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?
Source: https://en.wikipedia.org/wiki/Relay
Switching module 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 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 board 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’s 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’s 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 voltage | Rated DC±20% & AC±10% |
| Relay Mounting | Pluggable |
| Rated Load Current | 5A 250V AC/30V DC |
| Max Transient Load Current | 5A |
| Coil Power | approx.0.53W |
| Operate Time(at normal volt.) | ≤15ms |
| Release Time(at normal volt.) | ≤10ms |
| Input/Output Connections | Screw terminal block |
| Wire Range | 0.2～2.5mm² |
| Stripping Length | 6-7mm |
| DIN Rail Mountable | 15/28/35mm |
Relay Module vs. Relay
It is also important to note the difference between a relay vs. a relay module. A relay is a single device with an electromagnet and a switch, or it can be a solid-state type.
On the other hand, a relay module is a board with 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 in many different configurations. It can be a single-channel relay module for a single load or a multi-channel device with multiple relays to control several circuits.
Relay Module Working
How does a relay module work? The relay module’s working principle is 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 a 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.
Applications of Relay Modules
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 used 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 modules used 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.
Power Distribution Control: They isolate high-voltage DC circuits (up to 1000V) to prevent faults during rapid charging sessions, reducing downtime in public stations.
Safety Interlocks: In home EV setups, a 5V relay module integrated with IoT sensors can automatically disconnect power if anomalies like overheating are detected—critical for the 2025 push toward bidirectional charging (V2G).
Efficiency Gains: Unlike traditional fuses, relay modules offer programmable switching, aligning with new standards for ultra-fast charging up to 350kW.
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.
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.
Why Choose Industrial Grade Over Standard Relay Modules?
While searching for “relay modules” often yields cheap, bare-board products designed for hobbyists, our FY73x Series is engineered strictly for professional applications. Here is the crucial difference between standard DIY modules and our industrial-grade solutions:
| Feature | Consumer / DIY Grade (Standard Relay Module) |
Industrial / Professional Relay Terminal Block (Our FY73xC Series) |
|---|---|---|
| Appearance | Exposed PCB board, no protective casing. | Professional flame-retardant protective housing. |
| Installation | Requires drilling and screw mounting. Cannot be mounted on standard rails. | Snap-on DIN Rail mounting (Compatible with standard 15/28/35mm rails in control cabinets). |
| Compatibility & Protection | Basic circuitry, minimal protection. |
|
| Application | Student projects, makers, Arduino/Raspberry Pi DIY, basic smart home mods. | True Industrial Automation (CNC machines, automated assembly lines, elevator control cabinets). |
| Professional Terminology | Relay Module, DIY Relay. | PLC Amplifier Board, Relay Terminal Block. |
Types of relay modules
The types of relay modules mainly include electromagnetic relays, solid-state relays, hybrid relays, high-frequency relays, coaxial relays, vacuum relays, etc.
Electromagnetic relay module
An electromagnetic relay module is an electronic control device that has a control system (also known as an input circuit) and a controlled system (also known as an output circuit), typically used in automatic control circuits. An electromagnetic relay is an “automatic switch” that uses a smaller current and lower voltage to control a larger current and higher voltage. It plays a role in automatic regulation, safety protection, and circuit conversion in the circuit. The electromagnetic relay module uses electromagnets to control the opening and closing of contacts.
Advantages： low cost, high isolation, and strong load capacity
Disadvantage： they are large, limited in lifespan, and slow in response speed
Electromagnetic relays are widely used in aviation, aerospace, shipbuilding, home appliances, and other fields, mainly to complete functions such as signal transmission, execution control, and system power distribution. They are one of the key electronic components in various systems.
Solid state relay module
Solid state relay module (SSR): The SSR module provides similar functionality to EMR, but does not include any moving components, thereby improving long-term reliability. They use semiconductor switching elements such as thyristors, thyristors, and diodes to transmit and output signals. After activation, the input signal is used as a switch to allow the high-voltage signal to pass through the output component of the solid-state relay.
