Oooooh…the comma has me bamboozled
it’s a non 'merkan decimal point
Mechanical engineer from Finland, working in the Bay Area
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My suggestion would be simple (if possible)
Remove the group from the pack and bleed it manually to the same voltage as the others
when it’s saying over voltage do you see that cell 3 pgroup close to 4.2?
Any evidence it’s just slowly being bled over to the other cell groups but it’s bumping into 4.2 and causing the BMS to cut the pack charge?
At what voltage does the bms start balancing cells. any evidence that it’s doing so?
How did that one Pgroup get so high? were the close to begin with? does it have less capacity than the others?
no need to remove from the pack.
you can bleed and charge 2-3amps safely through the balance leads. I do this all the time
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Not directly. It stops charging the whole pack, and drains down the offending cell/group, then resumes charging. The BMS has no way to selectively not-charge a group, only discharge.
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Only on BMS’s with active balancing. Most just take the extra charge and turn it straight into heat with a resistor. Much cheaper and simpler and smaller than trying to shuttle the extra around to other cells.
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Volt measurements so I can match the cell voltages for the P group cells
thank you… In my mind power was bleeding from a high volt cell to a low volt cell… I appreciate the knowledge, and the explanation
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No problem, knowledge is meant to be shared.
There are some BMS’s that do active power transfer, but they’re usually reserved for very large battery systems like powerwalls or EVs, where there’s a significant amount of energy to be saved from becoming heat, and the extra size and cost don’t have as much of an impact.
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My ebike battery will have that option. Can’t wait to see it in action. Gonna feel like magic.
The bms was an extra 135$ on the price but I imagine it will be worth it
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haha, sorry buddy.
buried somewhere…
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Hello! I am looking at some molicel 21700 batteries for a 10s3p pack that would cost me 150eur, how much would it cost to have someone in europe build me a pack from these 30 cells :? Thanks!
What voltage do you try to get cells to before you weld pgroups? obviously the same voltage but a storage charge? a full charge? does it matter?
I would think a low storage charge would be optimal.
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Around storage voltage is better in general, when I get new cells they arrive at 3.40V usually so I just use them like that
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about here…
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Well it’s not perfect–got some not so pretty welds on the serial connections but they’re solid. Second battery build for me, 12s3p with 40Ts. Gimme the harsh criticism so I can get better!
I used that liquid flux that @MysticalDork loves so much and it left this yellow tinge around the welds. What is that?
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Literally anything between the sides of the pack
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