Using old of the refrigeration unit to create homemade devices is a popular practice among home craftsmen. Compressors from household refrigerators are ideal for inflating tires, airbrushing or supplying air to an aquarium due to their reliability and ability to create sufficient pressure. However, in order for the device to work stably and not burn out in the first minute, it is necessary to strictly follow the electrical connection diagram.
The main difficulty is that the motor-compressors are not connected directly to a 220-volt network, like conventional fans. They require a special one, which ensures correct starting of the motor and protects the windings from overheating. In this article we will look in detail at how to identify pins, select components and assemble a working system with your own hands. start-up and protective equipment, which ensures correct starting of the motor and protects the windings from overheating. In this article we will look in detail at how to identify pins, select components and assemble a working system with your own hands.
Before you begin installation, make sure that you have basic skills in working with electricity. Improper connection of wires may result in short circuit or electric shock. Always work only with de-energized devices and use an insulated tool.
Design and principle of operation of the motor-compressor
The heart of any refrigerator is piston compressor, which is enclosed in a sealed metal casing. Inside this “glass” there is an electric motor and the compression mechanism itself, operating in an oil bath. This design ensures low noise levels and effective cooling of rubbing parts with freon and oil.
The electrical part is an asynchronous motor with a squirrel-cage rotor. It has two main windings: starting and working. The starting winding has a higher resistance and a smaller wire cross-section; it is only necessary to create the initial torque. The working winding provides the main movement of the rotor during operation.
⚠️ Attention: Opening the sealed compressor casing is strictly prohibited without special equipment and skills. Violation of the tightness will lead to moisture and dust getting inside, which is guaranteed to damage the unit.
To start the engine, a special circuit is used, which briefly supplies current to the starting winding and then turns it off. This function is performed by a starting relay, which is also often combined with a thermal overcurrent protection relay.
Identification of contacts and search for a circuit
The first step in the connection process is to correctly identify the winding pins. On most modern and many older compressors, the contact group is located at the bottom of the casing and is covered with a plastic cover. Under this cover there are three or four pins arranged in a triangle or in a row.
To determine which pin is responsible for what, you can use a multimeter in resistance measurement mode. You need to “ring” all pairs of contacts with each other. The resistance between the operating and start terminals will be equal to the sum of the resistances of each winding relative to the common wire.
- 🔌 Common (C or Common): has the least resistance relative to the other contacts when viewed in terms of sum, but is often defined as the contact relative to which the other two have different resistances.
- ⚡ Working winding (R or Run): shows the average resistance (usually 10-30 Ohms) relative to the common wire.
- 🚀 Start winding (S or Start): shows the highest resistance (usually 30-60 Ohms) relative to the common wire.
If on The compressor housing retains the markings, making the task easier. The letter C or R (from English Run) indicates the working winding, the letter S (Start) indicates the starting winding, and the common wire can be designated as C (Common) or have no designation if it is central in the triangle.
For example, for compressors Atlant or Danfoss (Secop) the pin layout can be mirrored in relation to the units Indesit or Lg. Therefore, relying only on visual location without checking with a multimeter is risky.
Selection and connection of the starting relay
The key element of the system is the starting relay. It is this that automatically switches the windings at the moment of startup. There are two main types of relays used in household refrigerators: posistor (solid-state) and induction (with a moving core).
Posistor relays are a tablet made of special ceramics, which, when heated by current, sharply increases its resistance, breaking the starting winding circuit. They are compact, have no moving parts and are less sensitive to position in space. Induction relays operate due to an electromagnetic coil, which retracts the core when starting, opening the contacts.
| Relay type | Principle of operation | Position sensitivity | Resource |
|---|---|---|---|
| Posistor | Thermal (chip heating) | Low | High |
| Induction | Electromagnetic (current coils) | High (requires vertical) | Medium |
| Manual (button) | Mechanical (finger press) | Absent | Depends on the user |
When connecting a relay, it is important to observe its orientation. There is usually an arrow on the body of the product indicating the “Up” direction. If you install the relay upside down, gravity will not allow the core (in induction models) to return to its original position, and the starting winding will not turn off, which will lead to engine combustion.
For home-made installations, universal relays are often used or original ones from the same compressor manufacturer are selected. If you use a button to manually start, the circuit is simplified: you hold the button until the motor picks up speed and release it.
Assembling an electrical circuit according to the diagram
Assembling the electrical circuit should be sequential, carefully checking each connection. The standard connection diagram is as follows: a phase from the network goes to the relay input, then is distributed to the windings. The neutral wire is connected directly to the common point of the windings.
Consider the classic option using a starting relay. The phase wire is connected to the L (Line) terminal on the relay. Inside the relay, current flows to the working winding constantly, and to the starting winding through a posistor or contacts only at the moment of start. The common wire from the compressor is connected to the network zero.
