cap voltage for eve cells via xiaoxiang bms app

[xml]

Hi!

Im a bit of an amateur so maybe the reply will be "if you dont know what you are doing, dont do it" ?

Anyway I got instructions from my supplier that are using an older version of xiaoxiang app which only has 80% 60% 40% 20% settings for cap voltage, the latest version wants for 100, 90, 80, 70, 60, 50, 40, 30, 20, 10

I tried to reverse the calculations but couldnt get any formula that makes sense.

Based on the values you see in the screenshot, what would you fill in the blanks? I guess 3552 for 100%

 

[sunshine_eggo]

I wouldn't bother. Those numbers don't do anything but provide an estimate of SoC when the BMS has no idea what the actual SoC is.

The Cell full voltage is the only one that matters. Once that's attained, the BMS knows it's truly at 100%, and it will start tracking true SoC based on net current in/out.

 

[xml]

So leaving the inputs blank means no explicit values are set ?

 

[sunshine_eggo]

Yep.

To say it another way, if the BMS is using any of those to report SoC, the SoC is very inaccurate.

Again, the only one that really matters is the "cell full voltage" which is already populated.

 

[xml]

Yeah thanks, I understand. It's the app that's crappy that doesn't really allow you to skip these params.
The battery is operating fine, connected load works properly.
Time to charge it up for additional testing.

Should I config chargers depending on my preferred values on my bms? Charger victron blue smart (have one around here to test) in li-ion mode will automatically charge use absorption voltage with 14,2v?
The other planned main charger doesnt have documentation it just says "14,6v/13,8v" and this one is not configurable more than switching between agm, lead, lifepo4 so I just set it to lifepo4.

 

[sunshine_eggo]

Sorry. Didn't realize they were mandatory:

@Steve_S has a good chart:

General LiFePO4 (LFP) Voltage to SOC charts/tables 12/24/48V

I've looked at several places for a simple, easy to read at a glance "chart document" for LFP. I could not find anything comprehensive. I discovered an XLS Worksheet in my stored file and took parts of that to create this chart, I did not...

diysolarforum.com

 

[Steve_S]

There are TWO sets of numbers for LFP which 90% of folks are Befuddled by and keep repeating the twaddle of misunderstanding.

1st set:
The "Allowable Voltage Range" which is for the chemistry, this is the safe range of voltages for the individual cells where no harm/damage will occur. This is the 2.500-3.650 voltage range that they can handle.

2nd set:
The "Working Voltage Range" which is where the actual Amp-hours come from and are used. LFP will always settle to the top of the Working Range, Manufacturers TEST in that range to qualify cells and ensure their capacity to deliver XXX AH. This range is 3.000-3.400 Volts per cell (Vpc). This is WHY Nominal Volts per cell is 3.200 (50% SOC) which should make that obvious.

The "wives' tale" of 10% from Bottom & 10% from Top originates from keeping above 2.950 and below 3.450 ! and believe it or not those are the Cliffs in the voltage charts that we see and do represent roughly that 10% - 10%. Now you CAN go below 3.00 to 2.800 without causing damage etc BUT that Cliff Fall will be fast below 2.900. The top above 3.450 climbs fast and will most often trigger a High Volt Disconnect with some cells within a pack of cells, as they will RUN to 3.650 ahead of others. Part of this originated due to POOR TRANSLATIONS way back when and still pervades. A LOT of folks keep echoing this and also all over YT as well.

Every Single Battery Chemistry has an Allowable range that is safe (no harm) and a working range that provides optimal power.

Charge your batteries to 3.450, till they reach 0.05C (100AH X 0.05 = 5A) at which point they have reached 100% and saturated. The cells will then settle to 3.400Vpc post charge which is perfectly normal for LFP.
Cut off anywhere between 2.900-2.800Vpc and shutdown at 2.600Vpc if your BMS can do that. This will give you a "wee bit extra" and shutting down no lower than 2.600 leaves a margin allowing you to restart when a charge is applied.

I hope this helps to clarify, good luck.