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BMS in Li-Po Battery

A lithium battery management system (BMS) is an electronic device that monitors and controls the status of lithium-ion batteries to protect them from abnormal conditions such as overcharge, over discharge, overcurrent, and short circuit. Its purpose is to extend battery life and ensure battery safety.   In this article, we will explore what a BMS is and why it is important for lipo batteries.

A BMS typically consists of battery management chips, sensors, control circuits, communication interfaces, and other components. It monitors battery voltage, current, temperature, and other parameters in real time, and controls and protects the battery according to preset parameters. BMS is widely used in electric vehicles, energy storage systems, solar panels, and other fields.

BMS: Li-ion VS Li-Po Battery

Li-Po batteries and lithium-ion batteries are both types of lithium batteries. Their battery management systems (BMS) operate on the same principles. They must monitor the battery’s voltage, temperature, current, and other parameters to achieve charge and discharge control and protection. However, due to the differing electrochemical characteristics of polymer lithium batteries and lithium-ion batteries, there may be some differences in the specific implementation of their BMS.

For example, lipo batteries have good voltage stability but are sensitive to temperature changes. Therefore, the BMS needs to control the temperature of the battery more accurately. On the other hand, lithium-ion batteries are relatively stable in temperature but sensitive to voltage changes. Thus, the BMS needs to control the voltage of the battery more accurately. Additionally, the charging and discharging characteristics of lipo batteries and lithium-ion batteries differ, so their BMS may differ in specific implementation.

Functions of Li-Po Battery BMS


BMS can monitor various status indicators of the Li-Po battery, including voltage (the voltage of a single cell, the total voltage, or a specific voltage in between), temperature (average temperature, the temperature of a single cell), input/output current, the health status of a single cell, and the equilibrium state of the cell


BMS can calculate the many indicators of the amount of values, including voltage(the minimum and maximum cell voltage), indicating that charging is in what level of state of charge(SoC), a measure of the capacity of the LIPO battery state of Health(SoH), the security of the state(SOS), the maximum charging current that the charge current limit(CCL), the maximum discharge current discharge current limit(DCL), determine the open-circuit voltage of the batteries internal resistance, the total energy, the total working time, temperature monitoring, etc.;


The central controller inside the BMS can communicate with the internal hardware, or it can communicate externally in various ways (such as USB, CAN, or wireless communication protocols). Communication function of BMS mainly includes the following several aspects:

Between the battery module of the communication:
The battery pack consists of a plurality of battery modules, each battery module has its own control circuit and the communication interface. Between the battery module through the communication interface to realize data exchange and sharing, in order to BMS for the whole battery pack to manage and control.

Battery status real-time monitoring:
BMS through the battery module of the communication between, you can real-time monitoring of battery voltage, current, temperature, capacity and state and other information, so that the battery pack is precise management and control.

Fault diagnosis and alarm function:
BMS battery via the communication between the modules can be achieved on the battery pack fault diagnosis and alarm function. Once you find the battery pack fails, the BMS will promptly issue an alert in order to take timely measures for repair or replacement


BMS can also be the battery for more protection, in order to prevent the battery pack state exceeds the safe operating area(SOA), such as the charge/discharge overcurrent, charge/discharge over-voltage, over-temperature, over-pressure, as well as current leakage and the like.


Battery equalization works by adjusting the monomer between the battery charge and discharge current, the battery pack in each cell of the battery remain the same. When the battery pack in a single cell of the battery is too high or too low, the BMS control system will automatically adjust the battery pack in the other Monomer battery charge and discharge current, which with the exception of the battery is equal to maintain the battery pack to the overall balance.

The battery equalizer’s main role is to extend battery life, avoid the battery pack in a single cell because of the power imbalance and lead to premature failure. In addition, the battery equalizer can also improve the battery safety performance, to avoid the battery over-charge and discharge as a result of accidents.

