When one of those readings moves outside the safe range, the charger may reduce output, stop charging, open or short an internal protection circuit, or report an error code. The code is only the starting point. In the field, the real question is usually simpler: is this a wiring problem, a battery problem, a PV sizing problem, a communication problem, or a failed charger?
Before You Troubleshoot
Write down the exact code before resetting anything. Also note what the system was doing when the fault appeared. A code that appears at sunrise, under peak sun, during inverter startup, or after a firmware update can point to very different causes.
Record these details if you can:
Battery voltage and battery type
PV array voltage
PV array current
Charger input-voltage and current rating
Battery temperature
Ambient temperature around the charger
Whether another charger, inverter, generator charger, grid charger, or BMS is connected to the same battery
Whether the code is active now or only stored in history
A historical code is not always a problem. If the unit is running normally and the code is only in the log, treat it as context. An active code needs diagnosis.
A Field Workflow That Usually Works
Start outside the charger. Most faults are caused by the installation, not by the circuit board.
Identify the area involved: battery, PV input, temperature, wiring, inverter output, communication, firmware, or internal electronics.
Check whether the fault normally clears by itself. Temperature and voltage faults often do. Sensor, relay, firmware, and internal supply faults usually do not.
Inspect cables, terminals, fuses, contactors, and sense wires before replacing hardware.
Check settings against the real system. A 12 V setting on a 24 V battery bank can look like a charger fault when it is just bad configuration.
Do not keep restarting the unit if the same code comes back immediately. That usually means the unsafe condition is still present.
Disconnect PV and battery power only when the procedure calls for it, and use the correct order for the equipment.
Quick Reference
| Code | Fault area | Meaning | First place to look |
|---|---|---|---|
| Err 1 | Battery temperature | Battery temperature too high | Battery cooling and temperature sensor |
| Err 2 | Battery voltage | Battery voltage too high | Battery voltage setting and other chargers |
| Err 3, 4 | Temperature sense | Remote temperature sensor fault | T-sense wiring and connector position |
| Err 5 | Temperature sense | Remote temperature sensor connection lost | Sensor plug and cable continuity |
| Err 6, 7 | Voltage sense | Remote battery voltage sense fault | V-sense polarity and wiring route |
| Err 8 | Voltage sense | Remote voltage-sense connection lost | Sense-wire terminals and continuity |
| Err 11 | DC bus | High battery ripple voltage | Battery cable size, crimps, and tightness |
| Err 14 | Battery temperature | Battery too cold for charging | Lithium battery temperature limit |
| Err 17 | Charger temperature | Controller overheated after derating | Airflow, heatsink clearance, cabinet heat |
| Err 18 | Current | Controller over-current | Load surge and battery-side current path |
| Err 20 | Charge cycle | Maximum bulk-charge time exceeded | Battery condition and absorption settings |
| Err 21 | Current sensor | Current measurement out of range | Negative wiring path through the charger |
| Err 22, 23 | Internal temperature | Internal temperature sensor fault | Restart, then service if it remains active |
| Err 24 | Fan | Fan blocked, disconnected, or failed | Fan path and fan current draw |
| Err 26 | Terminals | Power terminals overheated | Cable type, strand type, torque, oxidation |
| Err 27 | Battery-side current | Charger short circuit or over-current | Contactors, battery wiring, inverter input capacitance |
| Err 28 | Power stage | Power-stage fault | Restart, then repair or replace if persistent |
| Err 29 | Battery over-charge | Over-charge protection active | PV string design, charge settings, other chargers |
| Err 33 | PV input | PV over-voltage | PV open-circuit voltage and panels in series |
| Err 34 | PV input | PV over-current | Array current, parallel strings, wiring faults |
| Err 35 | PV or internal DC | PV over-power or high internal DC voltage | PV sizing, firmware, internal measurement fault |
| Err 38, 39, 80-87 | PV shutdown | PV input shutdown to protect the battery | Battery voltage setting and over-charge sources |
| Err 40 | PV shutdown | PV input failed to shut down | Serious internal protection fault |
