Understanding Relays, Functions, Types and Symbols

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What is Relays?

Understanding Relays, Functions, Types and Symbols – We both agree that connecting an electrical circuit is simply using a switch. Before relays were invented, manual switches were one way of controlling electric current to flow and disconnect.

After the discovery of relays, manual switches have been abandoned in applications that carry high currents and high voltages.

Relay is one type of switch that can operate when a voltage is applied. Unlike the switch in general, which operates when touched or pressed.

The function of the relay is to disconnect / connect large currents and voltages. Such as turning on electric lights, air conditioning, trains, remote fans, audio selectors, smart homes, automotive systems and others, some of which are for 220v relays.

Type of Relay

Based on the type of material and how it works, relays are divided into two types, namely Mechanical Relays and Solid State Relays.

Mechanical Relay

As the name suggests, a mechanical relay is a relay that works based on a mechanical system by moving a lever to a contact, so that the contact can be connected or disconnected.

Mechanical relays are also called conventional relays because this type of relay is the oldest type of relay used until now.

The working principle of a mechanical relay is based on the attraction of an electromagnetic field to the push lever of the contact pin.

Inside a mechanical relay, there is a winding (selenoid), a push lever, and two contact pins.

When the coil is given an electric current, it will produce an electromagnetic field.

The push lever that is near the winding will be attracted by the magnetic field so that the push lever will push one of the two contact pins. As a result, the two contact pins touch each other.

There is one great video that has been made by jordi3736 to be able to understand relay basics, here:

Advantages of Mechanical Relay :

  • Large Current and Voltage. To my knowledge this mechanical relay can perform switching with currents up to 750A. For the voltage itself up to 250VDC and 495VAC.
  • Cheap price

Disadvantages of Mechanical Relays:

  • Make noise during operation
  • Bigger body size
  • Allows Sparks to Occur
  • Shorter lifespan than SSR
  • Operation may be interrupted when there is strong vibration

Solid State Relay

As the name implies Solid State Relay (SSR), this type of relay is a relay made of semiconductors. The shape is thin and smaller than mechanical relays.

For the working voltage that I know is up to 240VDC/AC. As for the current can reach up to 200A.

Advantages of Solid State Relay:

  • Low sound during operation
  • Smaller size than mechanical relay
  • No sparks
  • Longer lifespan
  • Uninterrupted operation when vibration occurs

Disadvantages of Solid State Relay:

  • Because it is made of semiconductor material, there will be a voltage drop on the trigger pin
  • There may be leakage current in this relay
  • The price is more expensive than the mechanical relay

Relay Symbol

The relay symbol is not much different from the switch symbol. The basics consist of:

  • SPST (Single Pole Single True)
  • SPDT (Single Pole Dual True)
  • DPST (Dual Pole Single True)
  • DPDT (Dual Pole Dual True)

Look at the following picture:

How to Operate the Relay

Before we operate the relay, we must know in advance how many volts the winding voltage we want to use? As far as I know, the minimum winding voltage is 1.1V.

Then after we know the winding voltage, then we must know the maximum winding current so that we can determine the driver (transistor) used.

If you want to control a relay using Arduino, for example, you can simply use three Driver components, namely resistors, transistors and diodes.

For more details, you can read the article How to Use Controlling Relays and Solid State Relays Using Arduino.

How to Choose Relay

Choosing a relay for your job is very important. Both in terms of quality, voltage, brand and capability.

Some well-known relay manufacturers include TE Connectivity, Omron Relay, Panasonic Relay, ABB Protection Relay, Siemens Relays, Pilz Relay, Schneider Relay and others.

If you want to use it as a hobby and a basic lesson, you can buy a relay module on the market. One manufacturer that sells relays at low prices is Songle.

Some of the products sold in the market are related to relays, namely TE Connectivity Schrack, PNOZ m1p, MainsPro – ComAp, Cell Relays, Pilz PNOV XV1P.

Thank you for visiting the website Chip Piko. May be useful.

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