JKESS Basic Knowledge of High Voltage Battery Management System

Caution

Working with high voltage is dangerous. Always follow local laws and regulations regarding high voltage work. If you are unsure about the rules in your country, consult a licensed electrician for more information.

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First Purchase FAQ：

If you have rarely dealt with high voltage energy storage before, the following FAQs will be of great help to you.

1.What is a BMS? What is it used for?

BMS stands for Battery Management System, which is like the "brain" of the battery. It is responsible for protecting the battery, monitoring voltage and temperature, preventing overcharging and over-discharging, and extending battery life.

2.What is included in the BMS sold?

We offer complete energy storage solutions: Small high-voltage BMS kits; Industrial and commercial energy storage cabinets, BMS and kits; High-voltage boxes; Master and slave controllers; Data acquisition harnesses, communication harnesses, power harnesses; Temperature control probes, plugs, fuses, and other accessories.

3.What are the differences between small high-voltage kits and industrial/commercial energy storage BMS?

Small high-voltage kits: Compact size, easy installation, suitable for homes, small devices, and small energy storage.

Commercial and industrial energy storage BMS: Higher power and safer, suitable for factories, large energy storage cabinets, and power plants.

4.What are the functions of the master controller and the slave controller?

Main controller: The central controller, responsible for overall control, protection, and connection to the computer/backend.

Slave controller: Responsible for collecting the voltage and temperature of each battery cell and performing equalization.

5.What is the purpose of a high-voltage box? Is it optional?

The high-voltage box is responsible for the safety switch of the battery high voltage and is essential. Without it, there is a risk of electric shock, fire, and equipment damage.

6.What is pre-charge? Why is it necessary?

Pre-charging serves as a safety buffer before startup, preventing damage to the equipment from high current surges. Without pre-charging, contactors are more likely to burn out, triggering protection mechanisms.

7.What is a wiring harness? Why buy the whole set?

The wiring harness connects the BMS and the battery, and is essential for voltage and temperature data acquisition and communication. Incompatible wiring harnesses can lead to inaccurate data and malfunctioning protection systems.

8.What is the purpose of a temperature probe (NTC)?

Monitor battery temperature to prevent overheating or undercooling, thus avoiding fire, damage, and rapid decline in battery life.

9.What is battery balancing? Why is it important?

Balancing ensures that the voltage of each battery cell remains consistent, preventing any single cell from being overcharged or over-discharged, thus improving the overall battery pack lifespan and capacity.

10.How accurate is the SOC (State of Charge) percentage?

It is factory calibrated, and will be even more accurate after a full charge and discharge cycle. We can provide remote calibration assistance.

11.What hazardous situations does BMS protect against?

1. Overvoltage, undervoltage

2. Overcurrent, short circuit

3. Overtemperature, undertemperature

4. Precharge failure

5. High-voltage circuit disconnected

6. Communication abnormality

12.Can this BMS be exported to Southeast Asia and Europe?

Yes, our products are compatible with export standards, we provide supporting documentation, and we support remote English language debugging.

13.I don't understand technology, can you help me with debugging?

Yes, we provide full remote debugging, wiring guidance, parameter configuration, and troubleshooting.

14.Does the BMS need to be connected to a computer?

Initial installation, parameter settings, and troubleshooting require connection to a computer; once running normally, it can operate independently without a computer.

15.Will this BMS be compatible with my battery?

We support standard lithium batteries. Just tell me the number of battery cells and the capacity, and we will match the corresponding model and configure it remotely.

Advanced Edition of Basic Knowledge on High Voltage Products FAQ：

After going through the above knowledge points, you have reached the beginner level. Next, we will study the key points of the entire high-pressure system.

BMS system

1.What is a BMS and what is its core function?

The BMS is the core control unit of the battery management system. It is responsible for monitoring battery voltage, current, temperature, and SOC/SOH, achieving equalization, overvoltage/undervoltage/overcurrent/overtemperature/low temperature protection, external communication and system linkage, and determining the safety, reliability and lifespan of the entire energy storage system.

2.Does the product support customized parameters?

