Register values show as very large numbers or -1. Why?

SMA uses proprietary NaN sentinel values on its Modbus profile. When the inverter's power stage is inactive, for example at night or in standby, registers return these sentinel values instead of zero. Treat any value matching the documented NaN pattern for int32 or uint32 as zero in your processing logic or alert rules.

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

Check that Modbus TCP is actively enabled in the inverter web interface under the external communication section. The interface is disabled by default. Also confirm the unit ID configured on the inverter matches the unit ID set in the ModbusCloud portal. A unit ID mismatch returns error code 11 from the inverter and no data is delivered.

Per-phase power registers all read zero even though grid power is flowing.

Registers powers_a through powers_f (31259 to 31269) are directional and unsigned: each register is zero when power flows in the opposite direction on that phase. Grid consumption shows on the WIn registers and feed-in shows on the W registers. Subtract the feed-in register from the consumption register for each phase to obtain the signed net power per phase.

Phase current registers return the same positive value regardless of direction. Is this correct?

Yes, this is by design. Registers 31435, 31437, and 31439 report unsigned magnitude only, independent of whether the phase is consuming or feeding. To determine direction, compare the corresponding per-phase consumption and feed-in power registers and apply the sign to the current reading in your dashboard or alert configuration.

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Registers (12)

12 read / 0 write

Name	Address	Function	Type	Unit	Access
power_a Total active power drawn from the grid, in watts.	30865	FC04	int32	W	R
power_b Total active power fed into the grid, in watts.	30867	FC04	int32	W	R
energy Cumulative energy drawn from the grid, in watt-hours.	30581	FC03	int32	Wh	R
currents_a Grid current phase L1, unsigned, independent of flow direction.	31435	FC04	int32	A	R
currents_b Grid current phase L2, unsigned, independent of flow direction.	31437	FC04	int32	A	R
currents_c Grid current phase L3, unsigned, independent of flow direction.	31439	FC04	int32	A	R
powers_a Power drawn from grid on phase L1, zero when no consumption.	31265	FC04	uint32	W	R
powers_b Power fed into grid on phase L1, zero when no feed-in.	31259	FC04	uint32	W	R
powers_c Power drawn from grid on phase L2, zero when no consumption.	31267	FC04	uint32	W	R
powers_d Power fed into grid on phase L2, zero when no feed-in.	31261	FC04	uint32	W	R
powers_e Power drawn from grid on phase L3, zero when no consumption.	31269	FC04	uint32	W	R
powers_f Power fed into grid on phase L3, zero when no feed-in.	31263	FC04	uint32	W	R