The most necessary device, both in the apartment, and in the private house, is the refrigerator. And with this statement is difficult to disagree, is not it? It is difficult to find a home where it is not. Like any appliances, refrigerators can break. But there are situations when the failure can be diagnosed independently.
Almost all domestic refrigeration equipment is equipped with a single-phase motor. To start it, you have to use the starting relay. If this simple but important detail fails, the compressor will stop running. But, knowing the principles of operation of the device, you can determine the problem and fix it.
This article will discuss how the starting relay of the refrigerator works and the signs of its malfunction. We will tell you how to fix problems with refrigeration equipment. The material is accompanied by videos that will help to understand the principle of operation of the starting relay, as well as, if necessary, to identify its malfunction.
The content of the article:
- Single-phase asynchronous motor start
-
The principle of operation of the starting relay
- Diagram of the device and connection to the compressor
- Contact closure by induction coil
- Regulation of current supply by posistor
- Implementation of current type protection
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Identification of possible faults
- № 1 - problems with the operation of the relay
- №2 - electrical contacts faults
- No. 3 - incorrect work of the posistor
- №4 - problems with the contact strip
- №5 - abnormal operation of current protection
- Conclusions and useful video on the topic
Single-phase asynchronous motor start
In essence, the motors of compressors installed in modern refrigerators are single-phase asynchronous motors with 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-circuited wiring.
The stator includes two windings: working (main) and launcher (starting). They are mutually positioned at an angle of 90 degrees, or have the opposite direction of winding - the so-called “bifilar”.
Alternating current, passing through the main winding, creates a magnetic field with a changing vector.
A pulsating field can be decomposed into two, rotating with the same period, but in opposite directions. This makes it easier to understand the physical essence of the process of acting on the rotor.
If the rotor is not static, then according to the law of electromagnetic induction the engine will develop or brake torque because the slip is relatively straight and reverse magnetic flux is different.
Therefore, to maintain the movement is enough alternating current passing through the working winding.
If the rotor is stationary, then with the same slip relative to the magnetic flux the resulting electromagnetic moment will be equal to zero. In this case, you must create a starting moment. For this, you need a starting winding.
The currents in the windings must be shifted in phase, so a phase-shifting element — a register, a choke, or a capacitor — is introduced into the motor. After the rotor has reached the required rotation, the supply of electricity to the starting winding is stopped.
Thus, to start a single-phase asynchronous electric motor, the current must pass through two windings, and to maintain the rotation of the rotor - only along the working winding.
To regulate this process in the circuit in front of the compressor of the refrigerator and set the starting relay.
The relays are located close to the compressor and in such a way that it can be easily removed. It is from checking this node that they start when the engine is running problem.
The principle of operation of the starting relay
Despite the large number of manufacturers of components for refrigerators, the scheme of work and the design of starting relays are almost the same. Having understood in principle, their actions can independently find and fix the problem.
Diagram of the device and connection to the compressor
The electrical circuit of the relay has two inputs from the power source and three outputs to the compressor. One input (conditionally - zero) passes directly, and the other (conditionally - phase) inside the device splits into two:
- the first passes directly to the working winding;
- the second passes through the disconnecting contacts to the starting winding.
If the relay does not have a footprint, then when connecting to the compressor it is necessary not to be mistaken with the order of connecting the contacts.
Common ways to determine winding types on the Internet by measuring resistance are not true in the general case, since in some engines the resistance of the starting and working winding are the same.
The electrical circuit of the start-up relay may have minor modifications depending on the manufacturer. The figure shows a diagram of the connection of this device in the refrigerator Orsk
Therefore, it is necessary to find the documentation or disassemble the compressor to understand the location of the loop-through contacts.
This can also be done if there are symbolic identifiers near the exits:
- “S” - starting winding;
- “R” - working winding;
- “C” - general output.
The relays differ in the way they are mounted on the frame of a refrigerator or on a compressor. They also have their own current characteristics, so when replacing it is necessary to pick up a completely identical device, and better - the same model.
