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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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#13
(01-11-2020, 11:51 PM)kc8adu Wrote: there are some precision resistors you can tweak if apcfix wont adjust to your desired setpoint.
without seeing your unit it would be hard to say which.
but the big units with expandable batteries,metal case,and internal fan make nice inverters.
Hi now back on track with my project, too many distractions both work and Home life, anyway Kc8adu you seem to imply with the above statement that there are components on the main board which could get me the voltage I need if you know the unit, the unit I'm using is a SUA3000RMI does this help or would you need a photo of the board? 

Thanks in advance
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