What is BMS (Battery Manager System)
What does BMS mean?
A battery management system (BMS) is an electronic system, usually a circuit board, that manages rechargeable batteries (cells or packs). It can extend the service life of the battery and protect the safety of electronic products by protecting the battery from working within a set range.
Why do we need BMS?
Temperature monitoring:
If the battery supplies a large amount of current for a long time, it may cause the battery to run out of control, resulting in a fire. The chemicals used to make batteries are highly volatile, and punctures by sharp objects can also cause batteries to catch fire. Among other things, temperature data can be used to determine whether the battery needs to be charged or discharged.
Data analysis and prediction:
The data collected by the BMS can be used to analyze the status and performance of the battery. Through historical data analysis, BMS can predict the future status and potential problems of the battery.
Status estimation:
BMS calculates the status parameters of the battery, such as remaining capacity (SOC) and state of health (SOH). This information helps users understand the current status and expected life of the battery.
Fault diagnosis:
BMS can diagnose potential problems with the battery by analyzing historical data and trends of battery parameters. This includes identifying mismatched battery cells, performance degradation, and other anomalies.
Hazardous handling:
If a battery problem is detected, BMS takes immediate action to protect the battery and the user.
Safe power-off:
When dangerous situations such as overcharge, over-discharge, overheating or short circuit occur, BMS will immediately disconnect the battery’s power supply to prevent the situation from deteriorating further.
Alarm and notification:
When the BMS detects a problem, it will alert the user or maintenance personnel and provide fault diagnosis information when necessary so that timely repair or replacement measures can be taken.
How does the battery management system(BMS) work?
Monitoring the voltage of each cell within a battery pack is critical to determining its overall health. All batteries have a voltage range. Make sure to charge and discharge within the range to ensure normal operation and battery life.
In the case of lithium-ion batteries, the operating voltage is typically between 2.5V and 4.2V. The voltage range depends on the chemical composition. Operating the battery outside the voltage range will significantly shorten the battery life and may cause the battery to fail.
SOC (State of Charge) and SOH (State of Health) are two important parameters used by BMS to evaluate and monitor battery status:
SOC (State of Charge):
This is a measure of the remaining power of a battery, usually expressed as a percentage.
SOC tells us how much energy is left in the battery, or how long the battery can be used when fully charged to its current state.BMS calculates SOC in real time by monitoring the battery’s charge and discharge current, voltage and other parameters so that users know when they need to be charged.
SOH (State of Health):
This is a measure of battery health, usually expressed as a percentage.
SOH reflects the battery’s current performance and capacity relative to new condition. The SOH of the battery will decrease with time and use, which is due to the decrease in capacity and increase in internal resistance caused by battery aging and long-term use.
BMS evaluates the SOH of the battery by long-term monitoring of the battery’s charging status, temperature, number of charge and discharge cycles and other factors.
By monitoring SOC and SOH, BMS can optimize the battery’s charge and discharge process. BMS uses SOC and SOH data to prevent potentially dangerous situations such as battery overcharge, over discharge, and overheating. Extend battery life and ensure batteries are operating at their best. Maintenance personnel can identify and resolve problems promptly.
Differences between car BMS and home energy storage BMS:
Although automotive BMS and home energy storage BMS are similar in basic functions, that is, monitoring and managing the status of the battery to ensure safety and improve efficiency, they have some differences in design and functional requirements:
| Category | Automotive BMS | Home Energy Storage BMS |
|---|---|---|
| Environmental Adaptability | Needs to adapt to a broader temperature range and harsher environmental conditions. Designed to be more robust to ensure normal operation under various conditions such as severe vibrations, high temperatures, or low temperatures. | Typically operates in a relatively stable and controlled environment, so might not need harsh environmental adaptability. |
| Performance Requirements | Needs to support high-speed charging and discharging. Must monitor and manage battery status in real-time to adapt to dynamically changing load demands. | Usually faces stable charging and discharging cycles with smaller load variations, thus lower immediate performance requirements. |
| Functionality and Complexity | May integrate more advanced features for complex vehicle application needs such as data exchange, fault diagnosis, and energy recovery management. | Focus more on battery life management, energy optimization, and safety protection, important for interoperability with HEMS or smart grids. |
Other Battery Management System Building Blocks
Other BMS functional blocks include battery authentication, real-time clock, memory and daisy chain. A real-time clock and memory are used in black box applications, where the RTC is used for timestamps and the memory is used to store data, allowing users to understand the behavior of the battery pack before a catastrophic event occurs.
The battery authentication block prevents BMS electronics from being connected to third-party battery packs. Voltage references/regulators are used to power peripheral circuits around the BMS system.
Finally, daisy chain circuits are used to simplify connections between stacked devices. Daisy-chain modules replace the need for optocouplers or other level-shifting circuits.
What is the role of BMS?
In actual use, batteries are connected in series or parallel to form a battery pack. Parallel connection increases the current drive of the battery pack, while series connection increases the overall voltage.
The charging performance of a battery changes with the amount of charge inside the battery: at time zero, the cells in the pack are charging and discharging at the same rate. As each cell cycles between charging and discharging, the rate at which each cell charges and discharges changes, resulting in varying power conditions across the entire battery pack.
When BMS is introduced to control the battery, it can effectively avoid the situation where some batteries are fully charged and other batteries are not fully charged, thereby protecting the battery and extending the life of the battery.
To ensure battery safety:
BMS can monitor the key parameters of the battery, such as voltage, current and temperature, and promptly detect and prevent dangerous situations such as overcharge, over-discharge, overheating, etc., thereby preventing battery damage and potential safety accidents. For example, if the BMS detects the battery temperature is too high, it can activate the cooling system or disconnect power to prevent a thermal runaway event.
Improve battery performance and efficiency:
By ensuring the battery operates at optimal working condition, BMS helps improve overall system energy efficiency and performance. For example, BMS can ensure that the battery pack is evenly charged and discharged by balancing the state of charge between battery cells, which helps improve the overall performance and efficiency of the battery pack.
Extend battery life:
BMS reduces battery aging and wear by controlling the charge and discharge process and conditions, extending battery life. For example, by preventing deep discharge and overcharging of batteries, BMS can reduce battery wear and extend its service life.
Real-time monitoring and diagnosis:
BMS provides real-time battery status information, including remaining power (SOC) and health status (SOH), helping users understand battery status and make appropriate usage decisions. In addition, BMS can also help diagnose battery problems and repair or replace them on time.
Meet regulatory requirements:
In many countries and industries, to ensure the safety of electric vehicles and battery energy storage systems, there are clear regulations requiring the installation of BMS.
What is the best BMS?
There are usually no fixed or unique standards for BMS. Technical design scope and implemented functionality are typically related to the following factors:
- Battery pack cost, complexity and size.
- Battery application and any safety, longevity and warranty issues.
- Certification requirements from various government regulations, costs and penalties will be critical if functional safety measures are inadequate.
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