Water damaged battery

Calpis

1 µW
Joined
May 22, 2018
Messages
3
Hi,
I dropped a 10S5P 18650 battery pack in to water. It was just really briefly for a few seconds. After drying it thoroughly and letting it sit for a while i connected the battery to the esc again but it would not turn on. After that i connected the pack to a charger and it would charge as normally and the pack would turn on the esc again.
But here is the problem. The charger will turn green as if the battery is fully charged, but connecting the pack to a voltmeter will show just 75% capacity. After that i disassambled the pack for further evaluation and measured all series groups voltages. Four of the five groups are showing readings of 39.5V and just one group is showing the full 41.5V at which the chargers stops charging.
I am clueless at what is the case here. Do i have damaged cells in four of the five groups or is there a faulty cell in the group which reaches the 41.5 at first? Or is the BMS damaged?

Thanks for your time reading this, i am really
looking forward hearing from more knowledgeable guys then i am!
 
You prob damaged the BMS. Or it unbalanced the pack to where it's taking forever to rebalance, to where you might have to manually discharge the high group or something. But it's hard to see how a few seconds of puddle time could do the second one... I could see it shorting out a BMS real fast.
 
Thanks for your reply!
Yes indeed, the BMS was closest to where the water penetrated the pack, hopefully i just have to replace the BMS. But how can i discharge the high group without tearing the pack apart?
 
I do most of mine with a pre LED bike headlight with two bulbs that are switchable, so you can change how fast it's discharging, with the the wire ends soldered and filed the right size to poke into the BMS plug leading to the battery. But you have to have steady hands... It's real easy to spark things just enough to mess up the plug. Then I set my phone timer so I don't forget to keep checking it.

Sometimes people go the other way and charge the low ones up, whatever works for you...
 
Okay, thanks for your advice!

The BMS is really tiny, if i would try to stick something in there i will likely damage it further then doing good.
I read somewhere that prolonged charging helps with balancing, would it be an option to connect the pack for a really long time to the charger?
 
That could possibly work... As long as the BMS is still functioning enough to limit the voltage on all the groups as they get full. Lots of double checking during charging would prob be a good idea, which of course gets tedious if it's taking hours or days.
 
I had one battery with a lame BMS that just shut off charging when the first group got high, but then didn't do any balancing. That made getting into some manual balancing unavoidable.
 
And I just re-read your first post... You do have 10 groups in there right, not just 5?

Also, all the cells in a group go to the same voltage, so one single cell wouldn't be going high first and throwing off the group reading, which doesn't mean one couldn't be getting crazy hot in the middle of a group during charging from being jacked up. It just wouldn't explain one group being high.
 
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