| Err 41 | PV insulation | PV isolation resistance too low | Panel and cable insulation |
| Err 42 | PV leakage | Ground leakage current above 30 mA | Wet connectors, damaged insulation, grounding |
| Err 43 | Ground fault | Neutral-ground voltage too high | AC grounding, polarity, backfeed |
| Err 50, 52 | Inverter load | Inverter overload or peak current | Motor starts, pump starts, large surge loads |
| Err 51 | Inverter temperature | Inverter temperature too high | Load level, fan, air outlet clearance |
| Err 53 | AC output | Inverter output voltage problem | Battery voltage and AC load |
| Err 54 | AC output | Inverter output voltage problem | Battery, load, and possible internal fuse fault |
| Err 55, 56, 58 | Inverter self-test | Inverter diagnostic test failed | Restart, then service if persistent |
| Err 57 | AC output | AC voltage already present on output | Backfeed or wrong AC wiring |
| Err 59 | AC input relay | AC input relay test fault | Stuck or welded relay contact |
| Info 65 | Communication | Parallel controller communication lost | Data cable and device power |
| Info 66 | Compatibility | Parallel devices have incompatible settings | Charge settings and firmware consistency |
| Err 67 | BMS | BMS communication lost | BMS cable, charge permission, control mode |
| Err 68 | Network | Conflicting network data sources | Duplicate communication paths |
| Err 69 | Network | Units on the same bus have different system settings | Phase and frequency configuration |
| Err 70 | Network | Unsupported device combination | System pairing |
| Err 71 | Network | Incompatible firmware across units | Firmware versions on all units |
| Err 72 | Phase rotation | Wrong three-phase order | L1, L2, L3 sequence |
| Err 73 | AC input | More than one active grid input per phase | Redundant grid input |
| Err 74 | Parallel system | Too many units in parallel for the transfer design | Parallel and grid-transfer configuration |
| Err 75 | Grid configuration | Selected grid code does not support the mode | Grid-code and three-phase settings |
| Err 76 | Network incomplete | Not enough powered units for the configured network | Unit power, CAN cables, unit count |
| Err 77 | Settings sync | Mixed settings-sync status | Enable or disable sync consistently |
| Err 114 | CPU temperature | CPU temperature too high | Cabinet temperature and airflow |
| Err 116 | Calibration | Calibration data lost | Service if active and the unit does not work |
| Err 117 | Firmware | Firmware update incomplete or incompatible | Retry with the correct firmware package |
| Err 119 | Settings | Settings data lost | Restore defaults and reconfigure |
| Err 121 | Factory test data | Tester failure record | Service if active and the unit does not work |
| Err 200 | Internal DC | Internal DC-DC converter fault | Restart, then service if persistent |
| Err 201 | Internal DC measurement | Internal high-voltage measurement fault | Firmware first, service if persistent |
| Err 202 | Leakage sensor | Internal residual-current sensor fault | Restart, then service if persistent |
| Err 203, 205, 212, 215 | Internal supply | Internal supply voltage fault | Restart, then service if persistent |
Battery and Charging Faults
Err 1: Battery Temperature Too High
The charger stops charging because the battery is too hot. The temperature may come from an internal sensor, an external battery sensor, or a BMS.
Look for poor ventilation, a battery installed near a heat source, high charging current in hot weather, a misplaced temperature sensor, or a battery that was already hot after heavy discharge.
This fault normally clears after the battery cools down.
Err 2: Battery Voltage Too High
The charger is seeing a battery voltage above the range it expects.
Common causes:
Another charger is connected to the same battery
The charger is set for the wrong battery voltage, such as 12 V on a 24 V or 48 V bank
Absorption, float, or equalization voltage is too high
Battery sense wiring is connected at the wrong point
The charger has an internal fault
If the code clears when battery voltage falls, check the rest of the charging system before blaming the MPPT charger.
Err 11: Battery High Ripple Voltage
High DC ripple means the battery-side voltage is not steady. This is usually a wiring, battery, or load problem.
Check for loose battery terminals, undersized DC cables, long cable runs, poor crimps, corrosion, high surge loads, or weak batteries. Inverter systems may restart after a ripple shutdown. After repeated shutdowns in a short period, some inverters stay off until manually restarted.
