18.09.2023

Connect the car relay to alternating voltage. Relay and its use in car alarms. Operating principle of electronic relays

What is a current relay? This question often arises among students and self-taught electricians. The answer to it is quite simple, but in textbooks and many articles on the Internet it contains a huge number of formulas and references to various laws. In our article we will try to explain what it is and how it works literally on your fingers.

First, let's look at the principle of a current relay and its design. On at the moment There are electromagnetic, inductive and electronic relays.

We will disassemble the structure of the most common electromagnetic relays. Moreover, they provide the opportunity to most clearly understand their operating principle.

  • Let's start with the basic elements of any current relay. It must have a magnetic circuit. Moreover, this magnetic circuit has a section with an air gap. There may be 1, 2 or more such gaps, depending on the design of the magnetic core. In our photo there are two such gaps.
  • There is a coil on the stationary part of the magnetic circuit. And the moving part of the magnetic circuit is secured by a spring, which counteracts the connection of the two parts of the magnetic circuit.

  • When voltage appears on the coil, an emf is induced in the magnetic circuit. Thanks to this, the moving and stationary parts of the magnetic circuit become like two magnets that want to connect. A spring prevents them from doing this.
  • As the current in the coil increases, the emf will increase. Accordingly, the attraction between the moving and stationary sections of the magnetic circuit will increase. When a certain current value is reached, the EMF will be so great that it will overcome the resistance of the spring.
  • The air gap between the two sections of the magnetic circuit will begin to decrease. But as the instructions and logic say, the smaller the air gap, the greater the attractive force becomes, and the faster the magnetic circuits connect. As a result, the switching process takes hundredths of a second.

  • Movable contacts are rigidly attached to the moving part of the magnetic circuit. They close with fixed contacts and signal that the current on the relay coil has reached the set value.

  • To return to starting position, the current in the relay should decrease as in the video. How much it should decrease depends on the so-called relay return coefficient.

It depends on the design, and can also be adjusted individually for each relay by tensioning or loosening the spring. This can be done with your own hands.

Purpose and methods of connecting a current relay

Current and voltage relays are the main elements of almost all basic protections. Therefore, let's take a closer look at their scope of application and connection diagram.

Purpose of current relay

And first of all, let's figure it out, why exactly is this current relay needed? To answer this question, we need to dive a little into theory. But we will try to make it as superficial and accessible as possible.

  • Any electrical installation has two main parameters of its operation - current and voltage. By monitoring these two parameters, you can assess the performance of the equipment and possible malfunctions.
  • The current relay, as you might guess, controls the current. And if its decrease only indicates a decrease in load, then its increase in most cases indicates serious malfunctions. In order not to consider the issue in more detail, let's take an electric motor as an example.

  • The electric motor has a rated current of, for example, 50A. A slight increase in current, say up to 55A, signals an overload. In this case, the engine should not be turned off immediately, because the overload can be temporary, and according to the PUE, most electric motors can be periodically overloaded.
  • But prolonged operation at a higher rated current may indicate a mechanical failure or other problems. Therefore, after loading, after a certain period of time, the engine must be turned off.
  • The current relay and time relay circuit allows for such protection. When the current increases above the rated value of 50A, the current relay is activated. With its contacts, it activates a time relay, which counts the permissible operating time of the engine in an overdriven state. If during this period of time the current relay has not dropped out, then the time relay is triggered and turns off the electric motor.

Hi all.

In today's review I will share with you my impressions of the 5-pin automotive relay, purchased on eBay, and will also show one of the possible options for its use.

The relay was ordered almost simultaneously with the DRL kit, which I talked about a few days ago. For what? Because when using a standard connection, when turning on the side lights or low/high beams, the DRLs still continued to light up. I didn’t find anything good in this, and therefore I began to think about automating their shutdown when turning on the headlights or low beam. The simplest and most logical option seemed to me to be using a relay.


By the way, this is one of the few purchases that I went to the local auto parts store before making. Imagine my surprise when in the VAZ store I saw the price: relay - 5 rubles (about $2.5), a block for it - 2.5 rubles ($1). Total, $3.5 per set offline with us without waiting, versus $1.66 with them. The choice is obvious :) I ordered 2 relays at once, since I initially planned to install one on each light bulb.

The seller sent the parcel a few days after payment, assigning it a track, all available events for which can be viewed.

It took the parcel about a month to get from China to Belarus, after which it was safely received at my post office. They are supplied in ordinary plastic bags without any identification marks or inscriptions (except for the barcode sticker).


