How I killed a lipo cell <update- almost>

[nutnspecial]

Let me start by saying it's probably dead, but I'm gonna try and lazarus that b*tch.

//And as an edit after these replies: every bms lover can come on over and beat up on me for not having one :lol: .

Been riding on a 20s set of 25/30c 5.8ah turnigys. 3 of the packs always stay balanced very well, even with higher draws of (15c) +60 amps that tend to warm the packs a little.

The fourth pack I've been keeping an eye on because one cell gets unbalanced on discharge. (about .1v lower when cell avg is 3.7v- where I normally stop.) Upon bulkcharge @1c it comes back inline.

I tried leveling the cell with the others (charge 1s to level) when at that soc, but upon bulkcharging it shot way above the rest, which tells me it had a permanently limitted capacity, and was the weak link of the chain. So I continued to use as stated, and would watch it level up on bulkcharge.

Due to voltage drop of high draws on 5.8ah, I usually take it very easy when the average cell level hits 3.75v, as full draw can start sagging the cells below 3.5v average.

2night I saw my boosted friend after I should've been calling it quits, and rode for another couple miles past my normal stop @ ~ 76v resting 20s. I made sure not to sag below 3.5 average (70v pack) and the pack seemed fine and spunky, with a resting voltage of 71v upon completion.

I had a bad feeling, knowing the one cell had diminished capacity, and expected to see possibly 3.25 or so on it.
Well, even with light careful draws, a cell avg of 20s 3.5v tonight resulted in that particular cell ending on ~1.5v, while the rest are still setting around 3.65v.
Seems odd it got that bad imo.

I'm not really sure what happened, possibly just a bad cell cell showing itself under high load. Weird how it always charged back up with .03 of the rest though. I don't think I ever discharged the pack to 71v though.

I wonder if balance charging more would have helped, I balanced the whole pack once/twice, but have had my eye on this cell since out of the box. I don't really see how much it would've helped seeing the bulk charge to 4.1 or 4.15 always leveled them out fine, although my other 5.8 pack got slow balanced the first 10 cycles, and it keeps better balance.

Surprisingly the 1.5v cell isn't noticibly puffed, so I'm planning on clamping the pack and trying to balance the pack very slowly until levels get to 3.3v, or actually I'll prob have to use the powersupply to hit the one cell till I can run the balancer even.

Even if cell lives to see another charge, I see no way to correct whatever caused this, other than limiting draw, so the weakest cell doesn't take a sh*t.

Time will tell as I re-enlist my 2nd pack and treat it similarly. Maybe the cell was the first in the 20s, thusly getting beat up more by 15c draws, maybe it was just a crap cell.

https://www.youtube.com/watch?v=VZekeEymN-A&feature=youtu.be

 

[Syonyk]

Good luck. Be sure to try to "lazarus that b*tch" in a fire safe location. I can't say I'd be tempted to try that.

 

[nutnspecial]

Lol, it beat the alternative enough to try.
She came up to about 2.85 w/ .01-.02a, in small increments, but quickly.
At that point, the cell seemed content to hover, signalling the capacity was starting to ramp up @ 2.85v.

Bumped up the charge to .05 (1% charge c-rate), and it climbed to 3v over 1/2hr.

Tried the icharger to start balance, but cell still too low for that.

Upon hooking back up just the low cell as before a very slight hiss became apparent eminating from where the leads exit the pack, and the balance leads became warm.

I read about hard low discharges dissolving copper conductors, and upon charging the copper can migrate and cause internal shorts. Possibly that's what's happening.

I'll give it a break, and check for volts to mitigate,
the noise however causes concern-
it's dying breath i may learn.
Time can only will tell
if it sees heaven,
or hell

 

[dnmun]

where did you read this stuff about current dissolving copper conductors? i could not follow any of this.

 

[nutnspecial]

I read it in the lithium failure modes paper that lfp linked in my 'theoretical lipo recovery" thread.
I actually tried to link it the other day when you and I were talking, but the link was bad already, so I found another paper to quote for that instance. I wish I'd copied the text though, it was very interesting. Maybe lfp can provide some other info to back it up.
Sorry if you're not following, but don't feel bad, it's mostly me- not you

Here's an update- after the hissing I pulled the balance extension & unclamped the battery. No puffing, seemed fine, although balance leads were warm.
Tried reconnection- same thing- warm leads and light hissing from bat. I then noticed the sound stopped when I removed the balance extension. (high quality silicone with soldered end, visually just fine).
Upon switching to another lead extension, I was able to resume charging as before.
Sitting around 3.5v now, up from 1.38v/1.9v resting, which was almost 2volts lower than the other 19cells.

Really weird, there is no appearance of defect in the other lead- I will fully test it to see whats up.

