lithium battery BMS reset

In most cases of faults requiring a lithium battery BMS reset, the most common cause is an unstable power supply due to plug/wiring or fuse issues, which triggers BMS protection.

Troubleshoot in order of increasing difficulty (each step: phenomenon → possible causes → solutions → precautions):

1) Check the main power switch/key/monitor

• Symptom: The vehicle/in-vehicle instrument panel is completely unresponsive, or there is power but the drive cannot be activated.
• Possible causes: main power switch not turned on, key switch in the wrong position, or BMS not powered on due to panel standby.
• Solution: Confirm that the main switch, key, and instrument panel are in the normal open position; turn off the power, wait 30 seconds, and then restart once.
• Precautions: Before restarting, ensure there are no dangerous personnel nearby to avoid accidentally turning on the power while in maintenance mode.

2) Check the fuses and circuit breakers (fuse)

• Symptom: No power supply to the vehicle or BMS, or intermittent power supply interruption.
• Possible causes: The main fuse, BMS input fuse, or external circuit breaker is blown or has poor contact.
• Solution: Disconnect the main power supply and check if the relevant fuses are blown or burnt; replace the fuses or circuit breakers with the original specifications.
• Precautions: When replacing, you must use the same rated value as the original; do not arbitrarily replace it with a larger rated value; disconnect the power supply before operation.

3) Check the plug and wiring (poor plug contact).

• Phenomenon: The fault occurs randomly and disappears/appears when vibrated or moved; the contact heats up or flickers during charging.
• Possible causes: Oxidation, looseness, or incorrect insertion of the battery pack main connector, BMS plug, or charger plug.
• Solution: After powering off, unplug and check if the contacts are oxidized, deformed, or burned; clean the contacts (with electrical contact cleaner), tighten the terminals, or replace the damaged plug; replug and confirm that the latch is in place.
• Precautions: When operating under power failure, ensure correct polarity; avoid short-circuiting live terminals with metal tools.

4) Verify that the voltage of the entire assembly is compatible with the charger (voltage mismatch)

• Symptoms: The charger fails to start or trips shortly after starting; the BMS displays “charger voltage abnormal”.
• Possible causes: The charger’s output voltage/type does not match the battery pack’s nominal value; the battery pack voltage is too low, causing the BMS to lock the input.
• Solution: Measure the battery pack’s static voltage with a multimeter and compare it with the charger’s output specifications; use a charger that matches the battery’s nominal voltage and chemistry; for deeply discharged batteries, wake them up with a low current under controlled conditions (follow the manufacturer’s procedure).
• Precautions: Do not use a charger with a voltage higher than the battery’s rated voltage; avoid high current when waking up a deeply discharged battery to prevent damage to the cell or triggering protection.

5) Check BMS fault codes and protection types (BMS protection)

• Symptom: The BMS indicator light illuminates or the instrument panel displays a specific error code, and the vehicle is restricted from charging/discharging or enters protection mode.
• Possible causes: Overvoltage, undervoltage, overcurrent, abnormal temperature, or communication failure triggering BMS protection.
• Solution: Refer to the user manual to read the meaning of the error code; if it is undervoltage/overvoltage, charge to the recovery threshold with a suitable charger as recommended in the manual; if it is short circuit/overcurrent, check the load and wiring; try turning off the power (main switch) for 1-5 minutes and then turning it back on to perform a soft reset.
• Precautions: If the error persists or is unclear, do not blindly and repeatedly power on the device. Contact experienced repair personnel or manufacturer technical support to avoid secondary damage.

6) Low temperature protection prevents charging and discharging (low temperature protection)

• Phenomenon: Charging is prohibited or discharging is limited in cold environments, and the BMS indicates low temperature.
• Possible cause: The BMS detected that the cell temperature was below the safe charging threshold and automatically prohibited charging or limited discharging.
• Solutions: Move the battery pack to a warm environment or preheat it in a garage; use a charger with temperature detection and compensation and charge it within the manufacturer’s set temperature range; slow charging helps with warming up.
• Precautions: Avoid charging below the manufacturer’s specified temperature. Low-temperature charging will cause lithium metal to leach out and permanently damage the battery cell.

7) Individual cell voltage imbalance or cell degradation (voltage mismatch/individual cell problem)

• Phenomenon: The overall voltage is normal, but there are large differences between individual units. The BMS repeatedly enters equalization or protection mode, or the voltage of a certain section is significantly lower.
• Possible causes: inconsistent cell capacity, aging of individual cells, or failure of the equalization circuit.
• Solution: Measure the voltage of each cell (or group) using a battery management tool while the battery is safely disconnected; if the difference is large, try equalization charging via BMS (if available); severe imbalance usually requires replacing the weaker cells or the entire battery module.
• Precautions: Replacement of individual battery cells requires the use of cells of the same model, capacity, and health condition; non-professional operation carries the risk of electric shock and fire, and is recommended to be handled by professionals.

8) BMS hardware or firmware failure (most difficult to handle)

• Symptoms: If the above steps fail to clear the fault, or if BMS communication fails, MOSFET is damaged, or firmware is abnormal.
• Possible causes: Damage to the BMS motherboard, communication module, temperature/voltage acquisition circuit, or firmware.
• Solution: Contact the manufacturer or authorized service center to read the logs using a dedicated diagnostic tool and perform firmware/parameter calibration; if necessary, replace the BMS module or the entire battery pack.
• Precautions: The BMS is a critical component for high-voltage safety. Non-professionals should not disassemble or solder the BMS motherboard; retain the original factory configuration to ensure compatibility and safety.

When should the charger be replaced?

• The charger is physically damaged (burnt casing, unusual smell, smoke) or has no power output.
• The charger’s output voltage/current deviates significantly from the nominal value or the BMS is frequently triggered during charging and the fault only occurs when the charger is used.
• The charging speed became abnormally slow, the charging time continued to increase, and there was no improvement even after multiple checks confirmed that the battery and wiring were normal.

Three recommended criteria for choosing a charger: 1) Output specifications match the battery: The output voltage must match the nominal voltage of the battery pack, and the output current should be within the battery’s allowable charging current range (commonly CC/CV mode). 2) Comprehensive intelligent and protection functions: Supports constant current/constant voltage (CC/CV), overcharge/overheat/short circuit protection, temperature sensor interface, and cell balancing function (if the battery supports balancing). 3) Quality and compatibility: Choose products with certifications (CE/UL, etc.), manufacturer technical support, and correct connectors/wiring harnesses; prioritize suppliers with charging procedures specific to the battery chemistry used (e.g., lithium iron phosphate/Li-ion).

If needed, I can quickly determine whether the voltage is compatible or recommend several suitable charger models based on your battery pack’s rated voltage/chemistry and charger parameters.