Refrigeration equipment has become so firmly established in our lives that it is even hard to imagine how it was possible to do without it. But the classic refrigerant designs are not suitable for mobile use, for example, as a travel cooler bag.
For this purpose, installations are used in which the principle of operation is based on the Peltier effect. Let's briefly talk about this phenomenon.
What it is?
This term refers to a thermoelectric phenomenon discovered in 1834 by the French naturalist Jean-Charles Pelletier. The essence of the effect is the release or absorption of heat in the zone where dissimilar conductors come into contact, through which an electric current passes.
In accordance with the classical theory, there is the following explanation of the phenomenon: an electric current transfers electrons between metals, which can accelerate or slow down their movement, depending on the contact potential difference in conductors made of various materials. Accordingly, with an increase in kinetic energy, it is converted into heat.
On the second conductor, the reverse process is observed, requiring replenishment of energy, in accordance with the fundamental law of physics. This is due to thermal fluctuation, which causes cooling of the metal from which the second conductor is made.
Modern technologies make it possible to manufacture semiconductor elements-modules with the maximum thermoelectric effect. It makes sense to briefly talk about their design.
Device and principle of operation
Modern modules are a structure consisting of two insulator plates (usually ceramic), with thermocouples connected in series between them. A simplified diagram of such an element can be found in the figure below.
Designations:
- A - contacts for connecting to a power source;
- B is the hot surface of the element;
- C - cold side;
- D - copper conductors;
- E is a p-junction based semiconductor;
- F is an n-type semiconductor.
The design is made in such a way that each side of the module contacts either p-n or n-p transitions(depending on polarity). p-n contacts heat up, n-p - cool down (see Fig. 3). Accordingly, a temperature difference (DT) occurs on the sides of the element. For an observer, this effect will look like a transfer of thermal energy between the sides of the module. It is noteworthy that a change in the polarity of the supply leads to a change in the hot and cold surfaces.
Rice. 3. A - hot side of thermocouple, B - cold side Specifications
The characteristics of thermoelectric modules are described by the following parameters:
- cooling capacity (Q max), this characteristic is determined on the basis of the maximum allowable current and the temperature difference between the sides of the module, measured in Watts;
- the maximum temperature difference between the sides of the element (DT max), the parameter is given for ideal conditions, the unit of measurement is degrees;
- allowable current strength required to ensure the maximum temperature difference - I max;
- the maximum voltage U max required for the current I max to reach the peak difference DT max ;
- the internal resistance of the module - Resistance, is indicated in Ohms;
- efficiency coefficient - COP (abbreviation from English - coefficient of performance), in fact, this is the efficiency of the device, showing the ratio of cooling to power consumption. For inexpensive elements, this parameter is in the range of 0.3-0.35, for more expensive models it approaches 0.5.
Marking
Consider how the typical marking of modules is deciphered using the example of Figure 4.
Fig 4. Peltier module marked TES1-12706 Marking is divided into three meaningful groups:
- Element designation. The first two letters are always unchanged (TE), indicating that this is a thermoelement. The next indicates the size, there may be letters "C" (standard) and "S" (small). The last digit indicates how many layers (cascades) are in the element.
- The number of thermocouples in the module shown in the photo is 127.
- The value of the rated current in Amperes, we have - 6 A.
The markings of other models of the TEC1 series are read in the same way, for example: 12703, 12705, 12710, etc.
Application
Despite the rather low efficiency, thermoelectric elements are widely used in measuring, computing, and household appliances. Modules are an important operating element of the following devices:
- mobile refrigeration units;
- small generators to generate electricity;
- cooling systems in personal computers;
- coolers for cooling and heating water;
- dehumidifiers, etc.
Let us give detailed examples of the use of thermoelectric modules.
Refrigerator on Peltier elements
Thermoelectric refrigeration units are significantly inferior in performance to compressor and absorption counterparts. But they have significant advantages, which makes their use expedient under certain conditions. These benefits include:
- simplicity of design;
- vibration resistance;
- lack of moving elements (with the exception of the fan blowing the radiator);
- low noise level;
- small dimensions;
- the ability to work in any position;
- long service life;
- small energy consumption.
These characteristics are ideal for mobile installations.