Also still wondering why the cell let go like that- maybe the problem was an intermittent micro shortage in the lead all along?
If that's the case, a real pcb bms wouldof saved the day, although who knows when the real problem would have become apparent.

 

[dnmun]

so you are talking about the copper sheet inside the pouch that the carbon layer is deposited on. this is the negative electrode.

i could not follow because there is so much verbiage and i don't know what it refers to.

why not just cut the pack open and take a picture of the pouches inside where you say there is this hissing sound.

 

[nutnspecial]

i could not follow because there is so much verbiage and i don't know what it refers to.

Yeah, I know. I struggle with it lol. Hard to write, harder to read .

The light hiss/sizzle and warm lead symptom is now gone and it's charging normally, since I got rid of that balance extension. (I'm running extentions from the original factory connections. Same high quality ones ykick uses)

I will certainly be playing operation though, when the time comes. Interested to see how the battery acts, and if some conditioning could improve it, or if the trouble was just the dam extention all along.

 

[Ykick]

Something’s goofy and I’m not following all of the verbiage either.

I’ve seen some problems with balance wiring over the years but if you qualify the wire, connections and measurements to be solid - I’d do an IR test of that cell and some others in the series string for comparison.

If a cell is sagging significantly during use you’re running a very real risk of creating a fireball. Years ago my coworker running 12S RC Lipo was running naked and bulk charging. I bought an iCell Bluetooth cell voltage meter and IOS app - one day plugged into his pack and rode alongside.

What a surprise to discover one of his cells sagging well below 2V under mild acceleration while the others were barely dropping below 4V. Needless to say, the cell was heating excessively but not puffy yet - just a bad deal and if I hadn’t checked the realtime operational voltage of individual cells the story may not have ended well.

After replacing the bad cell we also installed a BMS. Failure to monitor (manually or automatically) what the cells are doing at all times is foolish and quite dangerous.

 

[nutnspecial]

If a cell is sagging significantly during use you’re running a very real risk of creating a fireball. Years ago my coworker running 12S RC Lipo was running naked and bulk charging. I bought an iCell Bluetooth cell voltage meter and IOS app - one day plugged into his pack and rode alongside.

What a surprise to discover one of his cells sagging well below 2V under mild acceleration while the others were barely dropping below 4V

Yes, this is very well what could of been hapnen. I'll use the cellchecker to watch it under acceleration to see. Wish I'd thought of that lol. I'll do a ir test too, but after I see what it does. Thanks for pointing that out.

A little aggressive to insinuate the non-pcb-bms crowd are fools imo, but you're entiled and have a point.
Isn't 'fireball' being a little dramatic though? in my limited experience, the cell would just die, and if you fast charge it unaware, that's when there's some potential for big problems, yes?

I'm wondring if it wasn't a slight issue with the balance extension (same as you use). I cut the shrinkwrap off and there was corrosion around ground and #1 pin- (the low cell was #1). I don't know if I like the way they're setup with the shrinkwrap and naked cb, terminals, solder underneath.
Did you ever look at yours under the heatshrink Ykick?

 

[Ykick]

Please don’t attempt to put words into my mouth. I’m not calling anybody a fool, merely rating the practice/technique as foolish/dangerous. From someone who did it for many years…

Perhaps my iggy list needs updating?

 

[dnmun]

it is not aggressive to point out how difficult it is to monitor the battery as effectively as a BMS does.

i consider it to be putting other people who live in the same apartment building as you at great risk of total loss of their possessions and living space when a battery that you build catches on fire and destroys a multi unit apartment building.

the more of you guys who decide to build these powerful lipo batteries with no protection then the greater the risk of more fires caused by these designs that leave out the most critical part.

these fires will force the insurance industry to make ebikes illegal inside of a residential or commercial building so then they will become impossible for people to own and operate in the city where they are needed most. they are already illegal on most transit.

this is gonna happen sooner than later i fear at the rate this is all going on.

 

[nutnspecial]

Yah, maybe it's foolish in practice- and saying so comes with an insinuation imo. That's fine, i'm over it.
Iggy list?



Lol, do whatever you feel is right. I don't care you used the word foolish, just playfully pointing out the implication for the non bms camp. Not tryin to get anyone bent outa shape over that debate, or whether it's foolish or not.

it is not aggressive to point out how difficult it is to monitor the battery as effectively as a BMS does.

Of course not, my point was imo it was a bit aggressive to call the practice foolish. 'Unsafe' comes across nicer to many potential converts in the 'bms cause'. But even then it's an arguable one if you're not smarter than the bms for when it too fails.

And obviously users of energy, ALL FORMS, should be aware and responsbile of other's safety. Whether it's lipo, gasoline, a pogo stick, baseball, or a nuke. Imo that goes without saying.

How does this shit always end up on bms and non bms.