Externally, the relays are not much different from those that can be seen on the shelves in local stores. I have no particular complaints about their workmanship. The relays themselves generally look very decent. The contacts are securely sealed with a sealant very reminiscent of resin:


As you can see in the photo, each contact is signed, so there should be no problems with connection :)

On the top of the relay the principle of operation of the relay is shown, as well as the manufacturer and brief characteristics.


As you can see, this relay is designed for a voltage of 12-14 V and maximum current 40A. I can’t say whether it can really withstand such a load, since I didn’t have anything suitable for checking this parameter at the time of connection: (I have a maximum load on the network of about 4A, so there are no problems with this.

To secure the relay, the design includes a metal plate, which can be easily removed if necessary.


The delivery set includes the relay itself and a socket for it. The block comes immediately with wires, which greatly simplifies the installation process. The manufacturing quality of the pad will be somewhat worse. The main disadvantage is the abundance of flash that was not removed after the pad was cast. The length of the wires going to the block is about 15 centimeters.


But here it’s more likely to suffer appearance, since this does not affect the functionality in any way. If you believe the description, then each relay is capable of operating 10,000 on-off cycles, which is quite good.

In principle, there is nothing else interesting in the appearance of the relays, which means you can move on to checking their performance. But before doing this, I think it would be useful to remind you why these relays are needed at all.

In the normal state, the relay has 2 contacts that are permanently closed. These are contacts marked on the relay with numbers 30 and 87a (in some cases 88). When voltage is applied to contacts 86 and 85, circuit 30-87a is broken, and circuit 86-85 is closed. There is a free plus on the free contact (87) (we don’t need it). So we remove the wire from the block that goes to pin 87.


So let's get started. First of all, we cut the positive wire going to the DRL. Since in mine it is common, you can get by with one relay, installing it near the place where it is connected. We connect the wires going to contacts 30 and 87a into the section. Contact 86 is connected to ground, and contact 85 is connected to the positive wire going to side lights. We insulate the connection points of the wires and attach the relay somewhere under the hood. I got it something like this (I connected the ground wire to the fastening bolt):


All that's left to do is check how everything works. We turn on the ignition and see that our DRLs are glowing. So they didn't make things worse.


Next, turn on the dimensions/low beam:


As you can see, everything works as intended. When the headlights/low beams are turned on, the DRL lights turn off. For greater clarity, I made a short video on what it looks like live:


To sum up everything that was written here, I can say that I was pleased with the purchase. First of all, everything works the way I wanted it to. Secondly, the price of the purchased relay with a block is two times lower than ours. Thirdly, there is one more relay left in reserve :) And the idea arose to power the DRLs from the generator so that they start working only after the engine is started, and not when the ignition is turned on. Because if you are waiting for someone while sitting in the car and listening to the radio, the DRLs light up. True, with a total load of 0.4A they should not drain the battery, but still somehow I don’t really like it...

If desired, the relay can be used in a wide variety of variations. As far as I know, some even assemble anti-theft devices on them :)

That's probably all. Thank you for your attention and your time.

I'm planning to buy +14 Add to favorites I liked the review +23 +37

An electromagnetic relay is a switching device for switching electrical circuits using an electromagnetic field.

Applications

Electromagnetic switching is used in automation circuits, control of electric drives, electrical power and technological installations, control systems, etc. Electromagnetic relays allow you to regulate voltages and currents, perform the functions of storage and conversion devices, and record deviations of parameters from specified values.

Operating principle

An electromagnetic relay, the principle of operation of which is common to any type, consists of the following elements:

  1. Base.
  2. Anchor.
  3. A coil of turns of wire.
  4. Movable and fixed contacts.

All parts are attached to the base. The anchor is rotatable and is held by a spring. When voltage is applied to a coil winding, an electric current flows through its turns, creating electromagnetic forces in the core. They attract an anchor, which turns and closes the movable contacts with paired fixed ones. When the current is turned off, the armature is returned by a spring. The moving contacts move with it.

Only reed relays differ from the standard design, where the contacts, core, armature and spring are combined in a single pair of electrodes.

An electromagnetic relay, the diagram of which is shown below, is a switching device.

It is typical and generally shows how electrical energy is converted into magnetic energy, which then overcomes the spring force and moves the contacts.

