What Is A Relay?

One of the most common electrical controls is the relay, since it is responsible for 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.

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 passing 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 movable armature and a spring, stirrup 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 piece 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 passage 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: the Common (C), the Normally Closed (NC) and the Normally Open (NO). They are located inside the relay, but they are attached to the terminals that allow the relay to be connected.

How do relays work?

To understand the operation of a relay, one 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 flow of current to the electric fan, in fact, the characteristic rhythmic sound of the hazard 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 direct current voltage that the coil needs to operate. However, this low-power circuit is responsible for activating a high-intensity circuit, usually up to 250V alternating current, 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 wonder 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 function, but it is capable of activating high-power electrical appliances, such as washing machines, dryers, dishwashers, among others, which do consume a lot 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, the relays can be classified into electromechanical, moving core, solid state and hybrid.

Electromechanical relay

An electromechanical relay is like the one we have described above, since it consists of a few mechanical parts that with the help of an electromagnet are able to change 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 moving core relay, which is very similar to the electromagnetic one, but instead of armature they have a plunger, so it has a greater attraction force , so it is necessary to use a solenoid to close the contacts.

Solid state relay

In this case, the mechanical parts are replaced by semiconductor devices, in this way, an improvement in the switching speed of the apparatus occurs, so it works easier and faster. In addition, these types of relays tend to be more durable. The solid state relay is frequently used in the healthcare area to control medical equipment, but also in the domestic environment to activate water pumps and compressors.

Hybrid relay

To understand how a hybrid relay works, you have to think about the electromechanical and solid state ones, 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 relays we can also find the polarized ones, which have an armature like the electromechanical ones, but this is joined to a permanent magnet. One of the ends has a contact head, while the other 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 flip occurs the other way around. On the contrary, in non-polarized relays the coil has no polarities, therefore, even if there is an alteration in the polarity of the input signal, its operation remains stable.

Leave a Comment