12S Bluetooth Smart BMS from LithiumBatteryPcb has probably drained my Battery

[KidCe]

Hello there,

I just joined this forum because i though this would be the right place to talk about what happend to my Battery and BMS. Ive been reading alot here about the BMS ive got before i even used it. Now that i have used it and had it built into my system i have run in to a huge problem and i hope we can discuss about that here and maybe find a Solution.

I have bought the 12S SmartBMS from their AliExpress store and have been using it for many months now. At the beginnin everything seemd to be working perfectly. Charging, Discharging, Balancing were all fine. But now that the Corona Lockdown hit me, i were not able to use my device so it was standing unused in my room at about 44V Battery Voltage. After 3 Months of not using it i decided to start some work on it again and checked the Battery. I had to find out that the Battery was completely drained to 2.3V. So my 12S3P 10Ah Li-ion battery is now dead. I were really pissed because i thought a BMS should prevent exacty this....
Im Pretty sure i connected everthing the right way so the only thing that could drain the Battery could be the BMS itself. It is rated for a Sleep current 200uA which could never deplet the battery so much. I guess there was a problem with the BMS not entering Sleep more and therefore draining up to 20mA current.

Is there a specifiy way i should measure the BMS`s Idle current without a Battery? Maybe i could connect 44V from my Bench PSU to 12 Resistors in series to simulate the individual voltage cells.

Did anyone make some measurements of the BMS`s sleep current or has similar experiences with that BMS?

I think once the Lockdown ends and i will visit my local hackerspace again to Spotweld a new Battery. But before installing it i should have some safety mechanism to prevent the BMS from draining the Battery again. How would you go about that? Maybe just a Switch between the Batterys 0V and the B- Port of the BMS like in the Picture ?

Im not 100% sure if that would help since 0V it still conencted though the Balancing connector.

I tried contacting lithiumbatterypcb but atm they have the new years holidays in china so it will take some time for them to response.

I would be really happy if we can discuss about my case a little bit here.

Greetings
KidCe

 

[e-beach]

Well, I am not familier with your BMS, but sorry to say your story is an old one around here. BMS's being connected to a battery for a long time and draining the battery has happened many-many times. As you surmise, disconnecting the BMS for battery storage is the way to go. Either by switch (make sure your switch can carry the amperage needed) or by an adequate connector. Although, and I may be wrong on this, but I believe you must also disconnect the positive or negative sense wire to make sure there is no circuit connection to the battery.

The other option is to have it connected to a charger all the time to keep it topped off, or possibly having a timer between the A/C outlet and the charger set to go on for something like 12 hours once a week.

Anyway sorry about your battery.

 

[LeftieBiker]

Disconnecting the BMS and leaving the state of charge at roughly 50% is the way to go. If you keep it fully charged, the battery will degrade faster. The documentation for the BMS should have warned you not to leave the bike sitting unused for months with the BMS connected.

 

[amberwolf]

I had to find out that the Battery was completely drained to 2.3V.

Just to be sure...is that 2.3v per cell?

Or 2.3v at the BMS discharge output?

Or 2.3v across the entire actual cell section of the battery pack, from main cell + to main cell - (not measuring at/across the BMS)?

I ask because it's common for people to check the BMS output voltage and find it's "dead", while the cells themselves are only down to about the regular LVC 2.8-3.xV, when measured directly rather than at the BMS discharge (or charge) port, and the BMS output reading is only because it has shutoff the output to protect the cells from overdischarge, and then shut itself off.

But sometimes the BMS doesn't *have* a shutdown mode, being a "dumb" BMS, and always has the same drain on the whole pack to power itself.

Sometimes the BMS balance channels don't fully shut off, ever, and it continues to drain all cells very slowly.

Sometimes one (or more) channels get stuck "on", and drain just the cells in that group (probably not what's happening here).

 

[john61ct]

Basic principle

disconnect any circuitry so the cells themselves are fully isolated while not actively being cycled

BMS functions are only needed while the pack is actually being used

Aside from the issue of parasitic loads actively (not just "self-") discharging

many packs get destroyed by devices failing when the owner isn't around.

Why many call them Battery Murder Systems, can cause more problems than they solve.

 

[KidCe]

Alright, thank you guys for you answers
It seems like disconnecting the BMS completely is more common than i thought.
Sure this is the safest way to do it, but i find it a pretty unelegant solution cauz it at the end its dependent on me to always remember to unplug everthing.

@

I had to find out that the Battery was completely drained to 2.3V.

Just to be sure...is that 2.3v per cell?

Or 2.3v at the BMS discharge output?

Or 2.3v across the entire actual cell section of the battery pack, from main cell + to main cell - (not measuring at/across the BMS)?

Across the whole Batterypack without measuring the BMS. So + of the Top cell and - of the bottom cell.
So Cell Voltages were about 0.2 Volt per Cell.


BMS Product Page
BMS Specification:

@amberwolf
about the BMS not having a sleep mode or channels not shutting of, well... i think that *should* not be the case with my BMS, like seen in the specification there is a sleep more with rated Current consumption. So i am still pretty sure it was a fault that the BMS somehow did not enter sleep mode.

Also i wanted to add: a college from work got the same BMS and almost the same Battery. I asked him if he had his unused for some time, and as it turns out, he had his one standing around almost for the same time! and his batterypack only lost about 0.3V Volt over the same time.

