While I was engaged in the construction of a country house. I did not leave the desire to come up with how else you can use extrusion polystyrene foam. To date, this is one of the most effective insulation with a huge amount of advantages and a very affordable price. The first thing I realized that for traveling products to the hypermarket is very useful to have a container-thermos in which you can safely transport frozen foods. For the manufacture of such a box it took 160 rubles and half an hour of free time. But I decided to go further and modify the design in order to use it as an autonomous refrigerator.
Let's start making!
2. So, let's start with the thermos container. We will need one sheet of polystyrene foam with dimensions of 1200x600 mm, 50 mm thick, stationery knife and roulette. The cost of such a sheet in any construction store is 160 rubles. We cut the leaf on the template, take the mounting foam and glue this container.
3. Here is the sheet cutting scheme. The sheet has flights with a thickness of 20 mm, they need to be cut off from all sides, except for the bottom. Burnt of the sheets are glued with mounting foam. Technology is simple. Apply a little foam into the place of gluing, we are waiting for 1 minute, tightly press sheets to each other and then for 5 minutes manually control so that they do not move due to the expansion of the foam. Do not leave unattended. Experience only a small piece of polystyrene foam marked with gray in the diagram.
4. Pay attention to the design of the cover, one of the large sheets from the circuit from the top I cut into 3 parts on the place when gluing to ensure dense fixation. After that, the box outside can be painted. The paint has a little corrosive polystyrene foam, so it is better to paint in two stages. The resulting container weighs 820 grams and has incredible indicators on heat loss. In such a box, you can put a few kilograms of frozen products and to transport them without any problems within a few hours. The main thing is not to mix frozen and cooled products. You can add a cold battery design.
5. And you can refine the design to get a full-fledged refrigerator. For these purposes, we will use the Peltier element - the thermoelectric transducer, the principle of operation of which is based on the occurrence of temperature difference when the electric current occurs. It is such elements that are used in serial automotive refrigerators, as well as automotive seats with ventilation.
The cost of one peltier element is a maximum capacity of 60 W on Aliexpress - 130-150 rubles. Model TEC1-12706. In the process of operation, one side of the element is heated, the other is cooled. To the element is not burned, it is necessary to intensively distinguish heat from the hot side. To do this, we need a processor cooler with a radiator from a computer store, worth 250 rubles. To improve the circulation of air inside the refrigeration chamber and exclude the reflection of the radiator, I decided to install fans on both sides. We also use a thermostat with an external thermal sensor and relay, worth 170 rubles, which will allow you to control the specified temperature inside the container. Well, the wire extension with the connector for the car cigaretteve for 100 rubles.
So, proceed to the assembly.
6. Peltier element using thermal paste (comes with a cooler) set between two aluminum radiators. It is worth noting here that it is possible to increase the temperature gradient of the installation, if you make the assembly of the sequentially installed 2 or 3 Peltier elements. So that one element of Peltier cooled another. In this embodiment, in the container really get a negative temperature to -18 degrees Celsius. Around the perimeter between the element laying a piece of foam insulation.
7. Between themselves, radiators connect with standard mounting plates to the motherboard, connecting them with plastic clamps. This allows you to thermally isolate the cold and hot side from each other. Trial launch installation. The more intense we will cool the hot side, the lower the temperature on the cold side. Here the fans are directed to the influx of air on radiators, it is less efficient than to flip them over to blowing. In an improvised box, a temperature of -3 degrees was achieved, at ambient temperature +26. The photo is clearly visible model of coolers, their advantage in a large area of the supporting platform of radiators. And as a thermal insulation laying, I used a piece of thermal insulation for round pipes.
8. Now we will deal with the integration of the thermoelectric converter into a new cover for the container. For the convenience of placing the entire design, we will increase the thickness of the cover to 100 mm (2 sheet of polystyrene foam). This photo clearly shows a gasket around the perimeter between two radiators.
9. Art cutting on expanded polystyrene and handling of sandpaper. Pray again. After painting, the outer shell of the polystyrene is becoming stronger.
10. Seams with a sealant, both fans turn to blowing out. From potential improvements - it is possible to reduce the fan speed on the cold side (now both fans are operated at maximum speed).
11. Near the housing, install the thermostat fee and fix the power wire with such an unpaid way. First we press the plate with the help of screws, then fix the sealant.
12. Container assembly. The weight of the container without a cover is 800 grams, as much as the lid is weighted with the thermoelectric converter assembly. Total costs - 1000 rubles and a couple of time. Tests with oxidized products in the car trunk showed the system's ability to maintain the temperature at the bottom (!) Of the container within +5 degrees Celsius, at ambient temperature +29 degrees (yes, in the trunk is much warmer, even when air conditioning) and current consumption - 3 Ampere. It seems to me that this is an excellent result.
The following container is planning to make out of 3 consistently installed Peltier elements to get a full freezer.