Supports remote customization: protection points, equalization current, charging and discharging strategies, communication protocols, SOC calibration, port configuration, etc.

3.Does the product have protective features?

The entire system is equipped with multiple protections including overvoltage, undervoltage, overcurrent, overtemperature, low temperature, short circuit, equalization, pre-charge, and high voltage interlock.

Small high voltage kit

1.High-voltage box (including main control)

It is responsible for the switching of high-voltage circuits, driving of peripherals such as relays, pre-charging, and fans, short-circuit protection, communication, logic operations, protection strategies, parameter distribution, fault recording, and external communication (485/CAN/Ethernet), and is the BMS control actuator.

2.Slave control

Collect individual cell voltage and temperature, perform equalization, and upload the data to the main controller.

3.Wire harnesses and accessories

Data Acquisition Harness: Connects the slave controller to the battery cell, acquiring the voltage of each individual cell.

Temperature Control Harness: Connects to the NTC probe, acquiring the temperature.

Communication Harness: CAN/485, enabling communication between the master controller, slave controller, and host computer.

Power Harness: High-current, high-voltage cable, connecting the battery, high-voltage box, and load.

Control Harness: Controls contactors, fans, indicator lights, etc.

System Features:

Bidirectional PCS + photovoltaic inverter; excludes batteries, BMS, temperature control, and fire protection. Customers must assemble their own battery clusters, BMS, and distribution cabinet. Inverters, batteries, and BMS come from different manufacturers; compatibility and certification must be handled entirely by the customer. Primarily used in small shops, small factories, high-spec residential applications, and small-scale photovoltaic-storage systems.

Typical Power/Capacity: Mainly 10kW～100kW

Capacity: 50kWh～120kWh

Voltage: Mostly high voltage (DC 200～850V, AC 400V / three-phase)

Commercial and industrial energy storage cabinet (integrated commercial and industrial energy storage cabinet)

1.Air-cooled energy storage cabinet

Fan + airflow cooling: Low cost, simple structure. Suitable for: Small capacity, mild environment, limited budget. Disadvantages: Large temperature difference, high noise, and average protection level.

2.Liquid-cooled energy storage cabinet

Liquid cooling plate / immersion cooling.
Small temperature difference (<3℃), long lifespan, high efficiency, good protection.
Suitable for: high power, high density, export to the EU, high/low temperature environments.

System Features:

This is a plug-and-play energy storage system that integrates battery clusters, BMS, PCS, EMS, temperature control, fire protection, and power distribution into a single outdoor/indoor standard cabinet. It is specifically designed for industrial and commercial users such as factories, shopping malls, office buildings, data centers, and industrial parks.

Typical Power/Capacity:

Power: 50kW～500kW

Capacity: 100kWh～500kWh

Voltage: Mostly high voltage (DC 600～1000V, AC 400V/three-phase)

Equalization function

1.Passive Equilibrium

The high-voltage battery cell energy is consumed by resistors, resulting in a simple structure, low cost, and low efficiency.

2.Active Equilibrium

Energy transfer between battery cells is achieved through inductors/capacitors, resulting in high efficiency, low heat generation, but also high cost.

Customers need to consider their budget, cell consistency, and system capacity when selecting a model.

High-voltage box

1.Typical internal structure of high-voltage box

Main positive/negative contactor
Pre-charge contactor + pre-charge resistor
High-voltage fuse
High-voltage circuit breaker
Current sensor
Heat dissipation/fan control
Main control BCU, WIFI module, screen

2.What is pre-charging and why is pre-charging necessary?

Pre-charging involves slowly charging the downstream capacitor with a small current before the main contactor closes, preventing damage to the contactor, bus capacitor, or battery cells from a large current surge. Closing the circuit directly without pre-charging can lead to arcing, burnt contacts, and overcurrent protection failure.

3.What is the function of HVIL high-voltage interlock?

The mandatory disconnection of high-voltage output when the high-voltage box door is opened or the wiring harness is disconnected is an essential safety mechanism for exporting to Europe and Southeast Asia to prevent electric shock.

