The most necessary appliance, both in the apartment and in a private home, is the refrigerator. And it is difficult not to agree with this statement, isn’t it? It is difficult to find a house without a refrigerator. As with any appliance, refrigerators can break down. But there are situations where a breakdown can be diagnosed on your own.
Almost all household refrigeration equipment is equipped with a single-phase motor. To start it, you have to use a starter. If this simple, but important detail fails, the compressor will stop starting. But, knowing the principles of the device, you can identify the problem and fix it.
Starting a single-phase induction motor
In essence, compressor motors installed in modern refrigerators are single-phase induction motors with a starting winding. Their main components are a rotating rotor and a stationary stator.
The rotor is a hollow cylinder made of conductive material or containing short-circuit wiring.
The stator includes two windings: the operating winding (main winding) and the starting winding (starter winding). They are mutually arranged at an angle of 90 degrees, or have the opposite winding direction – the so-called “bifilar”. Alternating current, passing through the main winding, creates a magnetic field with a changing vector.
If the rotor is not static, the motor will develop or brake torque according to the law of electromagnetic induction, because the slip relative to the forward and reverse magnetic flux is different. Therefore, the alternating current flowing through the operating winding is sufficient to maintain motion.
If the rotor is stationary, the resulting electromagnetic torque will be zero if the slip with respect to the magnetic fluxes is the same. In this case, it is necessary to create a starting torque. This is what the starting winding is for.
The currents in the windings must be shifted in phase, so a phase-shifting element – register, choke, or capacitor – is introduced into the motor. After the rotor reaches the necessary rotation, the supply of electricity to the start winding is stopped.
Thus, to start a single-phase asynchronous electric motor, it is necessary to pass current through two windings, and to maintain the rotor rotation – only through the working winding. To regulate this process, a starting relay is installed in the circuit before the refrigerator compressor.
Principle of starting relay operation
Despite a large number of patented products from various manufacturers, the refrigerator circuits and starting relay operating principles are almost the same. Having understood the principle of their operation, you can find and eliminate the malfunction yourself.
Scheme of the device and connection to the compressor
The relay wiring diagram has two inputs from the power supply and three outputs to the compressor. One input (conditionally zero) goes directly.
The other input (conditionally phase) inside the device is split into two:
– The first goes directly to the work winding;
– The second goes through isolating contacts to start winding.
If the relay does not have a landing place, it is necessary not to make a mistake with the order of connection of contacts when connecting to the compressor. Common on the Internet ways of determining winding types by measuring the resistance is not correct in general, since some motors have the same resistance of the starting winding and the working winding.
Therefore, it is necessary to find documentation or disassemble the refrigerator compressor to understand the location of the through contacts.
This can also be done if there are symbolic identifiers near the outputs:
“S” – starting winding;
“R” – operating winding;
“C” – common output.
Relays differ in the way they are mounted on the refrigerator frame or on the compressor. They also have their own current characteristics, so when replacing you need to pick up a completely identical device, or better yet, the same model.
Closing the contacts by means of an induction coil
The electromagnetic starting relay works on the principle of contact closure to pass current through the starting coil. The solenoid coil, which is connected in series with the main winding of the motor, is the basic operating element of the device.
When the compressor is started, with the rotor static, a large starting current flows through the solenoid. This generates a magnetic field that moves the core (armature) with a conductive bar mounted on it which closes the contact of the starter winding. This begins to accelerate the rotor.
As the rotor speed increases, the current flowing through the coil decreases, so the magnetic field voltage decreases. Under the action of the compensating spring or gravity, the core returns to its original position and the contact opens.
The compressor motor continues to run in rotor rotation mode, passing current through the operating winding. The next time the relay will not be activated until the rotor has stopped.
Current control with a posistor
The relays available for modern refrigerators often use a posistor, a type of thermal resistor. There is a temperature range for this device, below which it passes current with negligible resistance, and above which the resistance increases sharply and the circuit is opened.
In the starting relay, the posistor is integrated into the circuit leading to the starting winding. At room temperature, the resistance of this element is negligible, so the current flows unimpeded when the compressor starts.
Because of the resistance, the posistor gradually heats up and opens the circuit when it reaches a certain temperature. It only cools down after the compressor is no longer energized and will trip again when the motor is restarted.
Implementation of the current type of protection
An asynchronous motor is a complex electrical device that is susceptible to breakdowns. If a short circuit occurs, the circuit breaker installed in the switchboard will trip.
If the fan, which cools the winding and the mechanical moving elements, fails, the compressor’s built-in thermal protection will react.
However, a situation can occur when the motor for a long time (more than 1 second) begins to consume a current of 2-5 times the nominal. This most often occurs when there is an unplanned load on the shaft, resulting from the motor jamming.
The amperage increases but does not reach the short circuit values, so a load-matched circuit breaker will not trip. The thermal protection also has no reason for tripping, since the temperature will not change in such a short period of time.
The only way to react operatively to the occurred situation and to avoid melting of the working winding is triggering of the current protection, which can be installed in different places:
– inside the compressor;
– inside the compressor; inside a separate overcurrent relay;
– inside the starting relay.
A device that combines the functions of starting winding and motor current protection is called an inrush relay. Most refrigerator compressors are equipped with such a mechanism.
The operation of current protection is based on three principles:
– As the amperage increases, the resistance decreases, and the heating of the conductive material increases;
– Metal expands under the effect of temperature;
The thermal expansion coefficient is different for different metals.
Therefore, a bimetallic plate is used, which is welded from metal sheets with different coefficients of expansion. Such a plate bends when heated. One end of it is fixed, and the other end, deflecting, open the contact.
The plate is designed to respond to temperature when a certain amount of current is flowing. Therefore, when replacing the starter relay, you must check its compatibility with the installed compressor model.
Whether you will be able to find the breakdown on your own or at some stage of the search calls a master – it is up to you to decide. We can only note that if you have no experience in disassembly and reassembly of the refrigerator, it is better to limit the external examination and search for simple damages and then call our master. Chula Vista Appliance Repair Company is happy to offer efficient refrigerator repair services in and around San Diego County. Our team of experts is well-equipped and ready to handle all types of refrigerator repairs, regardless of their complexity. We strive to provide superior repairs using only high-quality replacement parts backed by the manufacturer’s warranty, so you can rely on a refrigerator repair specialist to fix the problem and keep your refrigerator working properly for a long time.