Back on topic-
Maybe I need to change the title, cuz this cell is alive!
What was the cause of the malfunction: a crippled cell, or a devious balance lead extension?
Soon the cell group will be charged for trial, I'll watch v-sag on a cellular level, then maybe do a ir test.
There was something going on with the lead though, there was moisture under the heatshrink.

 

[Syonyk]

where did you read this stuff about current dissolving copper conductors? i could not follow any of this.

Search for "lithium battery copper plating" or such - it's an issue with a deeply discharged lithium battery in which copper drops out of the electrolyte and can cause shorts.

Sitting around 3.5v now, up from 1.38v/1.9v resting, which was almost 2volts lower than the other 19cells.

You should not be recharging this battery in the pack with other cells. If you do mess with it, it should be in a separate fireproof box or something that can contain a cell undergoing thermal runaway.

the more of you guys who decide to build these powerful lipo batteries with no protection then the greater the risk of more fires caused by these designs that leave out the most critical part.

these fires will force the insurance industry to make ebikes illegal inside of a residential or commercial building so then they will become impossible for people to own and operate in the city where they are needed most. they are already illegal on most transit.

this is gonna happen sooner than later i fear at the rate this is all going on.

Yup. BMS-less batteries are flat out dangerous to use and charge, especially when paired with lipo packs, which are running a very aggressive chemistry with a low thermal runaway temperature (I believe some will run away starting around 150C).

Yah, maybe it's foolish in practice- and saying so comes with an insinuation imo.

Foolish, unwise, dangerous... pick three.

Back on topic-
Maybe I need to change the title, cuz this cell is alive!
What was the cause of the malfunction: a crippled cell, or a devious balance lead extension?
Soon the cell group will be charged for trial, I'll watch v-sag on a cellular level, then maybe do a ir test.
There was something going on with the lead though, there was moisture under the heatshrink.

So you have no idea why the cell failed, but you're going to keep running it?

Keep the bike outside...

 

[nutnspecial]

something buggery def happened with that extention, it tested for continuity on ground to #1 until pulling off the wrap to reveal oxidation on those two. It may have just happened though, time may tell, the balancer kept ending before the cell took all it could.

All I know is these 4s packs have been shitty since new. Nothing like the 6s packs bought a few months prior. See the celllogs, this is all the time. I just beat the packs down from 4.15 to about 4 on high draws, it appeared there was no significant sag on the cell in question.
cellogs of the 4 sets making up the 20s. The 4s has never kept balance as well, and that one cell is a problem, but I guess I didn't kill it- yet
Can't believe it came back from 1.38 *(rested at 1.9 after 1/2hr)

So to retitle the thread, 'How I beat it like the proverbial yada yada.'
Or maybe 'My antitheft system- lipo fireball for the unknowing thief"

Thanks for the tip Ykick, I'll be watching this pack thru the whole discharge to learn what is goin on. Maybe I'll consider a bms <wink>.





ps, crosspost. Yeah, everybody come on over and beat up on non bms lipo users.

 

[Harold in CR]

nutspecial, what kind of discharger/balancer is that ?

I have 20 Leaf cells on my bici/moto. One group of 5 cells has/had a dodgy balance lead. I soldered on a new one from the cell to the lead connection. I used HK balance leads, but, they are not 100% perfect.

 

[nutnspecial]

I just use it as a reader, seems fairly worthless for any major balance/discharge. Either hk or ebay. http://www.hobbyking.com/hobbyking/store/__10328__HobbyKing_8482_Battery_Medic_System_2S_6S_.html
My balance extensions were not hk, but the 'high end' soldered pack end of the extension maybe shouldv been elimated with a direct solder job like you did. http://www.buddyrc.com/12-6s-jst-xh-extension-cable.html

 

[Harold in CR]

Thanks for the ifno. I have 3 cell testers and a cellog8 and they all read differently.

 

[nutnspecial]

Hopefully they're not too far off!


I ran my pack down closer to 1/2 soc (sparing no power ) and rechecked the cells.
Each pack is within .01v and there's a total span of .02v across all 20s. They're sitting around 3.8v.
That's way better than I ever remember, so here's lookin up.

I'll def be watching closer, and am planning on riding the pack down nice and low. If they stay inline, I can possibly assume the culprit was the buddyrc balance extension with the pcb female end, allowing for an light intermittent cellular short.

Surprised and happy I didn't kill the cell by taking it to 1.38v @ end of ride.

If anybody else has this happen: charge at less than 1/2% charge c-rate until you hit 3v. Cell compression didn't hurt. Obviously be careful, but upon no noticible puffing and clamping the pack, I simply charged that one low cell thru the balance lead, until I could run the balance charger for the whole pack.

There's a utube link in my first post of the charge.

 

[nutnspecial]

Update on the the cell in question. It's behaving questionably lol.