Contact closure by induction coil
The electromagnetic starting relay operates according to the principle of contact closure for passing current through the starting winding. The main acting element of the device is a solenoid coil connected in series with the main motor winding.
At the time of starting the compressor, with a static rotor, a large starting current passes through the solenoid.
As a result, a magnetic field is created, which moves the core (anchor) with a conductive strip mounted on it, which closes the contact winding. The acceleration of the rotor begins.
As the rotor speed increases, the current flowing through the coil decreases, resulting in a decrease in the magnetic field voltage.
Under the action of a compensating spring or gravity, the core returns to its original position and the contact opens.
On the relay cover with an induction coil there is an arrow “top”, which indicates the correct position of the device in space. If it is placed differently, contact will not open under the action of gravity.
The compressor motor continues to operate in rotor maintenance mode, passing current through the working winding. The next time the relay will work only after the rotor stops.
Regulation of current supply by posistor
Relays manufactured for modern refrigerators often use a posistor, a kind of thermal resistor.
For this device, there is a temperature range below which it transmits a current with little resistance, and above - the resistance increases dramatically and the circuit opens.
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 low, so when the compressor starts working, the current flows unhindered.
Due to the presence of resistance, the posistor gradually heats up and upon reaching a certain temperature the circuit is opened.
It cools down only after the current supply to the compressor is stopped and it is again triggered to pass when the engine is turned on again.
The posistor has the shape of a low cylinder, so professional electricians often call it a “tablet”
Implementation of current type protection
An asynchronous motor is a complex electrical device that is prone to breakage. If a short circuit occurs, the circuit breaker installed in the switchboard will trip.
In case of fan failure, which cools the winding and mechanical moving parts, the built-in thermal protection of the compressor will react.
Internal thermal protection of the motor is based on posistors. It responds to a general change in temperature inside the device, which can have both internal and external causes.
However, a situation may arise when a motor for a long time (more than 1 second) begins to consume a current 2-5 times larger than the nominal. This most often occurs when an unplanned load on the shaft arises due to engine seizure.
The current increases, but does not reach the values of short circuit, so the machine will not work. There are no reasons for switching off the thermal protection either, since the temperature will not change in such a short period of time.
The only way to quickly react to the situation and avoid reflowing the working winding is to trigger a current protection that can be installed in different places:
- inside the compressor;
- in a separate current protection relay;
- inside the start relay.
A device that combines the functions of starting the winding and the current protection of the engine is called start-up relay. Most refrigeration compressors are equipped with just such a mechanism.
The action of current protection is based on three principles:
- increasing the current increases the resistance, which leads to the heating of the conductive material;
- under the action of temperature, the metal expands;
- thermal expansion coefficient for different metals is different.
Therefore, use a bimetallic plate, which is welded from metal sheets with different coefficients of expansion. Such a plate bends when heated. One of its end is fixed, and the second, deviating, opens the contact.
To heat a bimetal breaker, a helix is usually placed next to which electricity passes. Although sometimes they implement the “direct” version in the form of a conductive plate
The plate is designed for temperature response during the passage of a current of a certain force. Therefore, when replacing the start-up relay, check its compatibility with the installed compressor model.
Identification of possible faults
Given the small number of elements of the relay, you can successively check them for operability. To do this, you need a flat screwdriver and a multimeter.
№ 1 - problems with the operation of the relay
From a constructive standpoint, a relay with a coil is a device with normally open contacts, and a posistor variant with normally closed contacts.
Although in this and in another case, there are options when at start there will be no supply of current to the starting winding or, conversely, it will not work to turn it off.
If the compressor is in good condition, but does not turn on when commanded by the control unit of the refrigerator, this indicates that there is no voltage on the stator starting winding.
The reason for this may be:
- open circuit;
- contact bar problem;
- overheating of the posistor;
- actuation of the electrical protection system and its non-return to the normal position.
If the refrigerator turns on for 5-20 seconds and then turns off, then most often this is due to the triggering of the protective mechanism of the relay. The reasons may be the following:
- the protective mechanism is intact, and the actuation occurs due to problems in the working motor winding;
- the protective mechanism is intact, but the relay does not open the contacts in the starting winding circuit;
- the protective mechanism is faulty, a false alarm occurs with slight heating.
