Product Overview
The BESTEP 1-Way Electromagnetic Relay Module is a high-performance, industrial-grade control module designed to provide a safe and reliable interface between low-voltage logic circuits and high-power devices. Operating at 12V DC, this module is ideal for automotive applications, PLC systems, industrial control panels, and 12V battery-powered projects .
Featuring dual optocoupler isolation, this module creates a robust physical and electrical barrier between your sensitive microcontroller (such as Arduino, STM32, or ESP32) and the high-voltage load side. This effectively eliminates electrical noise, protects against back-EMF spikes from motors and solenoids, and ensures system stability in demanding industrial environments .
This versatile module supports both High-Level and Low-Level Trigger modes, selectable via an onboard jumper, making it compatible with virtually any digital logic system without the need for external level shifters. With a relay contact rating of 10A at 250V AC or 10A at 30V DC, it can handle a wide range of loads, from LED lighting and fans to motors, pumps, and industrial machinery .
Key Features
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Dual Optocoupler Isolation: Features two optocouplers (typically PC817) providing enhanced electrical isolation between the control side and the high-voltage load side, ensuring superior noise immunity and protection against voltage spikes .
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12V DC Operation: Designed for 12V control systems, making it ideal for automotive electronics, PLC automation, and industrial controllers .
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Universal Trigger Modes: Supports both High Level (Active HIGH) and Low Level (Active LOW) trigger modes, selectable via an onboard jumper, allowing compatibility with any microcontroller or logic system .
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High Power Switching: Relay contacts rated for 10A at 250V AC or 10A at 30V DC, suitable for controlling lights, fans, motors, solenoids, pumps, and industrial equipment .
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SPDT Contact Configuration: 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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Clear Status Indicators: Onboard LEDs provide visual feedback: a green power LED illuminates when 12V power is applied, and a red relay status LED illuminates when the relay is activated .
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Standard Interface: Equipped with screw terminals for the high-voltage side and a 3-pin header (DC+, DC-, IN) for the control side, facilitating easy integration .
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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 Durable: Small form factor with mounting holes for secure installation in control cabinets, enclosures, or on DIN rails .
Technical Specifications
Pinout & Interface Guide
Input Side (Control Interface)
JD-VCC Jumpers (Relay Control Power)
Note: DC+ and JD+ are typically shorted with a jumper cap for single-supply operation. Removing this jumper allows separate power for the relay coil, providing full isolation .
Output Side (Load Terminals)
Jumper Settings (Trigger Mode Selection)
Status LEDs
Usage Guide
Wiring Instructions
IMPORTANT: Always disconnect mains power before wiring high-voltage loads.
Basic Connection (Control Side)
Load Connection (AC Example)
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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)
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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
Setting the Trigger Mode
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High Level Trigger (Active HIGH): Place the jumper on the H position. The relay activates when the IN pin is HIGH (3.3V–12V) .
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Low Level Trigger (Active LOW): Place the jumper on the L position. The relay activates when the IN pin is LOW (0V) .
Tip: Low Level Trigger is ideal for fail-safe applications where the relay should remain OFF if the control signal is lost.
Example Arduino Code (High Level Trigger)
const int relayPin = 7;
void setup() {
pinMode(relayPin, OUTPUT);
digitalWrite(relayPin, LOW);
}
void loop() {
digitalWrite(relayPin, HIGH);
delay(5000);
digitalWrite(relayPin, LOW);
delay(5000);
}
Example Arduino Code (Low Level Trigger)
const int relayPin = 7;
void setup() {
pinMode(relayPin, OUTPUT);
digitalWrite(relayPin, HIGH);
}
void loop() {
digitalWrite(relayPin, LOW);
delay(5000);
digitalWrite(relayPin, HIGH);
delay(5000);
}
Example ESP32 / ESP8266 Code (High Level Trigger)
ESP32 operates at 3.3V logic, which is sufficient to activate the relay in High Level Trigger mode .
from machine import Pin
import time
relay = Pin(7, Pin.OUT)
relay.value(0)
while True:
relay.value(1)
time.sleep(5)
relay.value(0)
time.sleep(5)
Important Considerations
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Power Supply: The module requires a stable 12V DC supply capable of providing at least 100mA. The relay coil draws approximately 65-80mA when active .
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Dual Optocoupler Isolation: The dual optocouplers provide enhanced protection against electrical noise and voltage spikes, making this module ideal for industrial environments where motors and solenoids may generate back-EMF .
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Inductive Loads: Although the module has built-in flyback protection across the relay coil, for high-power inductive loads (large motors, solenoids), adding an external flyback diode across the load terminals is recommended to protect the relay contacts.
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Fault-Tolerant Design: Even if the control line is disconnected, the relay will not operate, ensuring fail-safe behavior .
