Current and voltage readings look wrong by a factor of ten. Why?

SunSpec uses signed scale factor registers (dca_sf, dcv_sf, dcahr_sf) as power-of-ten exponents. A raw dca value of 1234 with dca_sf of -1 means 123.4 A. Confirm your Modbus client applies the scale factor before displaying or alerting on any measurement register.

The gateway connects but the repeating string block returns 0x8000. What now?

0x8000 is the SunSpec not-implemented sentinel for int16 registers. The combiner may support fewer strings than the block length suggests, or a string input has no CT attached. Read the n register first to determine how many repeating records are actually populated, and ignore slots beyond that count.

Model length register l returns an unexpected value. How do I parse the block correctly?

SunSpec Model 401 is variable-length. The number of repeating string records equals (l minus the fixed header length) divided by the per-record register width. Your Modbus client must read l first and calculate the repeating block size dynamically rather than assuming a fixed register count.

The evt or evtvnd register shows a non-zero value. What should I check?

Both evt and evtvnd are 32-bit bitmasks where multiple flags can be active simultaneously. Cross-reference the active bits against the SunSpec String Combiner event flag table. Common causes include current out of range on one or more strings, a communication fault to a sensing module, or a vendor-specific hardware condition reported in evtvnd.

Free Modbus template: SunSpec Model 401 — String Combiner (Current)

Name: SunSpec Model 401 — String Combiner (Current)
Brand: SunSpec
SKU: cdb2b6fc-8c56-4168-9dae-b6df02cbf4ad

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Free Modbus template: SunSpec Model 401 — String Combiner (Current) | ModbusCloud

Registers (13)

13 read / 0 write

Name	Address	Function	Type	Unit	Access
id SunSpec model identifier, fixed value 401 for this model.	•••	•••	•••		R
l Model block length in 16-bit Modbus registers.	•••	•••	•••		R
dca_sf Scale factor exponent applied to DC current readings.	•••	•••	•••		R
dcahr_sf Scale factor exponent applied to amp-hour accumulator readings.	•••	•••	•••		R
dcv_sf Scale factor exponent applied to DC voltage readings.	•••	•••	•••		R
dcamax Maximum rated DC current of the string combiner, amperes.	•••	•••	•••	A	R
n Number of input strings present in the repeating block.	•••	•••	•••		R
evt SunSpec event bitmask for combiner-level faults and alerts.	•••	•••	•••		R
evtvnd Vendor-defined event bitmask for device-specific fault flags.	•••	•••	•••		R
dca Total measured DC current across all strings, amperes.	•••	•••	•••	A	R
dcahr Cumulative DC amp-hours metered by the combiner.	•••	•••	•••	Ah	R
dcv DC bus voltage at the combiner output, volts.	•••	•••	•••	V	R
tmp Combiner enclosure or board temperature, degrees Celsius.	•••	•••	•••	°C	R

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SunSpec Model 401 — String Combiner (Current)

Overview

Use cases

Installation

Things to watch for

Registers (13)

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