However we look at a battery pack design we end up with lots of cells being connected together. In parallel to increase the capacity and in series to increase the voltage.
We end up with a complex system to manufacture and hence look for repeating patterns. These repeating patterns are important whether the pack is a modular or cell to pack design. As we connect the cells together in parallel and then in series the break points are in the series connections.
If we want a 350V battery pack and have 3.6V cells the closest is 97 cells. 97 is a prime and hence only divisible by itself and 1.
Looking at factors for different values of cells in series we can see that 96 is divisible by:
1, 2, 3, 4, 6, 8, 12, 16, 24, 32, 48, 96
12 is a useful factor as would mean we need 8 modules. Also being divisble by 4 is how we see some packs such as the Tesla Model 3 design where it is broken into 4 large modules.
In Microsoft Excel it is easy to calculate this list of factors:
This post has been built based on the support and sponsorship from: Thermo Fisher Scientific, Eatron Technologies, About:Energy, Quarto Technical Services and Alvatek.
Just to make this even easier, here is the excel function you can copy and paste:
=LET(Num, A2, All, SEQUENCE(Num), Factors, FILTER(All, MOD(Num, All)=0), TEXTJOIN(“, “, TRUE, Factors))
This module / sub-grouping allows us to manufacture repeated blocks. Thus improving throughput and quality. Also, we can build these repeated blocks and keep them at a safe working voltage (<60V).
Battery Calculations Workbook
The series and parallel calculation tab now includes a calculation of the factors of the series string.
When we look at the battery pack database we can see that for the “400V” battery packs the most common arrangement of cells is 96s, followed by 108s.
Histogram of the number of cells in series for all of the battery packs in the database.
This shows 96 as the most common and 108 as the second most selected arrangement.
See also: Series and Parallel