Peltier element as a generator of electricity
Thermoelectric modules can work as electricity generators if one of their sides is subjected to forced heating. The greater the temperature difference between the sides, the higher the current generated by the source. Unfortunately, the maximum temperature for the thermogenerator is limited; it cannot be higher than the melting point of the solder used in the module. Violation of this condition will lead to the failure of the element.
For serial production of thermogenerators, special modules with refractory solder are used; they can be heated to a temperature of 300°C. In ordinary elements, for example, TEC1 12715, the limit is 150 degrees.
Since the efficiency of such devices is low, they are used only in cases where it is not possible to use a more efficient source. electrical energy. Nevertheless, 5-10 W thermal generators are in demand among tourists, geologists and residents of remote areas. Large and powerful stationary installations operating on high-temperature fuel are used to power gas distribution units, meteorological station equipment, etc.
For CPU cooling
Relatively recently, these modules began to be used in cooling systems for the CPU of personal computers. Given the low efficiency of thermoelements, the benefits of such structures are rather doubtful. For example, to cool a heat source with a power of 100-170 W (corresponding to most modern CPU models), you will need to spend 400-680 W, which requires the installation of a powerful power supply.
The second pitfall is that an unloaded processor will emit less thermal energy, and the module can cool it below the dew point. As a result, condensation will begin to form, which, guaranteed, will disable the electronics.
Those who decide to create such a system on their own will need to carry out a series of calculations to select the power of the module for a specific processor model.
Based on the foregoing, it is not profitable to use these modules as a CPU cooling system; in addition, they can cause computer equipment to fail.
The situation is quite different with hybrid devices, where thermal modules are used in conjunction with water or air cooling.
Hybrid cooling systems have proven to be effective, but the high cost limits their circle of admirers.
Air conditioner on Peltier elements
Theoretically, such a device will be structurally much simpler than classic climate control systems, but it all comes down to low performance. It is one thing to cool a small volume of a refrigerator, another thing is a room or a car interior. Air conditioners based on thermoelectric modules will consume more electricity (3-4 times) than equipment operating on a refrigerant.
As for the use as an automotive climate control system, the power of a standard generator will not be enough to operate such a device. Replacing it with more productive equipment will lead to significant fuel consumption, which is not cost-effective.
In thematic forums, discussions on this topic periodically arise and various homemade designs, but a full-fledged working prototype has not yet been created (not counting the air conditioner for the hamster). It is quite possible that the situation will change when modules with more acceptable efficiency become widely available.
For cooling water
The thermoelectric element is often used as a cooler for water coolers. The design includes: a cooling module, a controller controlled by a thermostat and a heater. Such an implementation is much simpler and cheaper than the compressor circuit; in addition, it is more reliable and easier to operate. But there are also certain disadvantages:
- water is not cooled below 10-12°C;
- cooling takes longer than the compressor analogue, therefore, such a cooler is not suitable for an office with a large number of employees;
- device is sensitive to outside temperature, in a warm room, the water will not cool to a minimum temperature;
- installation in dusty rooms is not recommended, as the fan may become clogged and the cooling module will fail.
Desktop water cooler using a Peltier element Air dryer on Peltier elements
Unlike an air conditioner, the implementation of an air dryer on thermoelectric elements is quite possible. The design is quite simple and inexpensive. The cooling module lowers the temperature of the heatsink below the dew point, causing the moisture contained in the air passing through the device to settle on it. The settled water is discharged into a special storage tank.
Despite the low efficiency, in this case the efficiency of the device is quite satisfactory.
How to connect?
There will be no problems with connecting the module, it is necessary to apply constant voltage to the output wires, its value is indicated in the datasheet of the element. The red wire must be connected to the positive, the black wire to the negative. Attention! Reversing the polarity swaps the cooled and heated surfaces.
How to check the Peltier element for performance?
The simplest and reliable way- tactile. It is necessary to connect the module to an appropriate voltage source and touch its different sides. For a workable element, one of them will be warmer, the other colder.
If a suitable source is not at hand, you will need a multimeter and a lighter. The verification process is quite simple:
- connect the probes to the terminals of the module;
- bring a lit lighter to one of the sides;
- observe the readings of the device.
In the working module, when one of the sides is heated, an electric current is generated, which will be displayed on the instrument panel.
How to make a Peltier element with your own hands?