Here's my rundown and ot rambling video pt 1+2. Yeeeaaa!
1 https://www.youtube.com/watch?v=M21qRvo9b-U
2 https://www.youtube.com/watch?v=oaGT6o34hJY

 

[Syonyk]

Could you summarize for those who don't like watching rambling YouTube videos as a source of information?

 

[nutnspecial]

Eerrrmmm NO?
https://www.youtube.com/watch?v=Oyoc9rRSGl4

You should not be recharging this battery in the pack with other cells. If you do mess with it, it should be in a separate fireproof box or something that can contain a cell undergoing thermal runaway.

Yup. BMS-less batteries are flat out dangerous to use and charge, especially when paired with lipo packs, which are running a very aggressive chemistry with a low thermal runaway temperature (I believe some will run away starting around 150C).

Foolish, unwise, dangerous... pick three.

So you have no idea why the cell failed, but you're going to keep running it?
Keep the bike outside...

Not very constructively helpful comments imo. First of all, anyone who uses lipo most likely know it's like gasoline. And what's this with fireproof boxes and stuff?

Meow.


///PS and by the way, if that was too much rambling for you
G E T O U T with your nonbms sissy hatespeech

 

[Syonyk]

G E T O U T with your nonbms sissy hatespeech

Do you know what the difference is between an electric bike using a B-Grade Hobby King Lipo based pack is and one using a competent pack, when it burns a building down, as reported in the news?

Not a damned thing.

It's nothing more than an "electric bicycle responsible for a building fire."

I'd prefer electric bikes remain as freely available as possible, which generally requires they be as safe as possible, and not fire-prone. It does nobody any good if insurance companies and rental leases prohibit them as dangerous goods.

My suggestion about fireproof boxes is because you don't seem, so far, to have isolated the cell from the pack it's part of, and a cell undergoing thermal runaway can and will trigger this in adjacent cells.

Anyway, I'm done. Good luck, try not to catch anything on fire.

 

[nutnspecial]

My suggestion about fireproof boxes is because you don't seem, so far, to have isolated the cell from the pack it's part of, and a cell undergoing thermal runaway can and will trigger this in adjacent cells.

You're right, I understand that. When there are questionable charging circumstances the 4s has been moved from the rest, but i'm not cutting a pack up till that cell is dead. I understand enough about safety to keep the packs away from combustibles at all times. I understand lipo has a slightly lower runaway point. 5gallons of wet sand on hand, smoke detectors.

That's what I'm talking about, everytime someone wants to learn about lipo, all they get is all this negative nancy crap, and have to go in defense mode.

I'm over not getting much helpful input, but here's a genuine suggestion:

Why don't the concerned bms'ing :wink: parties make a thread (potentially sticky or wiki) about lipo safety and how and why to set up bms? Wouldn't it be nice to just link all that great information?

Sheesh

 

[Syonyk]

That's what I'm talking about, everytime someone wants to learn about lipo, all they get is all this negative nancy crap, and have to go in defense mode.

That's because people should not still be using lipo packs for ebikes. They're dangerous even before people start abusing them. If you run them with a BMS, you stand a good chance of catching a bad cell when the entire pack shuts off before you start driving it below 2.7v repeatedly, so the poor cells become annoying, rather than hazardous.

People just consider a 5% failure rate of pouch cells to be acceptable - this is insane to me. Quality 18650s have a nearly zero percent defect rate as shipped.

 

[nutnspecial]

.
.
Apparently lipo is a bee in your bonnet, and a monster in my parasol!
https://www.youtube.com/watch?v=hnLwHOVXkWE (just thought of the chorus, and am amused finding the subject matter of the video)


Are you not getting the point? If you wanna be helpful get together with others and put together some information for your cause, whether it's the cells you sell, or doing bms for lipo.
This would not only please me to no end (because this thread could be a little more towards my intention), but it would actually be constructive and helpful if you really care,

vs attacking naked lipo with the kind of rapidity and ferocity that's best reserved for the fairer sex in my bedroom.

You're right, I understand that. When there are questionable charging circumstances the 4s has been moved from the rest, but i'm not cutting a pack up till that cell is dead. I understand enough about safety to keep the packs away from combustibles at all times. I understand lipo has a slightly lower runaway point. 5gallons of wet sand on hand, smoke detectors.
That's what I'm talking about, everytime someone wants to learn about lipo, all they get is all this negative nancy crap, and have to go in defense mode.
I'm over not getting much helpful input, but here's a genuine suggestion:
Why don't the concerned bms'ing :wink: parties make a thread (potentially sticky or wiki) about lipo safety and how and why to set up bms? Wouldn't it be nice to just link all that great information?

There is no alternative for me with 84v 60a draws and about 5lbs minimum pack weight.