It is possible to connect LiFePO4 battery cells of different capacities in parallel to expand their capacity.
In fact, when they are connected in parallel, each group is sharing the current demand based on its normal capacity.
For example, you have a 12V 230Ah pack consisting of four 3.2V 230Ah LiFePO4 battery cells connected in series.
And you get 4 new 3.2V 280Ah LiFePO4 battery cells.
Then you can connect these 4 3.2V 280Ah LiFePO4 battery cells in series and connect them in parallel with the 12V 230Ah pack. Thus forming a new 12V 510Ah battery pack.
When planning this way you need to consider the power consumption of the system along with it to avoid instantaneous high current needs that exceed the limits that can be shared by the smaller capacity cells.
This is rarely the case for the above example, as a single 200Ah pack can withstand instantaneous currents of 200A-300A. Two packs can share an instantaneous current of 500A-600A. This is rarely the case in real life.
For smaller packs, such as 50Ah +100Ah packs, careful calculations are required. Because the input power of just one high power microwave is up to 1500W, this will pull 125A at the 12V battery pack. If other high power appliances running at the same time are added, the limits of a 50Ah pack may be exceeded. This causes the BMS to shut down the 50Ah pack.
So how to combine the battery packs is something that needs to be considered in terms of the overall system.
In fact, many of my customers use cells of different capacities in parallel to get more capacity, and they all work well.
However, there are a few things to keep in mind.
- The voltages of the two batteries should be as close as possible when they are first connected.
- They must have their own BMS.
- Replace/use the same AGW(size and length) leads to reduce the difference in voltage and resistance of two packs.
- It’s better to add fuses to each set of batteries for safety reasons.
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