Do i have a dead cell?

[Zynode]

EDIT 22.02.2022. The seller has agreed to repair the pack. Obviously no warranty due to mechanical damages.

EDIT 07.04.2022. The seller has repaired the pack and said that the nickel plating connection came loose for a cell group that made the pack go out of balance as well as bad BMS.

Hi. I have 48V17.25Ah battery pack 13S5P with Samsung SDI INR18650-35E cells from enerprof.de.

Specs: BMS Continuous Discharge Current: 22A. The problem is that i believe i have a dead cell. I charged the pack to full and then left for few hours to balance but it was only 52.2V instead of 54.6V. Okay i balanced it to 54.6V and now a week or so later it's again about 52.2V. I believe i've had this issue for a long time (probably since i crashed a few times at the start (oops)). And that would explain the various cutoffs i've had at max amps (22).

I don't think i'm pushing the pack as i'm running it around 22A. I have 4V sag at full load (~40km/h), ~2.4V at ~35km/hAccording to cell sheet it's 8A discharge, 5P is 40A so i'm running it conservatively? Cell spec sheet - https://lygte-info.dk/review/batteries2012/Samsung%20INR18650-35E%203500mAh%20(Pink)%20UK.html

So the question is - do i have a dead cell? But if so then how could i balance it back up to 54.6V after ~24 hours? And how does it empty so fast? Do i have to rebalance it multiplte times? Any help is appreciated. Already asked the seller for what to do.

 

[SafeDiscDancing]

I charged the pack to full and then left for few hours to balance but it was only 52.2V instead of 54.6V. Okay i balanced it to 54.6V and now a week or so later it's again about 52.2V.

So the question is - do i have a dead cell?

This is a textbook example of how you burn down your garage.

The fact of the matter is YOU DO NOT KNOW what each of those 13S cell groups are doing.

Trust the Science means your house burns down.

What you need to do is get into your pack with a voltmeter and actually check each of those 13S groups for voltage and prevent a nightmare.

52v is about 4.0 volts average... if you charged it to 4.2 volts it might drop to 4.15 volts but it should not be dropping this much.

This is why I repeat over and over you need to know what is going on.

Trust means fire.

---------------------

And another thing... the "cause" might have been a previous crash, but often the Battery Murdering System (BMS) is so badly imagined and implemented that it's actually causing the problem.

All it takes is for the BMS to have some screwed up logic and it's going to skew your default balance up... assuming it was even balanced at the start.

My advice is to take off whatever shrink wrap covers this pack and get in there to find out what voltages exist.

----------------------

Another "Rookie Mistake" is to charge your battery to full and then let it sit AT FULL which is bad for it.

Your routine should be to leave your pack at the middle of charge when resting.

Best to charge just before you ride.

 

[Zynode]

I charged the pack to full and then left for few hours to balance but it was only 52.2V instead of 54.6V. Okay i balanced it to 54.6V and now a week or so later it's again about 52.2V.

So the question is - do i have a dead cell?

This is a textbook example of how you burn down your garage.

The fact of the matter is YOU DO NOT KNOW what each of those 13S cell groups are doing.

Trust the Science means your house burns down.

What you need to do is get into your pack with a voltmeter and actually check each of those 13S groups for voltage and prevent a nightmare.

52v is about 4.0 volts average... if you charged it to 4.2 volts it might drop to 4.15 volts but it should not be dropping this much.

This is why I repeat over and over you need to know what is going on.

Trust means fire.

---------------------

And another thing... the "cause" might have been a previous crash, but often the Battery Murdering System (BMS) is so badly imagined and implemented that it's actually causing the problem.

All it takes is for the BMS to have some screwed up logic and it's going to skew your default balance up... assuming it was even balanced at the start.

My advice is to take off whatever shrink wrap covers this pack and get in there to find out what voltages exist.

----------------------

Another "Rookie Mistake" is to charge your battery to full and then let it sit AT FULL which is bad for it.

Your routine should be to leave your pack at the middle of charge when resting.

Best to charge just before you ride.

Thanks for taking the time to answer me. I only left it to balance overnights. It was at 100% only for a few hours. That would not cause it to degrade this much over a year. According to battery university they left a battery at 100% for a year at 25C and it lost 20% capacity. https://batteryuniversity.com/article/bu-808-how-to-prolong-lithium-based-batteries

I mainly charged from 50/60 to 80%. Not much more than 80% since i timed it and i have a multimeter. The second thing when it was unused in the winter for a few weeks i left it at ~50%. Then when i went for a ride i balanced it again to ride it. I've used them like this for 11 months basically. Charging to 54.6V ~2-4 times a month to keep them balanced. My question is mainly if i have a bad cell that needs to be replaced - how does it still balance up to 54.6V?

Also waiting for the seller to answer if they can repair this. I am interested in changing the cell but not myself. I don't have a spot welder so i don't have a reason to open the pack to check for the bad cell and i'm not interested in changing it myself because 1) i would need tools and 2) i would need to read books and procedures not to short the bomb due to lack of knowledge.

 

[SafeDiscDancing]

1) i would need tools and
2) i would need to read books and procedures not to short the bomb due to lack of knowledge.

Well... sounds like that's the answer.

If the seller refuses then you are out of luck and that's when you dive in and try to fix it.

 

[amberwolf]

My question is mainly if i have a bad cell that needs to be replaced - how does it still balance up to 54.6V?

One or more cell groups has a cell that is failing/failed and is draining the rest of the cells, or the bms has one or more channels that has a balancer stuck on that is draining the groups they're attached to, or there is a wiring failure where a balance sense wire insulation is crushed between something conductive and something else, and is "lightly shorted" draining the cell group(s) it's attached to (this condition can get worse and become a direct short and cause a fire, depending on what it's shorted to and how high the voltage difference is).

Also waiting for the seller to answer if they can repair this. I am interested in changing the cell but not myself. I don't have a spot welder so i don't have a reason to open the pack to check for the bad cell and i'm not interested in changing it myself because 1) i would need tools and 2) i would need to read books and procedures not to short the bomb due to lack of knowledge.

FWIW, if you don't want to diagnose it yourself, which will require disassembly and testing by you, then it doesn't matter what is wrong with it. You'd need to take it to a battery repair center of some type (you probably can't knowingly ship a defective battery unless you lie to the shipper), and have them diagnose it and repair it (if it is cost effective for you).

If you do want to diagnose it yourself, then as long as you are willing to answer questions in the detail requested by the helper, and provide the pictures the helper asks for, and perform the exact steps the helper provides (and do nothing except those steps without discussion first, so the helper knows what is going on and can warn you against problematic ideas and actions), then people here can help you do this.

 

[Audisport09]

Have to agree Blind charging is dangerous. You need either a Bluetooth bms or a smart charger.

 

[SafeDiscDancing]

Have to agree Blind charging is dangerous. You need either a Bluetooth bms or a smart charger.

Or simply go old school and actually know each cell group.

Like I've said before... people used to change their own spark plugs in their cars but these days people often wouldn't even know what a spark plug is or what it does or how to check it.

Being able to have access to the cell groups themselves seems to be the number one thing to have certainty about what is going on but that's just not considered a standard feature in most packs.

The moment this guy attempts to look inside he violates any warranty it might have.