How to Connect LFP Battery In Series and Parallel

The cell is the smallest unit that constitutes the LFP battery module. It generally comprises positive and negative electrolytes and casings and can realize direct conversion between electrical and chemical energy. The nominal voltage of LiFePO4 cells is 3.2V.

Because the cells are limited by voltage and capacity, to meet the requirements of high voltage and large capacity for electrical equipment and energy storage systems, LFP batteries are usually used in series, parallel or a combination of series and parallel.

How to Connect LFP Battery In Series

Series connection of LFP batteries is to connect two or more cells to increase the overall voltage of the battery pack. Series connection will not increase the capacity but will only increase the voltage.

For example, suppose four 3.2v100Ah cells are connected in series. In that case, a 12.8v100Ah battery pack is formed (the battery pack voltage is closer to 13.3v because these cells’ static and nominal load voltage is about 13.2v-13.35 v), and the battery capacity remains the same or 100Ah.

Series connection method: Connect the positive terminal of each cell to the negative terminal until all cells are connected. Then, connect the negative terminal of the first cell in the pack to the negative terminal of the app and the positive terminal of the last cell in the pack to the positive terminal of the app.

To configure a series-connected LFP battery, each cell must have the same voltage and rated capacity. The cell mismatch will cause the cells to become unbalanced, resulting in overcharging or undercharging individual cells or batteries. For example, you can connect two 3.2v100ah cells in series but not a 3.2v100Ah cell with a 3.2v200Ah cell.

lifepo4 cells in series-configurations 12V

Source: file:///E:/LiFePO4%20Cell%20Configurations.pdf

How to Connect LFP Battery In Parallel

Parallel connection of LFP batteries is to connect two or more cells to increase the overall capacity of the battery pack. Parallel connection will not increase the voltage but will only increase the capacity.

Batteries connected in parallel must also have the same voltage and rated capacity; otherwise, the batteries will be damaged.

For example, if four 3.2v100Ah batteries are connected in parallel, the battery’s capacity becomes 400Ah, and the voltage remains unchanged at 3.2v.

Parallel connection method connects the positive terminal of each cell to the positive terminal and the negative terminal to the negative terminal until all the cells are connected. Then, connect the negative terminal of the first cell in the pack to the negative terminal of the app and the positive terminal of the last cell in the pack to the positive terminal of the app.

In practical applications, LFP cells are almost never used separately in parallel.

How to Connect LFP Battery In Series and Parallel

In electric vehicles and grid energy storage applications, series and parallel connections often exist at the same time, which can increase the voltage and capacity of the battery at the same time.

For example, if eight 3.2v100Ah batteries are connected in series and parallel to form a nominal 12v200ah battery, it can be connected in twos in parallel and then in series, called 2P4S. It can also be connected in four series and then in parallel, called 4S2P.

From the perspective of the reliability of battery pack connection, the development trend of battery voltage inconsistency, and the impact on battery pack performance, the first parallel connection and then series connection method is better than the first series connection and then parallel connection method.

Advantages of Parallel First and Then Series

Reduce the impact of cell parameter inconsistency on the battery’s overall performance.

A cheaper BMS can be used (only need to monitor the voltage of the series cells, and the parallel cells maintain natural balance).

Reduced battery assembly difficulty (cell performance screening) and cost.

Source: file:///E:/LiFePO4%20Cell%20Configurations.pdf

Precautions for Series and Parallel Connection

When connecting in parallel or series, it is necessary to screen the cells for consistency. It is necessary to ensure that each cell’s voltage, capacity and internal resistance are similar to maintain the charge balance between each cell and avoid overcharging and over-discharging, or battery imbalance.

The cell must be used with BMS or PCM. Monitoring the state of charge of each cell is critical to maintaining balance and preventing any individual cell from being overcharged or undercharged. This helps ensure the longevity and safety of the entire battery pack.

Use cells from the same batch. Do not mix cells of different batches and brands.

In addition, appropriate safety measures need to be taken, such as using a matching protection circuit and suitable connecting wires, to ensure the safety and stability of the battery pack.

Conclusion

The choice of connecting LiFePO4 cells in series and parallel depends on the application’s specific needs. The series connection is the best choice if high voltage output is required. A parallel connection is the best choice if a large capacity is needed. Understanding the precautions when connecting these batteries is important to ensure optimum performance and safety.

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