Do not ignore ripple. It shortens inverter life and often points to heat building up somewhere in the DC path.
Err 14: Battery Low Temperature
This matters most with lithium iron phosphate batteries. Charging lithium cells below their allowed temperature can damage them permanently.
Check the actual battery temperature, sensor placement, battery heater if fitted, BMS charge permission, and the battery manufacturer's low-temperature charging limit.
Err 20: Maximum Bulk-Time Exceeded
During bulk charging, the charger pushes current until the battery reaches the absorption-voltage setpoint. If that never happens within the allowed time, the charger may stop and report this code.
Likely causes:
Battery capacity is too large for the charger
Battery is deeply discharged
A cell is shorted or damaged
Absorption voltage is set too high
Charge current is limited too far
Large DC loads are running while the battery is charging
In some older solar chargers, this code can also come from legacy firmware behavior. In AC chargers, the same idea is often used to catch a shorted cell when absorption voltage is not reached after about 10 hours.
Err 26: Terminal Overheated
Hot power terminals usually mean high resistance at the connection.
Check cable size, strand type, crimp quality, terminal torque, loose bolts, oxidation, and heat discoloration. The code may clear when the terminal cools, but the connection still needs to be fixed. A hot terminal is not a nuisance fault. It can become a fire risk.
Err 27: Charger Short Circuit
This is a battery-side over-current or short-circuit condition.
It can happen when a battery is connected through a contactor, when the charger starts while connected to an inverter with large input capacitance, or when the battery wiring is wrong.
Some chargers recover by themselves. If not, isolate the power sources, wait several minutes, and restart using the correct safety procedure. If the code returns immediately, the charger or battery-side wiring needs deeper inspection.
Err 29: Over-Charge Protection
The charger is limiting or disconnecting output because the battery is being pushed above the expected charging range.
Look for too many PV panels in series, the wrong battery-voltage setting, incorrect absorption or float voltage, another charger raising the battery bus, or a PV array that cannot be regulated properly by the controller.
If PV string voltage is too high, reduce the number of panels in series. Use parallel strings where the charger rating and wiring design allow it.
Sensors, Fan, and Temperature Measurement
Err 3 and Err 4: Remote Temperature Sensor Failure
The charger is not reading the remote temperature input correctly. A common mistake is wiring the temperature-sense input to battery positive or battery negative.
Check the sensor plug, cable, connector, sensor type, and mounting point. Also check for crushed insulation or contamination inside the connector.
Err 5: Remote Temperature Sensor Connection Lost
The charger previously detected a remote temperature sensor and then lost it. Inspect the sensor cable and connector. This code often needs a wiring fix before it clears.
Err 6 and Err 7: Remote Battery Voltage Sense Failure
Remote voltage sensing measures voltage at the battery terminals instead of at the charger. It improves charging accuracy, but only if the sense wires are correct.
Check that sense positive goes to battery positive and sense negative goes to battery negative. Also check for loose sense wires, broken conductors, and sense wiring routed through the wrong switch or fuse point.
Err 8: Remote Battery Voltage Sense Connection Lost
The voltage-sense circuit has lost connection. Depending on the charger design, it may fall back to local voltage measurement or stop charging.
Check continuity, terminal tightness, connector fit, and any fuse in the sense line.
Err 17: Controller Overheated Despite Reduced Output Current
MPPT chargers usually reduce output current as they heat up. If the temperature keeps rising after derating, the charger stops.
Look for a sealed cabinet, blocked heatsink, poor mounting orientation, dust, high ambient temperature, or nearby heat sources. The code normally clears after the charger cools.
Err 18: Controller Over-Current
The charger has detected current above its safe range.
Possible causes include a large DC load switching on or off, a sudden irradiance change, inverter overload causing a battery-side surge, a weak battery, or a wiring fault.
Start by reducing load and checking the battery-side current path. Cooling also matters because a hot charger has less margin.
Err 21: Current Sensor Issue
The current reading is outside the expected range. One practical cause is a negative wiring path that bypasses the charger's measurement circuit.
Check that PV negative and battery negative are wired through the correct charger terminals. If rewiring and restart do not clear the code, the current sensor or its internal circuit may be defective.
