BMS in lithium batteries: what is it and what is its function in cell balancing?

What is a lithium battery BMS?

Lithium batteries are high-performing devices and offer countless advantages over traditional batteries. They also have a weak point, however: manufacturers are unable to ensure production uniformity from one lithium cell to another.

Although all of their characteristics exceed rated values, the cells present:

• Differences in rated capacity
• Differences in internal resistance
• Differences in self-discharge

With use or, simply, with the passing of time, these differences, even if small, cause the cells inside the battery to go out of balance. This imbalance can lead to a 3% to 6% difference between the cells, depending on the conditions of use and ageing of the lithium battery.

Since the cells are connected in series inside the battery, they are charged and discharged with the same level of energy. This means that without an appropriate cell balancing system, the difference between the cells would increase more and more, gradually draining the available capacity.

Let’s discover the first function of a BMS in a lithium- ion battery: cell balancing.

BMS lithium-ion batteries and cell balancing

How does a conventional BMS affect balancing?

To counteract this phenomenon, a common BMS (battery management system) applies resistance to the cells with a higher charge until the weaker cells catch up to that level.

Let's look at the pros and cons of using this technology

How does Flash Battery’s proprietary Flash Balancing System work

Flash Battery has developed its own battery balancing system, called Flash Balancing System, that unlike a conventional BMS, can act on each individual cell with combined balancing, i.e., with both active and passive balancing, and with a current at least 20 times higher.

Other functions of a BMS in lithium batteries

This is the Battery Management System of a lithium battery explained in a nutshell: what it is, how the balancing phase works in a conventional BMS, and why Flash Battery decided to develop a totally new technology, its international patent-pending Flash Balancing System.

But wait, there’s more! A BMS – battery management system is considered the actual brain of the battery and when designed with cutting-edge electronics, it performs numerous other functions that control and monitor the behaviour of the lithium battery inside the application in real time.  Now, let’s discover the additional features of a smart BMS.