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APC UPS float voltage limit
#11
14S means you need voltage superior to 58.8 to fully charge them.
If you want to keep them at around 4.0V for good life-time, you still need over 56V of in-circuit voltage.
Therefore, a FV of 54.5 will be a little below your target.

Best thing is to practically test how well they charge - if this works fine enough you're in luck as APC UPSes have high quality components and high durability over time.
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#12
(01-13-2020, 12:29 PM)Overmind Wrote: 14S means you need voltage superior to 58.8 to fully charge them.
If you want to keep them at around 4.0V for good life-time, you still need over 56V of in-circuit voltage.
Therefore, a FV of  54.5 will be a little below your target.

Best thing is to practically test how well they charge - if this works fine enough you're in luck as APC UPSes have high quality components and high durability  over time.
I have 4 APCs with 7s7p 18650 batteries.   2 are the 3000va towers (with 2 x 7s7p batteries) and the others are the 1500 APC with a single 7s7p.   There's room to make a 7s14p that's within the size of original sealed batteries but that's overkill for my needs.

The APCs charge to 27.6v (+/- .1) which is 3.94v/cell.   This is great for me because I use them as UPSs....  so the cells are at 3.94 99% of the time and only deliver power briefly during  ATS switch-overs.     At this voltage/use they should last a very long time ... hopefully much longer than the original sealed batteries.

The low (to cut-off) is about 20v which is 2.85v/cell...   so even if something goes completely wrong and you have a total drain situation its still within safe operating parameters for 18650.
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