
BTW, this is my first post - I have learned so much from following this forum these past months - thank you!!!
READ THESE DETAILS IF YOU PLAN TO REPLY:
About two years ago I purchased a new Blomberg kitchen refrigerator. It wasn’t long before we noticed that our fresh greens were freezing regularly unless we placed them on the top shelf. They would freeze in the crisper shelf which was at the bottom of the fridge. During that first year we had a repair person come three times to try to fix it. Once he tried replacing the circulation fan and once replacing the fridge’s motherboard. I got to keep the “broken” parts (I tested the 12V fan he pulled out and it worked fine). Anyway, it’s now been two years and I’m not happy with the temperature control. Veggies keep freezing, but not as frequently, and something is definitely not working right, and I’m no longer under warranty and don’t want to pay the high repair bills.
Here’s what I’ve done so far: Using an MCU (an ESP8266 - Wemos D1 mini), I set up 4 calibrated temperature sensors on 4 different shelves in the fridge. I took readings every 3 minutes and sent them to an IoT cloud service. The results were very useful! (see attached graph)
I concluded the following:
- the difference between the warmest shelf (top) and coldest shelf (bottom, but above the one crisper drawer) was often around 20 degrees and sometimes more than that
- the circulation fan blows air from the top shelf down to the bottom shelves behind the back wall where there’s a cooling element.
- the circulation fan turns on just once every 3-4 hours and is on for approximately 15 minutes
My conclusion from all of this is that the circulation fan is just not staying on long enough.
I’m writing you for a review of my design to force the circulation fan to be on for longer periods, which should keep the fridge from having extreme temp differences between the top and lower shelves.
Here are the parameters I have to work with:
- I can access the power lines to the the circulation fan. It’s a 12V DC fan using 0.16A
- I can NOT access any continuous power source within the fridge
- I want to power the fan from the 5V power source that powers my ESP8266. I’ll run two wires into the fridge with 5V from a wall wart
- I’ll write an algorithm for the ESP8266 that will attempt to turn the fan on whenever the temperature difference between the top and bottom shelves is over a fixed amount (maybe 12 degrees)
- I want the fan to stay connected to its existing motherboard connection AND to alternatively power on by my device based on my algorithm whenever it’s not being powered by the motherboard. (i.e. I want the motherboard to think that everything is operating normally, and not throw an error code if it senses the fan isn’t connected). (Is this realistic? I don’t know! Any Blomberg engineers listening in???)
Please review the attached schematic. It uses a DPDT relay “controlled” (the coil) by the motherboard that turns on the circulation fan.
Do you think this will work? A simpler plan is to not use a relay and just disconnect the fan from the motherboard completely and power it only from my own source. Don’t know if this is a good idea or not.
BTW, this is my first post - I have learned so much from following this forum these past months - thank you!!!