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Example 16 identical battery cells rated as below:

  • 3.2V 100Ah
  • LiFePO4
  • Max Continuous Discharge 100A / 1C
  • Max Peak Discharge 200A / 2C for 100s
  • Max Continuous Charge 50A / 0.5C
  • Max Peak Charge 100A / 1C for 100s

Scenario 1 Cells arranged in 8S2P configuration (2 blocks in parallel, 8 of these in a row in series, 16 blocks total)

  • New voltage 25.6V
  • New capacity 200Ah

Scenario 2 Cells arranged in 2S8P configuration (8 blocks in parallel, 2 of these in a row in series, 16 blocks total)

  • New voltage 6.4V
  • New capacity 800Ah

Questions

  1. In each scenario, what are the values of continuous/peak charge/discharge currents and why?
  2. Does this change with differing battery chemistry (given otherwise same spec)?

Edit

  1. Purpose of this is to understand what loads can be attached to a given battery bank constructed from the cells (max discharge current) and what a safe charging current would/should be (max charge current).
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First of all, I don't have real experience with LiFeO4, but I have some basic knowledge about Li-Ion battery. So just want to tell what I think, hope it can be somewhat useful.

  1. Because you connect batteries in series & parallel, it's sure that current can't be simple multipled by spec of a single cell. Ex: About discharge, I believe that if 1 cell can discharge at 1C, 2 cells in series also can discharge at 1C, 8 cell in a series is the same. But depend on real capacity of the lowest cell, that cell will impact to total voltage (dropped),especially when one cell is empty. About charge, surely you need to do balance charge, this will make the charge-time longer, so it also mean you can't reach max current charge (1C) on every cell, at everytime. When a cell's voltage lower than the others, it should be charged, other cell need to wait, and vice versa. For peak charge/discharge, it's truly the same. We know that when peak charge/discharge, cell's voltage will reach its max/min limit. And surely, the worst cell will reach this limit faster than the better cell. So you still can source (discharge) at max current, but the time of discharge (100s) maybe can't reach. The peak charge is as the above example, balance charge, so you can't apply max peak charge. About parallel cells, higher voltage series will be discharged first, so when first series will source 1C, second series will source only 0.8C (for example) to reach the same voltage. mean total is 1.8C max. The real value depends on the difference of cell, can't tell exactly.
  2. I don't know there is an ideal battery chemistry that can reach max powwer when you seri/parrallel them. Should be no, because always exist difference between cell.
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  • \$\begingroup\$ Hi Nam, thanks for the response! So do you think there may be a way to put a formula against this to show how both maximum discharge and max allowed charge current change based on Series and Parallel setups? \$\endgroup\$ – DavidM Aug 14 at 10:28
  • \$\begingroup\$ If you care more about the discharge, I'm pretty sure that discharge is almost ideal, 2C for 8S2P for new batteries. Charge-time with balance can be a bit slower, but I don't think that it's a big problem in almost popular cases. But with aging of batteries, can't tell more. Anyway, LiFeO4 is strong of cycle - compare to other battery type, so hope it's not a problem, too. @DavidM \$\endgroup\$ – Nam Nguyen Ngoc Aug 14 at 11:09

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