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.

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.

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.

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.

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

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Free Modbus template: SMA Sunny Boy Storage 3.7/5.0/6.0 (Modbus) (battery) | ModbusCloud

Registers (9)

3 read / 6 write

Name	Address	Function	Type	Unit	Access
power AC power flow at the inverter terminals, signed, in watts.	•••	•••	•••	W	R
energy Cumulative AC energy throughput, 64-bit counter.	•••	•••	•••		R
soc Battery state of charge relative to present usable capacity, percent.	•••	•••	•••	%	R
batterymode_a BMS operating mode selector; controls overall charge/discharge behavior.	•••	•••	•••		W
batterymode_b Minimum battery charging power setpoint, in watts.	•••	•••	•••	W	W
batterymode_c Maximum battery charging power setpoint, in watts.	•••	•••	•••	W	W
batterymode_d Minimum battery discharging power setpoint, in watts.	•••	•••	•••	W	W
batterymode_e Maximum battery discharging power setpoint, in watts.	•••	•••	•••	W	W
batterymode_f Grid transfer power setpoint, signed, in watts.	•••	•••	•••	W	W

Loading registers…

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

Overview

Use cases

Installation

Things to watch for

Registers (9)

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