Sometimes a home master is faced with the task of starting refrigerator compressor without using a standard starting relay. Such a need may arise when testing the performance of the motor, using the unit for compressor units, or when disposing of an old refrigerator when the standard piping has already been dismantled. Understanding the principles of operation of the electric motor allows you to solve this problem, but requires strict adherence to safety precautions and accuracy in connections.
Direct connection to the network 220 Volt implies the creation of an artificial phase shift, which under normal conditions is provided by the starting winding and relay. Without this mechanism, the motor rotor will remain motionless, and the windings will quickly overheat and burn out. Therefore, the key point is the correct organization of the starting circuit, even if the standard relay PZP or RTP is missing.
In this article we will analyze in detail the electrical circuit, the necessary components and the procedure. You'll learn how to identify winding leads, calculate capacitance, and avoid common mistakes. Remember that working with high voltage carries risks, so every action must be conscious.
The principle of operation of a single-phase motor and the role of a relay
A standard refrigeration compressor is equipped with a single-phase asynchronous motor. The peculiarity of this design is the presence of two windings: working (main) and starting. The working winding occupies most of the stator slots and ensures rotation of the rotor after starting. The starting winding is made of a thinner wire and serves solely to create the initial torque.
In normal operation, starting relayis responsible for turning the starting winding on and off. It reacts to a current surge at start or a change in the magnetic field, closing the starting winding circuit for a fraction of a second. After gaining speed, the relay opens the contacts, and the engine continues to operate only on the working winding. When connecting directly, we will have to simulate this process manually or using a capacitor.
If you apply voltage only to the working winding, there will be a hum, but no rotation will occur. The rotor will begin to heat up, which will lead to thermal breakdown of the insulation. That is why a connection diagram without a relay always involves the use of an external element to create a phase shift. Most often, for this purpose they use capacitors a certain capacity.
⚠️ Attention: Operating a compressor without thermal protection (thermal relay) is extremely dangerous. If the rotor is jammed or overloaded, the motor will not turn off automatically, which can lead to a fire in the windings.
Identification of contacts and winding continuity
The first step before assembling the circuit is to determine the purpose of the contacts on the compressor terminal block. There are usually three of them, and they are arranged in a triangle. There may be markings on the case, but if they are erased or missing, you should use a multimeter. This is a critical step, an error in which will lead to a short circuit.
The testing process involves measuring the resistance between each pair of contacts. You need to find three values: the resistance between the working and starting windings (total), the resistance of the starting winding and the resistance of the working winding. The working winding always has less resistance, since it is wound with a thicker wire.
- 🔌 Find the contact with the least resistance relative to the common wire - this is the output of the working winding.
- 🔌 Find the contact with higher resistance - this is the output of the starting winding.
- 🔌 Third the contact, where the resistance is the sum of the two previous ones, is common (phase).
For convenience, the data can be summarized in a table so as not to get confused during assembly. Write down the values obtained, as the visual markings of the wires inside the casing may be damaged.
| Pair of contacts | Expected resistance | Pin assignment |
|---|---|---|
| Common - Working | Low (10-30 Ohm) | Work winding |
| Common - Start | High (30-100 Ohm) | Start winding |
| Work - Starting | Sum of values | Full circuit |
After identifying the pins, it is recommended to insulate the places of future connections with heat shrink or high-quality electrical tape. Do not allow bare twists, as vibration of the compressor can break the contact.
Choosing a capacitor to start the engine
To successfully start an engine without a relay, a circuit with a capacitor is most often used. The capacity of this element is selected experimentally or by calculation, based on the engine power. For household-grade refrigeration compressors, capacitors with a capacity of 10 to 50 uF are usually required.
It is important to use capacitors designed for a voltage of at least 350 Volt, or better 450 Volt. Using elements with a lower operating voltage will lead to their explosion or rapid failure. The type of capacitor must be non-polar, specifically designed for operation in alternating current (AC) circuits.
Is it possible to use several capacitors?
Yes, if there is no required capacitance, you can connect several capacitors in parallel. The total capacitance in a parallel connection is summed up. However, make sure that all elements are of the same type and voltage.
