Modbus RTU 4-Channel Relay Module User Manual

1. Introduction

This manual provides detailed instructions for the Modbus RTU 4-Channel Relay Module. This module is equipped with a mature and stable 8-bit MCU and an RS485 level communication chip. It utilizes the standard MODBUS RTU communication protocol via RS485 or TTL UART interfaces. It is designed to detect 4 input signals and control 4 relay outputs, making it suitable for digital detection and power control applications.

The module is available in two main power input variants: DC 7-24V and AC 220V. Please refer to the specific sections for details relevant to your module version.

2. Specifications

General Product Parameters

• MCU: Onboard mature and stable 8-bit MCU
• Communication Chip: MAX485 level conversion chip
• Communication Protocol: Standard Modbus RTU protocol
• Communication Interface: RS485 / TTL UART interface
• Communication Baud Rate: 4800/9600/19200 (default 9600bps), supports power-off save
• Optocoupler Input Signal Range: DC 3.3-30V (Note: This input cannot be used for direct relay control)
• Output Signal: Relay switch signal
• Output Modes: Manual, flash off, flash off mode
• Flash Delay Time Base: 0.1 seconds
• Maximum Flash Time: 0xFFFF * 0.1s = 6553.5 seconds
• Device Address: Range 1-255 (default 255), supports power-off save
• Relays: 4 onboard 5V, 10A/250VAC, 10A/30VDC relays
• Relay Lifespan: Can be activated continuously for 100,000 times
• Protection: Diode effusion protection, short response time
• Indicators: On-board relay switch indicator
• Certification: CE
• Theory: Electromagnetic Relay
• Contact Load: Low Power
• Protect Feature: Sealed
• Origin: Mainland China

Specific Power Supply Variants

The module is available with different power input options:

• DC 7-24V Version: Supports DC socket / 5.08mm terminal power supply, with input anti-reverse protection.
• AC 220V Version: Supports AC 220V power input terminal.

Figure 2.1: Detailed Product Parameters

Figure 2.2: Board Dimensions (93mm x 87mm, 100g)

3. Product Overview & Interface

The module features various connection points for power, communication, and relay outputs. Familiarize yourself with these interfaces before proceeding with setup.

Figure 3.1: Interface Diagram

Interface Descriptions:

1. DC-005 Socket: DC 7-24V power input socket (for DC version).
2. VCC, GND: DC 7-24V 5.08mm power input terminal (for DC version).
3. DC 3.3-30V Optocoupler Signal Input:
   • IN1: Channel 1 positive input
   • IN2: Channel 2 positive input
   • IN3: Channel 3 positive input
   • IN4: Channel 4 positive input
   • GND_IN: Common terminal negative for inputs
4. A+, B-: RS485 communication interface. Connect A+ and B- to the corresponding A+ and B- terminals of your external control device.
5. Relay Switch Signal Output: Each relay has three terminals:
   • NC (Normally Closed): Shorted to COM when the relay is off (before pull-in), open when the relay is on (after pull-in).
   • COM (Common): The common terminal for the relay switch.
   • NO (Normally Open): Open when the relay is off (before pull-in), shorted to COM when the relay is on (after pull-in).
6. GND, RXD, TXD: TTL level UART communication interface. Connect GND, RXD, TXD to the corresponding GND, TXD, RXD of your external control device.

Visual Reference (DC 7-24V Module)

Figure 3.2: DC 7-24V Modbus RTU 4-Channel Relay Module

Visual Reference (AC 220V Module)

Figure 3.3: AC 220V Modbus RTU 4-Channel Relay Module

4. Setup

Power Connection

• For DC 7-24V Module: Connect your DC power supply (7-24V) to either the DC-005 socket or the VCC/GND 5.08mm terminal. Ensure correct polarity.
• For AC 220V Module: Connect your AC 220V power supply to the designated AC power input terminal.

Communication Connection (RS485/TTL UART)

• RS485: Connect the A+ and B- terminals of the module to the corresponding A+ and B- terminals of your RS485 communication device (e.g., USB to RS485 converter, PLC).
• TTL UART: Connect the GND, RXD, and TXD terminals of the module to the corresponding GND, TXD, and RXD terminals of your TTL UART device (e.g., microcontroller, USB to TTL converter).

