Pack Died From Standing 2 Month?

[rg12]

A properly built 24S 30Ah 25R pack with busbars, 0.15 pure nickel all perfect work, had 120A limit from a Sabvoton controller (half the discharge rate of the cells), worked perfectly for 2.5 years (which I'm not complaining at all) and then sat for about 2 month fully charged.
When tried to use it it didn't charge and BMS cuts power.
Opened it up and two rows are at 0V and the rest of the rows are all over the place 4.10, 3.8, 4.04, 3.7...
Cut out 4 rows including the two dead ones to make it into a 20S and tested the cells of the two working rows that showed 4.04V and out of 24 cells (12 cells in each row) there were only two cells in each row that had voltage and the rest at 0V (from the rows that showed voltage).
Bottom line I assume that 80% of the pack is at 0V and is dead shorted and can't be charged with a PS and the IR tester shows nothing.

My question is, how can the sitting hurt it so much?
It worked great before it sat...

 

[john61ct]

Either really wasn't such a great pack in the first place

its prior usage / care patterns brought it to near death undetected just before stored

or the parasitic vampire draw of the BMS killed it.

Was anything else connected?

Should have been fully isolated

30-50% SoC

regularly checked, state maintained.

How often did you verify capacity, compare to initial benchmark?

Keep a log of increasing resistance?

Known genuine grade A cells new when assembled?

How cycled - C-rates, to what avg DoD%? How many times?

Usually kept at Full SoC?

 

[rg12]

Either really wasn't such a great pack in the first place

its prior usage / care patterns brought it to near death undetected just before stored

or the parasitic vampire draw of the BMS killed it.

Was anything else connected?

Should have been fully isolated

30-50% SoC

regularly checked, state maintained.

How often did you verify capacity, compare to initial benchmark?

Keep a log of increasing resistance?

Known genuine grade A cells new when assembled?

How cycled - C-rates, to what avg DoD%? How many times?

Usually kept at Full SoC?

Too many unknown variables that for sure dictate the life expectancy of the pack.
My question was different though...
Even if the pack wasn't in good health when stored, let's say high IR etc...
How come storing it (of course fully charged isn't recommended but still) causes a cell that went through alot to die from just being unused.
It seems that it would have lived longer if it was used during those two month instead of stored.

About the BMS, it didn't deplete the pack as the cells that were left healthy were almost fully charged and it can't just deplete 10 cells out of a 12 cell parallel row.

 

[john61ct]

Even if the pack wasn't in good health when stored, let's say high IR etc...
How come storing it (of course fully charged isn't recommended but still) causes a cell that went through alot to die from just being unused.
It seems that it would have lived longer if it was used during those two month instead of stored.

About the BMS, it didn't deplete the pack as the cells that were left healthy were almost fully charged and it can't just deplete 10 cells out of a 12 cell parallel row.

Of course it can! The cells going out of balance like that shows either really crappy to start with, or the crappy vampire circuitry involved.

First off, with many chemistries, cells just self-discharge. Less so if top quality, new/healthy, stored completely isolated, in cold temps at low SoC.

Much faster if hooked up to anything, if old/worn or poor quality, in high temps or starting at high SoC.

Allowing the voltage to drop below mfg spec (in practice use 3.0V) can murder the cells, rendered scrap.

Next issue, many crappy / cheap BMS only draw their power load from a single / couple cell groups, not evenly across the pack level voltage.

Ideally the BMS has a "completely OFF" setting with a 0mA draw, not just "low" draw sleep mode.

But really, best to rig the pack to completely disconnect the BMS (any / all circuitry) so the cells are 100% isolated.

If not, check voltage frequently and top up to your storage voltage when you see it drop.

Even best case isolated, in cold temps, I would not check less frequently than weekly at first, then scale back but only once I am 100% sure self-discharge is slow enough.

 

[DogDipstick]

Lol.

 

[rg12]

Even if the pack wasn't in good health when stored, let's say high IR etc...
How come storing it (of course fully charged isn't recommended but still) causes a cell that went through alot to die from just being unused.
It seems that it would have lived longer if it was used during those two month instead of stored.

About the BMS, it didn't deplete the pack as the cells that were left healthy were almost fully charged and it can't just deplete 10 cells out of a 12 cell parallel row.

Of course it can! The cells going out of balance like that shows either really crappy to start with, or the crappy vampire circuitry involved.

First off, with many chemistries, cells just self-discharge. Less so if top quality, new/healthy, stored completely isolated, in cold temps at low SoC.

Much faster if hooked up to anything, if old/worn or poor quality, in high temps or starting at high SoC.