There are two approaches to using capacitors. The first is the installation of a starting capacitor, which is connected only at the time of start, and then disconnected. The second is the use of a working capacitor, which remains in the circuit constantly. For refrigerator compressors, a hybrid version is often used or a capacity is selected that allows the engine to operate without overheating in constant mode.
If the capacity is too large, the engine will get very hot. If it is too small, it may not start under load or will hum. The optimal starting value for most household compressors with a power of 100-200 W is a capacitor with a capacity of 20-30 uF.
Scheme for connecting the compressor to a 220V network
Having collected all the necessary elements, you can begin installing the circuit. The connection diagram for a compressor from a refrigerator without a relay is quite simple, but requires care. You will need a power cord, a capacitor and, preferably, a button to briefly turn on the starting winding if you are not using a circuit with a permanent capacitor.
In the classic version, one end of the power plug (phase) is connected to the common contact of the compressor. The second end (zero) goes to the working winding. The starting winding is connected in parallel to the working winding through a capacitor. This circuit allows the engine to start on its own if the capacitor is selected correctly.
☑️ Check before turning on
For a more reliable start, you can use the button. In this case, the starting winding circuit is broken with a button. You press the button simultaneously with the power supply, the engine starts, and after 1-2 seconds the button is released. This simulates the operation of a standard relay and reduces the risk of overheating of the starting winding.
When assembling, use wires with a cross-section of at least 1.5 mm². Thin wires may not withstand starting currents that are 3-5 times the rated current of the motor. All connections must be made by soldering or through screw terminal blocks.
Safety precautions and precautions
Working with 220V electric current requires maximum concentration. Even briefly touching live parts can cause serious injury. In addition, the compressor contains refrigerant, and a leak in the system (if it has not been previously depressurized) or overheating of the oil can be dangerous.
- 🛡️ Carry out all work on assembling the circuit only with the power disconnected from the mains.
- 🛡️ Use dielectric gloves and insulated tools handles.
- 🛡️ Ensure reliable grounding of the compressor housing if it is metal.
Particular attention should be paid to the location of the compressor. It should stand on a flat surface, preferably on rubber vibration supports. During operation, the housing can heat up to 60-80 degrees, so do not cover the unit and ensure air flow.
⚠️ Attention: It is strictly forbidden to turn on the compressor if oil is coming out of its tubes or if the seal of the casing is broken. This can lead to oil getting on hot elements and ignition.
Diagnostics of problems at startup
Even with the correct assembly of the circuit, difficulties may arise. The engine may hum, but not rotate, or immediately knock out the circuit breakers in the panel. In such cases, it is necessary to conduct a diagnosis. Most often, the problem lies in a malfunction of the engine itself or incorrect selection of the container.
If a hum is heard, but the shaft stands still, the piston mechanism may have jammed or the oil has dried out. Trying to "unwind" it manually while the power is on is dangerous. It is better to try to apply voltage to the starting winding for a short time, simulating a push. If this does not help, the compressor is most likely mechanically faulty.
If the protection trips frequently, check the current consumption. To do this, an ammeter is connected in series to the circuit. If the current significantly exceeds the rated current indicated on the nameplate, it means there is a short circuit in the windings or a problem with the capacitor.
Frequently asked questions and answers (FAQ)
Is it possible to connect a compressor without a capacitor by simply applying voltage to both windings?
Theoretically, you can start if you briefly apply a phase to the starting winding and then remove her. However, you cannot constantly leave the starting winding energized - it will burn out in a matter of minutes, since it is not designed for long-term operation.
Which capacitor is better to use: dry or oil-based?
Specialized film capacitors (for example, the CBB60 or CBB61 series) are better suited for working with AC motors. They are more compact and safer than old paper or oil models, which can leak or explode.
Why does the compressor hum, but does not start?
This may indicate insufficient capacity of the starting capacitor, jamming of the compressor mechanism, or an interturn short circuit in the windings. Also, the reason may be low voltage in the network.
Is it necessary to change the oil in the compressor when connected directly?
If the compressor is removed from the refrigerator and is used as an air pump, it is advisable to replace the oil with a special compressor oil that does not foam. Standard refrigeration oil can foam upon contact with air and be released through the pipes.
Is it safe to use such a compressor in a residential area?
Using an open compressor inside the house is not recommended due to noise, vibration and the risk of oil splashing. It is better to place such installations in a garage, workshop or outdoors in a protected box.