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2 12volt battery bank help
#11
Wow guys thank you so much with the awesome info! 
All your help is certainly pointing me in the right direction 
Now all things considered since I purchased 40 headway cells 
I would create 2 20 cell packs 2 bms’s.. so all this said how would you calculate the ah of one 20 cell 12volt pack 4s5p  Each battery is 8ah.
Thanks again in advance
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#12
Hrmm, posted the same reply 3 times Huh Huh Huh , and apparently didn't read the FAQ yet. (that's where you can find how capacity is calculated)
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#13
Sorry about that, I have gone through the faq page and in your thread I see some info on ah calculations. Thanks so much. For all the good info.
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#14
Alright guys after a long time I got the packs together and took them out this past weekend and wow I’m blown away these batteries are amazing. Anyhow I have a charging question, when I charge up the pack the negative battery side aka 1s as a bms or balancer is labeled, it always is undercharged and the other 3 banks seem to be relatively equal. Example first cell bank on the negative side is 3.3, next is 3.53, next 3.55, and last bank closest to charge lead positive is 3.6volts which total charge is 87_89% charged I want 95% and up. What do I have to do the make this charge properly, do I just have to manually charge the lowest bank with a 3.5volt charger? Any help would be awesome
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#15
Sounds to me like your BMS isn't wired up correctly or is just plain not functioning. If it were working, then all cells/packs in series should be the same voltage.
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Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
Certified 18650 Cell Reclamation Technician

Please come join in general chit-chat and randomness at Discord Chat (channels: general, 3d-printing, linux&coding, 18650, humor, ...)
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#16
Ok so correct me if I’m wrong when the bms is wired up the pack negative is the starting point, and the first cell positive is directly under the negative which would be cell 1, next in series would be the next cell positive and so on till I reach the last positive which would be 4s and the last lead on the bms. If this is true it’s hooked up properly so that means bms isn’t working
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#17
Secondly I checked the wiring it’s in fact correct
FYI I am using a Chinese bms made by deli green that might be the reason huh? Any suggestions on 4s and 8s bms. Do you recommend a higher balance amperage ? I would think the higher the amperage the quicker the balance. I reconnected my cell monitor 8 and checked each voltage 1s 3.35 2s 3.42 3s 3.5 4s 3.68 so I shit it down and let my small balancer bring the 4s down to a safer voltage. I need this baby to give me 100% soc not 89-91%
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#18
After you guys help me with my last reply’s. Can someone recommend their personal bms/10amp balancer for 4s and for 8s. Please guys I’m going nuts here trying to figure this out.
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#19
Ok my only fix is balance charge the batteries with buck converters and all voltages set to 3.56 so it’s been working quite well I think that’s my fix.
And to answer the question to the bms having to balance, the balancer is only on at a set point of a fully charged battery.so not all cells would get up to that set balance voltage. So manually charging all 4s banks is my option or spend 200$ on a quality bms
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#20
Ok another update. I removed the bms’s on both my batteries. I top balanced all the parallel packs (meaning I charged then individually to a 3.6volt cut off) and went out with the boat and everything was within .03 volts which is awesome. So I’m charging the packs with my big charger and everything is staying balanced. No balancers no individual charging so crazy. I even unplugged the bms’s for now. So balance charging solved my problems so far.
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