It is almost impossible to make a self-made module at home, all the more it makes no sense, given their relatively low cost (about $4-$10). But you can assemble a device that will be useful on a hike, for example, a thermoelectric generator.
To stabilize the voltage, you need to assemble a simple converter on the L6920 IC chip.
A voltage in the range of 0.8-5.5 V is applied to the input of such a converter, at the output it will produce a stable 5 V, which is quite enough to recharge most mobile devices. If a conventional Peltier element is used, the operating temperature range of the heated side must be limited to 150 °C. In order not to bother tracking, it is better to use a pot of boiling water as a heat source. In this case, the element is guaranteed not to heat up above 100 °C.
Peltier thermoelectric cooler. 
The principle of operation was borrowed from the net: The operation of Peltier elements is based on the contact of two conductive materials with different levels of electron energy in the conduction band. When current flows through the contact of such materials, the electron must acquire energy in order to move to a higher energy conduction band of another semiconductor. When this energy is absorbed, the contact point of the semiconductors is cooled. When the current flows in the opposite direction, the point of contact of the semiconductors is heated, in addition to the usual thermal effect.
When metals come into contact, the Peltier effect is so small that it is invisible against the background of ohmic heating and thermal conduction phenomena. Therefore, when practical application two semiconductors are used.
Appearance of the Peltier element. When a current is passed, heat is transferred from one side to the other. The Peltier element consists of one or more pairs of small semiconductor parallelepipeds - one n-type and one p-type in a pair (usually bismuth telluride, Bi2Te3 and silicon germanide), which are connected in pairs using metal jumpers. Metal jumpers simultaneously serve as thermal contacts and are insulated with a non-conductive film or ceramic plate. Pairs of parallelepipeds are connected in such a way that a series connection of many pairs of semiconductors is formed with different type conductivity, so that at the top there are one sequence of compounds (n->p), and at the bottom opposite (p->n). Electric current flows sequentially through all the parallelepipeds. Depending on the direction of the current, the upper contacts are cooled and the lower ones are heated - or vice versa. Thus, the electric current transfers heat from one side of the Peltier element to the opposite side and creates a temperature difference.
If the heating side of the Peltier element is cooled, for example with a radiator and a fan, the temperature of the cold side becomes even lower. In single-stage cells, depending on the type of cell and the magnitude of the current, the temperature difference can be up to approximately 70 K/
Description
The Peltier element is a thermoelectric converter, which, when voltage is applied, is able to create a temperature difference on the plates, that is, to pump heat or cold. The presented Peltier element is used for cooling computer boards (subject to efficient heat removal), for cooling or heating water. Peltier elements are also used in portable and car refrigerators.
Peltier element powered by 12 volts.
For heating, you just need to reverse the polarity.
Peltier plate dimensions: 40 x 40 x 4 mm.
Working temperature range: from -30 to +70?..
Operating voltage: 9-15 Volts.
Current consumption: 0.5-6 A.
Maximum power consumption: 60W.
Funny little thing, we connect 12v + - it cools, we change the polarity, it heats up. Used in many auto refrigerators, at least I have one. You can attach a compact scheme to the glove compartment so that the chocolate does not melt in the summer! For use and effective use, you need to use a cooling radiator - as a test, I used a radiator from a computer processor, it is possible with a cooler. The better the cooling, the stronger and more efficient the Peltier effect. When connected to a car battery at 12v, the current consumption was 5 amperes. In a word, the element is voracious. Since I have not yet assembled the entire circuit, but only carried out trial tests, without instrumental temperature measurements. So in the cooling mode for 10 minutes, a light frost appeared. In the heating mode, the water in the metal cup boiled. The efficiency of this cooler is, of course, low, but the price of the device and the opportunity to experiment make the purchase justified. The rest is in the photo 
I became interested in home winemaking.
Read about the benefits of wine. Looking for good wine. I was horrified by what they offer us in stores. Even Crimean wines are of no use. Everything is pasteurized, made from concentrates, an exorbitant amount of preservatives. Homemade wines are godlessly diluted, it is not known in what conditions they are made ...
I decided to try making my own wine. It turned out just a wonderful grape wine. Dry, almost sugar-free, rich, very healthy, relieves fatigue...
But most importantly, I liked the process of making wine. Very interesting and doesn't take much time. I just got carried away with winemaking, and, I think, for a long time.
