That is a relay

One of the most common electrical controls is the relay, since it is in charge of opening and closing contacts to control a circuit. Although it is not a device that we commonly have in our toolbox, we use it frequently at home and in the car, so it is worth knowing about it.

Better known as a relay, the relay is basically a device that serves to divert or interrupt the flow of electrical current in a circuit. In other words, it is a switch, but in this case it is not necessary to turn it on and off by hand, since it works with a coil, so it creates an electromagnetic field that attracts the contacts to close the circuit, thus allowing the passage of electricity. Let’s look at this information in more detail.

The parts of a relay

A relay is made up of mechanical parts, among which are an electromagnet, several contacts, a yoga, a mobile armature and a spring, bracket or frame. Each one has a specific function in the internal area of ​​the device, so it is good to know them separately.

The electromagnet is the fundamental part of the relay. It is a metal in the form of a coil, which, when in contact with direct current, acquires magnetic properties. In this way, it is capable of attracting the mobile armature, which is the metal piece that is balanced on a support and is responsible for connecting and disconnecting the contacts to control the flow of current. However, the operation of this armature depends precisely on the coil being energized.

In this same sense, the yoke is a small piece of metal that is fixed to the core, to attract and keep the armature fixed while the coil is working. However, all this would not make sense without the contacts, which are normally three: Common (C), Normally Closed (NC) and Normally Open (NO). They are inside the relay, but they are attached to the terminals that allow the connection of the relay.

How do relays work?

To understand the operation of a relay, we must pay attention to one of its fundamental characteristics; It is indicated for high intensity electric current circuits. For example, in the car a relay is used to activate and deactivate the passage of current to the electric fan, in fact, the characteristic rhythmic sound of the emergency lights also comes from a relay.

Some experts agree that the relay is a kind of electrical amplifier, this is because it is a small circuit, usually 5, 12 or 24 volts. This voltage is marked on the surface of the relay and corresponds to the DC voltage that the coil needs to work. However, this low power circuit is responsible for activating a high intensity circuit, usually up to 250 V AC, hence the idea that the electromagnetic relay in a general sense can amplify electricity. 

In this sense, it is important to mention that the relay is an electronic device that works with low-intensity direct current, so we should not confuse it with a contactor, which is an electrical device and works with high-power alternating current. This is the main difference between contactors and relays. 

Relay Utility

If you are wondering what a relay is for, we must mention that one of its main advantages is the possibility of controlling devices remotely, in this way, it is not necessary to be in front of the device to turn it on. For this reason, we are facing a useful and practical solution.

In addition, a relay needs very little current to work, but it is capable of activating high-power appliances, such as washing machines, dryers, dishwashers, among others, which do consume a large amount of current. In this sense, we can say that it is an energy efficient device.

On the other hand, the relays can be connected in series, so that by means of a single signal it is possible to control many relays at the same time.

The main types of relays

Based on the principle of operation, relays can be classified into electromechanical, moving core, solid state, and hybrid.

electromechanical relay

An electromechanical relay is like the one described above, since it consists of a few mechanical parts that, with the help of an electromagnet, are capable of changing the connection of the contacts to interrupt the flow of current when necessary. This is the operation of a 12v relay that we can find in any electrical supply store.

moving core relay

If you want to know how to connect a 220v relay to control very high currents, it may be a good idea to use a mobile core relay, which is very similar to the electromagnetic one, but instead of an armature they have a plunger, so it has a greater attractive force., so the use of a solenoid is necessary to close the contacts.

Solid state relay

In this case, the mechanical parts are replaced by semiconductor devices, in this way, there is an improvement in the switching speed of the device, so it works easier and faster. In addition, these types of relays are usually more durable. The solid state relay is frequently used in the sanitary area to control medical equipment, but also in the domestic field for the activation of water pumps and compressors.

hybrid relay

To understand how a hybrid relay works, you have to think about electromechanical and solid-state relays, since it has mechanical parts, but also semiconductors, so it is very complete, functional and at the same time resistant.

Classification of relays according to polarity

Among the types of relay we can also find the polarized ones, which have an armature like the electromechanical ones, but this is joined to a permanent magnet. One end has a contact head, while the other end rotates within the poles of the electromagnet. When activating the latter, the armature moves, thus causing the contacts to close. If there is a change in polarization, the spin happens the other way around. On the contrary, in non-polarized relays, the coil does not have polarities, therefore, even if there is an alteration in the polarity of the input signal, its operation remains stable.