The electrical circuits of the coil and switching are not connected in any way. Due to this, small currents can control large ones. As a result, an electromagnetic relay is a current or voltage amplifier. Functionally, it includes three main elements:

  • perceiver;
  • intermediate;
  • executive.

The first of these is the winding, which creates an electromagnetic field. A controlled current passes through it, upon reaching a specified threshold value, an effect occurs on the actuator - electrical contacts that close or open the output circuit.

Classification

Relays are classified as follows:

  1. According to the method of controlling contacts - anchor and reed contacts. In the first case, the contacts close and open when the armature moves. In reed switches there is no core and the magnetic field acts directly on ferromagnetic electrodes with contacts.
  2. The control current can be constant or variable. In the latter case, the armature and core are made of electrical steel plates to reduce losses. For direct current, devices are neutral and polarized.
  3. According to the response speed of the relays, they are divided into 3 groups: up to 50 ms, up to 150 ms and more than 1 s.
  4. Protection from external influences includes sealed, covered and open devices.

With all the variety of types presented below, the action of an electromagnetic relay is based on general principle switching contacts.

The electromagnetic relay device is hidden inside the housing; only the winding and contact leads protrude from the outside. They mostly are numbered and a connection diagram is provided for each model.

Options

The main characteristics of the relay are:

  1. Sensitivity - switching from a signal of a certain power supplied to the winding, sufficient for switching on.
  2. Winding resistance.
  3. Actuation voltage (current) is the minimum threshold value of the parameter at which the contacts switch.
  4. Release voltage (current).
  5. Response time.
  6. Operating current (voltage) - the value at which guaranteed switching occurs during operation (the value is indicated within specified limits).
  7. Release time.
  8. Switching frequency with contact load.

Advantages and disadvantages

The electromagnetic relay has the following advantages over semiconductor competitors:

  • switching large loads with small dimensions;
  • galvanic isolation between the control circuit and the switching group;
  • low heat generation on contacts and coil;
  • small price.

The device also has disadvantages:

  • slow response;
  • relatively small resource;
  • radio interference when switching contacts;
  • the complexity of DC switching of high-voltage and inductive loads.

The operating voltage and current of the coil should not exceed the specified limits. At low values, contact becomes unreliable, and at high values, the winding overheats, the mechanical load on the parts increases, and insulation breakdown may occur.

The durability of the relay depends on the type of load and current, frequency and number of switchings. Contacts wear out the most when they open, forming an arc.

Non-contact devices have an advantage because they do not produce an arc. But there are also a lot of other shortcomings that make it impossible to replace the relay.

Electromagnetic current relays

Current and voltage relays are different, although their structure is similar. The difference lies in the design of the coil. The current relay has a small number of turns on the coil, the resistance of which is low. In this case, the winding is done with a thick wire.

The winding of the voltage relay is formed by a large number of turns. It is usually included in the existing network. Each device controls its specific parameter with automatic switching on or disconnecting the consumer.

Using a current relay, the current strength in the load to which the winding is connected is controlled. Information is transferred to another circuit by connecting a resistance to it with a switching contact. The connection is made to the power circuit directly or through instrument transformers.

Protective devices are fast and have a response time of several tens of milliseconds.

Time relay

In automation circuits there is often a need to create delays when the devices operate or to issue signals for technological processes in a certain sequence. For this purpose, time delay switches are used, which have the following requirements:

  • stability of exposure regardless of the influence of external factors;
  • small dimensions, weight and energy consumption;
  • sufficient power of the contact system.

To control electric drives, high precision requirements are not imposed. The shutter speed is 0.25-10 s. Reliability must be high, since work is often carried out in conditions of shaking and vibration. Power system protective devices must operate accurately. The shutter speed does not exceed 20 seconds. Triggering occurs quite rarely, so high demands on wear resistance are not imposed.

Electromagnetic time relays operate on the following deceleration principles:

  1. Pneumatic - due to the presence of a pneumatic damper.
  2. Electromagnetic - with direct current, there is an additional short-circuited winding in which a current is induced, preventing the increase in the main magnetic flux when triggered, as well as its decrease when switched off.
  3. With an anchor or clock mechanism, which is wound by an electromagnet, and the contacts are activated after counting down the time.
  4. Motor - supplying voltage simultaneously to the electromagnet and the motor, which rotates the cams that activate the contact system.
  5. Electronic - using integrated circuits or digital logic.

Conclusion

With the advent of the electronics era, the electromagnetic relay is gradually being replaced, but it is still developing, achieving new capabilities. It is difficult to find an alternative to it in places where current and voltage fluctuations occur when starting and shutting down devices that use electricity.

