Voltage and current registers show implausible values. What is wrong?

All voltage, current, power, amp-hour, and energy values must be multiplied by their corresponding scale factor registers (v_sf, c_sf, p_sf, ah_sf, kwh_sf). Each scale factor is a signed int16 representing a power-of-ten exponent. For example, a v_sf of -1 means divide the raw voltage integer by 10. Failing to apply scale factors is the most common source of incorrect readings.

The gateway connects but all registers return zero or NaN. Why?

SunSpec blocks on the OutBack AXS Port and MATE3 are dynamically addressed: the absolute Modbus register offset of the 64112 block changes depending on how many OutBack devices are on the network. Scan from base address 40001 for the SunSpec identifier, then walk the block chain to locate the 64112 block before reading offsets within it. Hardcoded absolute addresses will fail after any network change.

The MATE3 SunSpec interface was enabled but the gateway still cannot connect.

Confirm the MATE3 is reachable on the network at TCP port 502 (the default Modbus port). If OPTICSre cloud polling is also active, it can interfere with concurrent Modbus TCP connections. Reduce the polling frequency in the ModbusCloud portal to reduce connection contention, and ensure no other Modbus client is holding the connection open.

Data log registers return stale or repeated values. How do I step through log days?

The data log uses the cc_config_datalog_day_offset register as an index pointer. Incrementing this value shifts the log window to a different historical day. Always read cc_config_datalog_cur_day_off to confirm which day the controller has loaded before reading daily totals. Note: cc_config_datalog_clear can erase log data permanently; do not write to it unintentionally during testing or portal setup.

Free Modbus template: SunSpec Model 64112 — OutBack FM Charge Controller

Name: SunSpec Model 64112 — OutBack FM Charge Controller
Brand: SunSpec
SKU: 813bcc5a-c609-45eb-8057-93e99559e607

The OutBack FLEXmax charge controller is an MPPT solar charge controller used in off-grid and hybrid battery systems, commonly paired with the OutBack MATE3 or AXS Port gateway for remote access. SunSpec Model 64112 is the vendor-specific configuration block for this device, accessed over Modbus TCP. The template reads the full charge profile: absorption voltage and duration, rebulk threshold, float voltage, maximum charge current, equalization settings, and temperature compensation limits. It also exposes the complete auxiliary output configuration and retrieves historical data log records including daily kWh, amp-hours, peak power, and battery voltage extremes. This gives installers a permanent audit trail of charger behavior without manual log retrieval.

Registers (66)

