3.2V is the Mid Point of the Working Voltage range which is from 3.000-3.400. Every LFP Manufacturer uses the same values.
If adhering to the Allowable & Working voltage ranges, then one can consider 3.000 as 0% SOC while 3.400 is 100% SOC.
Remember, that when we test cells that are charged to 3.650 (while not allowed to settle) down to 2.500 this is a LIE as that is the Allowable Range which causes no harm but not the working range, as this includes the steep curves from 2.50-3.00 & 3.40-3.65. Actual Grade-A Capacity tests should be delivering the rated AH from that 3.00-3.40 range, not from 2.50-3.65. Also, remember that you can charge LFP to 3.65 until Amps Taken drops to 1.0A and letting that sit for 2 hours with no charge, the cells WILL settle closer to 3.45 +/-, which is perfectly natural & expected. The "KNEES" from 2.50-3.00 (Bottom) & 3.45-3.65 (Top) generally only add a few percent more AH but NOT significant, so a 280AH cell would rate at 290AH +/- "Gross Capacity" which is NOT the deliverable AH which comes from the working range. *Note that some vendors use that for trickery... we have all seen this.
Using a 48V/100AH example;
16 Cells X 3.2V nominal = 51.2V. 100AH cell capacity X 51.2V = 5120Wh or 5.12kWh
Charge (Bulk/Absorb) to 54.8 (3.425Vpc) or 55.2 (3.450Vpc) MAX as there is no gain above that only stress on cells and runner cells reaching HVD.
Float at 54.7 or 55.1
Active Balancer ON @ 3.300 *
* Active Balancer MOVES power from Hi to Lo Cells. It uses NOTHING when not initiated. It also DOES NOT WASTE energy as it moves it and there are too many misconceptions about that but it is observable & measurable (so much for wives' tales assumptions eh). Starting @ 3.30 (the last 25% of SOC) allows the cells to keep up at the higher side when cells will begin to deviate (usually above 3.350 and keep ahead of higher imbalances. This will occur on ANY Grade of cell and is relative to the amount of incoming charge, the higher the charge rate the faster & higher the deviations will occur.
There are people here that think Active Balancers need not be operating below 3.400 which to be honest is "silly" as there is no gain and you are leaving heavier lifting to the end by which time you are likely triggering HVD due to a runner cell which in the end is handicapping your pack. I have been running different active balancers for years and have done an obscene amount of tests that proved this out.
Case in point: I run 6 packs, 2 Bulk 280's, 1 A Grade 280, 1 A Grade 105, and 2 174AH (Used EV cells)
They reach float by noon and there will be deviations on the Bulk cells up to 100mv, By 1 pm with float & active balancing, all cells are under 0.010mv deviation while taking in minimal Amps while topic off & balancing. The amount of deviation varies depending on the Charge Input, the higher the input the more deviation but it all does balance out within an hour or so.
For the record, I have used QNBBM Active Balancers, Heltec Capacitive (the 2 types) and am now using the Active Balancers in the JK-BMS'...
Hope it helps, Good Luck.