I live in apartment building. For the production of wine, this does not create absolutely no problems. I have a large pantry, where the wine ferments and matures. How to store wine long time unclear.
The main requirement for wine storage is low temperature:
- 10 - 14 °C for dry wines;
- up to 16 °C for desserts;
- maximum allowable temperature 18 °C;
- 24°C just kills the wine.
- Sudden temperature changes are not allowed.
The problem is exacerbated by the fact that I prefer dry wines, which require the lowest storage temperature.
dialed in search engines requests.
- Storage of homemade wine.
- Wine storage at home.
- How to store wine in an apartment.
The only one real advice on this occasion - buy a wine cooler. But these devices are expensive. Especially if the useful volume of the wine refrigerator is not for 6-8 bottles, but for several bottles of wine. I don’t think that anyone makes homemade wine with volumes of less than 10-20 liters.
Requirements for a wine cooler.
I decided to make a wine cooler with my own hands. The problem is simplified, relative to traditional food refrigerators, by the fact that:
- The temperature in a wine refrigerator can be 14 °C, and even 18 °C, while in a food refrigerator 4-5 °C, and in a freezer - 20 °C. It is clear that to maintain more high temperature less refrigerator power is needed, less requirement for thermal insulation. It is enough to lower the temperature relative to environment at 5-7 °C.
- There are no special requirements for a wine cooler installed in the pantry. appearance. But if someone has such requirements, you can always order a beautiful outer case made of laminated chipboard.
- The wine fridge is rarely opened. This simplifies the requirements for the closing door of the refrigerator, in general, for the method of closing the case.
But there are certain requirements:
- Not high power consumption, so as not to go broke on electricity bills. I decided that the maximum power consumption should be no more than 15-20 watts.
- The control system must maintain the temperature with high accuracy, and most importantly - without sharp fluctuations. Relay thermostats from refrigerators are completely unacceptable here.
- As a cooling device -. This imposes more specific requirements on the refrigerator controller. I will write about this in my next post.
The last two points don't scare me at all. I have designed much more complex electronic controllers. Looking ahead, I’ll say something, but it turned out wonderful. Small in size, quite simple, convenient, with high performance. It maintains the temperature with an accuracy of 0.1 °C, limits the power to a given level, and generates ideal signals for the Peltier element.
Wine cooler body, choice of thermal insulation material.
What is the body of the refrigerator made of? I looked through articles on this issue on the Internet, thought, read about thermal insulation materials. I came to an unequivocal conclusion - the body should be made of extruded polystyrene foam. This material has:
- Low thermal conductivity - 0.031 W / (m °K).
- Sufficiently high strength, resistance to deformation. There are options with different densities. Strength depends on density.
- He is absolutely not afraid of moisture.
- In addition, expanded polystyrene is lightweight, easy to process, easy to glue.
Unlike the options on the Internet, in which a suitable plastic case was taken and sheathed heat-insulating material, I decided to make the refrigerator case from polystyrene foam boards and paste over with aluminum foil.
I calculated that I needed plates 5 cm thick, but in the nearest store I found Penoplex plates only 4 cm thick. I decided that it would be suitable for the first experiment. And bought them.
Given the size of the shelves in my pantry, I decided to make a refrigerator with a usable volume sufficient to store four five-liter cylinders.
Those. for 20 liters of wine in four bottles. Each cylinder is 5 liters, height 265 mm, diameter 180 mm. The internal dimensions of the refrigerator are 380 x 360 x 320 mm.
It turned out here is a drawing of parts for the case.
Parts list.
Sawed out these details for me furniture shop for 200 rubles The material is handled wonderfully. The edges are perfectly even.
Used this glue. There are probably many other options, but I liked this glue.
It remains to glue the details. It was not difficult, just poured too much glue on the first seam.
I glued the lid and tried it on until the glue was completely dry. Fit perfectly.
Then I pasted over the body of the refrigerator outside and inside with aluminum tape.
The refrigerator body is ready.
The design of the cooling unit of the refrigerator.
The optimal design of the cooling unit is obvious. I tried to portray how I see her.
The task is to transfer the cold from one surface to the refrigerator on its internal radiator. And the other, external radiator must remove heat from the other surface of the Peltier element.