SOC&SOH

1.SOCS(tate of Charge)

Battery percentage reflects the current remaining capacity.

2.SOH(State of Health)

Battery health reflects the degree of degradation in the battery's maximum usable capacity.

What are the different protection levels of a BMS?

1.Level 1 alarm

Limit power/reduce current, issue an alarm, and do not disconnect the main circuit breaker.

2.Level 2 protection

When the power limit is 0, charging and discharging will stop, an alarm will be issued, and the main circuit breaker will not be tripped.

3.Level 3 protection

Disconnect charging and discharging to force shutdown.

Common BMS Communication Protocols

1.CANopen

CAN1 and CAN2 connect to PCS or MES.

2.Modbus RTU

RS485_1 and RS485_2, sensors for screens, air conditioners, fire protection systems, and water immersion systems, etc.

Installation and Wiring of High voltage System FAQ：

After going through the above knowledge points, you have reached the beginner level. Next, we will study the key points of the entire high-pressure system.

Precautions

What are the safety red lines when using a BMS?

After receiving the goods, You didn't know how to install or connect them. The following knowledge points can teach you how to do it. Please save this link.

Before BMS installation

What preparations must be made before installing a BMS?

Power Off Confirmation: Ensure the battery pack is completely powered off, with no residual voltage at the positive and negative terminals (measured with a multimeter).

Environmental Check: The installation location should be dry, well-ventilated, away from flammable and explosive materials, and with sufficient space for heat dissipation (≥10cm).

Tools Preparation: Insulated screwdriver, crimping pliers, multimeter, heat shrink tubing, cable ties, insulating tape.

Data Verification: Confirm that the BMS model matches the battery string count and voltage; verify that the wiring diagram matches the actual interface.

Personnel Protection: Wear insulated gloves and safety goggles; avoid direct contact with high-voltage terminals.

What needs to be confirmed before connecting the BMS after the battery cells are connected in series and parallel?

Total Voltage: Meets the BMS rated voltage range (maximum ≤1000V).

Individual Cell Voltage Difference: After standing for 1 hour, the voltage difference between all individual cells should be ≤50mV (excessive voltage difference requires equalization).

Positive and Negative Terminals: The positive and negative terminals of the battery pack are clearly marked, eliminating the risk of reverse connection.

Insulation Resistance: The insulation resistance of the battery pack to ground, measured with a megohmmeter, should be ≥1MΩ (essential for high-voltage systems).

What are the key considerations for wiring the data acquisition harness?

Correspondence: The slave control acquisition port number corresponds one-to-one with the battery cell number (e.g., slave control CELL1 connects to the positive terminal of battery cell 1, CELL2 connects to the positive terminal of battery cell 2, and so on).

Polarity Prohibition: Reversing positive and negative terminals or connecting across sections (e.g., skipping battery cells and connecting directly) is strictly prohibited.

Secure Contact: Terminals must be crimped in place, without looseness or poor connection (you can gently pull the wire harness to confirm it does not come loose).

Insulation Protection: The acquisition cable connectors are wrapped with heat shrink tubing to prevent short circuits; the wire harness is kept away from power lines to reduce interference.

Redundancy: A 5-10cm redundancy length is reserved in the acquisition cable to prevent the connector from coming loose due to pulling.

What are the key requirements for wiring communication lines (CAN/485)?

CAN Cable:

Cable Selection: Use shielded twisted-pair CAN cable (e.g., CAN-H, CAN-L twisted, shield grounded).

Termination Resistor: A 120Ω termination resistor must be connected to both ends of the bus (master terminal and the furthest slave/host computer terminal).

Polarity Distinction: Connect CAN-H to CAN-H, CAN-L to CAN-L. Reversing the connection is strictly prohibited (reversed connection will result in no communication and no error message).

Shield Grounding: Ground at one end (master terminal grounded recommended) to avoid circulating current interference caused by grounding at both ends.

485 Cable:

Polarity Distinction: Connect A to A, B to B, common terminal GND is optional (recommended for long distances).

Cable Requirements: Shielded cable, length not exceeding 1200 meters (repeater required for longer distances).