Allowing the voltage to drop below mfg spec (in practice use 3.0V) can murder the cells, rendered scrap.

Next issue, many crappy / cheap BMS only draw their power load from a single / couple cell groups, not evenly across the pack level voltage.

Ideally the BMS has a "completely OFF" setting with a 0mA draw, not just "low" draw sleep mode.

But really, best to rig the pack to completely disconnect the BMS (any / all circuitry) so the cells are 100% isolated.

If not, check voltage frequently and top up to your storage voltage when you see it drop.

Even best case isolated, in cold temps, I would not check less frequently than weekly at first, then scale back but only once I am 100% sure self-discharge is slow enough.

First of all the pack was almost 3 years old and it's a 25R pack which means low cycle life so the surprise is less of a thing here but more the way it happened.

and why is high SoC so bad for the cells?
I know it is but don't understand why...
The cells have a longer way until they reach the bottom and in that pack's case it seems that something made many cells inside each row go to 0 from such a high spot in a very short time.

 

[john61ct]

Even with a new set of cells, supposedly top notch and well matched

there will be significant differences

over time some wear faster than others

and the way most are set up, a higher voltage range, more stress is put on the weakest cells makes them wear even faster

and this crisis is completely invisible to the owner, really the weak links should be replaced early on then the whole pack would last longer.

But no early failures end up cascading causing more problems through the pack, to the point that internal shorting or close to shorting current transfers, accelerated wear patterns spread.

With proper monitoring, resistance benchmarking, capacity tests etc you can be proactive and replace the old crappy pack long before its EoL actually manifests in any obvious ways.

But most people just keep using them until complete and total failure

or even build their packs from scrapped batteries that have already been discarded as reached EoL, from more mission-critical and well funded use cases.

 

[john61ct]

I do not know the "why" at the level of microscopic physics internal to the battery chemistry.

And there are many phenomena battery engineers and basic scientists are just starting to understand, about battery chemistries we've been using IRL for many years

By the time everything is understood, that chemistry is obsolete, long ago superseded by the next set of new hotness.

Fact remains, pushing charge current up past the voltage / SoC% "shoulder" areas is stressful

manufacturers spec the point where explicit obvious "damage" becomes obvious

if you want best lifespans treat those as "do not approach" maximums, while industry tries to push them as normal operating recommendations - shorter life, sell more stuff, higher profits! is my theory.

Lead banks live longer sitting at 100% so that is the "normal" conditioning, must be unlearned.

All LI chemistries prefer sitting at low SoC, really 20% is better than 40% but as you say that means checking them more frequently, need to find a balance that suits your situation.

But that's fully isolated, healthy cells.

Ones already at death's door left hooked up to active vampire loads, as you say no surprise

 

[rg12]

Even with a new set of cells, supposedly top notch and well matched

there will be significant differences

over time some wear faster than others

and the way most are set up, a higher voltage range, more stress is put on the weakest cells makes them wear even faster

and this crisis is completely invisible to the owner, really the weak links should be replaced early on then the whole pack would last longer.

But no early failures end up cascading causing more problems through the pack, to the point that internal shorting or close to shorting current transfers, accelerated wear patterns spread.

With proper monitoring, resistance benchmarking, capacity tests etc you can be proactive and replace the old crappy pack long before its EoL actually manifests in any obvious ways.

But most people just keep using them until complete and total failure

or even build their packs from scrapped batteries that have already been discarded as reached EoL, from more mission-critical and well funded use cases.

Can a week row hurt other rows or it's only limited to the cells that are paralleled with the bad cell?
* Aside from heating the nearby rows and damaging non directly

 

[neptronix]

Sounds like the work of a battery murdering system yet again.

 

[batteryGOLD]

Samsung 25R zero volt cells?

I did some recovery of those cells. They lost about 10% capacity or less. And still power! (maybe go more capacity with cycles)

Revive bus with low current up to 3.0V(maybe 100mA each cell- for a example 10P pack put 1000mA charge up to 3.0V) than standard charge and ready to go.

The other rows charge all up individually to 4.2V to get a balanced battery, after all buses at 4.2V you have a 24S fully charged battery.

Have a great time

 

[rg12]

Samsung 25R zero volt cells?

I did some recovery of those cells. They lost about 10% capacity or less. And still power! (maybe go more capacity with cycles)

Revive bus with low current up to 3.0V(maybe 100mA each cell- for a example 10P pack put 1000mA charge up to 3.0V) than standard charge and ready to go.

The other rows charge all up individually to 4.2V to get a balanced battery, after all buses at 4.2V you have a 24S fully charged battery.