Advantages： small size, long lifespan, fast response speed, and strong anti-interference ability,
Disadvantage： the cost is high and the isolation degree is relatively low
In addition, according to different application scenarios, relay modules can also be classified into low-power relays, medium-power relays, high-power relays, etc., as well as relays classified according to the working voltage of the control circuit, such as 5V, 12V, 24V, etc. These classifications help meet the needs of different fields and applications.
For more information about the types of relay modules, please click this blog
Key parameters of the relay module
Contact-rated current and contact-rated voltage
The rated current and rated voltage of the contacts are key indicators of relay module performance, representing the maximum current and voltage that the relay can withstand under normal operating conditions, respectively. These parameters may vary depending on different usage requirements. For example, for commonly used relays, the rated current of the contacts is usually between 5A and 30A, while for general relays, the rated voltage is 220V or 380V. For relays with special applications, their rated voltage and current can reach even higher levels.
Contact type
Including normally open (NO), normally closed (NC), and single pole double throw types, these forms determine the contact state of the relay under different excitation states.
Coil resistance
The resistance value of the coil varies depending on the type of relay module. Similarly, for 5A and 220V relays, the resistance value of small relays is larger than that of conventional relays. Typically, a resistance value of tens to hundreds of ohms is considered normal
The resistance value of the 12V5A relay coil is 400 ohms. If the switch terminal of the normally open contact relay is not closed, the resistance value is infinite. If the normally closed contact relay switch terminal is not engaged, the resistance value is 0
The resistance value of the relay switch’s pull-in can be ignored
Different relays have different resistance values, which can be measured with a multimeter. The two pins where the energy comes out of the resistance are the coil pins.
Choosing the Right Relay Module
Factors to Consider When Choosing a Relay Module
| Factor | Explanation |
|---|---|
| Voltage and Current Ratings | |
| Coil Voltage | The voltage at which the relay coil operates, common values are 5V, 12V, 24V, etc. Choose a coil voltage that matches your control circuit. |
| Contact Current Rating | The maximum current that the relay contacts can carry. Choose a contact current rating greater than the load current, with a certain margin. |
| Switching Voltage Rating | The maximum voltage that the relay contacts can switch. Choose a switching voltage rating greater than the load voltage. |
| Load Type | |
| AC Load | Choose an AC relay module. |
| DC Load | Choose a DC relay module. |
| Number of Channels | |
| Single Channel | Controls a single load. |
| Multi-Channel | Controls multiple loads, such as 2-channel, 4-channel, 8-channel, etc. |
| Mounting Type | |
| PCB Mount | Directly soldered onto a printed circuit board. |
| DIN Rail Mount | Mounted on a standard DIN rail, suitable for industrial control cabinets, etc. |
| Other Features | |
| Zero-Crossing Detection | Switches the load at the zero-crossing point of the AC voltage, reducing electromagnetic interference. |
| Reverse Polarity Protection | Prevents damage to the module due to reverse power supply connection. |
| LED Indicator | Indicates the working status of the relay. |
| Package Type | Choose a suitable package type according to the application environment, such as DIP, SMD, etc. |
Note: These are just some of the common factors to consider. Actual selection should be based on the specific application scenario and requirements. It is recommended to refer to the relevant product datasheets and application notes.
Conclusion
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.
FAQ
How to wire the relay module？
The basic steps for wiring relay modules can be summarized as follows:
Power off operation to ensure safety.
Identify the control coil terminals, normally open (NO), and normally closed (NC) contact terminals of the relay.
Connect the control coil terminals to the control signal source, paying attention to the positive and negative poles.
Connect the load to the normally open or normally closed contact terminals as needed.
Use cables of appropriate specifications to ensure a secure connection.
Recheck if the wiring is correct before powering on.
Test whether the relay works as expected after power is on.
Follow the product manual to ensure wiring is done according to the manufacturer’s instructions.
Consider electromagnetic compatibility and use insulation materials to prevent short circuits.