The side wall of the refrigerator is pierced at a right angle by an aluminum bar with a section of 40x40 mm. Through it, cold is transmitted into the body. In the chamber, an internal radiator is screwed to it, which cools the air. On the other hand, the Peltier element is pressed against the bar by an external radiator. The design is optimal in terms of physical processes:
- Minimum length of the cold transfer bar.
- Large cross-section, and hence the good thermal conductivity of the bar.
- The minimum contact surface of the cold part of the cooling unit with air, which means minimal losses.
- The external radiator is located parallel to the side wall, increasing the width of the entire refrigerator only by its own thickness. The thickness of the radiator is usually smaller than other sizes.
Flaws:
- The side surfaces of the aluminum bar must be perfectly flat.
- Complicated milling work required.
- Complicated fastening of external and internal radiators.
I am an electronics engineer, programmer, not a mechanic. I am sure that many people will make the mechanical design of this unit better than me. Submit a photo if you do.
I was not enough for such a design option. I made a simpler but less efficient design of the cooling unit.
It is clear from the pictures.
The internal radiator is at the top of the chamber because the cold air sinks down.
The disadvantages of this design are obvious:
- Chill-transmitting bar with a small section, only 40 x 10 mm.
- A significant part of it is in contact with warm air, large losses. It must be covered with insulating materials.
- The width of the refrigerator increases due to the width of the radiator. For the same reason, a wide radiator cannot be used.
Well, what could. I will redo.
The controller for the refrigerator on the Peltier element.
The controller turned out to be extremely successful. It will be dedicated to him. There I am:
- I will tell you in detail about the problems of controlling the Peltier element.
- I will describe the operation of the controller.
- I will bring circuit diagram Peltier element controller.
- I will lay out the resident software.
For now, I'll just say that the controller:
- Measures and stabilizes the air temperature in the refrigerator with an accuracy of 0.1 °C.
- Limits the power consumption to a given value.
- Monitors the external heatsink temperature and controls the fan.
- Forms a continuous current and voltage on, smoothes out ripples and voltage surges.
- Carries out diagnostics of temperature sensors and other elements of the system.
I would especially like to note that the controller does not turn on and off the Peltier element to control the temperature, but gradually reduces or increases the power on the element. Thus, a current always flows through the Peltier element, only its value is determined by the ambient temperature.
This allows:
- Keep the temperature value stable, without the slightest jumps.
- The Peltier element has a limited number of switching on and off. A relay regulator will ruin it in 2 months.
- To avoid the problem associated with the fact that the plate that transmits cold to the refrigerator chamber, when the Peltier element is turned off, begins to transfer heat from the external radiator to it.
The dimensions of the controller are only 110 x 90 x 38 mm.
And that's the whole fridge.
Tests and evaluation of results.
The controller displays:
- air temperature in the refrigerator;
- radiator temperature;
- electrical power on the Peltier element.
Therefore, the test was carried out without additional devices. I just turned on the refrigerator and watched.
With a maximum power setting of 15 W, the temperature in the refrigerator is reduced by 6 °C relative to the environment.
In principle, this is already enough to store wine. I wanted better results, but taking into account the design flaws of the cooling unit, the result was not bad.
Moreover, there is a huge number of reserves left to increase the efficiency of the refrigerator:
- Change the design of the cooling unit, as described above.
- Add air guides for the fan.
- Increase the area of the external and internal radiators.
- Increase the thickness of the walls of the refrigerator case at least up to the calculated one (50 mm).
I am sure that this can significantly increase the efficiency of the refrigerator:
- Achieve lower temperatures.
- Reduce power consumption, although 15 watts does not seem like a lot to me.
By the way, all industrial wine coolers contain a second fan on the internal heatsink. I think that you can do without it, as done in this development.
As for the cost of manufacturing this development, I didn’t exactly count, but I don’t think I spent more than a thousand on materials for the case. Everything else was made from improvised materials. It is difficult to evaluate everything together, I think that 2-2.5 thousand can be met.
You can bookmark.
It can be considered a luxury. But that's pretty useful thing. Here you can put ice cream, sparkling water, transport any frozen food and much more. In the store for such a device they will require a considerable amount, so it makes sense to assemble a car refrigerator with your own hands. In addition, it is interesting, simple and several times cheaper. You can also make a refrigerator of any shape and size so that it fits comfortably in the place prepared in the car. According to the author, the cost of such a homemade product is within 1000 rubles.