What are the steps and precautions for wiring the high-voltage box and BMS?

Steps:
1. Connect the high-voltage box control lines (contactor drive, pre-charge signal, HVIL circuit) to the corresponding ports on the main controller.

2. Connect the current sensor signal line to the main controller (ensure the positive and negative polarities align with the current flow direction).

3. Connect the high-voltage box cooling fan control line (if applicable).

4. Check the polarity of all control lines; secure the wiring harness after confirming no reverse connections.

Precautions:
High-voltage terminals: Tighten to the required torque (generally 8-10 N·m for M5 bolts) to avoid loosening and overheating.

HVIL circuit: Ensure good contact at the interlocking contacts of the high-voltage box door and wiring harness connectors; the circuit should trigger an alarm upon disconnection.

Pre-charge circuit: Ensure the pre-charge resistor wiring is secure and free of loose connections (loose connections will cause pre-charge failure).

What are the installation location and wiring requirements for the temperature control probe (NTC)?

Installation Location: Place the probe firmly against the surface of the battery cell (preferably near the positive terminal or in the middle of the battery pack where heat dissipation is poor), and secure it with cable ties to prevent it from being suspended in the air.

Wiring Requirements: The probe wires must be undamaged and free of short circuits, and the lengths must be compatible (avoid pulling).

When using multiple probes, the probe number must match the channel number set on the main control panel (e.g., probe 1 connects to the main control panel's TEMP1 port).

Do not attach the probe to power lines or the surface of heating elements (this will cause temperature detection distortion).

What are the safety regulations for power harness wiring?

Wire Diameter Matching: Select the wire diameter based on the system's maximum current (e.g., 16mm² copper wire for 100A current) to avoid overheating due to insufficient wire diameter.

Insulation Protection: Wrap power line connectors with insulating sleeves and keep them away from data acquisition and communication lines (distance ≥ 5cm).

Positive/Negative Polarity Marking: Clearly distinguish positive and negative polarities using red/black tape or labels to avoid reverse connection.

Securation Requirements: Secure the power line with brackets or cable ties to prevent vibration from causing the connectors to loosen.

BMS installation in progress

What are the self-test steps before powering on after installation?

Wiring Harness Inspection:

Acquisition Cables: No reverse connections, skipped connections, or loose connections; terminals are properly crimped.

Communication Cables: CAN/485 polarity is correct; terminating resistors are installed.

High-Voltage Control Cables: HVIL circuit continuity is normal; pre-charge circuit wiring is correct.

Power Supply: Main control power supply voltage meets requirements (e.g., 12V/24V); positive and negative terminals are not reversed.

Multimeter Testing: No short circuits at either end of the acquisition cables (measure resistance between adjacent acquisition cables; it should be infinite).

No short circuits between the communication cable shield and core wires.

No short circuits between high-voltage terminals; total voltage is normal.

After BMS installation

What is the correct operating sequence for the first startup after power-on?

Steps:

1. Power on the main controller (low voltage) and observe whether the main controller indicator lights are normal (power light on, no fault lights or alarms).

2. Connect the debugging software and read the slave controller communication status (all slave controllers are online, no disconnections).

3. Read the individual unit voltage and temperature data (data is stable, no abnormal values ​​such as 0V or full scale).

4. Trigger the pre-charge test (software or hardware trigger) and confirm successful pre-charge (pre-charge time is generally 1-3 seconds).

5. Close the main contactor and observe that there are no abnormalities before connecting the load or charger.

Incorrect installation operation

What are some common mistakes made during installation? What are the consequences?

Error 1: Reverse connection of acquisition lines/crossing sections → Consequences: Incorrect voltage acquisition, undervoltage/overvoltage fault reports, damage to slave control acquisition ports.

Error 2: Reverse connection of communication lines/missing terminating resistor → Consequences: No communication, data packet loss, parameters cannot be sent.

Error 3: High-voltage terminals not tightened → Consequences: Excessive contact resistance causing overheating, terminal burning, fire hazard.