66 read / 0 write

Name	Address	Function	Type	Unit	Access
id SunSpec model ID, value 64112 identifies this OutBack block.	•••	•••	•••		R
l Block length in 16-bit registers, value 64.	•••	•••	•••		R
port OutBack network port number of the charge controller, 0 to 10.	•••	•••	•••		R
v_sf DC voltage scale factor, applied to all voltage readings.	•••	•••	•••		R
c_sf DC current scale factor, applied to all current readings.	•••	•••	•••		R
h_sf Time-in-hours scale factor, applied to hour-based registers.	•••	•••	•••		R
p_sf Power scale factor, applied to all watt readings.	•••	•••	•••		R
ah_sf Amp-hours scale factor, applied to all Ah readings.	•••	•••	•••		R
kwh_sf Energy scale factor, applied to kWh readings.	•••	•••	•••		R
cc_config_fault Charge controller configuration fault flag, true indicates a fault.	•••	•••	•••		R
cc_config_absorb_v Configured absorption stage target voltage, volts.	•••	•••	•••	V	R
cc_config_absorb_hr Configured absorption stage maximum duration, hours.	•••	•••	•••	Tmh	R
cc_config_absorb_end_a Absorption end current threshold, charge terminates below this.	•••	•••	•••	A	R
cc_config_rebulk_v Battery voltage threshold that triggers a return to bulk charge.	•••	•••	•••	V	R
cc_config_float_v Configured float stage maintenance voltage, volts.	•••	•••	•••	V	R
cc_config_max_chg_a Maximum charge current limit setting, amps.	•••	•••	•••	A	R
cc_config_equalize_v Equalization charge target voltage, volts.	•••	•••	•••	V	R
cc_config_equalize_hr Equalization charge maximum duration, hours.	•••	•••	•••	Tmh	R
cc_config_auto_equalize Automatic equalization interval in days, 0 disables.	•••	•••	•••	Tmd	R
cc_config_mppt_mode MPPT operating mode selection enumeration.	•••	•••	•••		R
cc_config_sweep_width MPPT sweep width setting for array voltage tracking.	•••	•••	•••	V	R
cc_config_sweep_max MPPT sweep maximum voltage boundary setting.	•••	•••	•••	V	R
cc_config_u_pick_duty_cyc User-defined MPPT duty cycle percentage setting.	•••	•••	•••	Pct	R
cc_config_grid_tie Grid-tie mode enable setting, enumerated.	•••	•••	•••		R
cc_config_temp_comp Temperature compensation mode selection enumeration.	•••	•••	•••		R
cc_config_temp_comp_llimt Temperature compensation lower voltage limit, volts.	•••	•••	•••	V	R
cc_config_temp_comp_hlimt Temperature compensation upper voltage limit, volts.	•••	•••	•••	V	R
cc_config_auto_restart Auto-restart mode enable setting, enumerated.	•••	•••	•••		R
cc_config_wakeup_voc Minimum PV open-circuit voltage required to wake from snooze, volts.	•••	•••	•••	V	R
cc_config_snooze_mode_a Output current threshold below which snooze mode activates, amps.	•••	•••	•••	A	R
cc_config_wakeup_interval Interval between snooze wakeup attempts, seconds.	•••	•••	•••	Tms	R
cc_config_aux_mode Auxiliary output mode selection enumeration.	•••	•••	•••		R
cc_config_aux_control Auxiliary output control setting enumeration.	•••	•••	•••		R
cc_config_aux_state Current state of the auxiliary output, enumerated.	•••	•••	•••		R
cc_config_aux_polarity Auxiliary output polarity setting, normal or inverted.	•••	•••	•••		R
cc_config_aux_l_batt_disc Low-battery disconnect voltage threshold for aux output, volts.	•••	•••	•••	V	R
cc_config_aux_l_batt_rcon Low-battery reconnect voltage threshold for aux output, volts.	•••	•••	•••	V	R
cc_config_aux_l_batt_dly Delay before aux low-battery disconnect activates, seconds.	•••	•••	•••	Tms	R
cc_config_aux_vent_fan_v Battery voltage threshold that triggers the vent fan aux output, volts.	•••	•••	•••	V	R
cc_config_aux_pv_triggerv PV voltage threshold that activates the PV trigger aux output, volts.	•••	•••	•••	V	R
cc_config_aux_pv_trg_h_tm Hold time after PV trigger activates aux output, seconds.	•••	•••	•••	Tms	R
cc_config_aux_nlite_thrsv Night-light PV voltage threshold for darkness detection, volts.	•••	•••	•••	V	R
cc_config_aux_nlite_on_tm Night-light on duration after darkness is detected, hours.	•••	•••	•••	Tmh	R
cc_config_aux_nlite_on_hist Night-light on hysteresis window, seconds.	•••	•••	•••	Tms	R
cc_config_aux_nlite_off_hist Night-light off hysteresis window, seconds.	•••	•••	•••	Tms	R
cc_config_aux_error_batt_v Battery voltage level that triggers the aux error output, volts.	•••	•••	•••	V	R
cc_config_aux_divert_h_time Divert mode hold time before aux output activates, seconds.	•••	•••	•••	Tms	R
cc_config_aux_divert_dly_time Divert mode delay time before aux output releases, seconds.	•••	•••	•••	Tms	R
cc_config_aux_divert_rel_v Battery voltage at which divert aux output releases, volts.	•••	•••	•••	V	R
cc_config_aux_divert_hyst_v Hysteresis voltage around divert release threshold, volts.	•••	•••	•••	V	R
cc_config_majorfwrev Charge controller major firmware revision number.	•••	•••	•••		R
cc_config_midfwrev Charge controller mid firmware revision number.	•••	•••	•••		R
cc_config_minorfwrev Charge controller minor firmware revision number.	•••	•••	•••		R
cc_config_datalog_day_offset Data log day offset index for historical record retrieval.	•••	•••	•••	Tmd	R
cc_config_datalog_cur_day_off Current day offset within the data log, days.	•••	•••	•••	Tmd	R
cc_config_datalog_daily_ah Logged daily charge delivered to battery, amp-hours.	•••	•••	•••	Ah	R
cc_config_datalog_daily_kwh Logged daily energy harvested from PV array, kWh.	•••	•••	•••	kWh	R
cc_config_datalog_max_out_a Logged peak output current recorded for the log day, amps.	•••	•••	•••	A	R
cc_config_datalog_max_out_w Logged peak output power recorded for the log day, watts.	•••	•••	•••	W	R
cc_config_datalog_absorb_t Logged total time spent in absorption stage for the log day.	•••	•••	•••	Tms	R
cc_config_datalog_float_t Logged total time spent in float stage for the log day.	•••	•••	•••	Tms	R
cc_config_datalog_min_batt_v Logged minimum battery voltage recorded for the log day, volts.	•••	•••	•••	V	R
cc_config_datalog_max_batt_v Logged maximum battery voltage recorded for the log day, volts.	•••	•••	•••	V	R
cc_config_datalog_max_input_v Logged peak PV array input voltage for the log day, volts.	•••	•••	•••	V	R
cc_config_datalog_clear Data log clear command register, write to erase log entries.	•••	•••	•••		R
cc_config_datalog_clr_comp Data log clear completion status indicator.	•••	•••	•••		R

Loading registers…

SunSpec Model 64112 — OutBack FM Charge Controller

Overview

Use cases

Installation

Things to watch for

Registers (66)

Working with Modbus in your projects?

Question about your setup?

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