Err 22 and Err 23: Internal Temperature Sensor Failure
The charger's internal temperature reading is invalid. That can be a failed sensor, internal circuit fault, moisture damage, or past heat damage.
A restart may clear a temporary fault. If the code stays active, the unit usually needs service.
Err 24: Fan Failure
The charger powers the fan but does not detect the expected current draw. The fan may be blocked, disconnected, seized, or failed.
Check for dust, insects, cable obstruction, and free fan movement. A failed fan can turn an otherwise normal installation into an overheating problem.
Err 114: CPU Temperature Too High
The controller's processor area is too hot.
Check cabinet ventilation, air inlet and outlet clearance, dust buildup, ambient temperature, and installation orientation. If the code appears in a cool, open installation, suspect an internal fault.
PV Input and Solar-Array Faults
Err 33: PV Over-Voltage
PV voltage is above the charger's safe input limit. This often happens when too many panels are wired in series.
Do the calculation with cold-weather voltage, not just the panel label at standard test conditions. Solar-panel open-circuit voltage rises as temperature drops.
Check panel open-circuit voltage, series count, lowest expected site temperature, charger maximum PV input voltage, and the safety margin. Repeated PV over-voltage can damage the charger even if the code clears later in the day.
Err 34: PV Over-Current
PV current is above the rated input current, or the charger sees an abnormal current condition at the PV input.
Check for too many parallel strings, PV wiring faults, a shorted input path, or internal controller damage. If the array and wiring are correct and the code remains, the charger may need service.
Err 35: PV Over-Power or High Internal DC Voltage
This code can appear when the PV array delivers more power than the power stage can process, or when internal DC voltage rises too high.
Check PV array sizing, string design, firmware version, and whether the fault appears during sudden changes in sunlight. If the design and firmware are correct but the code keeps returning, the internal high-voltage measurement circuit or power stage may be damaged.
Err 38, Err 39, and Err 80 to Err 87: PV Input Shutdown
These codes usually mean the charger has shut down the PV input, or internally shorted it, to protect the battery from over-charging.
Likely causes:
Wrong battery-voltage setting
Another charger raising the battery above the expected limit
Absorption or equalization mismatch between devices
PV array outside the charger's controllable range
Fault in the PV protection circuit
Some versions clear after battery voltage drops. Others need PV and battery power disconnected in a controlled sequence. If the code stays active after the correct recovery procedure, suspect charger damage.
Err 40: PV Input Failed to Shut Down
This is one of the more serious PV-side faults. The charger tried to turn off or isolate the PV input and could not.
To protect the battery, it may stop charging and disconnect its output. A persistent Err 40 should be inspected by a qualified technician.
Err 41: Low PV Isolation Resistance
PV isolation resistance tells you how well the array is insulated from ground and other conductive parts. Low isolation can come from damaged cables, wet connectors, cracked panels, dirty junction boxes, or moisture inside the system.
Check PV cable insulation, connector sealing, panel condition, and leakage paths to ground.
Err 42: Ground Leakage Current Above 30 mA
The system has detected more than 30 mA of leakage current from the PV array. Treat this as a safety fault.
Look for wet connectors, insulation breakdown, damaged panel backsheets, incorrect grounding, or abraded cables. Leakage faults can create shock risk and often get worse over time.
Inverter, AC Output, and Grounding Faults
Err 43: Neutral-Ground Voltage Too High
The voltage difference between neutral and ground is too high.
Common causes include a missing ground, poor ground bond, reversed line and neutral, a faulty grounding relay, incorrect off-grid wiring, incorrect grid-connected wiring, or AC backfeed.
This code normally does not clear by itself. Inspect the AC wiring before restarting.
Err 50 and Err 52: Inverter Overload or Peak Current
Motors, pumps, compressors, and transformers can draw a much larger current at startup than they do while running. That surge can trip the inverter even when the running load looks acceptable.
Typical symptoms are output voltage sag, a restart after about 30 seconds, repeated overload shutdowns, or the inverter staying off after several failed retries.
