Battery Management Systems: Everything You Want to Know

When it comes to Li-ion batteries, it is inevitable to mention the battery management system(BMS), which is mainly found in Li-ion batteries and is not generally available for lead-acid batteries. So why do lithium batteries need a battery management system? What exactly is this management system managing? What role can it play?

What is a lithium battery management system(BMS)?

The battery management system(BMS) is the bridge between the battery and the load. The most basic functions of the BMS are to prevent the battery from being overcharged and overdischarged, to regulate the status of the battery and to extend the battery life. Once the battery pack is in an abnormal condition, the BMS can make timely instructions to cut off the battery current. In layman’s terms, the BMS is like the “brain” of the battery pack, an operating system that manages, controls and uses the lithium battery pack, sending and receiving information from within the battery pack and the ports and processing it.

Why do I need a lithium battery management system(BMS)?

Lithium batteries have gradually replaced traditional lead-acid batteries as the mainstream due to their high energy density, small size, no memory effect, long cycle life and many other advantages! However, precisely because the chemical activity of lithium batteries’ own chemical materials is much higher than that of lead-acid batteries, once a safety accident occurs, it will have more serious consequences; and when lithium batteries encounter a complete depletion of power, it will seriously damage the cycle life of the battery and cannot recover by itself, so BMS is a must for lithium batteries. So what functions is the BMS mainly used to achieve?

1. Voltage/current management

Voltage management: Each battery has its own reasonable working voltage range. One of the important functions of the BMS is to keep the voltage of the lithium battery within the specified working voltage range to avoid damage to the lithium battery caused by too high or too low voltage, which affects its service life.

In addition, because Li-ion batteries are made up of multiple cells in series and parallel, for example, the early Tesla Model 3’s powertrain is made up of more than 7000 21700 Li-ion cells in series and parallel, there is some slight pressure difference between the different cells, and if the value of the pressure difference is too large, it will also affect the overall performance of the Li-ion battery. The BMS with active equalisation can adjust the pressure difference between the cells to keep them in a dynamic balance.

Current management: Each battery has its own designed operating current range, once the design range is exceeded, safety problems are likely to occur and one of the functions of the BMS is to cut off the circuit in time to protect it.

2. Temperature management

The BMS system monitors the operating temperature of the battery pack and cuts off the circuit when the operating temperature range is exceeded to ensure that the lithium battery pack can operate at a safe The BMS system monitors the operating temperature of the battery pack and cuts off the circuit when the operating temperature range is exceeded to ensure that the lithium battery pack can operate at a safe ambient temperature.

The battery management system extended functions

Through the above introduction, I believe it is easy to see that the BMS can protect the safety of the battery pack and also improve the service life. in addition to the basic management and protection functions, the BMS is also gradually developing some other functions to meet the needs of different functions and equipment, today we take the Magi-C 12V LiFePo4 Battery from LYBESS as an example to introduce to you:

Communication functions:

The communication function usually refers to one or more channels of data transmission between the battery and the load device, sending and receiving some control commands between the battery and the load. At present, mainstream communication is divided into 3 categories, CAN communication, RS485 communication and Bluetooth communication; Magi-C 12V LiFePo4 Battery adopts Bluetooth communication, users can connect to the battery’s Bluetooth signal through the mobile phone APP, to understand the battery’s charge and discharge records, voltage difference of battery cell, cycle status and other information, which greatly improves the convenience of using management.

Heating function:

Some customers in alpine regions have reported that lithium batteries purchased elsewhere cannot be recharged or are slow to recharge at low temperatures, which is related to the performance of the lithium battery itself. When the ambient temperature is below 0°C, the lithium battery cannot be charged and the discharge range will be very poor. At this point, it is necessary to add a thermal chamber or other means to improve performance.

In some new energy vehicle powertrains, the main temperature management is generally done in two ways:

1. heat pump air conditioning;

2. PTC heating (heating through silicone heating sheets) The heating function of the Magi-C 12V LiFePo4 Battery uses the second technical route, which is able to maintain the internal temperature of the battery in the right range at all times. This feature allows customers in alpine regions to solve the problem of poor battery pack life and extend the life of the battery.

Having said all this, I believe you have a certain understanding of our BMS system, LYBESS Magi-C 12V LiFePo4 Battery’s BMS not only has all the above mentioned functions, but also supports series and parallel connection between multiple batteries to meet the needs of different power usage. Today we have only introduced the tip of the iceberg of BMS knowledge, BMS is a relatively complex system knowledge, we will lead you to unravel the magic of BMS step by step in the future.