Have a great time

Tried to put in 2V with 0.5A with a variable lab power supply and it just refuses to draw current.
Tested with my IR tested and it does nothing, like I connected the probes to wood.

What's weird is that a row that had 12 cells in it and showed 4V, after disassembly of all of that row's cells, 10 cell out of the 12 were 0V and was wandering how did the 2 living cells with 4V didn't get pulled back to zero with the rest of the cells since all 12 were paralleled.

 

[neptronix]

Samsung 25R zero volt cells?

I did some recovery of those cells. They lost about 10% capacity or less. And still power! (maybe go more capacity with cycles)

Revive bus with low current up to 3.0V(maybe 100mA each cell- for a example 10P pack put 1000mA charge up to 3.0V) than standard charge and ready to go.

The other rows charge all up individually to 4.2V to get a balanced battery, after all buses at 4.2V you have a 24S fully charged battery.

Have a great time

Beware that the further you go past the minimum voltage, the more irreversible damage has occurred. Many people have had fires after charging batteries afterwards. I even had a lipo puff up and almost explode on me after nursing it back up from 2.0v.

 

[john61ct]

In theory with a properly built pack, there is no current flow possible between (paralleled) groups connected in a string (series).

However, with a crappy / cheap BMS in the picture,

or maybe faulty wiring, cell cases shorting with each other, depending on plastic wrap for insulation

then all bets are off, many different possible failure modes enter the picture.

Just do not bother wasting time with salvaged cells or "resuscitating" damaged ones

unless IMO if you are truly poor and that's the only way you can play the game.

 

[batteryGOLD]

Beware that the further you go past the minimum voltage, the more irreversible damage has occurred. Many people have had fires after charging batteries afterwards. I even had a lipo puff up and almost explode on me after nursing it back up from 2.0v.

LiPo is different story . But any 18650 can be revived (not the short circuited ones, those are only few cases easy to identify)
Thats why to revive 18650 need low initial charge current until go up to 3.0V (and check temperature, if many heat stop reviving. But most cases are successful about 80% possible to revive easy )

I've revived many cells and many batteries from trotinetes 42V7Ah that were left long time no charge so went to zero.

LiPo is a kind of a clock countdown explosive fragile pack , just play with it for a good youtube video exploding some one or cutting at half : ) But keep secure distance.

Regards

 

[Hillhater]

What's weird is that a row that had 12 cells in it and showed 4V, after disassembly of all of that row's cells, 10 cell out of the 12 were 0V and was wandering how did the 2 living cells with 4V didn't get pulled back to zero with the rest of the cells since all 12 were paralleled.

Yes...very weird. !
I would say it is only possible if the 10 “0v” cells had gone open circuit for some reason.
One odd cell might have failed randomly like that,..but 10 together is too much coincidence.
Do these cells have any protection circuits, or overload fusible links inside them. ? ( tear one open to check for sure ? )

 

[rg12]

What's weird is that a row that had 12 cells in it and showed 4V, after disassembly of all of that row's cells, 10 cell out of the 12 were 0V and was wandering how did the 2 living cells with 4V didn't get pulled back to zero with the rest of the cells since all 12 were paralleled.

Yes...very weird. !
I would say it is only possible if the 10 “0v” cells had gone open circuit for some reason.
One odd cell might have failed randomly like that,..but 10 together is too much coincidence.
Do these cells have any protection circuits, or overload fusible links inside them. ? ( tear one open to check for sure ? )

Yeah totally weird, just a regular 25R cell...

About 0V cells, I build only brand new grade A cell packs and if I run into an old pack with 0V cells I either not mess with the pack at all or in rare occasions when a physical damage happened to the pack while it's still healthy I would just replace the 0V.
My try of resurrecting it was purely for research purposes as the whole pack was toast.
Still, a 25R pack close to 3 years of daily use at high currents (even though still no more than half the rated discharge rate) I would say it's pretty bad ass.
Only packs I've seen last that long are low C rate with small controllers that go 3-5 years.

 

[mulp]

You don't mention why it was stored or where, especially the temperature. Lion batteries should not be stored fully charged at very low temps, but July-September suggests it wasn't subzero. Really high temperatures?

Given the multiple batteries in a string, it suggests a BMS fail. Maybe an obscure software bug triggered by a sensor glitch that triggered an attempt to balance voltages to zero. I did product quality, and this is our nightmare and why we required a minimum of two units under constant test for months to ship, and then years after as long as customers had the product. 5 and 6 sigma still means lots of failures.

 

[spinningmagnets]

I'd bet it's a couple bad cells self-discharging, or...a BMS failure