Module voltage readings look ten times too high or too low.

SunSpec uses signed scale-factor registers (modv_sf, cellv_sf, tmp_sf) that represent a power-of-ten multiplier. If your client reads the raw integer without applying the scale factor, values will be wrong by a decade. Read the scale-factor register and multiply: raw_value * 10^sf.

The gateway connects but all voltage registers return 0x8000 or 0xFFFF.

0x8000 on a signed int16 and 0xFFFF on a uint16 are SunSpec 'Not Implemented' sentinels. The device supports the model block structurally but has not populated those points. Confirm the BMS firmware version supports Model 807 and that the string is active and not isolated for maintenance.

No data appears even though the TCP connection is established.

SunSpec devices place Model 807 at a dynamic offset within the register map, not at a fixed address. The block starts immediately after the preceding model ends. Use the model length register (l) of each preceding block to walk the map and locate the correct base address for Model 807 before polling its registers.

Event bitfields evt1 and evt2 show non-zero values. What do they mean?

Evt1 and Evt2 are 32-bit bitfields defined in the SunSpec Energy Storage specification. Each bit maps to a named alarm condition such as over-charge current, high pressure, or contactor fault. Decode them by consulting the SunSpec Energy Storage Models document, table of StrEvt bit definitions. Vendor-specific flags appear separately in evtvnd1 and evtvnd2.

Free Modbus template: SunSpec Model 807 — Flow Battery String Model

Name: SunSpec Model 807 — Flow Battery String Model
Brand: SunSpec
SKU: dba6c4d6-e858-446f-9895-415d01fd442a

SunSpec Model 807 is the standardized Modbus information model for flow battery strings, covering chemistries such as vanadium redox, zinc-bromine, and iron-chromium. The template reads string-level and cell-level voltage extremes (maximum, minimum, and average for both modules and cells), temperature spread across all modules, module count and connected module count, and two layers of event bitfields for alarms. Scale-factor registers accompany every measured group so your client applies the correct decimal exponent at runtime. Using Modbus TCP, the ModbusCloud Gateway polls any SunSpec-compliant flow battery controller and surfaces degradation trends and fault events in the portal without vendor-specific configuration.

Registers (31)

31 read / 0 write

Name	Address	Function	Type	Unit	Access
id SunSpec model identifier, fixed value 807 for this model.	0	FC03	uint16		R
l Model block length in registers, used to size repeating blocks.	1	FC03	uint16		R
idx String index within the battery bank, starting at 1.	2	FC03	uint16		R
nmod Total number of flow battery modules in this string.	3	FC03	uint16		R
nmodcon Number of modules currently connected electrically in the string.	4	FC03	uint16		R
modvmax Highest module voltage measured across all modules, volts.	5	FC03	uint16	V	R
modvmaxmod Module number reporting the maximum module voltage.	6	FC03	uint16		R
modvmin Lowest module voltage measured across all modules, volts.	7	FC03	uint16	V	R
modvminmod Module number reporting the minimum module voltage.	8	FC03	uint16		R
modvavg Average voltage across all modules in the string, volts.	9	FC03	uint16	V	R
cellvmax Highest individual cell voltage in the string, volts.	10	FC03	uint16	V	R
cellvmaxmod Module number containing the highest cell voltage.	11	FC03	uint16		R
cellvmaxstk Stack number within the module containing the highest cell voltage.	12	FC03	uint16		R
cellvmin Lowest individual cell voltage in the string, volts.	13	FC03	uint16	V	R
cellvminmod Module number containing the lowest cell voltage.	14	FC03	uint16		R
cellvminstk Stack number within the module containing the lowest cell voltage.	15	FC03	uint16		R
cellvavg Average cell voltage across all cells in the string, volts.	16	FC03	uint16	V	R
tmpmax Highest temperature reading across all modules, degrees Celsius.	17	FC03	int16	°C	R
tmpmaxmod Module number reporting the maximum temperature.	18	FC03	uint16		R
tmpmin Lowest temperature reading across all modules, degrees Celsius.	19	FC03	int16	°C	R
tmpminmod Module number reporting the minimum temperature.	20	FC03	uint16		R
tmpavg Average temperature across all modules in the string, degrees Celsius.	21	FC03	int16	°C	R
evt1 Standard string event bitfield 1, encodes alarms and fault conditions.	22	FC03	uint32		R
evt2 Standard string event bitfield 2, additional alarm and fault flags.	24	FC03	uint32		R
evtvnd1 Vendor-defined event bitfield 1 for manufacturer-specific alarms.	26	FC03	uint32		R
evtvnd2 Vendor-defined event bitfield 2 for manufacturer-specific alarms.	28	FC03	uint32		R
modv_sf Scale factor (power of ten) applied to module voltage registers.	30	FC03	int16		R
cellv_sf Scale factor (power of ten) applied to cell voltage registers.	31	FC03	int16		R
tmp_sf Scale factor (power of ten) applied to temperature registers.	32	FC03	int16		R
soc_sf Scale factor (power of ten) applied to state-of-charge values.	33	FC03	int16		R
ocv_sf Scale factor (power of ten) applied to open-circuit voltage values.	34	FC03	int16		R