Why does the id register return a value other than 143?

The Modbus base address for SunSpec models is device-dependent. The gateway may be pointing at the wrong offset within the SunSpec model chain. Use a SunSpec discovery scan to locate the correct starting address for model 143, then update the base address in the portal accordingly.

The modena register reads false even though ride-through should be active. Why?

Some inverters require the LFRTX function to be explicitly enabled via their local web interface or a grid-code commissioning tool before the modena bit reflects true over Modbus. Check the inverter's grid protection or grid-code settings menu and enable the low-frequency ride-through function there first.

Frequency values from curve points look wrong after scaling. What is the issue?

Frequency curve point values must be multiplied by 10 raised to the power of hz_sf, which is a signed scale factor (typically negative). Confirm that your data pipeline applies hz_sf correctly. Similarly, time values require tms_sf. Skipping either scale factor produces readings that are off by an order of magnitude.

Is it safe to write actcrv and modena remotely during live operation?

Writing actcrv or modena during live grid operation can immediately change the inverter's protective response to grid frequency deviations. This may cause the inverter to trip or to remain connected outside the intended protection window. Always coordinate write operations with the grid operator, follow the inverter manufacturer's commissioning procedure, and revert to the default curve if in doubt.

Free Modbus template: SunSpec Model 143 — LFRTX

Name: SunSpec Model 143 — LFRTX
Brand: SunSpec
SKU: dc809b9f-4250-4c97-8cd5-976fb6c82f00

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Free Modbus template: SunSpec Model 143 — LFRTX | ModbusCloud

Registers (12)

12 read / 5 write

Name	Address	Function	Type	Unit	Access
id SunSpec model identifier, fixed value 143 for LFRTX.	0	FC03	uint16		R
l Length of this model block in Modbus registers.	1	FC03	uint16		R
actcrv Index of the active low-frequency ride-through curve set.	2	FC03	uint16		R/W
modena Enable flag for the LFRTX function, true means active.	3	FC03	bool		R/W
wintms Randomized delay window before activating the curve, seconds.	4	FC03	uint16	Secs	R/W
rvrttms Reversion timeout to return to default curve, seconds.	5	FC03	uint16	Secs	R/W
rmptms Ramp time for transitioning to the new curve, seconds.	6	FC03	uint16	Secs	R/W
ncrv Number of frequency ride-through curve sets supported.	7	FC03	uint16		R
npt Maximum number of points per curve set.	8	FC03	uint16		R
tms_sf Scale factor applied to time values in curve points.	9	FC03	int16		R
hz_sf Scale factor applied to frequency values in curve points.	10	FC03	int16		R
crvtype Curve type identifier indicating trip or momentary-cessation behaviour.	11	FC03	uint16		R

SunSpec Model 143 — LFRTX

Overview

Use cases

Installation

Things to watch for

Registers (12)

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