Invite to Troubleshoot with me: ... on my 5th Morning of Top Balancing Attempt on 8 x 280Ah EVE cells; Charging at 10A (w some 7A cycles) on 8 LiFePO4 cells wired in Parallel; Stuck at 3.365 Volt top for last 24 + hours; while wanting the Full 3.650 Volts Top Balance Charge !!! . This is my second set of LiFePO4s which I intend to add my 1st DIY 24v 280Ah set to get a 24 volt 560 Ah battery bank; for my 3 x MPP LV2424s with 6000 Watts of PV input. I recently received this second set of 8 EVE cells from China via sea freight to USA measuring 3.304 v - 3.305 volts. I think: I may have one below par cell(s) holding me back from achieving my full 3.650 Volt Top Balance Charge ???
Studying a few recent Threads here related to top balancing, after my earlier 1st DIY LiFePO4 and Top Balance lessons; has been helpful. I documented one below par cell on my first DIY LiFePO4 build set here in this forum, and got that one cell replaced for free by Xuba (took time of documenting the problem, then the sea freight shipping). Further testing of that one below par cell (now on my shelf) revealed it getting only 225 Ahs (max as measure on that 200 watt fan heater unit Will P has turned us on to; ... originally estimated to be 170 Ah via my earliest Chargery BMS info. that it bottomed out early) ... out of its' 280 Ah Rating. That same cell also shows it is below par by NOT being able to take a full charge to 3.600v or 3.650v; had higher internal resistance than the other good cells, and it will only charge up to a 3.360 volt MAX (its' max top charge voltage). That history is why I currently think I may have one below par cell holding me back from getting a Full Top Balance Charge on this second set ???
REFERENCES # 1: I did some math calculations to estimate how long it might take me to get to 3.650 Volts on a Top Balance effort; and estimated about 67.2 hours = 2.8 days from this math: 280 Ahs x 8 cells in parallel = 2,240 Ahs; ... & my 3.305 volts starting point = about 70% SOC; so charging 30% of 2,240 Ah worth of my LiFePO4s to full 3.650 Volts, to 100% SOC @ 10 Amps Charge; Math: 2,240 Ah x 30% = 672 Ah / divided by 10 Amps (charging) = 67.2 hours = 2.8 days. I realize this is not perfect/ might have other factors involved. After 96 + hours of charging at 10 Amps (with a few cycles of 7 A charging when adjusting Power supply voltage downward/ closer to 3.650 V ); I have been stuck at 3.360 to 3.650v for that last day and half (@ about 3.365v for last 24 hours) !!! ... I just turned my power supply charging off, and my new 8 cell battery banks drops to 3.350 v within an hour/ and is 3.348 v two hours later (might be normal). ... After 1 + day at same voltage/ with no climb; Does anyone think I would benefit from more parallel charging?
REFERENCES # 2: I copied some comments from recent forum threads to register my lessons (thank you to the authors): While this is may be redundant; these posts below speaks to my lesson junction; ... from folks w similar 8 or 16 new 280 Ah LiFePO4 sets:
one post: ... So after days and days of slowly charging my battery bank and getting everything top balanced I was finally able to fully assemble my battery today. The 4 groups of parallel cells all showed either 3.600 or 3.601 prior to making the series connections. ... Once the cells get past 3.5V they should start filling up a lot faster (my comment: I notice that too, good to be watching past 3.5v, to avoid, then easily overcharging/ I did that once!) ... 10A is fine.... but can take a long time if the cells start in a low state of charge. Even at 10 amps your are only getting 10A * 3.65V = 36.5W.
a GOOD IDEA : I would do this next time for the larger Ah LifePO4s/ *** quotes (mixed w my comments)
*** What I do is first wire the cells into the 24 V bank (with the BMS) and then charge to 29.2V till one of the cells hits 3.65. This allows me to push 29.2V * 10A = 292 watts. However, even this can take quite a while if the cells are in a very low state of charge. Note: Initially the charge will be limited by the 10 amp limit of the supply ... Once the cells are mostly charged, take the bank apart and re-wire them all in parallel and then charge them to 3.65V till the current drops to near zero.
(MY NOTE: ... or I could much more quickly charge and discharge via one, or up to three of my currently wired up and working MPP Lv2424s All In Ones for up to 0.5C / 140 Amps or more, to get close to my full charge (w view of cell balancing act), ... & then reconfigure battery bank for its' full top balance / then go for my 580 Ah battery bank. )
REFERENCE # 3: Picture Attached shows 2 DMMs; one w a DC amp clamp confirming my 30V /10A rated Bench Power Supply putting out Amps to my 8 batteries for my top balance effort. I had question about if my $60 Power Supply might be malfunctioning, as it does not allow me to dial my desired voltage when 1st turned on, until I hook it to battery (wish I had spent an extra $20+ for a better model). My DMM with DC Amp Clamp Meter has also confirmed 10 Amps IN to battery when I dial up the voltage (max).
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Troubleshoot Options: I think any of these ideas will lead me to a below par battery.
... I will see by proceeding one step at a time.
Option #1: Disconnect batteries and charge one cell at a time for one hour: Look at which ones gets to higher voltage, and which one(s) might not. I have a timer switch to easily do one hour cycles. If I find one cell that will not charge like the others, I will Ah test that cell's Ah Capacity (1st) with the 200 Watt fan heater unit I have here. While I wish I had an Ah tester w good cut off voltage option that could draw more watts (amps), that 200 watt fan heater allows me to set a low voltage cut off to stop its' smallish current draw when battery hits < 2.5v volts. That its' plus !!!
Option # 2: I could also hook my new 8 cells in series w my 2nd Chargery BMS, and connect BMS charge side trigger to a battery cut off relay; and charge with my 30v/10A rated Bench Power Supply to see what the BMS info shows for individual cell voltages.
Option # 3: I could replace my current 24v LiFePO4 set with these new ones have have been top balance to only 3.365v (vs 3.650v ), and put them through some charge and discharge cycles at up to 140A (0.5C) to see what my Chargery BMS8T information shows. ...
If I find a below par cell, I wonder if a few full charge and discharge cycles at various amps up to 140 Amps in and out could help it???
Open to comments while hoping for the best. Currently Attracted to Option #1 while going to posting this first :+) Bill