 

[amberwolf]

It seems like disconnecting the BMS completely is more common than i thought.
Sure this is the safest way to do it, but i find it a pretty unelegant solution cauz it at the end its dependent on me to always remember to unplug everthing.

It is a quite ugly solution...but it is too often the only realistic one, without replacing stuff with more expensive hardware. (when a better one even exists)

I dont' use a BMS on my EIG packs, partly because of stuff like this, and partly because a BMS is only really necessary when cells are expected to get out of balance thru using them near their limits (common on ebike packs) rather than using them closer to just the middle of their capabilities, or when using low quality cells (also common on ebike packs) or poorly-matched cells (ACOEP...seeing a pattern? ), etc.

Every time I think about getting one of these neat new bluetooth BMSs so I can be curious and monitor pack data more closely, just for the heck of it, another thread like this comes up, and I damp those thoughts right down.

When using quality well-matched cells, and using them well within their limits (not charging nearly to full, not discharging nearly to empty, not charging or discharging near their current limits, etc), then a controller pack-level LVC taht's set well above "empty" voltage will protect against overdischarge, and a trustworthy charger set for HVC well below "full" voltage will protect against overcharge, for the most part. The older the pack gets, the more likely it is a cell will begin to age differently than the rest and behave differently, but as long as they *are* still wellmatched....

Just out of curiosity I periodically check cell voltages but I have not had any noticeable imbalances...not the case with the one "actual" ebike pack I have made of 18650s, even when used at low current levels (vs what it is "rated" at), which pretty much needs balancing every time it is used even a little. I wouldn't use them *without* a BMS, because I don't trust the cells (I also dont' trust the BMS taht's on it either...but it's not worth buying a better one for it).

I don't recommend most people "go naked" with their batteries...but it is possible to do so in the above circumstances.

Across the whole Batterypack without measuring the BMS. So + of the Top cell and - of the bottom cell.
So Cell Voltages were about 0.2 Volt per Cell.

Yowch. Yeah, that is a very toasted-dead battery pack. Can't even recharge the cells to revive it.

about the BMS not having a sleep mode or channels not shutting of, well... i think that *should* not be the case with my BMS, like seen in the specification there is a sleep more with rated Current consumption. So i am still pretty sure it was a fault that the BMS somehow did not enter sleep mode.

Could be it's software crashed and locked up the MCU, or some other hardware defect or software bug. The other guy's result means it shouldn't be a global issue with it...so you were just the unlucky recipient of the fried guineapig award. :/

 

[KidCe]

Yowch. Yeah, that is a very toasted-dead battery pack. Can't even recharge the cells to revive it.

Well... i thought the same for the last few days, but i got convinced to try it out. There are some researchpapers which state that as long as a Li ion doesnt get reverse charged it should still be pretty safe to revive it. There is also a video from BigClive which covers this:
https://youtu.be/sRwoYJyjZNo

I will run some tests inside a Aluminium Case with a electronic load and see i if the cells get warm or anything. If that goes well i might reuse the Battery.... even tho i have a very bad feeling about this.

Could be it's software crashed and locked up the MCU, or some other hardware defect or software bug. The other guy's result means it shouldn't be a global issue with it...so you were just the unlucky recipient of the fried guineapig award. :/

I hope the manufacturer answers me after the chines New years Holidays ends, hopefully they want to investigate this problem.

 

[amberwolf]

Well... i thought the same for the last few days, but i got convinced to try it out. There are some researchpapers which state that as long as a Li ion doesnt get reverse charged it should still be pretty safe to revive it. There is also a video from BigClive which covers this:
https://youtu.be/sRwoYJyjZNo
I will run some tests inside a Aluminium Case with a electronic load and see i if the cells get warm or anything. If that goes well i might reuse the Battery.... even tho i have a very bad feeling about this.

The catch is...there can be damage to the cells that you cannot see, cannot know about, and cannot predict the results of. Even if the cells behave normally afterward, they can still be damaged in invisible ways. The only way to find out if it is there is to encounter the results of the damage, and if the damage is of the type that produce dramatic self-disassemblage or immolation, you might get no warning of it except for "hey, what's the that smell...oh crap!" and then the giant fireball of the entire pack being involved as one cell rapidly heats the next, etc.

To me, it is not worth the risk (even when I had no money)...but: I did successfully revive a drained-dead *EV GRADE* cell pack (EIG NMC C020 20Ah pouches) (only used for bike lighting, not traction) by very very slowly bringing it back up to "LVC level" voltage, then slowly charging back to full...but the cells were never the same as they had been, more voltage sag, less capacity, etc., and I did not use them anywhere near their original capabilities. They might not have survived usage at their original ratings. This pack did last some years more...but again, not as a traction pack, and I never "trusted" it.

But 18650 cells are a whole different ballgame, and especially since they are used much much harder than the pack I revived--often right up at their max ratings...which I would never trust on a revived cell.

 

[john61ct]

The word "damage" applied to cells, is as ill defined as"love".

For me, any event that significantly reduces life cycles, well beyond what normal operation in that use case usually does,is Damage.

"Only" reducing lifespan by 20-40% may be tolerable, but it's major damage.

As stated, even that major a damage, may not be detectable to normal users with normal gear.

But the likelihood of a "rapidly expanding sudden fire" (aka an explosion) may now be 500x greater than before the event.