Product Overview
The 24V 2-Way Electromagnetic Relay Module is a simple, cost-effective switching solution designed to control two independent high-power AC or DC loads directly from a 24V logic or industrial control system. Unlike more complex relay modules that incorporate optocoupler isolation, this module uses a direct transistor driver circuit (typically NPN transistors such as 2N2222, BC547, or S8050) to activate each relay coil . This design offers a lower cost and simpler circuit, making it ideal for PLC automation systems, industrial control panels, building management systems, and projects where isolation is not critical.
This dual-channel module allows you to control two separate devices independently from your 24V controller. With each relay rated for 10A at 250V AC or 10A at 30V DC, it can handle lights, fans, motors, pumps, solenoids, and other industrial equipment . Onboard status LEDs provide visual confirmation when each relay is activated, simplifying operation monitoring and troubleshooting.
Designed with a low-level trigger, the relays activate when the control pins are pulled LOW (0V) and deactivate when pulled HIGH (24V) . This active-LOW behavior provides a degree of safety—the relays remain off during power-up or if the control signal is lost, preventing accidental activation of connected devices.
Important Note: This module does not include optocoupler isolation. The control circuit and the high-voltage load share a common ground path . Exercise caution when wiring high-voltage loads and ensure proper insulation and clearance for safety.
Key Features
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Dual Independent Channels: Two separate relay channels allow independent control of two different loads from a single module .
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Low-Level Trigger (Active LOW): Each relay activates when its corresponding IN pin is pulled LOW (0V) and deactivates when HIGH (24V). This ensures the relays remain off during power-up .
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Direct Transistor Drive: Uses simple NPN transistors to drive each relay coil, eliminating the need for optocoupler components .
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10A High Switching Capacity: Each relay contacts rated for 10A at 250V AC or 10A at 30V DC, suitable for controlling motors, pumps, lights, and industrial equipment .
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SPDT Contact Configuration: Each channel provides Common (COM), Normally Open (NO), and Normally Closed (NC) terminals for maximum wiring flexibility—use NO for OFF-by-default operation or NC for ON-by-default operation .
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Status Indicator LEDs: Onboard LEDs for each channel illuminate when the corresponding relay is activated (IN pin LOW), providing clear visual feedback .
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24V Logic Compatibility: Designed for 24V PLC automation, industrial controllers, and building management systems, with a control signal range of 0V–24V .
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Fault-Tolerant Design: Even if the control line is disconnected or broken, the relay will not operate unintentionally, ensuring fail-safe behavior .
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Compact and Mountable: Small PCB footprint with mounting holes for easy integration into control cabinets, DIN rails, or enclosures .
Technical Specifications
Pinout & Interface Guide
Input Side (Control Interface)
Output Side (Load Terminals) – Channel 1
Output Side (Load Terminals) – Channel 2
Status LEDs
Usage Guide
Wiring Instructions
IMPORTANT: Always disconnect mains power before wiring high-voltage loads.
Basic Connection (Control Side)
Load Connection (AC Example for One Channel)
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Connect the Live (L) wire from your AC source to the COM terminal
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Connect the load (lamp, fan, motor) to the NO terminal for OFF-by-default operation
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Connect the load’s Neutral (N) wire directly to the AC source neutral
Load Connection (DC Example for One Channel)
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Connect the positive (+) supply to the COM terminal
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Connect the load’s positive wire to the NO terminal
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Connect the load’s negative wire directly to the power supply ground
Control Logic
Since this module is low-level triggered, the relay behavior is as follows:
Example PLC Ladder Logic Concept
For PLC control with a low-level trigger, use a normally open contact to energize an output coil. When the contact closes, the output goes LOW, activating the relay.
Example Arduino Code (with External 24V Supply)
const int relay1Pin = 7;
const int relay2Pin = 8;
void setup() {
pinMode(relay1Pin, OUTPUT);
pinMode(relay2Pin, OUTPUT);
digitalWrite(relay1Pin, HIGH);
digitalWrite(relay2Pin, HIGH);
}
void loop() {
digitalWrite(relay1Pin, LOW);
delay(3000);
digitalWrite(relay1Pin, HIGH);
delay(1000);
digitalWrite(relay2Pin, LOW);
delay(3000);
digitalWrite(relay2Pin, HIGH);
delay(1000);
digitalWrite(relay1Pin, LOW);
digitalWrite(relay2Pin, LOW);
delay(2000);
digitalWrite(relay1Pin, HIGH);
digitalWrite(relay2Pin, HIGH);
delay(2000);
}
Important Considerations
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Power Supply: The module requires a stable 24V DC supply capable of providing at least 50mA (15-20mA per relay when active). For industrial applications, use a regulated 24V power supply .
