Finished the DIY build and cap testing
Total weight of the 8 cells is 43.05kg
Out of the box, each cell has ranged from 3.297v to 3.301v.
The 8 cells were placed in parallel and were top balanced to approx 3.6v.
Then setup in a square 2p4s config and further charged with victron bluesmart 25a charger using default victron settings for li-ion which I think only got the battery bank to 90% SOC which is what the Daly BMS reported before I began the discharge/cap test. Not sure how accurate the BMS was reporting the SOC on its first go. More on that below.
Discharged @ 180w (though I did increase this to 185w for the last few hours). This was approx 13a which rose to 15a in the last few hrs as the voltage dropped.
Set amps and voltage to variable to force the constant wattage.
The first hour was 13.3amps and 179wh
Cutoff voltage was managed by the BMS...not the cap tester.
Expected results:
640ah X .9 (for 90% of total capacity) is 576ah
@ 13.3a/hr it should take 43hrs to deplete.
Actual results:
44hrs = 3hrs + 41hrs (I accidentally stopped the test at 3hrs when playing with the capacity meter menu and had to restart
)
615ah = 43ah + 572ah
So, depending on the accuracy of the BMS original SOC 90% (which also reported 0% SOC for the last 5 hrs of the test - likely it has a few more cycles before it becomes more accurate) then I guess I'm somewhere in between the calc'd 90% 576ah and the 100% 640ah and expect the next full charge/discharge to report more accurate SOC after the BMS learns a bit more from the low/high voltage cutoff.
At 615ah, I am very very happy.
I'm not going to get picky about the 25ah difference between actual 615ah to expected 640ah because I used conservative voltage cutoff so I may actually have gotten more.
So, all in all, I'd say it was a successful purchase from liitokala on Aliexpress.
N.B. re the faulty DALY BMS SOC - I have since learned that there's a bug in some recent Daly BMS firmware which incorrectly reports the SOC. It doesn't affect the capacity of the battery either, and for many people, especially those who use external battery monitors (I use a Victron BMV-712), they will never even notice it. It only affects those who monitor their battery capacity via the SMART BMS App.