Connection diagram:220V network (Phase) --> Relay input (L)
220V network (Zero) --> Common compressor output (C)
Relay output (R) --> Running winding (R)
Relay output (S) --> Starting winding (S)
All connections outside the factory compressor block must be made using terminal blocks or high-quality soldering with heat shrink insulation. Twists in this case are unacceptable, since vibrations from a running motor can weaken the contact, causing sparking and heating.
☑️ Check before the first start
Installation of protective automatic equipment and capacitors
The safety of operating a homemade compressor depends not only on the correct circuit, but also on the presence of protective elements. In factory refrigerators, a thermal relay is responsible for this, which opens the circuit when the current or temperature is exceeded. When assembling your installation, this element is often lost or ignored, which is a mistake.
It is recommended to set the circuit breaker to a current slightly higher than the operating current of the motor (usually 6-10 Amps for household models). This will protect the wiring from fire in the event of a piston group wedge or short circuit.
⚠️ Attention: Do not use fuses with a large safety margin (“bugs”). The current consumption of a working compressor at the moment of startup can be 3-5 times higher than the rated one, but this lasts a fraction of a second. Thermal protection should respond to prolonged overheating, and not to a starting surge.
If you use a three-phase compressor (rarely found in everyday life, more often in industry) or want to improve starting characteristics at low voltage, you may need starting capacitor. Its capacity is calculated based on the engine power, usually 30-50 µF per 1 kW of power. However, for standard single-phase refrigerators with a capacity of up to 300 liters, an additional capacitor, as a rule, is not required, since this function is performed by a built-in relay.
It is also worth thinking about protection from moisture. Since the compressor is often used to pump air, condensation from the atmosphere can get inside. Installing a simple filter-moisture separator at the inlet (if it is a vacuum system) or at the outlet will extend the life of the unit.
Is it possible to use a car battery to power the compressor?
Theoretically, it is possible, but you will need a powerful inverter 12V -> 220V with a power reserve. The starting current of the compressor can reach 10-15 Amperes at 220V, which in terms of 12V will give a current of more than 100 Amperes. An ordinary car battery will quickly discharge, and a cheap inverter will be used for protection.
First start-up and fault diagnosis
After assembling the circuit, it is necessary to conduct a test run. Connect the device to the network. If everything is assembled correctly, you will hear a characteristic humming sound, after 1-3 seconds the relay clicks (disconnecting the starting winding) and the smooth hum of a running motor. A flow of air should come from the outlet pipe.
If the compressor hums, but does not start, and after a few seconds a click is heard and the hum stops, it means the starting circuit is not working. Check the relay: it may be faulty or installed on the wrong side. Also, the cause may be a jammed piston if the device has been left idle for a long time.
- 🔥 Strong heating of the housing: if the casing heats up in 2-3 minutes, check the current consumption. Perhaps an interturn short circuit in the windings or a lack of cooling (for some models, the air flow around the casing is important).
- 🔌 The machine knocks out: breakdown of insulation on the housing or short circuit in the relay. Urgently turn off the power and check the circuit with a multimeter.
- 🔇 No sound: check for voltage at the relay input. The thermal protection may have tripped or the fuse in the plug has blown.
It is important to ensure good ventilation during long-term operation. In a refrigerator, the casing is washed by natural air flow, but in a homemade installation it can overheat. It is recommended not to operate the unit continuously for more than 30-40 minutes without a break, unless a forced cooling system is provided.
Frequently asked questions (FAQ)
Is it possible to connect the compressor directly without a relay?
You can start it if you manually apply current to the starting winding at the moment of switching on, but you cannot work this way all the time. Without a relay, the starting winding will burn out in a few seconds, since it is not designed for long-term operation. For constant operation, a relay or its analogue (for example, a timer) is required.
What pressure does a typical refrigerator develop?
Household compressors are capable of creating pressure up to 6-10 atmospheres (bar) and higher, but their productivity (liters per minute) is low. They are quite enough to inflate the tires of a light car, but for pneumatic tools (spray gun, impact wrench) the performance will not be enough.
Why does the compressor get very hot?
Heating up to 70-90 degrees for a piston compressor in oil is normal. If the temperature is higher, check the oil level, air flow for cooling and the integrity of the windings. Also, heating can be caused by operation in vacuum mode (suction) without load.
Is it possible to turn the compressor over during installation?
It is strictly not recommended. There is oil inside the casing that lubricates the rubbing parts. When turning over, oil can get into the working chambers or into the outlet pipe, and the mechanism will remain without lubrication, which will lead to rapid wear. The permissible tilt is no more than 10-15 degrees.
How long can you use an old compressor?
The resource depends on the condition. If the unit has no mechanical damage and its windings are intact, it can work for years. However, it is worth considering that old oils could lose their properties, and rubber seals could become hard. Periodic oil changes (if the design allows) prolongs the life of the device.