Reduce AC load, start large loads one at a time, use soft-start equipment where appropriate, or use an inverter with more surge capacity.
Err 51: Inverter Temperature Too High
The inverter is too hot, usually because of high load, poor airflow, blocked fan outlets, dust, or high ambient temperature.
It may restart after cooling, but repeated overheating shortens component life. Fix the ventilation or load problem rather than treating the restart as a cure.
Err 53 and Err 54: Inverter Output Voltage Problem
Low battery voltage plus high AC load can keep the inverter from maintaining stable output voltage.
Check for a discharged battery, undersized battery cables, high surge load, weak battery bank, or poor DC connections. If the code appears immediately with no load and a full battery, an internal fuse or inverter component may be damaged.
Err 55, Err 56, and Err 58: Inverter Self-Test Failed
The inverter runs internal checks before energizing AC output. If one of those tests fails, the inverter should not start.
A restart may clear a temporary fault. Persistent self-test failure usually means internal hardware damage.
Err 57: AC Voltage Already Present on Output
The inverter sees AC voltage on its output before it turns on. That usually means backfeed.
Check whether the output is connected to grid power, another inverter, a generator, or a transfer switch wired incorrectly. Do not restart until the unwanted AC source is removed.
Err 59: AC Input Relay Test Fault
The AC input relay did not pass its test. A common cause is a stuck or welded relay contact.
If the fault returns after restart, the AC input stage needs professional service.
Communication, BMS, and Network Faults
Info 65: Communication Warning
Communication with a parallel controller has been lost.
Check data cables, connector seating, device power, bus termination if used, and the parallel configuration.
Info 66: Incompatible Device or Settings
Parallel chargers normally need the same battery type, charge algorithm, absorption voltage, float voltage, equalization settings, and compatible firmware.
If one unit is configured differently, charging can become unstable. Match the settings before running the system in parallel.
Err 67: BMS Connection Lost
A charger in BMS-controlled mode expects charge-permission signals. If those signals disappear, the charger may stop charging or reduce output for safety.
Check BMS power, the communication cable, charge-permission status, and the charger's control mode. Some chargers remember BMS-controlled mode after power cycling. If the charger is moved into a system without a BMS, it may need to be reset to standalone operation.
Err 68: Conflicting Network Sources
The charger is receiving the same kind of data from more than one source. For example, battery voltage may arrive from both a wired data bus and a wireless network.
If two sources have equal priority, the charger may not know which value to trust. Remove duplicate data paths and leave one primary control source.
Err 69: Different System Configuration on the Same Bus
Networked chargers or inverters must agree on system configuration. All units should use the same phase mode and frequency, such as single-phase or three-phase, and 50 Hz or 60 Hz.
If the units disagree, the system may shut down until the configuration is corrected.
Err 70: Unsupported Device Combination
Some devices cannot operate together in the same networked setup. Correct the pairing before restarting.
Err 71: Incompatible Firmware Across Units
Networked power devices often need compatible firmware. If one unit has been updated and another has not, control logic may fail.
Bring all units in the network to compatible firmware versions.
Err 72: Phase Rotation
Three-phase systems need the correct phase order: L1, L2, then L3. Wrong phase rotation can prevent the inverter system from connecting to the grid.
Err 73: Multiple AC Inputs
Only one active grid input per phase is normally allowed. More than one can create backfeed or synchronization problems.
Remove or switch off the redundant input before reconnecting.
Err 74: Too Many Units in Parallel
A parallel inverter system must stay within the transfer capability of its relays and control design. Too many units in parallel, especially with a grid connection, can exceed the supported design.
Correct the system layout before operating it.
Err 75: Unsupported Grid-Code Configuration
Some grid codes do not permit certain operating modes, including some three-phase configurations. The inverter may run internally but refuse to connect to the grid until the grid-code and phase settings match.
Err 76: Network Incomplete
A networked setup may require a fixed number of powered units. If one unit is off, missing, or disconnected, the system may shut down.
Check unit power, data cables, CAN bus termination, configured unit count, and missing-phase settings if used.
Err 77: Settings Synchronization Disabled
In a multi-unit system, settings synchronization should be consistent. Enable it on all units or disable it on all units. A mixed state can trigger a warning.
