Cell balancing is a fundamental technique that improves battery life by maximising the capacity of a battery pack with multiple cells in series. By ensuring that all cells have a similar state of charge, cell balancing ensures that all of the battery's energy is available for use. In this article, we will explore how cell balancing improves battery life and examine active and passive cell balancing methods.
The balance of cells and its importance
Cell balancing is a key function in a battery management system, such as those found in lithium-ion battery packs, electric vehicles and energy storage applications.
The individual cells in a battery pack often have different capacities and SOC load states. Without load redistribution, discharge must stop when the cell with the lowest capacity becomes empty, even if the rest are not yet empty, thus limiting the power supply capacity of the pack.
If cell balancing is not done, there is a weak point in the cell with the lowest capacity. In this sense, the BMS has this as its primary function, along with other vital functions such as thermal control, charging and other factors that maximise the life of the battery pack.
How does cell balancing improve battery life?
Cell balancing improves battery life by ensuring that all cells in a battery pack have a similar state of charge.
On the one hand, cell balancing ensures that all cells of the battery are discharged in a balanced manner, allowing the full capacity of the battery pack to be used to the maximum.
In addition, cell balancing prevents some cells from being overcharged or discharged more than others, which can damage them irreparably and reduce the life of the battery.
The risk of thermal runaway caused by overcharging or over-discharging is also reduced, helping to keep the battery temperature within safe ranges.
Finally, it is important because it minimises degrading processes by preventing some cells from being overcharged or discharged more than others, which prolongs the life of the battery by maintaining its capacity and efficiency over time.
There are 2 types of cellular equilibrium: active balancing and passive balancing.
Active cell balancing: advantages and limitations
Active cell balancing involves transferring energy from one cell to another within the battery pack. This is achieved through converter circuits that channel energy from cells with higher voltage or charge to those with lower voltage or charge. Some advantages of active cell balancing include:
- Improving capacity utilisation.
- Increased energy efficiency by avoiding the dissipation of energy in the form of heat.
- Extension of cell life.
- Rapid balancing.
Although active cell balancing has a number of benefits, it also has some limitations, such as:
- Energy loss during load transfer (approximately 10% to 20%).
- Limitation to transfer load only from an upper cell to a lower cell.
- Increased complexity in control algorithms and higher production cost due to the need for additional power electronic interfaces.
Passive cell balancing: advantages and limitations
Passive cell balancing involves burning excess energy from the cells with the highest load through resistive elements until the load is equalised across all cells.
Some advantages of passive cell balancing include:
- It does not require balancing a battery pack.
- It avoids wasting energy from a cell that does not have it.
- Allows all cells to have the same state of charge (SoC).
- It offers a cost-effective approach to balancing cells.
Passive cell balancing also has some limitations, such as:
- Poor thermal management.
- It is not fully balanced throughout the SoC, which means that surplus energy is wasted.
- Low power transmission efficiency due to thermal and switching losses.
- It does not improve the runtime of a battery-powered system.
Balancing the cells of a battery pack focuses on matching the state of charge (SoC) of each individual cell, rather than matching their total capacity. If the battery pack is balanced correctly from the factory, the Battery Management System (BMS) only needs to monitor the balancing current. This is especially beneficial, as battery packs can be built that are already balanced, eliminating the need for a BMS to perform a full balance.
The goal of any balancing method is to allow the battery pack to operate at peak performance and extend its useful capacity. For those who wish to minimise costs and correct any long-term imbalance in cell self-discharge current, passive balancing is the best option. With passive balancing, a cell cannot waste energy it does not have. Only when the energy bank is fully chargedIn this way, a cell has enough energy to balance itself, thus avoiding any unnecessary waste of energy.
NCPOWER's patented technology that improves battery performance and efficiency through cell balancing, the NCPOWER System is a third alternative to traditional balancing systems.
The NCPOWER System prevents the disadvantages of the 2 previous balancing systems and also improves the positive parts of these systems.
What makes NCPOWER different, what exactly is the NCPOWER System? Here we show you the NCPOWER System.