The term cell balancing is normally associated with lithium ion batteries in question. It is a procedure that lengthens the lifespan of each cell while enhancing the capacity of a battery pack which is made up of several cells that are often connected in series.
In this blog we are going to discuss the importance and types of cell balancing in a lithium-ion battery.
Importance of cell balancing:
Cell balancing ensures that all cells in a lithium-ion battery pack are charged and discharged equally in the lithium-ion battery. If some cells in the battery are in a state of more discharge than the others then it leads to a hampering of the performance, reduction of battery capacity and even safety concerns.
In lithium-ion batteries, there are multiple cells that are connected in series to increase voltage. In the process of charging or discharging, some cells may become fully charged or discharged before others, leading to an imbalance in the state of charge (SOC) across the battery pack. Here is where cell balancing comes into the picture. The capacity or SOC levels of the individual cells in the battery pack vary and differ from each other.
Types of Cell balancing
1.Passive cell balancing:
In this method a balancing resistor is connected in parallel with each cell of the lithium ion battery pack. The balancing resistor begins to dissipate the extra energy as each cell’s voltage hits its maximum during charging state, allowing other cells to continue charging.
This method is a simple and cost-effective method, but it is not suitable for high-power applications due to excessive heat generation and reduction in the overall efficiency of the battery pack. Since 100% of the surplus energy from a higher energy cell is wasted as heat in this process, this approach is less advantageous to utilize during discharge due to the clear impact on battery life time.
2.Active cell balancing:
This method is more efficient as compared to the passive approach.
In this case, a dedicated electronic circuit monitors the SOC of each cell and actively transfers energy between cells to balance the SOC.
Here it shuttles the energy between the cells differing in SOC. Even though it is an effective method of cell balancing, there is a requirement of additional electronic components leading to increase in the complexity and cost of the BMS system of the battery.
Summary
Since battery cells are delicate and can be permanently damaged if they overcharged or over-discharged hence it is essential to perform cell balancing when grouping multiple battery cells together to power a device.. When cells with various SOCs are combined, their voltages may drop until the cell with the lowest energy storage reaches its discharge cut off voltage.
Cell balancing is an efficient process that ensures the safety and longevity of lithium-ion battery packs. This helps to prevent overcharging, over-discharging, and thermal runaway, which can cause battery failure and even fire.
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