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JD-VCC Jumper: For applications requiring complete isolation (separate power for relay coil), remove the jumper between DC+ and JD+ and supply 12V to JD+ and JD- independently .
Q: What is the difference between High-Level and Low-Level trigger?
High-Level trigger (Active HIGH) activates the relay when the control pin receives a positive voltage (3.3V–12V). Low-Level trigger (Active LOW) activates the relay when the control pin is connected to Ground (0V). The onboard jumper lets you select which mode fits your system
Q: What is the advantage of dual optocoupler isolation?
Dual optocouplers provide enhanced electrical isolation between the control circuit and the high-voltage load. One optocoupler isolates the control signal, while the second isolates the relay coil drive circuit, offering superior protection against electrical noise, back-EMF spikes, and ground loops
Q: What is the maximum load this relay can handle?
The relay contacts are rated for 10A at 250V AC or 10A at 30V DC . For inductive loads like motors or solenoids, it is recommended to derate to 5A–7A to account for startup surges.
Q: Can I control this 12V relay module with a 5V Arduino or 3.3V ESP32?
Yes. The module accepts control signals from 3.3V to 12V . For High Level Trigger mode, a 3.3V HIGH signal is sufficient to activate the relay. For Low Level Trigger mode, a LOW signal (0V) works regardless of the logic voltage.
Q: What happens if I set the jumper incorrectly?
If the jumper is set to High Trigger but your code sends a LOW signal, the relay will not activate (and vice versa). Simply adjust the jumper position to match your code’s logic or change your code to match the jumper setting
Q: What power supply do I need for this module?
The module requires a stable 12V DC power supply capable of providing at least 100mA. The relay coil draws approximately 65-80mA when active, plus a small quiescent current of about 5-10mA .
Q: Does the module include a flyback diode?
Yes. The module includes a built-in flyback diode across the relay coil to protect the driving circuit from voltage spikes when the relay de-energizes . This protects your microcontroller from back-EMF.
Q: The relay clicks but my load doesn't turn on. What's wrong?
This indicates the relay is activating but the load circuit is incomplete. Check:
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The load is correctly wired between COM and NO (or COM and NC)
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The load’s neutral/ground is connected correctly
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The load itself is functional
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The load’s current does not exceed the relay’s 10A rating
Q: The relay clicks when I power on my controller. Why?
During power-up, microcontroller pins may briefly float or be in an undefined state. For Low Level Trigger mode, this should not activate the relay because the pin needs to be pulled LOW. Adding a 10kΩ pull-up resistor on the IN pin to VCC can ensure the relay remains OFF during startup if needed.
Q: Can I use this relay 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: What is the JD-VCC jumper for?
The JD-VCC jumper allows you to separate the relay coil power from the control logic power. For normal operation, the jumper shorts DC+ to JD+, so both share the 12V supply. For full isolation, remove the jumper and supply 12V separately to JD+ and JD- .
Q: The module's status LED lights up but the relay doesn't click. What's wrong?
The LED indicates the control signal is reaching the optocoupler. If the relay doesn’t click, check:
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The VCC power supply is stable at 12V
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The power supply can provide enough current (at least 100mA)
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The jumper is set correctly for your trigger mode
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The JD-VCC jumper is properly connected
Q: Can I use multiple relay modules with a single microcontroller?
Yes. Connect each module’s DC+ and DC- in parallel to the same 12V supply (ensure the supply can handle the total current), and connect each IN pin to a separate digital output pin on your controller.
Q: What can I build with this 12V relay module?
Popular applications include:
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Automotive: 12V lighting, window controls, power locks, fan control
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Industrial control: PLC output expansion, motor control, conveyor systems
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Home automation: Lighting control, appliance switching
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Security systems: Alarm triggers, access control, gate openers
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HVAC systems: Fan control, thermostat switching
Q: Can I use this to control a 12V DC motor or pump?
Yes. The relay contacts are rated for 10A at 30V DC, so it can safely switch 12V DC motors and pumps within the 10A limit . Ensure the motor’s stall current does not exceed the relay’s rating.
Q: Can I use this module without a microcontroller?
Yes. You can trigger the relay by manually connecting the IN pin to VCC (High Trigger mode) or GND (Low Trigger mode). This can be done with a simple push button or toggle switch.
Q: What is the expected lifespan of this relay?
The relay is rated for approximately 100,000 electrical operations at rated load . Actual lifespan depends on switching frequency and load type. For applications requiring very frequent switching, consider using a solid-state relay (SSR).
Q: Does this module have any certifications?
The BESTEP modules are designed to meet international security standards with isolation grooves between the control area and load area, and are widely used in industrial automation, PLC control, and smart home applications
