Long trips by car are often marred by the inability to store food fresh, which is especially important for families with children or lovers of long trips to the country. Creation do-it-yourself car refrigerator becomes the optimal solution, allowing you to save a significant amount compared to purchasing ready-made factory-produced equipment. A home-made device can be adapted to specific trunk dimensions and volume needs, which is impossible to do with serial models.
The creation process begins not with the purchase of parts, but with a careful calculation of thermal insulation and selection of a compressor capable of operating from the on-board network or through an inverter. Thermal box, assembled in compliance with all technological standards, is capable of maintaining a low temperature even when the compressor is turned off for several hours. In this article, we will analyze each stage of creating an effective cooling system, eliminating the common mistakes of beginners.
The principle of operation and the choice of type of cooling
Before you begin assembly, you need to clearly understand what type of cooling you need, since the complexity of the design and energy consumption depend on this. The most effective option is considered compressor refrigerator, which operates on the principle of a conventional household unit, but with a compressor adapted to vibration. An alternative is absorption models that run on gas or electricity, but their independent production in a garage is almost impossible due to the complexity of the refrigerant circulation system.
For home-made designs, the compressor circuit is most often chosen, since it allows you to reach negative temperatures and quickly cool products. The key element here is compressor from an old household refrigerator or a specialized automotive unit operating on 12 or 24 volts. It is important to consider that household compressors require an inverter to convert battery DC to AC, which reduces the overall efficiency of the system.
⚠️ Attention: Using a household compressor without an anti-tilt system may lead to its failure, as oil in the crankcase may enter the cooling circuit.
The third option is to use the Peltier effect, where cooling occurs due to the passage of current through semiconductor elements. This method is easy to implement, but has extremely low efficiency and is not capable of creating a temperature difference of more than 15-20 degrees relative to the environment. For serious food supplies in hot weather thermoelectric modules they are poorly suited; they rather support already cooled items.
Calculation of power and selection of components
The central element of any refrigeration unit is the compressor, and its the right choice determines the entire project. If you are using a unit from an old household refrigerator, you will need an inverter with a capacity of at least 1 kW, since the motor starting currents can be very high. Specialized car compressors (for example, Danfoss BD35 or their analogues) do not have this drawback, since they are equipped with an electronic start system and operate directly from 12 volts.
Equally important is the calculation of the thermal insulation of the housing, which is often underestimated, relying only on the power of the refrigerator. For effective operation, it is necessary to use materials with a low thermal conductivity coefficient, such as expanded polystyrene (XPS) or polyurethane foam. The thickness of the walls of the thermal container should be at least 50 mm, and ideally 80-100 mm, in order to minimize cold loss and reduce the load on the compressor.
To control the system, you will need a thermostat that will turn the compressor on and off when the set temperature is reached. Simple mechanical relays are less accurate, so it is better to use electronic controllers with a remote sensor installed inside the camera. It is also necessary to provide a system for protecting the battery from deep discharge so that the car can be started after parking.
Below is a table comparing the main characteristics of various types of compressors suitable for conversion:
| Compressor type | Supply voltage | Current consumption | Inverter requirement |
|---|---|---|---|
| Household (from the refrigerator) | 220 V (AC) | 1-2 A (at inverter input) | Required (powerful) |
| Automotive (Danfoss) | 12/24 V (DC) | 4-6 A | Not required |
| Air conditioning (car) | Belt drive | Depends on engine speed | Not applicable |
Manufacturing thermally insulated housing
Creating a high-quality thermal box is the foundation of the entire system, and here you cannot skimp on materials. The best option is to use sheets of extruded polystyrene foam, which are glued together with a special glue that does not destroy the structure of the foam. All joints must be carefully foamed with polyurethane foam with a low coefficient of expansion and taped with aluminum tape to create a vapor barrier layer.
The inner surface of the box must be lined with food-grade plastic or stainless steel to ensure hygiene and mechanical strength. External cladding can be made of plywood treated with moisture-proofing compounds, or sheet metal, if maximum durability is important. Pay special attention to the hatch cover: it should fit as tightly as possible; it is advisable to use sealing rubber from the door of an old refrigerator or car.
When assembling the body, it is important to avoid the formation of “cold bridges” - places where the inner cold layer comes into contact with the outer warm one through a solid material. All fasteners passing through the wall must be insulated. If you are making a built-in refrigerator, make sure that the back wall has a ventilation gap to remove heat from the condenser.