Relay Output Connection

Connect your load to the relay output terminals (NC, COM, NO) as required by your application. For example, to switch a device on when the relay is activated, connect the device between COM and NO. To switch a device off when the relay is activated, connect it between COM and NC.

Optocoupler Input Connection

Connect your input signals (DC 3.3-30V) to the IN1-IN4 positive terminals and the GND_IN common negative terminal. Remember, these inputs are for signal detection only and cannot directly control the relays.

5. Operating Instructions (Modbus RTU)

Modbus devices perform operations by receiving Modbus RTU instructions from an external control terminal (e.g., host computer, MCU). A typical instruction frame consists of a device address, function code, register address, register data, and a CRC check code. The first byte is the device address (1-255, default 255), and the last two bytes are the CRC check code.

Generating CRC Check Code

When using host computer software (like a Modbus RTU configuration tool), the CRC check code is often automatically generated. However, if using serial port debugging software (like SSCOM), you may need to manually generate and place the CRC check code in the sending frame.

Figure 5.1: Example of CRC Calculation in Modbus RTU Configuration Tool

Basic Operation Example (Using Host Computer Software)

To turn on Relay 1 and 2 using a host computer software with RS485 interface, assuming device address 255 and baud rate 9600:

1. Connect L and N to 220V power supply (if using AC 220V module) or DC 7-24V power supply.
2. Connect A+ and B- of the module to the A+ and B- outputs of your RS485 module (e.g., USB to RS485 converter).
3. Open the host computer software (e.g., "Modbusrtu configuration tool"), select the correct COM port and set the baud rate to 9600. Set the device address to 255. Click "open serial port".
4. Click "JD1 Open" (or similar button for Relay 1) to turn on Relay 1. The indicator for Relay 1 will illuminate.

Common Modbus RTU Commands (Device Address 255)

The following commands are examples for controlling the module. All commands are in hexadecimal format.

Relay Control (Manual Mode)

• Turn on Relay No. 1:
      Send: FF 05 00 00 FF 00 99 E4
      Return: FF 05 00 00 FF 00 99 E4
      Remarks: Bytes 3-4 (0x0000) represent Relay 1 address. Bytes 5-6 (0xFF00) mean turn on.
• Turn off Relay No. 1:
      Send: FF 05 00 00 00 00 D8 14
      Return: FF 05 00 00 00 00 D8 14
      Remarks: Bytes 5-6 (0x0000) mean turn off.
• Turn on Relay No. 2:
      Send: FF 05 00 01 FF 00 C8 24
      Return: FF 05 00 01 FF 00 C8 24
      Remarks: Bytes 3-4 (0x0001) represent Relay 2 address.
• Turn off Relay No. 2:
      Send: FF 05 00 01 00 00 89 D4
      Return: FF 05 00 01 00 00 89 D4
• Turn on all relays:
      Send: FF 0F 00 00 00 08 01 FF 30 1D
      Return: FF 0F 00 00 00 08 41 D3
• Turn off all relays:
      Send: FF 0F 00 00 00 08 01 00 70 5D
      Return: FF 0F 00 00 00 08 41 D3

Device Address Configuration

• Set device address to 1:
      Send: 00 10 00 00 00 01 02 00 01 6A 00
      Return: 00 10 00 00 00 01 02 00 01 6A 00
      Remarks: 9th byte (0x01) is the new device address.
• Set device address to 255:
      Send: 00 10 00 00 00 01 02 00 FF EB 80
      Return: 00 10 00 00 00 01 02 00 FF EB 80
      Remarks: 9th byte (0xFF) is the new device address.
• Read device address:
      Send: 00 03 00 00 00 01 85 DB
      Return: 00 03 02 00 FF C5 C4
      Remarks: 5th byte (0xFF in this example) is the read device address.

Status Reading

• Read relay status:
      Send: FF 01 00 00 00 08 28 12
      Return: FF 01 01 01 A1 A0
      Remarks: 4th byte (0x01 in this example) represents relay 1-8 status. Bit0-Bit7 correspond to Relay 1-8. 0 = closed, 1 = open.
• Read optocoupler input status:
      Send: FF 02 00 00 00 08 6C 12
      Return: FF 02 01 01 51 A0
      Remarks: 4th byte (0x01 in this example) represents IN1-IN8 status. 0 = low level, 1 = high level.

