The id register reads a value other than 123. Why?

The SunSpec register map is self-describing and chained: Model 123 is not always at a fixed absolute address. The absolute Modbus address of the model block depends on which models precede it in the chain. Use a SunSpec model discovery scan or consult the device's PICS table to find the correct starting address, then update the template offset in the portal.

I wrote wmaxlimpct but inverter output did not change. What now?

Writing the setpoint register alone is not sufficient. The wmaxlim_ena register must be written to enable the throttle function after the setpoint is set. Control values do not take effect until the associated enable register is written. Confirm wmaxlim_ena is set to the enabled enumeration value after updating wmaxlimpct.

Scaled register values look wrong by a factor of 10 or 100. How do I fix this?

SunSpec uses scale-factor registers (wmaxlimpct_sf, outpfset_sf, varpct_sf) that store a signed exponent applied as a power of ten. If these scale factors return a non-zero value, the raw register value must be multiplied by 10 raised to that exponent. Ensure your ModbusCloud template read them and applies scaling before displaying or comparing values.

The gateway connects but write registers return no response or an error. What should I check?

Several inverter manufacturers protect Model 123 write registers behind an unlock code or restrict writes to a single Modbus client at a time. Check whether another client such as an EMS or data logger already holds an exclusive session. Also verify that write registers (conn, wmaxlimpct, outpfset, var setpoints, and their enable flags) are within the device's stated supported range, as writing an unsupported value returns a Modbus exception 3. Use write registers with caution: issuing a disconnect (conn = 0) or an extreme power limit can affect inverter output and may invalidate grid-operator agreements.

Free Modbus template: SunSpec Model 123 — Immediate Controls

Name: SunSpec Model 123 — Immediate Controls
Brand: SunSpec
SKU: 397ee5c1-a527-4d9e-8ac4-8bfaeef3b925

SunSpec Model 123 is a standardized inverter control model defined by the SunSpec Alliance for grid-connected distributed energy resources. This Modbus TCP template targets the Immediate Controls block used by SMA, Fronius, Kostal, and other SunSpec-certified inverters. It exposes grid connection control (conn), active power limiting (wmaxlimpct and wmaxlim_ena), fixed power factor (outpfset and outpfset_ena), and reactive power setpoints (varwmaxpct, varmaxpct, varavalpct, varpct_ena) together with their time-window, reversion, and ramp registers. Importing this template into ModbusCloud gives installers a ready-made interface to read and write Model 123 controls across any compliant device without manual register mapping.

Registers (26)

26 read / 21 write

Name	Address	Function	Type	Unit	Access
id SunSpec model identifier, fixed value 123 for Immediate Controls.	0	FC03	uint16		R
l Length of the model block in registers, read-only.	1	FC03	uint16		R
conn_wintms Time window in seconds before connect or disconnect executes.	2	FC03	uint16	Secs	R/W
conn_rvrttms Reversion timeout in seconds for connect or disconnect command.	3	FC03	uint16	Secs	R/W
conn Grid connection control: 0 = disconnect, 1 = connect.	4	FC03	uint16		R/W
wmaxlimpct Active power limit setpoint as percentage of WMax.	5	FC03	uint16	% WMax	R/W
wmaxlimpct_wintms Time window in seconds before power limit change takes effect.	6	FC03	uint16	Secs	R/W
wmaxlimpct_rvrttms Timeout in seconds after which power limit reverts to default.	7	FC03	uint16	Secs	R/W
wmaxlimpct_rmptms Ramp time in seconds to transition to the new power limit.	8	FC03	uint16	Secs	R/W
wmaxlim_ena Enable or disable the active power throttle control function.	9	FC03	uint16		R/W
outpfset Output power factor setpoint, cos(phi), signed int16.	10	FC03	int16	cos()	R/W
outpfset_wintms Time window in seconds before power factor setpoint executes.	11	FC03	uint16	Secs	R/W
outpfset_rvrttms Reversion timeout in seconds for power factor setpoint.	12	FC03	uint16	Secs	R/W
outpfset_rmptms Ramp time in seconds to reach the new power factor setpoint.	13	FC03	uint16	Secs	R/W
outpfset_ena Enable or disable the fixed power factor control function.	14	FC03	uint16		R/W
varwmaxpct Reactive power setpoint as percentage of WMax.	15	FC03	int16	% WMax	R/W
varmaxpct Reactive power setpoint as percentage of VArMax.	16	FC03	int16	% VArMax	R/W
varavalpct Reactive power setpoint as percentage of available VAr capacity.	17	FC03	int16	% VArAval	R/W
varpct_wintms Time window in seconds before VAr limit change takes effect.	18	FC03	uint16	Secs	R/W
varpct_rvrttms Timeout in seconds after which VAr limit reverts to default.	19	FC03	uint16	Secs	R/W
varpct_rmptms Ramp time in seconds to transition to the new VAr setpoint.	20	FC03	uint16	Secs	R/W
varpct_mod Enumerated VAr percent limit mode selection.	21	FC03	uint16		R/W
varpct_ena Enable or disable the VAr percent limit control function.	22	FC03	uint16		R/W
wmaxlimpct_sf Scale factor for WMaxLimPct, applied as power of ten.	23	FC03	int16		R
outpfset_sf Scale factor for OutPFSet, applied as power of ten.	24	FC03	int16		R
varpct_sf Scale factor for VAr percent setpoints, applied as power of ten.	25	FC03	int16		R