charging problem

[rodagaster]

Hi guys i needa bit of advice regards charging a 3s5p 18650 pack i made 3 of these packs and 2 charge fine but 1 pack is so slow it can take days to charge from 10.6v upto 12.3v i have fitted a new bsm board thinking that may be the problem to no avail then i resoldered all the connections still no change the cells i am using are samsung 1500mA and they tested between 1350mAH to 1470mAH i am using a b-max clone ,i am also having the same problem with a 3s10p pack so any help or suggestions would be appreciated thank you .

 

[Redpacket]

Maybe check the problem packs for one of the sections self discharging? Might have a couple of cells gone bad?

 

[Korishan]

+1 with Redpacket. That was my first thought, too. Check the voltages of each section before, during, and after charging to see which section might be slacking. The bms is probably doing it's job by keeping the other sections from going to high and overcharging.
Another thing to note with checking while charging. Sometimes a bad cell will take a charge really quickly, jumping in voltage. So if 1 section is lower than the others, then it jumps higher during the charge, then drops low again afterwards, you know definitely which section it's in.

 

[rodagaster]

Maybe check the problem packs for one of the sections self discharging? Might have a couple of cells gone bad?

Hi Redpacket thanks will have a look in the morning .

---

+1 with Redpacket. That was my first thought, too. Check the voltages of each section before, during, and after charging to see which section might be slacking. The bms is probably doing it's job by keeping the other sections from going to high and overcharging.
Another thing to note with checking while charging. Sometimes a bad cell will take a charge really quickly, jumping in voltage. So if 1 section is lower than the others, then it jumps higher during the charge, then drops low again afterwards, you know definitely which section it's in.

Hi Korishan thanks i never though to check the voltage during charging will see in the morning how it goes .

 

[jonyjoe505]

when I had a similar problem it was caused by 1 cell (out of 24) that was slow discharging. The battery pack would just not fully charge and I tried with different chargers.

I took the battery apart and checked every cell, the bad cell when charged to 4.2 would discharge quickly when removed from charger. Replacing that cell fixed the problem. It would also give me balancing problems.

Its a lot of work but you can narrow it down by seeing which row of batteries has a lower voltage then the rest.

 

[Geek]

when I had a similar problem it was caused by 1 cell (out of 24) that was slow discharging. The battery pack would just not fully charge and I tried with different chargers.

I took the battery apart and checked every cell, the bad cell when charged to 4.2 would discharge quickly when removed from charger. Replacing that cell fixed the problem. It would also give me balancing problems.

Its a lot of work but you can narrow it down by seeing which row of batteries has a lower voltage then the rest.

Had you checked cells for self discharge beforehand? When I test cells, I charge them fully and let them sit for a few weeks, then check voltage again. Anything lower than ~4.14v gets set aside. Anything lower than 4.1v goes to the bin.

 

[rodagaster]

when I had a similar problem it was caused by 1 cell (out of 24) that was slow discharging. The battery pack would just not fully charge and I tried with different chargers.

I took the battery apart and checked every cell, the bad cell when charged to 4.2 would discharge quickly when removed from charger. Replacing that cell fixed the problem. It would also give me balancing problems.

Its a lot of work but you can narrow it down by seeing which row of batteries has a lower voltage then the rest.

Hi mate when i checked the pack this morning i had 1 row at 3.76v 1 row at 3.72v and the last at 3.74v so i charge the low ones up to 3.76v and then charged the whole pack again which charged up like normal but when checked again later on i had 1 row at 0.2v lower so i will take that row out and check them properly

---

when I had a similar problem it was caused by 1 cell (out of 24) that was slow discharging. The battery pack would just not fully charge and I tried with different chargers.

I took the battery apart and checked every cell, the bad cell when charged to 4.2 would discharge quickly when removed from charger. Replacing that cell fixed the problem. It would also give me balancing problems.

Its a lot of work but you can narrow it down by seeing which row of batteries has a lower voltage then the rest.

Had you checked cells for self discharge beforehand? When I test cells, I charge them fully and let them sit for a few weeks, then check voltage again. Anything lower than ~4.14v gets set aside. Anything lower than 4.1v goes to the bin.

Hi mate no i didn't but i wont make that mistake again , i was a bit impatient i suppose but a lesson learnt .