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Battery Management Systems for Large Lithium-Ion Battery Packs

Section 6.1.1.3.1 Addenda

Cell self-balance time

The time required to balance a set of Li-Ion cells by connecting them in parallel (before building a pack), without a power supply, depends on these factors, in order of importance:

Depending on the above factors, the self-balance time in on the order of hours to days.

The best case is for LiFePo4 cells, when most cells are full, and just a few are just below 100 % SOC. In that case:

Let's look at an example of that:

Then:

So:

So, what is the time, when you consider all these factors? I used a spreadsheet to calculate this, and the result was:

What about the worse case?

Let's look at an example of that:

To analyze this case, we need to employ a Monte Carlo statistical analysis. I have not yet done so. Once I do, I will add those results here.

For now, let me say that my guess is that it will take a week to two weeks to balance these cells.

Compare that to how long a BMS would take to balance those cells once they are in a pack will all the cells in series (assuming 100 mA balance current:

book/6.1.1.3.1.add (last edited 2010-12-11 16:10:01 by DavideAndrea)