Where’d you get M35a cells?
1 Like
Team-Legit in SoCal. Out of stock now!
https://team-legit.com/molicel-m35a-18650-3500mah-10a-li-ion-cell.html
Did I damage my cells by accidentally shorting them through a multimeter?
I built 3s3p section of my pack (Molicel P42a) and I went to probe the voltage with a multimeter, not realizing that the positive probe was accidentally plugged into the terminal that’s supposed to be used to measure current. (On my multimeter this terminal doesn’t have a fuse and says “10A max”)
I noticed this a few seconds after connecting the probes and by that point the multimeter and the probe wires had gotten quite hot. I’m wondering if I did any damage to the cells in this amount of time - I felt them immediately afterward and they didn’t seem warm at all. The cell voltages have now dropped by about 0.01V, but that’s the only difference I noticed.
1 Like
They should be fine - The meter and probes/wires probably had enough resistance to stay well below the safe pulsed discharge current of three P42A cells in parallel.
2 Likes
The meter should have a fuse so you are probably good, but you might want to check/replace that fuse for the future…
3 Likes
A friend charged his 12s3p P42A pack overnight and apparently used a 13s charger.
He told me about the odd values this morning, and I just told him to discharge that pack ASAP. He went for a ride and now the cells are at 4V/cell again.
I’m super glad it didn’t catch fire in his apartment…
max. cell- and battery voltages are set up properly.
Now that the pack isn’t an immediate fire hazard anymore, I’d like to know why the BMS couldn’t stop the charging. The voltages were way over the 4,25V cutoff voltage and reached up to 4,57V…
Also, what do you guys think? Is this pack safe to use after this incident if everything is checked and maybe cycled a few times with precaution, or is it time to bin it?
Maybe @Battery_Mooch can chime in and maybe enlighten us what happens to the cells if they are charged that high.
(this is a brand-new pack built by me)
12s3p P42A, 20A LLT BMS set up as charge only
Cells manufactured batch: 01 December 2020
3 Likes
Metal box or a bucket of sand should do the job
3 Likes
Maybe the llt is defective? Mine cuts power when the cells hit 4.18 just fine…
1 Like
I would set the limit down to 4V or something and double check if the bms does cut off at that value. If no, than definitely something wrong with the bms.
3 Likes
We can’t say that there is no fire hazard. Overcharging can start a sequence of events that can (but very unlikely) eventually lead to one or more cells going into thermal runaway and catching fire.
No idea what happened but @Andy87’s suggestion for testing at 4.0C/cell is a great one. Charge slowly and carefully monitor each cell’s voltage and temperature.
Unfortunately there’s no way for anyone to know. Your friend will have to decide how to proceed.
Overcharged li-ion cells can plate metallic lithium onto places where it shouldn’t belong. If it happens for long enough then one or more cells can short-circuit internally. This can be a slow self-discharge or, less likely, a cell can go into violent thermal runaway.
The longer the overcharge goes on, and the higher the voltage, the worse the damage will be. There is no way to quantify the damage or risk though, too many variables.
All we can say is that what happened was bad. Whether the cells are noticeably damaged or there’s an increased risk in using them we don’t know.
Your friend can try that slow 4.0V/cell charge to test the BMS. Check every cell to make sure none are getting a lot warmer than the others.
Then let the pack rest for at least a couple of hours, even a day, and accurately measure each cell’s voltage. Leave the pack for at least a week in a room temperature location with no electronics of any kind connected (so no current is pulled from the pack) and then recheck each cell’s voltage. If any cell has gone down more than a few millivolts then those cells could be damaged.
Keep the pack in a non-flammable location at all times. The odds of anything bad happening are tiny but the consequences can be huge if the pack does catch fire.
6 Likes
Following my adventures, I took the p group out of the pack and the welds on the whole negative side were so weak I pulled them apart without much effort and 1 row of the positive side was also easy to tear off.
I am going to redo that group with .15 as I think it will.likely be easier to weld.
4 Likes
Glad you found the issue! Might be worth inspecting the other p groups welds as well.
3 Likes
That’s what I was thinking but this will be so much work so I am building motivation up right now.
3 Likes
Did you ever figure out you motors not starting @ the same time?
Also, try turning up your welder a tad. Has worked for me when I find weak welds.
1 Like
This actually happens only when I gently push the thumb well, the master side does turn first and the second side catches up as I gradually give more throttle. But if I give it more throttle from the start they both spin together. I have been told it could be normal so I did not keep investigating.
I am using a malectrics and was following the recommended 26ms settings with a 680A battery. And for the nickel on nickel welds I turned it up to 50ms. Do you think I should turn it up some more?
Also, I noticed these small indentations caused by me gorilla pressing those probes too hard maybe? Can this cause issues?
2 Likes
Shibby.
Car battery or what?
Those dents, while I dont think it would be an issue in MY build, i wouldnt allow it to a client. They also look like they didnt even weld @ all. What ms did you have set on those welds?
Edit: nvm see where you said 26ms. Crank it to 30ms and try a few practice welds (find a shit cell). Keep cranking till you actually get a solid weld.
2 Likes
Those dents are probably just nickel that was vaporized / welded to the nickel strip and came off even though the weld wasn’t super strong
1 Like
Yes car battery
I think I am.going to disassemble the whole pack. Do you think I can just redo some welds at the same spots as my initial welds? Other wise I will tear off all the welds and redo it completely.
I might have been too optimistic with my abilities and maybe shouldn’t have used .2 thick.
1 Like
Am I safe reusing those dented cells?
I mean re-welding on top
1 Like