How do different battery chemistries affect the number of BMS strings?

The effect of different battery chemistries on the number of BMS strings is mainly reflected in the following aspects:

1. Cell Voltage Limitations:

– The primary limiting factor in using BMSs with different cell chemistries is the maximum cell voltage measurable per CMU channel. For example, lithium-iron-phosphorus cells have a maximum voltage of 3.65 volts, while widely distributed nickel-manganese-cobalt cells have a maximum voltage of 4.2 volts. This means that for lower voltage cell chemistries, such as lithium iron phosphate, more cells may need to be connected in series to achieve the desired total voltage.

2. Battery type and package construction:

– Battery type mainly affects the OCV (Open Circuit Voltage) characteristics, where battery type refers not only to the material system (the electrochemical characteristics of ternary battery and LiFePO4 are not the same), but also to the package structure of the battery (the internal characterization parameters of square, flexible pack and cylindrical batteries are not the same either). Different package structures and material systems may affect the consideration of the number of strings in BMS design.

3. Charge and discharge characteristics:

– Different battery chemistries have different charge/discharge characteristic curves. For example, LiFePO4 has a very flat charge/discharge characteristic curve, which requires accurate measurement (within 1mV) of the open-circuit voltage of the battery in order to establish a mapping relationship with the SOC, which makes it difficult to accurately estimate the SOC.

4. Self-discharge rate and temperature sensitivity:

– The self-discharge rate of lithium iron phosphate is larger, and under the same storage conditions, the self-discharge rate of lithium iron phosphate is significantly larger than that of ternary, so lithium iron phosphate requires high-frequency equalization management. In addition, lithium iron phosphate batteries are more sensitive to temperature, the open-circuit voltage varies greatly with temperature, while the open-circuit voltage of ternary batteries varies less with temperature.

5. Battery consistency requirements:

– For battery packs with high battery consistency requirements, the low utilization rate of the remaining cells after capacity division and grouping will invariably increase the cost, and there is no online replacement function for battery modules. This may affect the consideration of series-parallel configuration during BMS design.

6. Energy density and power density:

– Energy density and power density do not directly affect the battery management system, but they determine other factors that affect the BMS, such as the total number of cells that need to be connected in series and parallel to power the system. Batteries with higher energy and power densities will allow equipment to run longer and may require fewer batteries in series to meet energy requirements.

In summary, the characteristics of different battery chemistries, such as voltage range, charge/discharge characteristics, self-discharge rate, temperature sensitivity, etc., can have an impact on the design of the number of strings in a BMS.These factors need to be considered in the design of the BMS to ensure the performance and safety of the battery system.

Shenzhen Kinglisheng New Energy Eechnology .,Ltd

How do different battery chemistries affect the number of BMS strings?

1. Cell Voltage Limitations:

2. Battery type and package construction:

3. Charge and discharge characteristics:

4. Self-discharge rate and temperature sensitivity:

5. Battery consistency requirements:

6. Energy density and power density:

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