**Editor's Note**
A large battery pack consists of lithium polymer or lithium iron phosphate (LiFePO4) cells connected in series. These packs offer high energy density and peak power, making them ideal for use in pure electric vehicles (EVs or BEVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and energy storage systems (ESS). As the EV market continues to expand, there is a growing demand for efficient and reliable battery solutions that can support long-range driving and extended lifespans.
For EVs and PHEVs, battery performance directly correlates with the distance the vehicle can travel on a single charge. To stay competitive, manufacturers must not only deliver high-performance batteries but also provide long-term warranties that guarantee minimum driving range. However, as more electric vehicles hit the road and usage increases, battery aging has become a critical issue. This degradation reduces overall capacity and affects the vehicle’s range over time.
Despite rising demand for high-capacity battery cells, their cost remains one of the highest components in EVs and PHEVs. A battery capable of supporting hundreds of kilometers typically costs around $10,000. While using lower-cost or refurbished cells may reduce initial expenses, it can lead to greater capacity mismatch, which limits the usable range after each charge.
Even with high-quality cells, repeated use causes aging and imbalance. Two common approaches to address this are either using larger batteries from the start or implementing active equalization technology. Active equalization is a modern solution that helps restore battery capacity and improve performance by redistributing charge across the pack.
**Fully Connected Battery Cells Need to Be Balanced**
Battery balance refers to ensuring all individual cells within a pack have the same state of charge (SoC). SoC represents the ratio of remaining capacity to the maximum capacity of a cell. For example, a 10 Ah cell with 5 Ah left has an SoC of 50%. Maintaining proper SoC ranges is crucial to prevent damage and extend battery life.
In EVs and grid storage systems, SoC ranges are often limited between 20% and 100% for runtime, or 30% to 70% for longer lifespan. The Battery Management System (BMS) plays a key role in monitoring and controlling these levels. While parallel-connected cells tend to self-balance, series-connected cells can experience SoC variations due to factors like temperature, impedance, and load differences. Without regular equalization, these imbalances can accumulate and reduce overall performance.
**Passive vs. Active Equalization**
Passive equalization is simple and low-cost but inefficient, as it dissipates excess energy as heat. It also reduces the overall capacity of the pack to match the weakest cell. In contrast, active equalization redistributes charge between cells, allowing higher efficiency and better capacity recovery. This method is essential for maintaining optimal performance in large battery packs.
**Mismatch Can Significantly Reduce Run Time**
Capacity or SoC mismatches between cells can severely limit the usable capacity of the entire pack. Even with a 10-cell series pack, a ±10% capacity difference can reduce available range by up to 25% without balancing. Passive equalization helps during charging, but it cannot prevent early discharge cutoffs. Only active equalization can redistribute charge effectively, ensuring all cells operate at their full potential.
**High Efficiency, Two-Way Equalization for Maximum Recovery**
The LTC3300-2 is a high-efficiency, bidirectional active equalizer designed for advanced BMS systems. It can simultaneously balance up to six lithium-ion or LiFePO4 cells, offering improved performance and faster charge redistribution. With over 90% efficiency in both charging and discharging modes, it significantly reduces heat generation and improves system longevity.
**Conclusion**
As EVs, PHEVs, and ESSs continue to grow in popularity, consumers expect long-lasting, reliable performance. Battery aging and mismatch remain major challenges that affect range and lifespan. By using advanced technologies like active equalization, manufacturers can maintain optimal performance and ensure batteries last longer. Solutions like the LTC3300-2 help overcome imbalances, enabling battery packs to perform at their best throughout their lifecycle.
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