SunSpec Model 135 — LFRT

Installation

1. 1Enable Modbus TCP on the inverter or gateway device under its communication or SunSpec settings menu, noting the assigned IP address and TCP port (default 502).
2. 2Connect the inverter to the same LAN segment as the ModbusCloud Gateway and confirm IP reachability with a ping; SunSpec devices typically use unit ID 1 or 126 depending on the manufacturer.
3. 3In the ModbusCloud portal, add the Gateway, import the SunSpec Model 135 LFRT template, and assign the correct unit ID and base register offset matching the device's SunSpec map start address.
4. 4Trigger a single register read of the id register (address 0) and confirm the returned value is 135; then read ncrv and npt to verify the device reports its expected curve capacity.

Things to watch for

01

Why does the id register return an unexpected value?

SunSpec models are chained sequentially in memory; the absolute Modbus address of model 135 depends on all preceding models. If you poll address 0 and get a wrong ID, you are likely pointing at a different model in the chain. Use SunSpec device discovery (scan from the base address) to find the correct offset for model 135.

02

The modena flag reads false after I write true. What is wrong?

Several SunSpec-compliant inverters require a separate grid-guard or write-enable unlock before control registers accept writes. Check the manufacturer's documentation for any prerequisite enable sequence. Also confirm you are using function code 16 and that the unit ID matches the inverter, not the communication gateway.

03

hz_sf and tms_sf return negative numbers. Is that correct?

Yes. SunSpec scale factors are signed exponents of 10. A tms_sf value of -2 means divide the raw curve time values by 100 to get seconds. Always apply these scale factors before interpreting any curve-point data; ignoring them will produce values that are off by one or more orders of magnitude.

04

How should I handle writing to actcrv and modena safely?

Writing to actcrv selects a different protection curve, which directly affects how the inverter responds to low-frequency grid events. Always verify the target curve is fully programmed before activating it. Test changes during a maintenance window; an incorrect LFRT curve can cause the inverter to trip unnecessarily or fail to trip when required, potentially violating grid-code obligations.

Registers (11)

11 read / 5 write

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