Error 4: Temperature control probe not secured → Consequences: Inaccurate temperature detection, false triggering of over-temperature protection, risk of battery overheating.

Error 5: Connection without power disconnection → Consequences: Electric shock, short circuit, damage to BMS or battery.

Debugging and Fault Diagnosis FAQ：

Collection link. The following content will cover debugging and troubleshooting. Professional high-voltage energy storage engineers share FAQ.

Fault Category:Power supply faults

1.Fault phenomenon:The high-voltage box is not powered on, and the power indicator light is off.

Possible reasons:

1. Insufficient power supply voltage/reverse connection;

2. High-voltage box manual ON/OFF position;

3. Loose/damaged main control power interface;

4. Power supply failure.

Investigation steps:

1. Use a multimeter to measure the power supply voltage (e.g., 12V/24V) to confirm it meets requirements and that the positive and negative terminals are not reversed;

2. Check the manual ON/OFF status of the high-voltage box;

3. Re-plug the power connector to check for looseness;

4. Replace the power supply (e.g., adapter, battery) and test if the power supply is normal.

Solution:

1. Adjust the power supply voltage and correct the polarity;

2. Switch to the ON position;

3. Repair or replace the main control power interface;

4. Replace the faulty power supply.

2.The high-voltage box was powered on and then immediately de-energized.

Possible reasons:

1. Insufficient power supply current;

2. Main control unit short circuit (internal fault);

3. Overload protection triggered.

Investigation steps:

1. Check if the rated current of the power supply meets the main control requirements (generally ≥2A);

2. Disconnect all loads on the main control (such as slave controllers and contactor drives), and supply power to the main control alone. Observe if there is a power failure;

3. Use a multimeter to measure the resistance to ground of the main control power supply terminal. If it is 0Ω, it indicates an internal short circuit.

Solution:

1. Replace with a power supply with one that provides higher current;

2. If power loss persists even with a separate power supply, the main controller is faulty; request a replacement;

3. Check for short circuits in the load, repair them, and then reconnect.

Fault Category:Communication failures

1.Communication between the host computer and the BMS was interrupted.

Possible reasons:

1. Communication protocol incompatibility;

2. Wiring error;

3. Communication address conflict;

4. BMS communication parameter setting error.

Investigation steps:

1. Confirm that the communication protocol (e.g., Modbus RTU, CANopen) and channel selection are consistent between the host computer and the BMS;

2. Check the RS485/CAN/Ethernet wiring to ensure it is correct;

3. Ensure that the BMS communication address does not conflict with other devices;

4. Verify the BMS communication parameters (e.g., baud rate, data bits, stop bits, parity bits).

Solution:

1. Standardize communication protocol;

2. Correct wiring;

3. Reset BMS communication address;

4. Adjust communication parameters to match.

2.The host computer cannot connect to the main control unit.

Possible reasons:

1. Incorrect serial port number/baud rate settings;

2. Driver not installed/installation failed;

3. Loose/reverse connection of communication cable;

4. Damaged main control communication port;

5. Incompatible software version.

Investigation steps:

1. Verify the serial port number (check in Device Manager) and baud rate (default is generally 9600 for RS485/500k for CAN, refer to the manual);

2. Reinstall the driver (provide the corresponding driver file);

3. Check the communication cable connections (e.g., whether the high/low voltage/positive/negative polarity is reversed), and reconnect them;

4. Replace the communication cable and USB-to-serial adapter, and test if it works normally;

5. Upgrade the debugging software to the latest version.

Solution:

1. Correctly configure the serial port number and baud rate;

2. Install the matching driver;

3. Correct the communication cable wiring;

4. Replace the faulty communication device;

5. If the connection still fails, determine that the main control communication port is faulty and request repair.

3.Communication between master and slave controllers is abnormal (some/all slave controllers are out of service).

Possible reasons:

1. Communication line interruption;

2. Communication line reversed/loose/short circuit;

3. Slave control hardware failure.

Investigation steps:

1. Check the reliability of the communication lines at each node;

2. Check the CAN/485 communication cable wiring, correct any reverse connections, reconnect and unplug the connectors, and measure for short circuits (infinite resistance);

3. Connect each slave controller individually to the master controller to test for normal communication and locate the faulty slave controller.

