Sunway wattsonic (battery)
The Sunway wattsonic is a hybrid PV inverter with integrated battery storage, sold in residential and light-commercial installations across Europe. This ModbusCloud template targets the battery subsystem over Modbus RTU and reads battery power flow and state of charge from holding registers 40258 and 43000. It also exposes the on-grid minimum SOC setpoint at register 52503, letting your portal enforce a discharge floor without opening the inverter app. Together these three registers give installers a compact, actionable view of battery behaviour in any wattsonic-equipped site.
- Protocol
- Modbus RTU
- Connection
- RS485
- Registers
- 3, read and write
- Brand
- Sunway
- 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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Use cases
- Monitor battery charge and discharge power in real time to verify the system follows its configured energy strategy.
- Track state of charge over days and weeks to detect gradual capacity loss across the battery modules.
- Alert on SOC dropping below a threshold during peak-demand evenings to catch unexpected overnight discharge.
- Write the minimum SOC setpoint remotely to reserve battery capacity before a forecast grid outage.
- Compare measured battery power against PV production readings to verify self-consumption ratios on a site.
Installation
Enable Modbus RTU on the wattsonic inverter by confirming the RS485 port is active under the communication settings in the WattDesk app or inverter display menu.
Wire the ModbusCloud Gateway RS485 terminals to pins 13 and 14 of the wattsonic inverter using a shielded twisted-pair cable; set line parameters to 9600 baud, 8N1, no termination resistor unless the Gateway is the last device on the bus.
In your ModbusCloud portal, add the Gateway, import the Sunway wattsonic (battery) template, and assign unit ID 247 to match the inverter's default Modbus slave address.
Spot-check the connection by reading register 43000 (soc) in the live register view; a value between 0 and 100 confirms communication is working correctly.
Things to watch for
Register 43000 returns zero or a constant wrong value. Why?
The SOC register on this platform can read zero immediately after a system restart because the inverter recalculates state of charge from battery voltage on boot. Wait for a full charge or discharge cycle to complete before the value stabilises. Confirm unit ID is set to 247 and baudrate to 9600.
Register 40258 shows large swings or garbage values.
Register 40258 is a signed 32-bit value spanning two Modbus registers. Confirm your polling tool requests two consecutive holding registers starting at 40258 with function code 3. Incorrect register count (requesting only one register) returns a truncated value that looks like an implausible spike.
The Gateway connects but no readings appear in the portal.
Check that the RS485 wiring uses a shielded cable and is connected to the correct pins (13 and 14). Modbus RTU on this inverter requires 9600 baud, no parity, one stop bit. A missing shield or incorrect baudrate causes CRC errors and silent timeouts. Increase the poll timeout to at least 10 seconds if errors persist.
Is it safe to write to the limitsoc setpoint register 52503?
Write register 52503 with caution. It sets the on-grid battery end SOC floor and accepts only values from 100 to 900, representing 10 to 90 percent. Writing a value outside this range or writing repeatedly in quick succession may cause the inverter to reject the command or behave unexpectedly. Always validate the written value and restore the original setting if testing.
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