Changed the BMS to a JK 200A with active balancing and the cells holding well. A new (or first?) top balancing did the job.
Top Balancing "How to"
- Thread starter snoobler
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Hey. I'm still new to building packs. First 2 I had balanced normaly, but the last one 8 (paralleled pack) cells of EVE 280Ah won't stop consuming power and won't charge over 3.38v. I believe there's a faulty cell. But overall, what would be the steps identify the problem?
Ampster
Renewable Energy Hobbyist
Patience. A faulty cell would not stop the voltage from increasing. A faulty connection could. Have you checked the settings on your power supply? What is the current going into that group of cells?
It's a cheap amazon PSU. Current was and remained over last 12 hours at ~3.454 amps. Started at around 3.7 amps
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Ampster
Renewable Energy Hobbyist
You have 2240 Ahrs of capacity. Assuming they were 50% SOC it might take 324 hours at 3.54 Amps to add 50% to fill that group of cells. Since you already have 12 hours you now only have 312 hours left. Mark your calendar for early next year or get a bigger power supply.
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Yes, I did the charge in series via BMS with a victron 24/12 chareger at 12 amps. One of the cells got to 3.6v and then I unplugged the BMS. Remainng cells were around 3.4volts. Then I decided to do the top balancing and it just won't stop using current.
Ampster
Renewable Energy Hobbyist
Maybe the current is not getting to the cells. Have you checked connections and used ring terminals and not banana plugs or alligator clips?
Alligator clips it is. Ok, I will give it a try. Thank you.
sunshine_eggo
Happy Breffast!
8 * 280Ah = 2240Ah
At 3.454A, that would take 648 hours to fully charge those 8 cells.
In other words, 12h / 648h = 1.9% of the total capacity.
At 3.4V/cell you were no more than 95% charged.
Do you think 12 hours is excessive?
of rource not, that's why I charged it with bms untill first cell reached 3.6 volts. Just mentioned it in one of the next comments.
TorC
Solar Enthusiast
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From what I read, chances are your connections are limiting current to a cell that's still below the knee and holding overall voltage down. Until that cell rises, the bank voltage won't rise, and you don't have enough potential difference for the high cells to push current into the low ones. Fix your connections or wait a few days.
MisterSandals
Participation Medalist
Can you post a pic of your charging wiring/setup?
They started at around equal voltage, if I remember correctly. But yes, I will discharge that one first.
sunshine_eggo
Happy Breffast!
"equal voltage" is not "equal state of charge." The latter matters. The only thing you can say with any confidence is that cell is at 100% while the others are not.
Hedges
I See Electromagnetic Fields!
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Equal voltage does not indicate equal SOC. Except up around 3.6V/cell
You mean check that cell voltage? In parallel, poor connection could leave one cell undercharged. In series, all get identical current (except to the extent balancer works.)
But yes, poor connection can cause BMS to report higher voltage. Checking cell voltage directly on cell terminals (not busbars) would confirm.
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