Solution:

1. Reconnect the wiring harness;

2. Repair the communication line wiring and replace the damaged communication line;

3. Replace the faulty slave controller.

4.BMS and inverter (PCS) communication error / inverter has no BMS data or reports a communication error.

Possible reasons:

1. Communication line interruption;

2. Communication line reversed/loose/short circuit;

3. Incorrect communication interface definition;

4. Communication protocol mismatch.

Investigation steps:

1. Check the reliability of each node's communication line connection;

2. Check the CAN/485 communication line wiring, correct any reverse connections, reconnect and unplug the connectors, and measure for short circuits (infinite resistance);

3. Individually check the vehicle's BMS communication interface definition and the PCS interface definition;

4. Check if the BMS host computer correctly matches the inverter protocol.

Solution:

1. Reconnect the wiring harness;

2. Repair the communication cable connections and replace any damaged communication cables;

3. Re-tighten the communication connections;

4. Configure the correct communication protocol on the host computer.

Fault Category:Collection and protection type faults

1.Individual cell voltage acquisition is abnormal (displaying 0V / full scale / large fluctuations)

Possible reasons:

1. Loose, reversed, or short-circuited acquisition cable;

2. Damaged slave acquisition port;

3. Damaged battery cell (e.g., open circuit/short circuit);

4. Interference affecting the acquisition cable.

Investigation steps:

1. Reconnect and unplug the acquisition cable, check if the wiring is correct (corresponding to the cell number), and measure whether there is a short circuit/open circuit at both ends of the acquisition cable;

2. Replace the slave acquisition channel (e.g., connect the acquisition cable of the abnormal channel to the spare channel) and observe whether it returns to normal;

3. Directly measure the voltage of the abnormal cell with a multimeter. If the cell voltage is abnormal (0V/too high), replace the cell;

4. Check if the acquisition cable is close to the power line, rewire it, and add shielding measures.

Solution:

1. Repair the data acquisition cable wiring and replace the damaged data acquisition cable;

2. Replace the faulty slave controller;

3. Replace the damaged battery cell;

4. Optimize the wiring to reduce interference.

2.Temperature alarm (false alarm / no alarm)

Possible reasons:

1. Temperature probe not connected / connected backwards / damaged;

2. Poor probe contact;

3. Inappropriate temperature protection parameter settings;

4. Faulty slave temperature acquisition channel.

Investigation steps:

1. Check the temperature control probe wiring to ensure it is not reversed or loose. Measure the probe resistance (NTC probes are typically 10kΩ/50kΩ at room temperature). If the resistance is 0 or infinite, replace the probe.

2. Re-secure the probe, ensuring it is firmly attached to the battery cell surface and not suspended.

3. Verify the temperature protection parameters (over-temperature protection point is typically 45-55℃, under-temperature protection point is typically -10-0℃), and adjust according to actual needs.

4. Replace the slave temperature acquisition channel and test if normal operation is restored.

Solution:

1. Repair probe wiring and replace damaged probe;

2. Re-secure probe;

3. Adjust temperature protection parameters;

4. Replace faulty slave controller.

3.Total pressure reading is abnormal (displayed as 0V / actual value is different)

Possible reasons:

1. The main circuit connection of the power line is loose / the manual control is not turned on;

2. The main control acquisition port is damaged.

Investigation steps:

1. Reconnect and unplug the main power cable, check if the wiring is correct, and use a multimeter to directly measure the total voltage at both ends of the system to check for short circuits/open circuits. Confirm that the manual control is enabled;

2. Reinforce the main control acquisition channel connection and observe if it returns to normal.

Solution:

1. Unplug and replug the power cable, then close the manual switch;

2. Replace the faulty main control unit or replace the high-voltage box directly.

4.Charge/discharge protection shutdown (reports overvoltage/undervoltage/overcurrent/overtemperature faults)

Possible reasons:

