Solinteng wattsonic (battery)
The Solinteng wattsonic is a hybrid solar inverter with integrated battery storage, sold under several OEM labels including Sunway, Solinteng, A-Tronix, and St-ems. This Modbus RTU template exposes the three most operationally critical registers: real-time battery power (40258), battery state of charge (43000), and the writable minimum-SOC-on-grid setpoint (52503). Together they give you continuous visibility into battery charge and discharge behaviour, and let you set a hard floor on how far the battery drains while the grid is available. For installers running ModbusCloud, this template turns raw RS485 data into actionable dashboard readings without manual register mapping.
- Protocol
- Modbus RTU
- Connection
- RS485
- Registers
- 3, read and write
- Brand
- Solinteng
- Compatible models
- wattsonic
- Last updated
Registers (3)
2 read, 1 write
| Name | Unit | Access | Address (Hidden until you enter your email) | Function (hidden) | Type (hidden) |
|---|---|---|---|---|---|
| power | W | Read | |||
| soc | % | Read | |||
| limitsoc | % | Write |
Loading registers…
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If a device is not in the library yet, we build the template for free as soon as we have the register data.
Use cases
- Monitor real-time battery power at register 40258 to confirm charge and discharge cycles match the expected schedule.
- Track battery state of charge over days to detect capacity fade or abnormal self-discharge between solar sessions.
- Alert on state of charge falling below a project-specific threshold to prevent deep-discharge events during grid outages.
- Verify that the minimum-SOC setpoint at register 52503 holds the configured floor after firmware updates or inverter restarts.
- Compare battery power readings against site consumption data to report self-sufficiency ratios for building owners.
Installation
Enable Modbus RTU on the Solinteng wattsonic by entering the inverter's communication settings menu, then confirm the RS485 address (default 247) and line parameters: 9600 baud, 8 data bits, no parity, 1 stop bit.
Wire the RS485 bus from the ModbusCloud Gateway to pins 13 (B) and 14 (A) on the inverter's multifunction communication port using a twisted pair; note that the inverter has a built-in 120 Ohm termination resistor that can be activated with a small screwdriver.
In the ModbusCloud portal, add the ModbusCloud Gateway, import the Solinteng wattsonic (battery) template, and set the unit ID to match the inverter's configured RS485 address.
Spot-check the connection by reading register 43000 (SOC) in the portal's live data view and comparing the displayed percentage against the inverter's front-panel display.
Things to watch for
Register 40258 always reads zero. What is wrong?
Register 40258 reports battery power only when the inverter is actively charging or discharging. During standby with the battery idle, the value is legitimately zero. If zero persists during an expected charge cycle, verify the RS485 unit ID matches the inverter address (default 247) and that polling uses function code 3 on a holding register.
The gateway connects but the SOC register returns an error.
Community reports confirm that some Wattsonic firmware variants require the register address to be offset by 1 in the request frame. If register 43000 returns an illegal data address exception, try polling 43001 instead. Also confirm baud rate is exactly 9600 and parity is set to none.
RS485 reads are slow or produce frequent CRC errors.
Increase the Modbus poll timeout to at least 10 seconds. The Wattsonic RS485 interface is known to be slow, and short timeouts cause CRC mismatches and serial timeouts. Ensure the RS485 cable is a proper twisted pair, keep total bus length short, and do not share the bus with the inverter's internal smart meter connection.
Is it safe to write to the limitsoc setpoint register 52503?
Register 52503 sets the minimum battery SOC the inverter will maintain while on-grid. Valid values are 100 to 900, representing 10 to 90 percent. Writing outside this range or writing repeatedly in quick succession may cause unexpected inverter behaviour. Always confirm the intended value before writing, and note that the Wattsonic cloud app may not reflect Modbus-written changes immediately.
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