. Intermediate electromagnetic relays are used in many electronic and electrical circuits and are intended for switching electrical circuits. They are used to enhance and transform electrical signals; remembering information and programming; electrical energy distribution and operation control individual elements, devices and equipment units; coupling of elements and devices of radio-electronic equipment operating at different voltage levels and operating principles; in alarm, automation, protection circuits, etc.

An intermediate electromagnetic relay is an electromechanical device that can switch electrical circuits and also control other electrical device. Electromagnetic relays are divided into relays permanent And AC.

The operation of an electromagnetic relay is based on the interaction of the magnetic flux of the winding and a moving steel armature, which is magnetized by this flux. The figure shows the appearance of the intermediate relay type RP-21.

1. Relay device.

The relay is reel, the winding of which contains a large number of turns of insulated copper wire. Inside the coil there is a metal rod ( core), mounted on an L-shaped plate called yoke. The coil and core form electromagnet, and the core, yoke and anchor form relay core.

Located above the core and coil anchor, made in the form of a metal plate and held with return spring. Rigidly anchored moving contacts, opposite which the corresponding pairs are located fixed contacts. Relay contacts are designed to close and open an electrical circuit.

2. How the relay works.

In the initial state, until voltage is applied to the relay winding, the armature, under the influence of the return spring, is at some distance from the core.

When voltage is applied, current immediately begins to flow in the relay winding and its magnetic field magnetizes the core, which, overcoming the force of the return spring, attracts the armature. At this moment, the contacts attached to the anchor, moving, close or open with the stationary contacts.

After turning off the voltage, the current in the winding disappears, the core is demagnetized, and the spring returns the armature and relay contacts to their original position.

3. Relay contacts.

Depending on design features intermediate relay contacts are normally open(closing), normally closed(breaking) or changeover.

3.1. Normally open contacts.

As long as the supply voltage is not applied to the relay coil, its normally open contacts are always open close, closing the electrical circuit. The pictures below show the operation of a normally open contact.

3.2. Normally closed contacts.

Normally closed contacts work the other way around: as long as the relay is de-energized, they are always closed. When voltage is applied, the relay is activated and its contacts open, opening the electrical circuit. The figures show the operation of a normally open contact.

3.3. Changeover contacts.

At changeover contacts with a de-energized coil average the contact attached to the anchor is general and is closed with one of the fixed contacts. When the relay is triggered, the middle contact, together with the armature, moves towards the other fixed contact and closes with it, simultaneously breaking the connection with the first fixed contact. The pictures below show the operation of a changeover contact.

Many relays have not one, but several contact groups, which makes it possible to control several electrical circuits simultaneously.

There are special requirements for intermediate relay contacts. They must have low contact resistance, high wear resistance, low tendency to weld, high electrical conductivity and long service life.

During operation, the contacts with their current-carrying surfaces are pressed against each other with a certain force created by return spring. A current-carrying surface of a contact in contact with a current-carrying surface of another contact is called contact surface, and the place where the current passes from one contact surface to another is called electrical contact.

The contact of two surfaces does not occur over the entire apparent area, but only in separate areas, since even with the most careful treatment of the contact surface, microscopic tubercles and roughness will still remain on it. That's why total contact area will depend on the material, the quality of the contact surfaces and the compression force. The figure shows the contact surfaces of the upper and lower contacts in a greatly enlarged view.

Where current passes from one contact to another, electrical resistance occurs, which is called contact resistance. The magnitude of the contact resistance is significantly influenced by the magnitude of the contact pressure, as well as the resistance of the oxide and sulfide films covering the contacts, since they are poor conductors.

During long-term operation, the contact surfaces wear out and can become covered with soot deposits, oxide films, dust, and non-conductive particles. Contact wear can also be caused by mechanical, chemical and electrical factors.

Mechanical wear occurs when contact surfaces slide and impact. However, the main reason for contact failure is electrical discharges, arising when opening and closing circuits, especially DC circuits with an inductive load. At the moment of opening and closing, the phenomena of melting, evaporation and softening of the contact material, as well as the transfer of metal from one contact to another, occur on the contact surfaces.

Silver, alloys of hard and refractory metals (tungsten, rhenium, molybdenum) and metal-ceramic compositions are used as materials for relay contacts. The most widely used material is silver, which has low contact resistance, high electrical conductivity, good technological properties and relatively low cost.

