Help me set up my LifePO4 system - I am kinda "lost"...

[besugosolar]

Hello! Long post, please read and try to clarify my doubts, will be much appreciated!!!

So a few weeks ago I asked here if B-Cells would be ok, and some of you told me what to expect, the store manager, by e-mail told me they would be fine, and gave a 1 month return window, etc etc... So I went for it, these were sold by European Store NKON which has a STELLAR reputation and cost me 590 Euros for 8X130Ah Cells, which is a great price... They arrived well packaged, no signs of anything wrong, and all read the exact same with my 2 digit only cheap multimeter 3,26V, for a total of 26,2V

Bad news - weather went horrible for 2 straight weeks, no sun... To make matters worse I only have 2 panels installed right now, working on putting the rest on the roof, so only roughly 500W of solar power - that most of the time was generating 20-30W from 9am to 5pm... So I set my BMS (Jiabaida\JBD) to trigger cut-off at 2,6V and it did one night - I know I was almost zero, but I am living totally off-grid, my lead acid batteries died, and I had to go to almost 0% SOC... Anyway soon after weather started changing and some sun started to show up and this is where it all starts

My system right now (only 2 panels installed as I said)

8S 130Ah Cells
MPPT charge controller
500W solar panel power +-
4000W peak inverter\2000W continuous
JBD 100A BMS
Xiaoxiang App on Android and iOS

So...

I wanna know how to set this up correctly for the best useability\longevity ratio

Want the cells to last for a long time, but I don't really discharge more than 20% overnight... More like 10 to 15% since I only run the inverter, lights, fridge, a efficient laptop and maybe 3 mins microwave at night... And in fact the BMS confirms - 10% drain overnight...

Thing is... Since I never got to 100% yet I don't know my SOC right now, and how close I am to 100%! And if the cells delta etc is ok

So this is what I'm getting and what I configured, you tell me what's wrong and what you would do

Weather here: Never below 0ºC, no worries, never above 30º inside no worries either

BMS settings

High cut-off: 3.65V
Low cut-off: 3,0V

BMS cell voltages set from 0 to 100% using iOS app using a chart, or several, I found online, and I do know they are resting voltages - that i know, not a total noob

So, now what I wanna ask is... Today my BMS read 100% for the first time, and honestly with 4 consecutive sunny days I thought they could really be there, in fact they should be close, but they kept receving the same 12A charge, around that, as they were receiving before getting to 100% in the BMS, and the voltage never above 27.2V, around 3,4V per cell... The highest cell read around 3,41V, the lowest around 3,39 - 20mV delta... Is this acceptable?

I know JBD BMS has a low balance current, and these are B-Grade probably not matched cells, but they seem close... Now that I'm almost reaching 100% do you think the BMS will be able to bring them to balance?

Also about the settings in the MPPT...

Charge Voltage (Absorption): 28,8V (3,6V per cell)
Float Voltage: 27,2V (3,4V) per cell... Probably will lower these after the first cycles to try to mantain 90% max charge or something

When the MPPT senses they are full the current will drop, right? Since the voltage never really got to 28,8V I can assume despite the BMS claiming SOC was 100% they weren't? (Sun is setting now, no production anymore, and the voltage has dropped to 3,36V per cell, more or less, so I think they definitely are not 100%, but close right?)

What would you change? What can you advise me? Thanks!!!

 

[time2roll]

20mV delta at 3.4vpc is balanced fine. Delta may increase some as the cells approach 3.60 volts. Charging to 28.80 does not leave much headroom for a few cells to be high and BMS shuts down for over volt. Ok to reduce charging voltage to 28.00 and see where things are at the top. Never going to be perfectly matched. Generally balancing will probably stop at about 15mV delta so all is real close and none to worry about.

Anything above 27.2 is virtually full charge so the 100% capacity reading is not far off. Maybe 98%-99%.

For long cell life a little lower top voltage will be fine.

 

[besugosolar]

20mV delta at 3.4vpc is balanced fine. Delta may increase some as the cells approach 3.60 volts. Charging to 28.80 does not leave much headroom for a few cells to be high and BMS shuts down for over volt. Ok to reduce charging voltage to 28.00 and see where things are at the top. Never going to be perfectly matched. Generally balancing will probably stop at about 15mV delta so all is real close and none to worry about.

Anything above 27.2 is virtually full charge so the 100% capacity reading is not far off. Maybe 98%-99%.

For long cell life a little lower top voltage will be fine.

Ok thanks for all the insight! Right now sun is starting to shine and the SOC dropped to 85% overnight - 15% drain. Reads around 3,33vpc... I will let it go to 28,8V today again and see if it gets there and settles there... Then I will try to adjust for lower top voltage. Thanks!