A Peltier element is used as a cooling element (this is a plate that, when voltage is applied to it, heats up on one side and cools on the other). You will also need one or more (depending on the size of the refrigerator) computer coolers with heatsinks. They can also be obtained for free if there are computers that are not needed.
Materials and tools for homemade:
- extruded polystyrene foam;
- ruler;
- a pen, felt-tip pen or other writing instrument;
- stationery knife;
- Peltier elements (you can buy, they are not expensive);
- computer coolers with radiators;
- polyurethane foam;
- wire with a connector for the cigarette lighter;
- thermostat board;
- soldering iron, scissors and more.
Refrigerator manufacturing process:
Step one. Container manufacturing
In general, the author initially wanted to make a thermos container that would keep the cold inside. That is, for transporting chilled products over short distances. But then the container turned into a full-fledged refrigerator.
A container is assembled from expanded polystyrene, polyurethane foam is used as glue. This is good because the foam hermetically seals all the cracks. The most important thing in design good thermal insulation the better the cold is kept, the more efficient and economical the refrigerator will work.
You can choose any dimensions, according to your needs, the author needed a sheet of expanded polystyrene with dimensions of 1200x600 mm and a thickness of 50 mm for assembly. The sheet is simply cut according to the template, and then glued into the treasured box using mounting foam.
In the picture you can see a diagram for cutting a sheet, if you want to assemble exactly such a refrigerator. There are sides on the sheet, the thickness of which is 20 mm, they must be cut off from all sides, leaving the bottom.
For gluing, the foam is applied and wait 1 minute, then you need to press the parts for 5 minutes and at the same time make sure that they do not move. As a result, only a small piece of polystyrene foam will be superfluous, it is marked in gray in the diagram.
After the box is ready, it can be painted. You need to paint in two passes, as the paint can corrode the polystyrene foam. However, it is desirable to choose suitable paint for these purposes. The container weighs 820 grams, it contains frozen food for quite a long time.
Step two. Cooling element installation
To make a full-fledged refrigerator, a cooling element is needed, here it is electric - this is the Peltier element. The peculiarity of this device is that when voltage is applied to it, one side of it becomes very cold, while the other heats up. So, in order for the Peltier element not to burn out, heat must be removed from its hot side. A cooler from a computer with a radiator that cools the processor does an excellent job with this task.
The most powerful Peltier element will cost about 130-150 rubles (power 60 W).
To with inside the radiator did not freeze, and the air was cooled evenly, it was also decided to install a cooler on the inside of the refrigerator. For the system to work autonomously, you will need a temperature controller with an external sensor, its cost is within 170 rubles.
Now the degree of cold in the refrigerator will be controlled by electronics, this will also reduce energy losses.
The author installs the Peltier element between two radiators; thermal paste is used for better heat transfer. As a result, one radiator will cool one side of the element, and the other radiator will be located inside the refrigerator and distribute cold over it. One such element is enough to keep the temperature inside the refrigerator at -3 degrees at an ambient temperature of +26. If you install 2-3 such elements in series, then theoretically the temperature in the refrigerator can be lowered to -18 degrees.
Radiators are interconnected using standard brackets, with which they are attached to motherboard. Still need plastic clamps. The greatest efficiency was achieved when both fans worked for blowing out from the radiator.
Pieces of thermal insulation for round pipes were used as thermal insulation.
Step three. Construction assembly
A hole must be made in the lid of the refrigerator to install the cooler. The shape of the hole should be the same as in the photo. Then the seams are smeared with sealant and a structure of radiators is installed. It is important here not to confuse where the cold side is, and where the hot one is. The cover can be pre-painted, which increases the rigidity of the polystyrene foam.
While I was building country house I had a desire to think of another way to use extruded polystyrene foam. Today it is one of the most effective heaters with a huge number of advantages and very affordable price. The first thing I realized was that for grocery shopping trips to the hypermarket, it is very useful to have a thermos container in which you can safely transport frozen food. It took 160 rubles and half an hour of free time to make such a box. But I decided to go further and refine the design in order to use it as a stand-alone refrigerator.
Let's start making!
2. So, let's start with a thermos container. We need one sheet of expanded polystyrene with dimensions of 1200x600 mm, a thickness of 50 mm, a stationery knife and a tape measure. The cost of such a sheet in any hardware store is 160 rubles. We cut the sheet according to the template, take the mounting foam and glue such a container.