Importance of BMS

Functional safety in the BMS of the most important. In the charging and discharging during operation, to prevent by monitoring any cell or module of voltage, current and temperature exceeds the defined SOA limit is essential. If the limit is exceeded for a period of time, not only may damage may be expensive battery pack, and may appear dangerous thermal runaway conditions. In addition, strict monitoring of the low voltage threshold limits, in order to protect the lithium-ion battery and functional safety. If lithium-ion batteries maintain such a low voltage state, the copper dendrites may end up on the anode growth, which will lead to self-discharge rate increased and caused a possible security issues. Lithium-ion power system of the high energy density in the battery management error is almost no room for the price. Due to the BMS and lithium-ion improved, which is today the most successful and safe battery chemistry one.

Battery pack performance is the BMS of the next most important characteristic, which relates to the electrical and thermal management. In order to optimize the overall battery capacity, the need to balance the battery pack in all of the battery, which means that the entire Assembly is adjacent to the SOC of the battery is substantially equal. This is very important, because not only can achieve the optimal battery capacity, but also helps to prevent widespread degradation and the reduction due to weak battery Overcharge and cause potential hot spots. Lithium-ion battery should be avoided in below the low voltage limit decentralization of power, because this would lead to memory effect and a significant loss of capacity. The electrochemical process on the temperature of the highly sensitive, the battery is no exception. When the ambient temperature drops, the capacity and the available battery power is significantly decreased. Therefore, the BMS will probably resides in the use of electric vehicle battery liquid cooling system on an external line heater, or turn mounted on a helicopter or other device in a battery pack module below reside heater Board the aircraft. In addition, due to the low temperature lithium ion battery charging is not conducive to the battery life, performance, and therefore the first fully raise the temperature of the battery is very important. Most lithium-ion batteries at temperatures below 5°C when not fast charging below 0°C should not charging. In order to in a typical operation the use of the process to obtain the best performance of BMS thermal management is typically to ensure that the battery in the narrow adapted to run within the region to run for 30 – 35°C.

Benifits of BMS:

FUNCTION SAFETY:No doubt, for large size lipo battery pack, it is particularly prudent and necessary. But as is well known, even if it is a laptop such as the use of a smaller format also will catch fire and cause huge damage. Contains lithium-ion powered systems the products the user’s personal safety of the battery management error left a very small room.

LIFESPAN & RELIABILITY:  Lipo battery protection and management, electrical and thermal protection, to ensure that all batteries are in the Declaration of SOA within the required range of use. This delicate oversight to ensure that the battery is not subjected to excessive use and fast charging and discharging cycles, and will inevitably produce a stable system, the system may provide many years of reliable service.

PERFORMANCE: BMS battery pack capacity management, which uses the battery to the battery balance balancing battery pack Assembly adjacent to the SOC of the battery, in order to achieve the best battery capacity. If you do not have this BMS function to solve the self-discharge, charge/discharge cycle, temperature effects and aging in General the changes, the battery pack may eventually become useless.

COMMUNICATION & DIAGNOSTICS: Diagnosis, data collection, and external communication. Monitoring tasks include continuous monitoring of all the battery cells, wherein the data record itself can be used to diagnose, but usually used to calculate the task to estimate the components of all the battery’s SOC. This information is used for balancing algorithm, but can be common relay to an external device and the display to indicate the available permanent energy, according to the current use-case estimate of the expected range or scope/life, and provides battery state of Health.

COST REDUCTION:  Although the increase in the BMS will increase costs, but the battery is expensive and potentially dangerous. System more complex, the security requirement is higher, resulting in the need for more of BMS supervision exists. But the BMS in functional safety, longevity and reliability, performance, and range, diagnosis and other aspects of the protection and preventive maintenance ensures that reduce overall costs, including the warranty-related costs.

In conclusion, BMS plays a crucial role in ensuring the safety and longevity of lithium-ion batteries. It regulates the charging and discharging process, prevents overcharging and over-discharging, and monitors the battery’s temperature and voltage. With the increasing demand for portable electronic devices and electric vehicles, the importance of BMS in lipo batteries cannot be overstated. As technology continues to evolve, we can expect further advancements in BMS design and functionality, leading to even safer and more efficient lithium-ion batteries.

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