Voltage and current readings look wrong by a factor of 10 or 100. Why?

SunSpec uses signed integer scale factors. Read the v_sf and a_sf registers and apply the exponent: actual value equals raw register value multiplied by 10 raised to the power of v_sf or a_sf. A v_sf of -2 means divide raw volts by 100. Confirm the portal is applying these scale factors.

The gateway connects but all harmonic array registers return zeros or errors.

The vhara, vharb, vharc, ihara, iharb, iharc, iinthara, iintharb, and iintharc registers are large string-typed arrays at high offsets (31 to 1380). Some Modbus TCP implementations limit single read length to 125 registers. If your gateway issues one large read request, it will be rejected. Configure the ModbusCloud Gateway to split reads into smaller chunks covering each array separately.

The gateway shows no data after import. What should I check first?

Confirm the unit ID in the portal matches the simulator's configured Modbus slave address. SunSpec devices using base address 0 require the client to start reading at 0, not 40001. Also confirm TCP port 502 is reachable from the Gateway host using a Modbus scanner or ping before ruling out network issues.

Is it safe to write vset, vseta, freq, or output during a live test?

Exercise caution with all write registers (vnom, vmax, imax, freq, vset, vseta, vsetb, vsetc, vslew, freqslew, output, relay, regen, enaprof). Writing unexpected voltage or frequency values during an active test can disrupt the device under test, trip protection relays, or invalidate test results. Always confirm the test sequence is paused before issuing writes from the portal.

Free Modbus template: SunSpec Model 64411 — AC Simulator Control Interface

Name: SunSpec Model 64411 — AC Simulator Control Interface
Brand: SunSpec
SKU: a8120918-f80a-4709-85d2-5433297d9f93

SunSpec Model 64411 is a Modbus TCP control interface for AC grid simulator instruments used in DER compliance testing labs. The template reads measured per-phase voltages (va, vb, vc), currents (ia, ib, ic), and output frequency (hz), and writes simulator configuration registers including nominal voltage (vnom), per-phase voltage setpoints (vseta, vsetb, vsetc), frequency (freq), voltage and frequency slew rates (vslew, freqslew), output and relay enable flags, and harmonic and THD readback arrays across all three phases. Scale factor registers (v_sf, a_sf, hz_sf, thd_sf) apply SunSpec exponent scaling to all numeric readings. Connecting this template in the ModbusCloud portal gives test engineers live visibility into simulator state during inverter certification runs.

Registers (50)

50 read / 16 write

Name	Address	Function	Type	Unit	Access
id SunSpec model ID identifying this information block.	0	FC03	uint16		R
l Model block length in registers, excluding id and l.	1	FC03	uint16		R
phases Number of AC output phases to simulate (1 or 3).	2	FC03	uint16		R/W
phaseangle Phase angle between simulated AC output phases, in degrees.	3	FC03	uint16		R/W
vnom Nominal AC output voltage setpoint, volts.	4	FC03	uint16	V	R/W
vmax Maximum AC output voltage limit, volts.	5	FC03	uint16	V	R/W
imax Maximum AC output current limit, amperes.	6	FC03	uint16	A	R/W
freq Simulated AC output frequency setpoint, hertz.	7	FC03	uint16	Hz	R/W
output Output enable flag; activates or disables AC output.	8	FC03	uint16		R/W
relay Relay state control; connects or disconnects output relay.	9	FC03	uint16		R/W
regen Regenerative mode enable flag for energy recovery.	10	FC03	uint16		R/W
vset AC voltage setpoint applied to all phases equally, volts.	11	FC03	uint16	V	R/W
vseta Per-phase voltage setpoint for phase A, volts.	12	FC03	uint16	V	R/W
vsetb Per-phase voltage setpoint for phase B, volts.	13	FC03	uint16	V	R/W
vsetc Per-phase voltage setpoint for phase C, volts.	14	FC03	uint16	V	R/W
freqslew Frequency slew rate, rate of frequency change in Hz/s.	15	FC03	uint16	Hz/s	R/W
vslew Voltage slew rate, rate of voltage change in V/s.	16	FC03	uint16	V/s	R/W
va Measured actual AC voltage on phase A, volts.	17	FC03	int32	V	R
vb Measured actual AC voltage on phase B, volts.	19	FC03	int32	V	R
vc Measured actual AC voltage on phase C, volts.	21	FC03	int32	V	R
hz Measured actual AC output frequency, hertz.	23	FC03	int32	Hz	R
ia Measured actual AC current on phase A, amperes.	25	FC03	int32	A	R
ib Measured actual AC current on phase B, amperes.	27	FC03	int32	A	R
ic Measured actual AC current on phase C, amperes.	29	FC03	int32	A	R
vhara Voltage harmonic spectrum array for phase A, volts.	31	FC03	string	V	R
vharb Voltage harmonic spectrum array for phase B, volts.	181	FC03	string	V	R
vharc Voltage harmonic spectrum array for phase C, volts.	331	FC03	string	V	R
ihara Current harmonic spectrum array for phase A, amperes.	481	FC03	string	A	R
iharb Current harmonic spectrum array for phase B, amperes.	631	FC03	string	A	R
iharc Current harmonic spectrum array for phase C, amperes.	781	FC03	string	A	R
iinthara Interharmonic current spectrum array for phase A, amperes.	931	FC03	string	A	R
iintharb Interharmonic current spectrum array for phase B, amperes.	1081	FC03	string	A	R
iintharc Interharmonic current spectrum array for phase C, amperes.	1231	FC03	string	A	R
vthda Total harmonic distortion of voltage on phase A, percent.	1381	FC03	uint16	%	R
vthdb Total harmonic distortion of voltage on phase B, percent.	1382	FC03	uint16	%	R
vthdc Total harmonic distortion of voltage on phase C, percent.	1383	FC03	uint16	%	R
ithda Total harmonic distortion of current on phase A, percent.	1384	FC03	uint16	%	R
ithdb Total harmonic distortion of current on phase B, percent.	1385	FC03	uint16	%	R
ithdc Total harmonic distortion of current on phase C, percent.	1386	FC03	uint16	%	R
enaprof Enable flag to trigger execution of a waveform profile.	1387	FC03	uint16		R/W
profrslt Result code from the last executed waveform profile run.	1388	FC03	uint16		R
nprof Number of waveform profiles available in the simulator.	1389	FC03	uint16		R
npt Number of time-domain points per waveform profile.	1390	FC03	uint16		R
v_sf Scale factor exponent applied to all voltage readings.	1391	FC03	int16		R
a_sf Scale factor exponent applied to all current readings.	1392	FC03	int16		R
tms_sf Scale factor exponent applied to time-domain values.	1393	FC03	int16		R
hz_sf Scale factor exponent applied to frequency readings.	1394	FC03	int16		R
hzslew_sf Scale factor exponent applied to frequency slew rate.	1395	FC03	int16		R
vslew_sf Scale factor exponent applied to voltage slew rate.	1396	FC03	int16		R
thd_sf Scale factor exponent applied to THD percentage readings.	1397	FC03	int16		R