What does a Battery Management System (BMS) manage?

In new energy vehicles, energy storage power stations, and lithium battery equipment, the safe, efficient, and long-life operation of lithium battery packs relies heavily on a BMS (Battery Management System). Many people only know that batteries have power and can store energy, but they are unaware that the BMS is the crucial "brain" of the battery. This article, combining five core functions, fully breaks down the key aspects of battery management managed by the BMS.

The entire BMS chip works around five dimensions, forming a complete battery management closed loop: sensing, protection, balancing, thermal management, and communication.

1. Sensing: Real-time Monitoring, Understanding the Complete State of the Battery

The BMS is like the "five senses" of the battery, continuously collecting three core data points 24/7: voltage, current, and temperature. Through total voltage, individual cell voltage, total circuit current, and multi-point temperature data collection, it accurately captures the real-time operating conditions of each cell, providing the data foundation for all functions.

2. Protection: Four-fold shield to safeguard battery safety. Based on data collected by sensors, the BMS incorporates a four-layer safety protection mechanism to eliminate the risks of battery fire, bulging, and failure: overcharge protection, over-discharge protection, overcurrent protection, and over-temperature protection. Once the data reaches a dangerous threshold, the circuit is immediately cut off and power is limited.

3. Balancing: Cell coordination for synchronized charging and discharging. Lithium-ion battery packs consist of dozens or even hundreds of cells connected in series. Differences in cell capacity and voltage can occur between the factory and long-term use, and the "weakest link" effect significantly reduces the overall usable capacity of the pack. The balancing function unifies cell voltage, eliminates voltage differences, and improves the overall battery capacity and lifespan.

4. Thermal Management: Maintaining optimal battery operating temperature. Lithium-ion battery performance is highly temperature-dependent: low-temperature charging easily leads to lithium plating and cell damage, while high-temperature charging and discharging accelerates degradation and poses safety hazards. The BMS, in conjunction with the thermal management system, activates heating elements to preheat the battery at low temperatures and activates fans and liquid cooling pipes to dissipate heat at high temperatures, locking the battery within its optimal operating range.

5. Communication: Upward and downward communication, facilitating information exchange between the vehicle and the user.

The BMS acts as the battery's external "spokesperson." Internally, it collects data from each cell via a daisy-chain connection. Externally, it interacts with the vehicle's VCU and charging stations via the CAN bus, simultaneously synchronizing data to the cloud and a mobile app. It can output power and battery level signals to the vehicle and display remaining range and battery health status to the owner.

ACEY-BP24-300A400A bms tester machine is a high-precision testing platform designed for comprehensive functional verification of lithium battery protection boards and battery management systems (BMS).

1. Comprehensive Collection of Raw Battery Data

The BMS relies on four types of data acquisition hardware to achieve data sensing:

• Total Voltage Measurement: Detects the overall voltage of the battery pack to determine the overall energy reserve;
• Individual Cell Voltage Measurement: Collects the voltage of each individual cell to accurately locate faulty cells with abnormal voltage;
• Total Current Measurement: Monitors the charging and discharging circuit current to calculate the amount of charge and discharge;
• Multi-point Temperature Measurement: Deploys temperature probes at multiple locations within the battery pack to monitor cell temperature rise in real time.

After collecting raw data, the BMS automatically calculates four core state parameters, transforming the raw data into effective information that users and the vehicle can understand.

2. Four-fold Protection Shield

Upon detecting abnormal data, the BMS immediately activates tiered protection to eliminate the risk of thermal runaway at its source:

• Overcharge Protection: When the cell voltage reaches its upper limit during charging (4.25V for conventional lithium batteries), the charging circuit is automatically disconnected, preventing further charging and cell bulging and fire.
• Over-discharge Protection: When the discharge voltage drops to its lower limit (2.8V for conventional lithium batteries), the discharge output is cut off to prevent permanent damage from deep cell depletion.
• Overcurrent Protection: When the charging/discharging current exceeds the safety threshold, the fuse or high-voltage switch is triggered to disconnect, preventing high current from breaking down the cell.
• Over-temperature Protection: When the battery temperature exceeds the safety limit (typically 55℃), the output power is limited or even shut down, initiating cooling and heat dissipation.

In short: Sensing is the BMS's eyes, protection is its hands and feet; only by accurately identifying danger can it quickly take action to protect battery safety.

1. Cell Balancing: Overcoming the Barrel Effect and Maximizing Battery Capacity
When multiple cells are connected in parallel or series, a significant voltage difference occurs: during charging, the cell with the highest voltage is fully charged first, forcing the system to stop charging, while the remaining lower-voltage cells cannot be fully charged; during discharging, the cell with the lowest voltage is discharged first, forcing the system to shut down, while the high-voltage cells still retain a large amount of charge. This is the barrel effect, where the weakest link cell determines the overall usable capacity of the battery pack. The BMS smooths out the cell voltage difference through two balancing methods:

Passive Balancing: Relies on resistors to dissipate excess charge from high-voltage cells as heat. This method is simple in structure and low in cost, but energy is wasted. It is mostly used in low-cost energy storage and low-speed equipment.

Active Balancing: Uses capacitors and inductors as energy carriers to transfer excess charge from high-voltage cells to low-voltage cells. This method has no energy waste and high balancing efficiency, and is widely used in mainstream new energy vehicles and high-end energy storage.

After balancing, the cell voltages are consistent, increasing the usable capacity of the battery pack and significantly extending its cycle life.

2. Dual-layer communication network for data interoperability

BMS communication consists of two networks: internal and external.

• Internal communication (daisy-chain): Cell acquisition chips are connected in series to synchronously collect voltage and temperature data from each cell, which is then aggregated to the main control MCU.
• External communication (CAN bus + cloud): Interacts with the vehicle controller (VCU) and charging piles via CAN lines; simultaneously, data is uploaded to the cloud platform and mobile app, allowing owners to check battery level, range, battery health, and fault alarms at any time.

Lithium batteries are extremely temperature-sensitive energy storage components: Low ambient temperatures can cause lithium deposition inside the cells during charging, permanently damaging battery capacity; continuous high-power charging and discharging at high temperatures accelerates electrolyte decomposition, easily leading to thermal runaway. The BMS (Battery Management System) works in conjunction with the entire thermal management system to achieve bidirectional temperature control:

• Low-temperature conditions: Built-in heating elements are activated to evenly heat the battery pack, allowing high-power charging and discharging only after reaching a suitable temperature;
• High-temperature conditions: Cooling fans and liquid cooling pipes are activated to remove heat from the cells, reducing the overall temperature of the battery pack, while limiting output power to prevent further overheating. A stable temperature control environment is crucial for extending battery cycle life and preventing safety accidents.

If we compare a lithium battery pack to a warehouse, and the cells to shelves storing electrical energy, then the BMS is the all-round manager, acting as a butler, bodyguard, doctor, and coordinator:

Whether it's new energy passenger vehicles, electric tricycles, electric bicycles, industrial and commercial energy storage, or portable lithium battery devices, a well-designed and fully functional BMS is a core prerequisite for the safe and stable operation of lithium battery systems, and an indispensable core component in the research, development, production, and recycling processes of the lithium battery industry.

We provide lithium battery BMS and BMS testing equipment. Please feel free to contact us if you have any questions.

Acey New Energy is specialized in researching and manufacturing of high-end equipment for lithium-ion batteries. We can provide one-stop solution for lithium battery pack assembly line, if you are new in lithium ion battery industry, and want to build your own lithium ion battery production line or lithium ion battery pack assembly line, we can provide you professional technical support and guidance, please feel free to contact us!

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