Baud Rate Configuration

• Set baud rate to 4800:
      Send: FF 10 03 E9 00 01 02 00 02 4A 0C
      Return: FF 10 03 E9 00 01 C5 A7
      Remarks: 9th byte (0x02) sets 4800bps.
• Set baud rate to 9600:
      Send: FF 10 03 E9 00 01 02 00 03 8B CC
      Return: FF 10 03 E9 00 01 C5 A7
      Remarks: 9th byte (0x03) sets 9600bps.
• Set baud rate to 19200:
      Send: FF 10 03 E9 00 01 02 00 04 CA 0E
      Return: FF 10 03 E9 00 01 C5 A7
      Remarks: 9th byte (0x04) sets 19200bps.
• Read baud rate:
      Send: FF 03 03 E8 00 01 11 A4
      Return: FF 03 02 00 04 90 53
      Remarks: 5th byte (0x04 in this example) represents the read baud rate (0x02=4800, 0x03=9600, 0x04=19200).

Flash Mode Control

• Open Relay No. 1 (Flash Close Mode 2S):
      Send: FF 10 00 03 00 02 04 00 04 00 14 C5 9F
      Return: FF 10 00 03 00 02 A4 16
      Remarks: Bytes 3-4 (0x0003) represent Relay 1 address for flash mode. Bytes 10-11 (0x0014) set a 2-second delay (0x0014 * 0.1s = 20 * 0.1s = 2s), after which the relay automatically turns off.
• Turn off Relay No. 1 (Flash Mode 3S):
      Send: FF 10 00 03 00 02 04 00 02 00 1E A5 99
      Return: FF 10 00 03 00 02 A4 16
      Remarks: Bytes 10-11 (0x001E) set a 3-second delay (0x001E * 0.1s = 30 * 0.1s = 3s), after which the relay automatically turns off.

6. Maintenance

• Cleaning: Keep the module clean and free from dust and debris. Use a soft, dry cloth for cleaning. Avoid using liquids or abrasive cleaners.
• Environment: Operate the module within its specified temperature and humidity ranges. Avoid exposure to extreme temperatures, moisture, or corrosive environments.
• Connections: Periodically check all wiring connections to ensure they are secure and free from corrosion. Loose connections can lead to intermittent operation or damage.
• Power Supply: Ensure a stable and correct power supply voltage is provided to the module. Incorrect voltage can damage the components.
• Relay Life: While relays are rated for 100,000 operations, frequent switching of high-current or inductive loads can reduce their lifespan. Consider using external contactors for very heavy loads if continuous high-frequency switching is required.

7. Troubleshooting

• Module Not Responding:
  • Check power supply connections and ensure the correct voltage is applied.
  • Verify communication wiring (RS485 A+/B- or TTL RXD/TXD/GND) for correct polarity and secure connections.
  • Confirm the baud rate and device address settings in your control software match the module's configuration.
  • Ensure the serial port on your computer/MCU is correctly configured and open.
• Relays Not Activating:
  • Check the Modbus RTU command for the correct relay address and function code (e.g., 0xFF00 for ON).
  • Verify the power supply is sufficient for both the module and the relay coils.
  • Inspect the relay indicator lights; if they don't illuminate, the command might not be reaching the module or the relay itself is faulty.
• Intermittent Operation:
  • Check for loose wiring connections, especially for power and communication.
  • Ensure there is no electromagnetic interference affecting the module or communication lines. Use shielded cables for RS485 if in a noisy environment.
  • Verify the stability of the power supply.
• Incorrect Optocoupler Input Readings:
  • Ensure the input signal voltage is within the DC 3.3-30V range.
  • Check the wiring to the INx and GND_IN terminals for correct connections.

8. User Tips

• Start Simple: When first setting up, begin with basic commands like turning a single relay on/off to confirm communication before implementing complex sequences.
• Documentation: Keep a record of your device addresses and baud rate settings, especially if you modify them from the defaults.
• CRC Calculation: For manual Modbus RTU command generation, double-check your CRC calculations to avoid communication errors. Online CRC calculators can be helpful.
• Power Isolation: For AC 220V versions, always exercise extreme caution and ensure power is disconnected before making or changing any connections.

9. Warranty and Support

For technical support, troubleshooting assistance, or warranty inquiries, please contact the seller or manufacturer directly. Retain your purchase records for proof of purchase.