1. Cell voltage/temperature exceeds protection range;

2. Protection parameter settings are inappropriate;

3. Current sensor malfunction;

4. Poor wiring harness contact;

5. Load/charger malfunction.

Investigation steps:

1. Use a multimeter to measure the total cell voltage, individual cell voltage, and temperature to confirm if the protection range is truly exceeded;

2. Verify the BMS protection parameters (overvoltage point is generally 1.1 times the nominal cell voltage, undervoltage point is 0.85 times, and overcurrent point is 1.2-1.5 times the system rated current). If the settings are unreasonable, adjust the parameters;

3. Check the current sensor wiring and measure the sensor output signal. If abnormal, replace the sensor;

4. Check the power harness and connectors for looseness and retighten them;

5. Disconnect the load/charger and test the BMS separately. If the protection no longer applies, troubleshoot the load/charger.

Solution:

1. Balance cell voltage / Adjust ambient temperature;

2. Optimize protection parameters;

3. Replace faulty current sensor;

4. Repair wiring harness contact issues;

5. Replace faulty load / charger.

5.The equalization function is not working.

Possible reasons:

1. Balancing function not enabled;

2. Cell voltage difference not reaching balancing threshold;

3. Balancing module damaged;

4. Abnormal communication between slave and master controllers;

5. Inappropriate balancing parameter settings.

Investigation steps:

1. Use debugging software to check if the equalization function is enabled (it is usually enabled by default). If not, manually enable it.

2. Measure the voltage difference of individual cells. If the voltage difference is less than the equalization threshold (generally 50-100mV), let the battery pack stand until the voltage difference reaches the threshold before observing.

3. Power on again, perform a system self-test, and determine the equalization status.

4. Check the communication between the master and slave controllers to ensure normal communication.

5. Adjust the equalization parameters (such as equalization current and equalization time).

Solution:

1. Enable the equalization function;

2. Allow the battery pack to stand still or manually create a differential pressure;

3. If a fault is displayed, replace the damaged slave control board;

4. Fix communication faults;

5. Optimize equalization parameters.

Fault Category:High-voltage box related faults

1.Pre-charge failed (pre-charge fault reported)

Possible reasons:

1. Precharge resistor damaged (open circuit/short circuit);

2. Precharge contactor faulty (not engaging/contacts stuck);

3. High-voltage circuit open circuit/short circuit;

4. Main control precharge signal not issued.

Investigation steps:

1. Measure the pre-charge resistance (typically 10-100Ω). If it is 0 or infinite, replace the pre-charge resistor.

2. Power the pre-charge contactor separately and observe if it engages. Measure the contact continuity. If faulty, replace the pre-charge contactor.

3. Check the high-voltage circuit (battery pack, high-voltage box, load) for open/short circuits and repair any faults.

4. Use debugging software to check if the main controller sends a pre-charge signal. If not, check the main controller parameter settings or for a main controller fault.

Solution:

1. Replace the pre-charge resistor;

2. Replace the pre-charge contactor;

3. Repair the high-voltage circuit fault;

4. Adjust the main control parameters or replace the main control unit.

2.The relay is not engaging (main contactor / precharge contactor)

Possible reasons:

1. Main control drive signal not issued

2. Contactor coil damaged/insufficient power supply

3. Contactor contacts stuck/mechanically jammed;

4. Protection status not deactivated (e.g., overvoltage/overtemperature protection).

Investigation steps:

1. Use an oscilloscope to measure the output of the main control drive port. If there is no signal, check the main control parameters or check for a main control fault.

2. Measure the contactor coil supply voltage (typically 12V/24V) to ensure normal power supply. Measure the coil resistance (typically tens of ohms). If abnormal, replace the coil or contactor.

3. Manually trigger the contactor and observe if it is stuck. If stuck, disassemble, clean, or replace the contactor.

4. Check the BMS protection status and disable any protections (such as cooling or voltage equalization).

Solution:

1. Repair the main control drive signal or replace the main control unit;

2. Ensure coil power supply and replace the faulty contactor;

3. Clean or replace the stuck contactor;

4. Deactivate BMS protection.

4. Adjust the main control parameters or replace the main control unit.