Firmware, Calibration, and Internal Hardware Faults
Err 28: Power-Stage Issue
The power stage converts PV input into controlled battery-charging output. If this section fails, the charger cannot regulate power safely.
Possible causes include failed switching components, a driver-circuit fault, internal measurement errors, or damage from previous over-voltage or overheating. If a restart does not clear the code, repair or replacement is usually required.
Err 116: Calibration Data Lost
Calibration data lets the charger interpret voltage, current, and temperature readings correctly.
If this code is active and the unit does not operate, the charger is likely faulty. If the code appears only in history and the unit works normally, it may be an old factory or startup record.
Err 117: Incompatible or Incomplete Firmware
A failed firmware update can leave a device only partly updated.
Common causes are power loss during the update, a disconnected data cable, an interrupted wireless update, or the wrong firmware file. Retry the update with the correct firmware package for the exact device.
Err 119: Settings Data Lost
The charger cannot read its configuration. It may no longer know the battery type, charge voltage, or operating limits, so it stops.
Typical recovery:
Restore factory defaults.
Disconnect power using the safe procedure for the equipment.
Wait several minutes.
Restart the charger.
Re-enter the battery type, battery voltage, charge profile, and system settings.
If the code returns, internal memory may be defective.
Err 121: Tester Fail
This may be a factory-test or internal-test record. If the unit works and the code is only historical, it may not matter. If the code is active and the unit will not run, service is required.
Err 200: Internal DC Voltage Error
The charger or inverter checks its internal DC-DC converter during startup. Err 200 means that converter is not behaving as expected.
If installation checks and restart do not clear it, the internal DC-DC stage may be faulty.
Err 201: Internal DC Voltage Measurement Error
An internal high-voltage measurement does not match the expected range.
Older firmware can sometimes trigger this too easily, so update firmware first if that applies. If the code remains, the voltage-measurement circuit or high-voltage section may be damaged.
Err 202: Internal Residual-Current Sensor Error
The residual-current sensor failed its self-test. Since this sensor is used to detect leakage current, a persistent Err 202 is a safety-related internal fault.
Err 203, Err 205, Err 212, and Err 215: Internal Supply Voltage Error
The control board needs several internal supply voltages for sensors, drivers, processors, and protection circuits. If one supply is out of range, the device may stop.
Persistent internal supply-voltage errors usually need service.
Codes That Often Need Service
These codes are more likely to point to hardware trouble if they remain active after basic checks:
Err 21: current sensor issue
Err 22 and Err 23: internal temperature sensor failure
Err 24: fan failure
Err 28: power-stage issue
Err 34: PV over-current that persists after wiring checks
Err 35: PV over-power or internal DC fault after configuration and firmware checks
Err 40: PV input failed to shut down
Err 55, Err 56, and Err 58: inverter self-test failure
Err 59: AC input relay test fault
Err 116: active calibration data loss
Err 117: firmware update cannot be completed
Err 119: settings data loss that returns after reconfiguration
Err 121: active tester failure
Err 200: internal DC voltage error
Err 201: internal DC voltage measurement error
Err 202: internal residual-current sensor error
Err 203, Err 205, Err 212, and Err 215: internal supply-voltage error
Final Field Checklist
Before replacing a charger, check the basics one more time:
Confirm the exact error code.
Check whether it is active or historical.
Measure the real battery-bank voltage.
Compare that voltage with the charger setting.
Check absorption, float, and equalization settings.
Inspect battery cables, PV cables, and sense wires.
Tighten terminals to the correct torque.
Look for heat marks, corrosion, and poor crimps.
Calculate PV open-circuit voltage at the lowest expected site temperature.
Confirm PV current and power are within the charger rating.
Check whether another charger is raising the battery voltage.
Confirm BMS communication and charge permission.
Check data cables and network settings in multi-device systems.
Improve ventilation if temperature codes appear.
Retry firmware only with the correct package for the exact device.
Restore factory defaults only when configuration data is lost or a reset is required.
Call a qualified technician if internal sensor, relay, power-stage, firmware, calibration, or internal voltage faults remain active.