How to wire the relay module？
The basic steps for wiring relay modules can be summarized as follows:
Power off operation to ensure safety.Identify the control coil terminals, normally open (NO), and normally closed (NC) contact terminals of the relay.
Connect the control coil terminals to the control signal source, paying attention to the positive and negative poles.
Connect the load to the normally open or normally closed contact terminals as needed.
Use cables of appropriate specifications to ensure a secure connection.
Recheck if the wiring is correct before powering on.
Test whether the relay works as expected after power is on.
Follow the product manual to ensure wiring is done according to the manufacturer’s instructions.
Consider electromagnetic compatibility and use insulation materials to prevent short circuits.
How to Determine if a Relay Module is Damaged
If you suspect a relay module is damaged, follow these inspection steps to diagnose the issue:
1. Safety First:
- Disconnect Power: Before any inspection, disconnect all power to the circuit containing the relay module. This is crucial to prevent electrical shock and further damage.
- Use Appropriate Tools: Use tools with insulated handles and wear safety glasses when working with electrical components.
2. Visual Inspection:
- Check for Damage: Carefully examine the relay module for:
- Burning: Discoloration, charring, or a burnt odor around contacts or the coil.
- Physical Damage: Cracks, broken parts, loose connections, or bent pins.
- Deformation: Any warping or melting of the module’s casing.
3. Coil Resistance Test:
- Use a Multimeter: Set your multimeter to measure resistance (ohms, Ω).
- Measure Coil Resistance: Touch the multimeter probes to the coil terminals.
- Expected Values: A typical coil resistance is between tens of ohms to a few thousand ohms. Refer to the relay’s datasheet for the exact specification.
- Abnormal Values:
- Too High: An open circuit in the coil (coil is broken).
- Zero or Very Low: A short circuit in the coil.
4. Control Signal and Contact Operation Test:
- Apply Control Voltage (With Caution):
- Important: If you are comfortable working with live circuits, apply the rated control voltage to the coil terminals. Ensure you are following proper safety procedures.
- Observe Relay: Does the relay click, indicating activation?
- No Click: A problem with the coil, internal circuitry, or insufficient control voltage.
- Test Contacts: Use the continuity test mode on your multimeter:
- Normally Open (NO) Contacts: Should be open (no continuity) when the relay is off, and closed (continuity) when the relay is energized.
- Normally Closed (NC) Contacts: Should be closed (continuity) when the relay is off, and open (no continuity) when the relay is energized.
5. Load Test (If Possible and Safe):
- Connect a Test Load: If you can safely create a test setup, connect a known working load to the relay’s output contacts.
- Activate Relay: Apply the control signal and observe if the relay can switch the load on and off as expected.
6. Additional Tests (If Necessary):
- Response Time: Use an oscilloscope or a timer to measure the time it takes for the relay contacts to switch after applying and removing the control signal. Compare to the datasheet specifications.
- Sound Check: Listen for any unusual noises (buzzing, grinding, arcing) during relay operation.
- Electromagnetic Interference (EMI): If applicable, use an EMI meter or observe if the relay causes interference with nearby sensitive electronics.
7. Relay Replacement Test:
- If Possible: If you have a known good relay module with the same specifications, carefully replace the suspect relay and retest the circuit. If the problem is resolved, the original relay was likely faulty.
8. Professional Testing:
- Advanced Diagnostics: For more complex issues or if you are unable to determine the cause of the problem, consult a qualified electrician or use specialized relay testing equipment.
9. Datasheet Reference:
- Essential Information: Always consult the relay module’s datasheet for specific testing procedures, expected values, and safety precautions.
Important Notes:
- Fault Isolation: If the tests above do not clearly indicate a faulty relay, the problem may lie in the control circuit, wiring, or the load itself.
- Replacement: If you determine that the relay module is damaged, replace it with an identical or equivalent part that meets the circuit’s requirements.
What are the common faults of relay modules?
Common faults of relay modules include contact adhesion, coil burnout, mechanical wear, etc. Regular inspections and maintenance can prevent electrical accidents caused by these malfunctions.
