SMA Sunny Boy Storage 3.7/5.0/6.0 (Modbus) (battery)

Installation

1. 1Log into the Sunny Boy Storage web interface, navigate to the communication or Modbus section under External Communication, and activate the Modbus TCP server on port 502.
2. 2Connect the inverter's RJ45 Ethernet port to the same local network as the ModbusCloud Gateway, confirming the inverter receives a static IP address or a DHCP reservation.
3. 3In the ModbusCloud portal, add the Gateway, import the SMA Sunny Boy Storage 3.7/5.0/6.0 template, and set the unit ID to 3 (or the value assigned to your inverter; SMA documentation also references unit ID 126 for direct access).
4. 4Verify the connection by checking that register 30845 returns a plausible state-of-charge value and register 30775 returns a signed AC power reading in the portal's live view.

Things to watch for

01

Register 30775 always returns NaN or 2147483648. Why?

SMA inverters return the NaN sentinel value 0x80000000 (2147483648 for a uint32 interpretation) when a register is unavailable, for example outside daylight hours or during a fault state. Confirm the inverter is in feed-in or standby operation, and read the register as a signed int32 as specified in the SMA Modbus profile.

02

The gateway connects but no live values appear. What now?

The Modbus TCP server is disabled by default on the Sunny Boy Storage. Open the inverter's web interface, go to the Modbus section under External Communication, and explicitly activate the TCP server on port 502. Also confirm no firewall on the local network is blocking that port.

03

I wrote batterymode_a but the inverter ignores it. What is wrong?

The SMA Sunny Boy Storage requires all six BMS registers (40236, 40793, 40795, 40797, 40799, and 40801) to be written within a 60-second window, and they must continue to be written cyclically. Writing only one register has no effect. Configure your portal automation to send all six values together in each cycle.

04

Is it safe to write BMS setpoint registers during normal operation?

Use caution. Writing incorrect values to the BMS operating mode or power limit registers can override the inverter's internal protection logic, force unintended charge or discharge cycles, and may affect warranty conditions. Always validate setpoint values against the SMA Modbus parameter documentation before deploying automated writes to these registers.

Registers (9)

3 read / 6 write

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