WSAL17658 – Modbus RTU Relay/en

Documentation notice: This technical documentation was independently rewritten from an archived supplier source. Check technical details and commands against the product version and manufacturer documentation before use.

Summary

Concise technical guide for the Waveshare Modbus RTU 8-channel relay module with RS485 bus, V3 protocol, and safety guidelines.

Related products at JW Tech

WSAL17658 – Industrial Modbus RTU 8-ch Relay Module with RS485 Interface, Multi Isolation Protection Circuits, 5V Power Supply
WSAL25739 – Industrial Modbus RTU 8-ch Relay Module (B) with RS485 Interface, Multi Isolation Protection Circuits, 7~36V Power Supply

Technical overview

The module provides 8 relay channels over an RS485 interface using the Modbus RTU protocol.
Two variants exist: WSAL17658 with a 5 V power supply and WSAL25739 (variant B) with a 7–36 V power supply.
From September 2024, the V3 development protocol is used; it is backward compatible with V2 and adds new features.
The serial interface uses standard parameters: 9600 baud, 8 data bits, no parity.
For computer interfacing, SSCOM can send hex commands with Modbus CRC16 checksum, or Modbus Poll can read/write relay states.
Demo environments are described for Raspberry Pi, STM32 (NUCLEO-F103RB), Arduino (UNO PLUS), and PLC (SIMATIC S7-200 SMART).
RS485 must not be connected directly to a Raspberry Pi serial port; an RS485 level converter or the corresponding HAT/shield module is required.
The relay environmental specification is -15 °C to +70 °C at 40–85 % relative humidity.

Commands and examples – verify before use:

sudo raspi-config
sudo reboot
enable_uart=1
#dtoverlay=pi3-miniuart-bt
sudo apt-get install unzip
wget https://files.waveshare.com/wiki/Modbus-RTU-Relay/Modbus_RTU_Relay_Code.zip
unzip Modbus_RTU_Relay_Code.zip
cd Modbus_RTU_Relay_Code/Python3
sudo python3 main.py

Notes and version constraints

All statements regarding compatibility, electrical values, commands, prices, stock, certifications, warranty, or safety require confirmation by a qualified professional, as they may be version-sensitive.
The exact register addresses and function codes of the V3 protocol are only listed as headings in the source; concrete values are missing from the provided text.
The 'Development Protocol V3' section contains no complete tables or command examples in the excerpt; these must be supplemented from the original source.
Command formats such as 'Control Single Relay' or 'Set Baudrate Command' appear only as topic headings in the source; exact byte sequences are not included here.
Power consumption figures (0.18 W standby / 2.9 W active at 5 V) refer to the 5 V variant; no comparable figures are available for the 7–36 V variant.

Source and revision record

Modbus RTU Relay - Waveshare Wiki
Source revision: 107667
Captured: 2026-08-31T04:28:43+00:00
SHA-256: 6511a0398311bf916805f224a92ffef4268876b19c222d34788c6e7dd9a36863