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What Is a Relay Module and What Does it Do?

2-channel relay module
2-channel relay module

With many electrical systems requiring higher power than what a microcontroller can provide, the relay module finds use in a lot of different applications. So, what exactly is this useful little device and how does it work? In this article, you will learn the following about the relay module:

  • Relay module meaning
  • Relay module function
  • Relay module working
  • Relay module uses and price

What is a Relay Module?

Relay modules are simply circuit boards that house one or more relays. They come in a variety of shapes and sizes, but are most commonly rectangular with 2, 4, or 8 relays mounted on them, sometimes even up to a 16 relays.

Relay modules contain other components than the relay unit. These include indicator LEDs, protection diodes, transistors, resistors, and other parts. But what is the module relay, which makes the bulk of the device? You may ask. Here are facts to note about it:

  • A relay is an electrical switch that can be used to control devices and systems that use higher voltages. In the case of module relay, the mechanism is typically an electromagnet.
  • The relay module input voltage is usually DC. However, the electrical load that a relay will control can be either AC or DC, but essentially within the limit levels that the relay is designed for.
  • A relay module is available in an array of input voltage ratings: It can be a 3.2V or 5V relay module for low power switching, or it can be a 12 or 24V relay module for heavy-duty systems.
  • The relay module information is normally printed on the surface of the device for ready reference. This includes the input voltage rating, switch voltage, and current limit.

Relay Module Function

What does a relay module do? The relay module function is mainly to switch electrical devices and systems on or off. It also serves to isolate the control circuit from the device or system being controlled.

This is important because it allows you the use a microcontroller or other low-power device to control devices with much higher voltages and currents.

Another relay module purpose is to amplify the control signal so that it can switch the higher currents using only a small out of power from a microcontroller.


GEYA 2NO2NC Omron Plug in Relay Module FY-2NG2R Technical Parameters:

Input operating voltageRated DC±20% & AC±10%
Relay MountingPluggable
Rated Load Current5A 250V AC/30V DC
Max Transient Load Current5A
Coil Powerapprox.0.53W
Operate Time(at normal volt.)≤15ms
Release Time(at normal volt.)≤10ms
Input/Output ConnectionsScrew terminal block
Wire Range0.2~2.5mm²
Stripping Length6-7mm
DIN Rail Mountable15/28/35mm

Relay Module vs. Relay

It is also important to note the difference between a relay vs. relay module. A relay is a single device that has an electromagnet and a switch, or it can be the solid-state type.

A relay module, on the other hand, is a board that has one or multiple relays on it and several other components to provide isolation and protection.

Because of its modular construction, this type of switching and control device can be many different configurations. It can be a single-channel relay module for a single load or it can be a multi-channel device with multiple relays to control several circuits.

_Relay motor working demonstrated
Relay motor working demonstrated

Relay Module Working

How does a relay module work? The relay module working principle is actually quite simple. It uses an electromagnet to open and close a set of electrical contacts. Here is the sequential working of relay module devices for easier understanding:

  • The typical relay module connection points include an input side that consists of 3 or 4 jumper pins, and an output side that has 3 screw terminals.
  • When the control signal is applied to the input side of the relay, it activates the electromagnet, which attracts an armature.
  • This in turn closes the switch contacts on the output (high voltage) side, allowing electricity to flow and power the device or system that is connected to it.
  • To prevent flyback voltage from damaging the relay module circuit and the input device, a diode is often placed in parallel with the electromagnet coil. This diode is known as a flyback diode. It allows current to flow in only one direction.
  • When a higher level of isolation is required, an optocoupler is used. An opto-isolated relay module has the photoelectric device on the input side, which is used to control the electromagnet’s switching action.

Relay modules are available with either normally open (NO) or normally closed (NC) switch configurations.

  • A NO switch is open when the electromagnet is not activated, and closed when it is activated.
  • An NC relay switch, on the other hand, remains closed by default, and only opens when the relay is activated.

How to use a relay module for motor control
How to use a relay module for motor control

Relay Module Uses

Relay modules are used in all sorts of applications, from controlling lights and motors to more complex systems such as automation processes and safety or security systems. Here are just a few examples of the relay module uses in different applications.

Home Automation Relay Module

Relay modules are also used in home automation systems to control lights, appliances, and other devices. The home automation relay module is often used with mains electricity. So it’s mostly rated for 10A or less for maximum current, and up to 250V AC.

Industrial Relay Module

In industrial applications, the industrial relay module is used to control machinery, process controls, and other industrial equipment. Other relay module uses in industrial settings include lighting control and the control of alarm or security systems.

Automotive Relay Module

Relay modules are widely used in automotive applications. The automotive relay module controls things like headlights, turn signals, and even the starter motor. A car relay module is also found in many other automotive circuits such as those that operate remote starters or theft alarms.

Arduino Relay Module

Hobbyists often use a relay module with Arduino in their projects. An Arduino is a microcontroller board that is widely popular in DIY electronics projects. The relay module, when paired with an Arduino, can control various appliances and devices.

Single-channel relay module
Single-channel relay module

Relay Module Price

Are you looking to buy relay module switching devices for your business or power system control needs? Price is an important factor to consider when purchasing these products, as well as the quality, features, and specifications.

The relay module price range will usually depend on the type, number of relays, voltage and current rating, and other factors. A typical module will cost anywhere from $5 to $50.

When it comes to buying relay modules, it is important to buy from a reputable supplier that offers high-quality products at competitive prices.


A relay module is a relay that’s been mounted on a board with other components to provide isolation and protection. This makes them easier to use in a variety of applications. The use of relay module devices offers a simple and convenient way to control electrical equipment systems remotely.

Picture of William

I am William, Electrical Engineering Author. Dedicated to writing technical articles on Timer Relay, Monitoring Relay, Surge Protection Device and other electrical devices. With 7 years of writing experience, I am committed to providing accurate and in-depth expertise to my readers.


    Are you dumb or what, if someone is searching for relay module then you must explain that first. What is a relay? What can we understand by relay module? What is the use of relay module.
    You could have explained thta it is a device used for …..

    Yes, you are really a dumb because I have to read all then I read about main topic “What is an relay moudel” how it works etc.

    Bonjour, j’ai un module relais avec 4 relais 12 volts. l’interface module comprend 6 bornes : dc+, dc-, IN1 à IN4. Les entrées IN sont des entrées de commande à travers d’optocoupleurs. Je soppose que DC + et DC- sont cunnectés au 12 volts mais les entrées de commande sont connectées à quelle tension ? (12 volts ou moins ?)

    The last two comments > you have no cooking clue how this works – it seems clear from your illogical/incompetent statements!
    The author did good in his discussion and explanations!

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