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What is a relay?


We could define relay or relay as a button that can be controlled electrically or also as an electromagnetic element. Its main function is to open and close inputs and outputs by means of a coil and an electromagnet.

The electromagnet is the main piece that will allow us to open and close the inputs and outputs, and then the coil creates a magnetic field to establish a connection between the two. The relay was invented in 1834 by Joseph Henry.

what is a relay
In this image we explain what a relay is and how it works

How does a relay work?

The relay or also known as a relay is used as a push button that is managed by an electrical circuit.

As we have already mentioned in the previous paragraph that by means of a coil and an electromagnet one or several contacts are executed that will allow us to open other inputs and outputs.

Since the relay has the possibility of controlling an electrical circuit with more power than the input one, we can also call it an electrical amplifier.

parts of a relay
In the following image we show the different parts of a relay in detail

Types of Electric Relay

There are many models and classes of relays, everything will depend on the type of current, the times they use, the number of contacts they have... In the following text we show you the different types of relays or electrical relays.

Solid state relay

It works as an electrical switch that switches between the open and closed states, it is very similar to the electromechanical relay, its use is for operations that require continuous use of the relay contacts, without having to produce mechanical deterioration.

Apart from their extensive operating range with electrical power loads, solid-state relays have the benefit of changing state at high speeds, measured in nanoseconds.

Solid state relay
Image of a solid state relay

Electromechanical relays

When we talk about this relay we are naming the armature type relay, this type of relay contains a coil, core and electromagnet which are the main parts so that it can perform its operation.

This relay works like a pushbutton or switch, first current passes through the coil, the core is magnetized and becomes a magnet providing power depending on the percentage of the force that produces the current.

The parts of an electromechanical relay would be:

  • Contacts
  • coil connection
  • Core
  • Coil
electromechanical relay
The following image shows an example of an electromechanical relay

Polarized Relays

They are composed of a shield and a permanent magnet. The lower corner (right or left) revolves inside the electromagnet while the other part contains a contact head.

By moving the electromagnet, the shield is set in motion and the contacts are closed. In case of polarizing it backwards, the rotation will be the other way around, that is, in the opposite direction, opening the contactors or closing the circuit.

alternating current relays

When the coil of a relay is energized with alternating current, the magnetized flux in the magnetized circuit is also alternating, generating a pulsating force, usually double, towards the contacts.
In alternating current relays, the resonance of the contactors is changed to prevent oscillation.

Delayed action relays

They are relays that, due to their design or the way in which the coil is powered, have pauses between connections and disconnections.

Relays with connection delay

We have the probability that there will be a delay in the disconnection either due to the decrease in pressure or by mechanical means, this will depend on the different factors of the situation that occurs at that moment.

Relays in parallel with capacitor

It is very easy to explain, it is a relay that has a capacitor in parallel and every time there is a power outage, there will be a delay in the disconnection due to the discharge of the capacitor in the coil, with this function the times are very exact sometimes they can exceed the second of time.

moving core relay

They are formed by a plunger. They have a high pull force, and a solenoid is used to open and close the contactors. It is frequently used in cases where very high currents must be controlled.

reed relays

Formed by a glass part, with contactors inside, on top of thin metal sheets. These contacts are switched by the activation of a coil, which is located near the previously named glass part.

Relay position held

The main characteristic of these types of relays is that they use rivets with a high remanence, these are located in the holes that are in the part of the core, as well as the armature, which are both in the same way.

The pole faces are rectified when we close the magnetic circuit of the relay, it will end up in that position due to magnetic remanence and even if the coil is disconnected, it will return to the initial position only when the reverse current opens the contactor again.

Relay with shorted winding

They contain 2 windings: one of them called primary or drive and another auxiliary that is short-circuited.

Whether the primary winding is connected to or disconnected from the supply voltage, the consequent change in flow will induce a current in the auxiliary winding that, opposing the cause that generates it, differs from a change in it, with which it is generated In this way, a time delay is applied both to the connection and to the disconnection of said relay.

This would be the explanation of this type of relay that is not as common as those previously named.

Reed relay

It is used for different frequencies. It consists of an electromagnet moved with alternating current that enters and attracts the pins tuned to sound frequencies. The pin that is ringing at that moment makes its contact, the rest will not carry out any action. This type of relays are usually used for remote control.

thermal relay

It is an electromechanical element invented to provide security to electric motors, thus increasing their durability and protecting them at all times through factors such as overheating or overloads. They are composed of a thin metal sheet with different types of expansion.

The two sheets that make up this relay, one is made of iron and the other is made of nickel. When the motor starts, it energizes the coil and the motor begins to perform its operation.

When it receives current, the resistance that produces heating and the metal sheets heat up.

The relay will be activated when there is a fault or overload, the foil will bend up and slide a layer of fiber. This will release the lever in charge of opening the coil contacts, and will stop both the circuit and the motor and thus prevent these elements from burning.

thermal relay
image of a thermal relay in perfect condition

Explanatory video about what a relay or relay is

If you want to learn more about electronics, visit our article that explains what is software.

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