Smallest Portable Mini Fridge

Ashwini Kumar Sinha

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A Mini Fridge that can work with any power bank and without using harmful CFC gases.

Ever heard of a 5V portable freezer? Yes, you heard it right. In this DIY we design a 5V portable freezer that is easy to carry even while traveling. 

A freezer/refrigerator/fridge work on the same principle ie. Pumping heat from one system to another and thermally isolating both the systems so that the pumped heat from one system cools down. Meanwhile, the other system keeps getting hotter. The system generally acts like a radiator and transfers heat to a sink which is often the environment. Hence the heat transfer from the target system to the environment is done. 

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The same principle is used to make the 5V portable freezer. The heat is pumped using a thermoelectric generator. This can generate electricity based on the heat difference or it can pump the heat from one side to another side. 

While out on picnics or outdoor activities, having a cold drink is what everyone wishes for especially on a hot day, and hence we wish to have some cold storage or a mini fridge. Since these are only found in luxury cars and vanity vans, and apart from being expensive, the CFC gas is quite dangerous to our environment, especially the ozone layer. 

This freezer does not use a CFC gas system that causes harm. Also, it is portable and can operate even with less power. It can run on our phone’s power bank and battery. We can attach it to any car or bus to enjoy chilled drinks, ice cream, etc. on ours. The freezer is portable and can be carried in a travel bag and set against the car dashboard. It works on a 5V-1.5A power source, like a power bank/battery/solar panel.

Bill of Material

If you want a reference in Constructing a Power bank, you can watch the given video.

Designing 

The body of the freezer has to be thermally isolated as much as possible, hence that is designed first. Thermal isolation is much needed since any freezer works on the heat transfer principle, where heat is transferred from one system to another, making a part of the system much colder. Since the heat is pumped to another system, it makes the temperature of the recipient increase, so if the thermal isolation is not good, heat continues to enter the system and it becomes hard to maintain the temperature inside the freezer. 

Here we use the PLA 3D printed design of the freezer case and isolate it with thermal isolating material like Polystyrene/thermal isolator spray and paint. For the body of the freezer, one side of the box is kept open while the other 3 are closed. The open side is for inserting the heatsink and thermoelectric cooler module. 

World smallest Freezer design
Fig 1. Mini Fridge body
Refrigerator top design
Fig 2. Mini Fridge top part 

Connections

The components are connected according to the circuit diagram. The red wire is connected as a +ve wire of the thermoelectric cooler and fan with a 12V power source (battery). The -ve wire is connected with the -ve terminal of the battery and to the -ve wire of the thermoelectric cooler and 12V fan.

The next step is to fix the 3D printed parts and cover the edges with thermal insulator spray foam. Then the door of the freezer is added. A same-size transparent acrylic sheet is cut out and then fixed, such that using a magnetic-based lock system, we can use the door for opening and closing. Magnets are also fixed, on the door and fridge on the body as in Fig 6.

Thermoelectric TEC Peltieer connection for mini fridge
Fig 3 . Thermoelectric TEC Peltier connection for mini fridge
Fig 4. Components used for designing a mini-fridge
World smallest refrigerator
Fig 5. Mini Fridge in Action
Attached magnet within the mini fridge
Fig 6. Attached magnet within the mini fridge

The heatsink and fan are fixed, afterwhich the thermal paste is added and sandwiched between the thermoelectric cooler module and the heatsinks. The fan is added next to the top of the big heat sink fan as in shown in the figures below. (Refer Fig 7,8,9,10,11,12).

Heat Sink
Fig 7
Heat sink paste
Fig 8.The thermal paste on a heat sink 
Thermoelectric fixed and sandwiched between the heatsink
Fig 9. Thermoelectric fixed and sandwiched between the heatsink
Fan added to heatsink fin
Fig 10. Fan added to heatsink fin

Now the heatsink fan is fixed on the top of the refrigerator while inserting the smaller heat sink inside the refrigerator case. Warm the cut part of the refrigerator body and keep the fan exposed on the other side of the refrigerator. (Refer Fig 13,14,15,16).

The fin fixed on the top part of refrigerator body
Fig 11. The fin fixed on the top part of the refrigerator body
Lowest powered smallest refrigerator
Fig 12. The small heatsink fin fixed inside the refrigerator body
Fan exposed to open
Fig 13. Fan exposed to open
Refrigerator ready after fixing components.
Fig 14. Refrigerator ready after fixing components.

Testing 

World smallest referigerator
Fig. 16
smallest thermoelectric freezer design
Fig 15

Now power the freezer, which means the fan and thermoelectric cooler will now wait for a few minutes. The heat is now transferred from the inside of the freezer to the outside, making the inside cooler. After 15 minutes the freezer temperature goes down to around 0 degrees Centigrade, making it ready to use.

Your portable freezer is now ready to use and chilled water, ice, beer, and cool drinks can be stored. It can also be carried around anywhere you go, be it for picnics, outings, hiking or can be fixed in the car. 

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