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No Optocoupler Isolation: This module does not provide electrical isolation between the control circuit and the high-voltage load. The control and load circuits share a common ground path. For applications requiring isolation, consider an optocoupler-isolated relay module .
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Inductive Loads: For motors, pumps, or solenoids, add a flyback diode across each load to protect the relay contacts from voltage spikes . The module typically includes flyback diodes across each relay coil, but external diodes across inductive loads are recommended.
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Control Signal: For 5V Arduino outputs, the 5V HIGH signal is sufficient to deactivate the relay (threshold is typically 4.5V). For 3.3V controllers, the HIGH signal may be below the threshold—use a level shifter or NPN transistor buffer .
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Default State: The low-level trigger design means the relays stay OFF when the IN pins are HIGH or unconfigured, preventing unwanted activation during power-up .
Q: What is the difference between this module and an optocoupler-isolated relay module?
This module uses direct transistor drivers to activate the relay coils, without optocoupler isolation. Optocoupler-isolated modules have an optical barrier between the control circuit and the load, providing electrical isolation . This module is more cost-effective but does not provide isolation between your controller and the high-voltage load.
Q: What is the advantage of low-level trigger?
Low-level trigger means the relay activates when the IN pin is pulled LOW (0V). This is a safety feature—the relay remains off during power-up or if the control signal is lost, preventing accidental activation of connected devices .
Q: Can I control this 24V relay module with a 5V Arduino or 3.3V ESP32?
Yes, with caution. The trigger HIGH voltage threshold is typically 4.5V . A 5V Arduino output (HIGH = 5V) will reliably deactivate the relay. For 3.3V ESP32, the HIGH signal (3.3V) may be below the threshold—use an NPN transistor buffer or level shifter for reliable operation . The LOW signal (0V) works regardless.
Q: What is the maximum load each relay can handle?
Each relay contacts are rated for 10A at 250V AC or 10A at 30V DC . For inductive loads like motors, it is recommended to derate to 5A–7A to account for startup surges.
Q: What is the difference between NO and NC terminals?
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NO (Normally Open): The circuit is open when the relay is OFF. When the relay activates, it closes. Use NO for devices that should be OFF by default .
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NC (Normally Closed): The circuit is closed when the relay is OFF. When the relay activates, it opens. Use NC for devices that should be ON by default .
Q: What power supply do I need for this module?
The module requires a stable 24V DC power supply capable of providing at least 50mA (15-20mA per relay when active). For industrial applications, use a regulated 24V power supply .
Q: The relays click but my loads don't turn on. What's wrong?
This indicates the relays are activating but the load circuits are incomplete. Check:
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Each load is correctly wired between COM and NO (or COM and NC)
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Each load’s neutral/ground is connected correctly
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The loads themselves are functional
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The load currents do not exceed the relay’s 10A rating
Q: What is the expected lifespan of these relays?
Each relay is rated for approximately 100,000 electrical operations at rated load . Actual lifespan depends on switching frequency and load type.
Q: Can I use this relay module for 220V AC applications?
Yes. The contacts are rated for 250V AC, which is suitable for 220V/240V systems . Ensure proper insulation and clearance between the control and load sides for safety.
Q: Do I need flyback diodes for inductive loads?
The module typically includes flyback diodes across each relay coil to protect the transistors . However, for high-power inductive loads (motors, solenoids), adding external flyback diodes across each load terminal is recommended to protect the relay contacts.
Q: Can I use multiple relay modules with a single PLC or microcontroller?
Yes. Connect each module’s DC+ and DC- in parallel to the same 24V supply (ensure the supply can handle the total current), and connect each IN pin to separate digital output pins on your controller.
Q: What can I build with this 2-channel 24V relay module?
Popular applications include:
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Industrial control: PLC output expansion, motor control, conveyor systems
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Building automation: HVAC control, lighting systems, fan control
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Home automation: Appliance switching (with 24V control)
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Security systems: Alarm triggers, access control
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Motor control: Control forward/reverse for a single DC motor using two relays
Q: Can I control a single motor's direction using two relays?
Yes. Using two relays, you can create an H-bridge configuration to control forward and reverse direction of a DC motor . Connect the motor between the COM terminals, and wire the NO and NC contacts appropriately.
Q: Can I use this module without a microcontroller?
Yes. You can trigger each relay by manually connecting the IN pin to GND (to activate) or leaving it disconnected (to deactivate). This can be done with simple push buttons or toggle switches connected between each IN pin and GND .
Q: Is this module suitable for use with 24V industrial PLCs?
Yes. The 24V coil voltage and control logic are perfectly suited for industrial PLC outputs. Ensure the PLC output can sink sufficient current (typically 3-5mA) to pull the IN pin LOW .
