but one cell will always hit OVP before the rest. So I'll virtually never hit float charge cycle, because one of the cells would've reached 100%
What you are describing here is a very typical case of a Runner cell, this isn't new and is not unusual from bulk cells. A "high runner", will start to run usually around the 3.425-3.475 +/- a bit, They can shoot up by 1mv per AH of of cell capacity quite quickly. IE 200mv for a 200AH cell. There are also "lo runners", which will drop faster than the rest below the 2.850-2.800 these do pop up but less frequently.
A Culprit Lurking in the Open ! 2P.
1) Unmatched cells can wreak havoc in parallel cell configurations.
2) the parallel connections between cells has to be perfect ! No Burrs or ridges on busbars, no grease, wax or oils. Clean with alcohol, lightly/gently sand with 600 grit (emery cloth is good too, just to soft scrub teh surface really), wipe down again with alcohol. apply extremely thin OxGuard if non-tinned bars.
3) sense lead placement MUST be correct and very good as well, even the slightest oil/wax etc can throw them off.
OVP is Over Voltage Protection, this is not Cell Differential, Chargery BMS calls this "Diff of cell Voltage" in their settings, others use similar terms.
The trick is to not allow the runners to take off as such and to find that sweet spot where the cell differential is not to the cutoff point with the Bulk Charging. Then to get float to kick in at what we need to see as "100% SOC" (it isn't 3.650, it is 3.500 tops), 3.475Vpc is most commonly used). As I show in my charge profile, I Float 27.9V (3.4875vpc) & Rebulk Voltage: 27.7 (3.4625vpc), keeping it pretty tight and I'm in float by noon usually if not sooner. Float is only Constant Voltage which is perfect for keeping cells topped at
"our designated 100%" (in my case, 3.48Vpc).
NOTE: Many BMS' will see the Lowest Voltage Cell and calculate Pack SOC based on that (safest). Some "seem" to base it off the Hi Cell in the pack (bad idea_ others take an aggregate of all cells monitored (can fool you too, because of differentials and imbalance would be hidden). These are not the same "highly specific" type of BMS as used in EV's and such, so there are many compromises.
"our designated 100%"
This is where a great deal of confusion about SOC comes from. Many think that 100% means 3.650Vpc, it is not,
that is the Max Allowable Voltage. The 2.500Vpc Low Threshold is also the Maximum Low Allowable, this is not a working voltage. As stated, you can charge the cells to that for hours, the moment you stop charging they start settling towards their "Working Voltage". That is LFP and the way it is. Similar applies slightly differently across other Lithium chemistries as well. LFP in general is conservatively 3.000-3.400 with 3.200 being the nominal voltage that everything is calculated o(like AH, kWh etc)
Our Designated 100% can be 3.450 and our 0% could be 2.900 and that would still give you about 87-90% which is the norm, as most leave off that 10% top/bottom collectively. With perfect Matched, Batched & Binned cells you could do 2.750-3.500 comfortably tight with little differntial between cells.
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