It should be remembered that there are no absolutely reliable contacts, therefore, to increase their reliability, parallel and serial connection of contacts is used: when sequential connection contacts can break a large current, and parallel connection increases the reliability of the electrical circuit.

4. Electrical diagram of the relay.

On circuit diagrams the coil of an electromagnetic relay is represented by a rectangle and the letter “K” with the number of the relay serial number in the diagram. Relay contacts are designated by the same letter, but with two numbers separated by a dot: the first number indicates the relay serial number, and the second indicates the serial number contact group this relay. If in the diagram the relay contacts are located next to the coil, then they are connected by a dashed line.

Remember. In the diagrams, the relay contacts are shown in a state when voltage has not yet been applied to it.

The manufacturer indicates the electrical diagram and numbering of the relay terminals on the cover covering working part relay.

The figure shows that the coil terminals are indicated by numbers 10 And 11 , and that the relay has three groups of contacts:
7 — 1 — 4
8 — 2 — 5
9 — 3 — 6

Here under electrical diagram the electrical parameters of the contacts are indicated, showing what maximum current they can pass (switch) through themselves.

The contacts of this relay switch AC no more than 5 A at a voltage of 230 V, and D.C. no more than 5 A at a voltage of 24 V. If more than the specified current is passed through the contacts, they will very soon fail.

On some types of relays, the manufacturer additionally numbers the terminals on the connection side, which is very convenient.

For ease of operation, replacement and installation of relays, special blocks are used that are installed on a standard DIN rail. The blocks have holes for relay contacts and screw contacts for connecting external conductors. Screw contacts have a contact numbering that matches the relay contact numbering.

Also on the relay coils the type of current and operating voltage of the relay winding are indicated.

Let's leave it at that for now, but let's look at main parameters And connection of electromagnetic relays, where in examples simple circuits Let's analyze the operation of the relay.

See you on the pages of the site.
Good luck!

Literature:

1. I. G. Iglovsky, G. V. Vladimirov - “Handbook on electromagnetic relay", L., Energy, 1975.
2. M. T. Levchenko, P. D. Chernyaev - “Intermediate and indicating relays in relay protection and automation devices”, Energy, Moscow, 1968, (Electrician’s Book, issue 255).
3. V. G. Borisov, “Young radio amateur”, Moscow, “Radio and Communications” 1992

Relay is essential for automation and load management systems. In addition, relays are the best way for galvanic isolation between high-voltage and low-voltage sections of the circuit. There is a huge variety various types relay. Let's first find out how a relay works.

How does a relay work?

Step one - contacts

Each relay has at least two contacts inside. Relay contacts work the same way as contacts simple switch or buttons. You can see the operation of the contacts in the following figure:

Both terminals act as a switch. When the contacts are closed, current flows from pin 1 to pin 2.

There are two types of contacts:

  • normally open (N.O.)
  • normally closed (N.C.)

With Normally Open (N.O.) contacts, in the de-energized (normal) state, no current can pass through those contacts. Conversely, a de-energized relay with normally closed (N.C.) contacts allows current to flow freely through the contacts.

The animation below shows how a relay with normally open contacts turns on a light bulb:

As for a relay with normally closed contacts, it works exactly the opposite. Watch the following animation:

Step two - contact combination

The relay may have a combination of the above contacts. Look at the picture below

In this case there is a 3rd pin called "Common". Due to this, the NC and NO pins only work with this common pin. There is no contact between the NC and NO terminals! The following animation shows how this pair works:

Step three - what defines normal?

Okay, in a relay we have normally open and normally closed contacts. But what condition is considered normal? Let's take one more step towards explaining the principle of operation of the relay - take a look at the figure below. A new element has been added to the previous figure - a spring.

This spring determines the normal position of the common contact. If you noticed in the previous animation, the switching force (F) has its effect on the common contact every other time, since there is another (opposite) force that is constantly pulling the contact in the opposite direction. This force comes from the spring:

Thus, the spring determines the normal state of the contacts. In other words, the normal state is a contact position in which there is no action on the common terminal other than the action of the spring.

Step four - what causes the common contact to move?

The element that causes the common contact to move is actually an electromagnet! The electromagnet coil is located directly under the contact.

When current flows through this coil, a magnetic field is created. Strength magnetic field overcomes the force of the spring and attracts the common contact towards itself, changing its position. Below is a complete animation of the operation of an electromagnetic relay:

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