Why do WMaxLimPct or WSet have no effect on the device?

Each control group has a dedicated enable register. If WMaxLimPctEna or WSetEna is set to 0, the DER stores the setpoint value but does not apply it. Write 1 to the relevant enable register to activate the control. Once enabled, subsequent setpoint changes take effect without re-writing the enable register.

Reversion timer registers show zero. Is the control stuck?

A reversion timeout of zero means the setpoint persists indefinitely until changed manually. The remaining-time registers will read zero in this state. Set a non-zero value in the RvrtTms register before enabling the control if you want automatic reversion to the fallback setpoint after a fixed period.

The Gateway connects but all register reads return errors or NaN.

SunSpec model blocks are located at a dynamic offset within the holding register space, not at a fixed absolute address. Confirm the absolute base address of the Model 704 block on your specific device by scanning from the SunSpec SunS identifier at register 40001. The addresses in this template are model-relative offsets.

Is it safe to write WSet or VarSet repeatedly from automation scripts?

Writing setpoints outside the device's rated range can trigger protection limits or trip the DER offline. Always verify the device nameplate ratings via the Model 120 registers before writing. Avoid rapid cyclic writes to non-volatile configuration registers, as some implementations store settings to flash memory and excessive writes can cause premature wear.

Free Modbus template: SunSpec Model 704 — DER AC Controls

Name: SunSpec Model 704 — DER AC Controls
Brand: SunSpec
SKU: c4241740-ad7d-4c97-883f-c4d1e07caead

SunSpec Model 704 DER AC Controls is a standardized Modbus TCP information model defined by the SunSpec Alliance for controlling distributed energy resources such as inverters and battery storage systems. Part of the IEEE 1547-2018 aligned 700-series, it exposes power factor setpoints for injection and absorption modes, active power setpoints and percentage limits with reversion timers, reactive power setpoints and ramp rates, and an anti-islanding enable flag. Scale factor registers accompany each control group. The template lets you monitor enable states and remaining reversion times, and write setpoints from the ModbusCloud portal without opening a device web interface.

Registers (45)

45 read / 32 write

Name	Address	Function	Type	Unit	Access
id SunSpec model identifier, fixed value 704 for DER AC Controls.	0	FC03	uint16		R
l Model length in registers, fixed value 65.	1	FC03	uint16		R
pfwinjena Enable flag for power factor setpoint when injecting active power.	2	FC03	uint16		R/W
pfwinjenarvrt Reversion enable flag for power factor setpoint when injecting active power.	3	FC03	uint16		R/W
pfwinjrvrttms Reversion timeout in seconds for power factor injection setpoint.	4	FC03	uint32	Secs	R/W
pfwinjrvrtrem Remaining reversion time in seconds for power factor injection setpoint.	6	FC03	uint32	Secs	R
pfwabsena Enable flag for power factor setpoint when absorbing active power.	8	FC03	uint16		R/W
pfwabsenarvrt Reversion enable flag for power factor setpoint when absorbing active power.	9	FC03	uint16		R/W
pfwabsrvrttms Reversion timeout in seconds for power factor absorption setpoint.	10	FC03	uint32	Secs	R/W
pfwabsrvrtrem Remaining reversion time in seconds for power factor absorption setpoint.	12	FC03	uint32	Secs	R
wmaxlimpctena Enable flag for maximum active power percentage limit.	14	FC03	uint16		R/W
wmaxlimpct Maximum active power limit expressed as percentage of nameplate rating.	15	FC03	uint16	Pct	R/W
wmaxlimpctrvrt Reversion value for maximum active power limit percentage.	16	FC03	uint16	Pct	R/W
wmaxlimpctenarvrt Reversion enable flag for maximum active power percentage limit.	17	FC03	uint16		R/W
wmaxlimpctrvrttms Reversion timeout in seconds for maximum active power percentage limit.	18	FC03	uint32	Secs	R/W
wmaxlimpctrvrtrem Remaining reversion time in seconds for maximum active power percentage limit.	20	FC03	uint32	Secs	R
wsetena Enable flag for active power setpoint control.	22	FC03	uint16		R/W
wsetmod Mode selector for active power setpoint: watts or percentage.	23	FC03	uint16		R/W
wset Active power setpoint in watts; positive exports, negative absorbs.	24	FC03	int32	W	R/W
wsetrvrt Reversion active power setpoint in watts applied after timeout.	26	FC03	int32	W	R/W
wsetpct Active power setpoint as percentage of nameplate rating.	28	FC03	int16	Pct	R/W
wsetpctrvrt Reversion active power setpoint as percentage of nameplate rating.	29	FC03	int16	Pct	R/W
wsetenarvrt Reversion enable flag for active power setpoint control.	30	FC03	uint16		R/W
wsetrvrttms Reversion timeout in seconds for active power setpoint.	31	FC03	uint32	Secs	R/W
wsetrvrtrem Remaining reversion time in seconds for active power setpoint.	33	FC03	uint32	Secs	R
varsetena Enable flag for reactive power setpoint control.	35	FC03	uint16		R/W
varsetmod Mode selector for reactive power setpoint: vars or percentage.	36	FC03	uint16		R/W
varsetpri Priority setting for reactive power setpoint relative to other controls.	37	FC03	uint16		R/W
varset Reactive power setpoint in vars; positive injects, negative absorbs.	38	FC03	int32	Var	R/W
varsetrvrt Reversion reactive power setpoint in vars applied after timeout.	40	FC03	int32	Var	R/W
varsetpct Reactive power setpoint as percentage of nameplate reactive capacity.	42	FC03	int16	Pct	R/W
varsetpctrvrt Reversion reactive power setpoint as percentage of nameplate reactive capacity.	43	FC03	int16	Pct	R/W
varsetenarvrt Reversion enable flag for reactive power setpoint control.	44	FC03	uint16		R/W
varsetrvrttms Reversion timeout in seconds for reactive power setpoint.	45	FC03	uint32	Secs	R/W
varsetrvrtrem Remaining reversion time in seconds for reactive power setpoint.	47	FC03	uint32	Secs	R
wrmp Active power ramp rate in percent of maximum per second.	49	FC03	uint16	%Max/Sec	R/W
wrmpref Reference value used for active power ramp rate calculation.	50	FC03	uint16		R/W
varrmp Reactive power ramp rate in percent of maximum per second.	51	FC03	uint16	%Max/Sec	R/W
antiislena Enable flag for anti-islanding protection function.	52	FC03	uint16		R/W
pf_sf Scale factor exponent applied to power factor registers.	53	FC03	int16		R
wmaxlimpct_sf Scale factor exponent applied to maximum active power percentage registers.	54	FC03	int16		R
wset_sf Scale factor exponent applied to active power setpoint in watts.	55	FC03	int16		R
wsetpct_sf Scale factor exponent applied to active power setpoint percentage registers.	56	FC03	int16		R
varset_sf Scale factor exponent applied to reactive power setpoint in vars.	57	FC03	int16		R
varsetpct_sf Scale factor exponent applied to reactive power setpoint percentage registers.	58	FC03	int16		R