Since there may be several causes of a malfunction, it is necessary to conduct a full diagnosis of the start-up relay of the refrigerator.
The cost of start-up relays for brands such as Atlant or Biryusa does not exceed 500 rubles. If you quickly purchase and install a new working device, the refrigerator will not even have time to be frozen.
№2 - electrical contacts faults
Malfunction of the start-up relay can be detected with a multimeter. To do this, you need to ring three parts of the electrical circuit:
- If there is a break in the area from the input to the output to the working winding, then it is necessary to check the place of contact opening by the protective mechanism. It is possible that it worked and did not return to the initial state or the breakable contacts were oxidized.
- If there is no contact in the area from the input to the output to the starting winding, then in addition to the banal rupture conductive cores are possible in two ways: opening the circuit by a protective mechanism or the absence of contact through the bar.
- A break in a straight (zero) section means mechanical damage to the chain — it is easiest to find and fix it.
If the relay is based on the use of an induction coil, then it is necessary to forcibly raise the bar - otherwise there will be no contact.
Using a multimeter is easy to detect faulty contacts by calling them through resistance. It is important not to rush and perform testing alternately on each section of the chain.
No. 3 - incorrect work of the posistor
To make sure that the posistor is working properly, you need to check it in a cold and heated state.
First of all, you have to wait until the posistor has cooled down (2-3 minutes is enough if it is idle) and ring it with a multimeter. If there is no current or a large resistance is detected, the posistor is faulty and must be replaced.
If the device is working properly, then when it is checked in a cold state, the multimeter should show the presence of slight resistance
To check the ability of disconnection, you need to connect to the posistor of the consumer of electricity, for example, stowatt incandescent lamp.
To do this, you need an electrical plug with two terminals that are connected to the input of the device. The wires from the lamp is connected to the connectors leading to zero and the starting winding.
When you turn on the plug in the socket the light will come on. Since the rated current flow in the experiment is significantly lower than when the compressor is started, the posistor will heat up for a long time - for a 100-watt lamp, the response time will be 20-40 seconds.
If after a while the light goes out, the device is working properly. If the consumer is not de-energized, it means that the posistor is non-working.
At home, its repair is impossible, it is inexpensive, so you need to purchase an element similar in parameters.
№4 - problems with the contact strip
There are two types of problems with contact strip:
- current does not pass when the contacts are closed;
- the bar sticks and does not fall.
The first problem may occur due to contact oxidation. In this case, you need to clean them with sandpaper.
Also the cause may be curvature, then you need to install it horizontally.
To clean the contacts and remove dirt or traces of oxidation, you can use fine sandpaper to put it on a needle or a thin flexible awl
A more difficult problem is the place of articulation of the strap and the pin, which is affected by the magnetic field of the solenoid. The solution to the problem is individual and depends on the type of fault.
Sticking strap It is expressed in the fact that it does not move away with the core. To do this, you need to clean the contacts to remove the adhesive and make them smooth.
№5 - abnormal operation of current protection
If the ringing reveals the absence of contact from the input to both windings, then most likely a breakage occurred in the protection zone.
In most cases, this is either a contact waste, which opens the bimetallic plate, or damage in the area of the heating coil.
The bimetallic plate and the spiral heating it cannot be bent, displaced or other actions with them that will cause a change in the set response mode
If the damage can not be fixed otherwise, you will have to acquire a new relay.
Conclusions and useful video on the topic
Overview of the principle of operation, types and basic faults of the start-up relay:
Signs of breakdowns of a common PCT starting relay. Connecting an external capacitor to compensate for unstable voltage:
Rang motor and relay. Repair coil:
The simple design of the starting relay allows you to independently find faults and easily eliminate them. You do not need deep knowledge in electrics or special tools.. However, it is necessary to observe punctuality, since the functionality of expensive equipment depends on the quality of the work done.