3. Here is a sheet cutting scheme. The sheet has sides 20 mm thick, they need to be cut off from all sides except the bottom. Sheets are glued together mounting foam. The technology is simple. Apply a little foam to the gluing area, wait 1 minute, press the sheets tightly against each other and then manually control for 5 minutes so that they do not move due to foam expansion. The main thing is not to leave unattended. Only a small piece of polystyrene foam will remain, marked in gray in the diagram.
4. Pay attention to the design of the lid, I cut one of the large sheets from the diagram above into 3 parts in place when gluing to ensure tight fixation. After that, the outside of the box can be painted. The paint corrodes the polystyrene foam a little, so it is better to paint in two stages. The resulting container weighs 820 grams and has incredible heat loss performance. In such a box, you can put several kilograms of frozen food and transport them without problems for several hours. The main thing is not to mix frozen and chilled foods. It is possible to supplement the design with a cold accumulator.
5. Or you can modify the design to get a full-fledged refrigerator. For these purposes, we will use the Peltier element - a thermoelectric converter, the principle of operation of which is based on the occurrence of a temperature difference when an electric current flows. It is these elements that are used in serial car refrigerators, as well as car seats with ventilation.
The cost of one Pelte element with a maximum power of 60 watts on aliexpress is 130-150 rubles. Model TEC1-12706. During operation, one side of the element heats up, the other side cools down. so that the element does not burn out, it is required to intensively remove heat from the hot side. To do this, we need a processor cooler with a heatsink from a computer store, costing 250 rubles. To improve air circulation inside the refrigerator compartment and prevent freezing of the radiator, I decided to install fans on both sides. We also need a thermostat with an external temperature sensor and a relay, costing 170 rubles, which will allow us to control the set temperature inside the container. Well, an extension cord with a connector for a car cigarette lighter for 100 rubles.
So, let's start assembling.
6. Install the Peltier element using thermal paste (included with the cooler) between two aluminum radiators. It is worth noting here that it is possible to increase the temperature gradient of the installation by assembling 2 or 3 Peltier elements installed in series. So that one Peltier element cools the other. In this embodiment, it is realistic to get a negative temperature in the container up to -18 degrees Celsius. Along the perimeter between the element we lay a piece of foamed thermal insulation.
7. We connect the radiators to each other with standard mounting plates to the motherboard, connecting them with plastic clamps. This also makes it possible to thermally isolate the cold and hot sides from each other. Trial run of the installation. The more intensively we cool the hot side, the lower the temperature on the cold side will be. Here, the fans are directed to the flow of air to the radiators, this is less efficient than if they are turned over to blow out. In an impromptu box, it was possible to achieve a temperature of -3 degrees, at an ambient temperature of +26. The photo clearly shows the model of the coolers, their advantage is in the large area of the radiator support pad. And as a heat-insulating gasket, I used a piece of heat-insulation for round pipes.
8. Now let's integrate the thermoelectric converter into the new lid for the container. For the convenience of placing the entire structure, we will increase the thickness of the cover to 100 mm (2 sheets of expanded polystyrene). This photo clearly shows the perimeter gasket between the two radiators.
9. Artistic cutting on polystyrene foam and sanding. We paint again. After painting, the outer shell of the expanded polystyrene becomes stronger.
10. We coat the seams with sealant, turn both fans over for blowing. Of the potential improvements - it may be worth reducing the fan speed on the cold side (now both fans are running at maximum speed).
11. Next to the case, we install the thermostat board and fix the power wire in such an unpretentious way. First, we press the plate with self-tapping screws, then we fix it with sealant.
12. Container assembly. The weight of the container without the lid is 800 grams, the lid with the assembled thermoelectric converter weighs the same. General expenses - 1000 rubles and a couple of hours of time. Tests with refrigerated products in the trunk of a car showed the system's ability to maintain the temperature at the bottom (!) of the container within +5 degrees Celsius, at an ambient temperature of +29 degrees (yes, it's much warmer in the trunk, even when the air conditioner is on) and current consumption - 3 Ampere. I think this is an excellent result.
I plan to make the next container from 3 sequentially installed Peltier elements in order to get a full-fledged freezer.
