Sunways STH Modbus RTU

Installation

1. 1Connect the ModbusCloud gateway (MCG or MLP series) to the Sunways STH RS-485 port using a twisted-pair cable with correct A, B, and GND wiring.
2. 2Set the Sunways STH Modbus slave address via the inverter display or configuration menu, and note the address for gateway configuration.
3. 3Confirm the inverter baud rate is set to 9600, matching the template default.
4. 4In the ModbusCloud portal, add a new device and import the Sunways STH Modbus RTU template from the template library.
5. 5Enter the configured Modbus slave address in the device settings on the ModbusCloud portal.
6. 6Verify data is flowing by checking live register values on the dashboard, paying attention to PV power and battery SOC readings.

Things to watch for

01

I see zero values for all registers. What should I check?

Verify that the RS-485 wiring is correct, with A and B lines not swapped. Also confirm the Modbus slave address in the gateway matches the address configured on the Sunways STH inverter.

02

Energy total values seem incorrect or extremely large. Why?

Energy totals use uint32 format spanning two consecutive registers. Make sure the gateway is reading both registers together with the correct byte order. The template handles this automatically, but manual register reads may show split values.

03

Can I control the inverter or change charge settings through this template?

No. All 49 registers in this template are read-only. The template is designed for monitoring only and does not include writable registers.

04

Battery and BMS data points are not updating, but PV and meter values work fine. What is wrong?

Battery and BMS registers are in separate address ranges (402xx, 420xx, 430xx). Some Sunways STH firmware versions may require a specific firmware update to expose all BMS registers via Modbus. Check the inverter firmware version and update if necessary.

Registers (49)

49 read / 0 write

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