☑️ Checking the tightness of the case
Installation of the refrigeration unit and condenser
Installation compressor and condenser (radiator) requires a competent approach to vibration isolation and heat removal. The compressor must be mounted on shock-absorbing pads so that noise and vibration are not transmitted to the car body and do not destroy the soldering of the tubes. The condenser must be placed in an area with good airflow, for example, in the engine compartment or behind the bumper, but with protection from dirt and water.
The connection between the evaporator (inside the box) and the condenser (outside) is made by copper tubes, which must be covered with a thick layer. thermal insulation. If the tubes are not insulated, cold will be lost on the way to the chamber, and condensation and ice may form on the external areas, leading to corrosion. For automotive systems, ready-made evaporative units are often used, which are easier to install into the space.
When soldering copper connections, use nitrogen purge or special fluxes so that copper oxide does not remain inside the system, which can clog the capillary tube. After assembling the circuit, a vacuum procedure and a leak test are required before charging with refrigerant. Without professional equipment, this step is difficult to complete, so they often use ready-made sealed blocks from faulty refrigerators, redoing only the electrical part.
⚠️ Attention: Filling a refrigerator with freon requires a license and special equipment. Self-refueling without evacuation will lead to ineffective operation or breakdown of the compressor.
Is it possible to use an old household refrigerator as a whole?
Theoretically it is possible, but it will have to be completely disassembled, removing the outer metal walls and leaving only the insulated box with the evaporator. However, the weight and dimensions of a household refrigerator often make its installation in a passenger car impossible without serious modifications to the interior.
Electrical circuit and battery protection
Correct connection to the vehicle's on-board network is the key to safety and stable operation of the system. Direct connection of a powerful compressor to the cigarette lighter is unacceptable, since standard car wiring is not designed for such currents and may melt. It is necessary to lay a separate line from the battery through a fuse, the rating of which is selected in accordance with the current consumed by the unit.
A critical element is the battery protection unit, which turns off the refrigerator when the voltage at the battery terminals drops to a critical level (usually 11.8 V for 12-volt systems). This will prevent a situation where after spending the night you will not be able to start the engine. To implement this function, you can use ready-made discharge controllers or assemble a simple circuit using a voltage relay.
If you are using an inverter for a household compressor, take into account its own energy consumption even in idle mode. Sine wave inverters they are more efficient and safe for the compressor engine than modified ones, but they are more expensive and larger. The wiring from the battery to the inverter should be made as short as possible and with a cross-section corresponding to the load current.
Testing and operating nuances
After assembling all the components, it is necessary to test run the system in a static position, and then in motion. Check how the compressor behaves when shaking, whether there are any extraneous sounds or vibrations. Measure the actual current consumption with an ammeter and compare with the calculated one to make sure that the components are selected correctly and there are no leaks.
During operation, it is important to monitor the cleanliness of the capacitor, which can become clogged with lint and dirt, especially if it is installed in the engine compartment. Regularly cleaning the radiator will improve heat transfer and reduce the load on the compressor. Also periodically check the condition of the door seals, as their wear will lead to rapid cooling of the chamber.
A homemade car refrigerator is a project that requires technical knowledge and accuracy, but the result is worth it. You get a device completely customized to your needs, which will last for many years with proper maintenance. Do not forget that safety on the road is paramount, so all fastenings and electrical connections must be made with a margin of safety.
Is it necessary to register the conversion of a car?
In most cases, installing additional equipment in the trunk or interior does not require changes to the design of the vehicle if this does not affect traffic safety and does not significantly change the weight of the vehicle. However, if you cut the unit into the body or change the power system, it is better to consult with the local traffic police department.
How often do you need to add freon to the system?
In a properly assembled and sealed refrigerator system, freon circulates in a closed circuit and is not consumed. If the refrigerator stops freezing, it means depressurization has occurred, and repairs are required, not just refueling.
Can such a refrigerator be used in winter?
Yes, but difficulties may arise in starting the compressor due to frozen oil. Some systems require the compressor crankcase to be preheated before starting in cold weather. It is also important that the thermostat can operate at low ambient temperatures.
How much battery capacity is needed for autonomous operation?
To operate for 8-10 hours without recharging from the generator, it is recommended to use an additional traction battery (AGM or Gel) with a capacity of at least 100 Ah, connected via a separate charging system.