Theoretical lipo low cell recovery

[nutnspecial]

I've heard of the 'golden' lipo rule. Do unto others. . . Hmmm no that wasn't it. Minimum cell levels.

Anyway, I think it could be a bad idea to leave your power wires plugged to charger when charger is off. Some power supplies/chargers probably will drain down their capacitors, and thus your battery overtime.
Not noticible in an hour or two. But almost 24hr on a sub midlevel pack probably wouldn't be good.

So lets say -theoretically- or maybe not hehe, you did this and are aghast when the cell checkers don't even read the cells. Measuring pack voltage hints of average cell levels sub 3v- uhoh.

The first thing (besides preparing for some fiery excitement) I would think is parallel all like celled packs to help level any low cells.
Next step start a balance charge on parallel packs equalling less than .1c
So If I were trying to bring up 6s2p 1c charge =10ah from 2.4v cell average, .05a might still even be daring. Is someone making popcorn?


Anyway, do you think extreme low charging in parallel can have any benefit to get the cells out of danger level,
and afterwards, if they haven't swelled, can there be any lasting negative (ie dangerous, not just dropping a few cycles) effects on the cells? (I'm not a master of chemistry) What happens if they do swell?

I looked at more than 50 hits and a half dozen keyword combinations, but found nothing answering this. My next step would be search the actual net, but decided to ask people here that surely would have experience with this firsthand?

Nighty night, sleep tight, don't let the lipo bite!!!

 

[amberwolf]

How low exactly did the cells get? Are those the actual individual cell voltages in the pic?

You say "2.4V" average, but how low were the low ones?


I've never tried to recharge *and use* cells that dropped below the critical levels, for RC LiPo. I've only done it as a destructive test, at really high currents and overvoltage...and only one of them burst into flame on it's own, IIRC. I had to help the other one along by puncturing it with a screwdriver. :lol:


I *have* done it with LiFePO4 cylindrical 18650 cells in an old Vpower pack, where one cell in a string had internally gone semishorted and drained the rest in parallel down. They recovered, but were not nearly as good as they used to be, in any way. I never got to fully test it out to death, cuz it was stolen after the housefire during the cleanup (along with a bunch of other stuff), so I don't know the final life stages of the cells.

I also have done it with EIG NMC 20Ah prismatic cells, 3 of them that were drained to zero on a >0.5C (maybe less than 0.25C?) load, and they recovered much better, though theyv'e enver been used at high rates near their spec limits, either, as they are part of my lighting pack. But they did keep their capacity.


There are threads/posts for each of those, somewhere in my posts, though I don't presently ahve a link.

 

[dnmun]

2.82V is not totally discharged.

the BMS does not somehow drain down the cells in your battery. none of the stuff you cooked up about lipo has any basis in fact and the cell is not even fully discharged.

 

[nutnspecial]

Thanks AW. theoretically . . . . ahahaha-ehem(my pride). about 2.2 -2.6 across 6 cells 2p.
Thanks for the input. I guess if they don't puff, I'll just mind them like usual so as not to pass cell high or low limits.
But I'm gonna beat the shit outa em with high discharge- maybe it's an archaic way of thinking, but I was always told to break in an ice like how you wanted it to run lol. Plus I'm pissed at them lol.


Puffing while charging is gas building up from electons not settling where they're supposed to?

Would this be irreversable? ie, the chemicals necessary for the reaction to store the energy are vaporized?

I'm thinking that once puffed, chemicals are depleted for individual cells that thusly will always cause uneven charge/discharge capacities vs their partners, meaning imbalance.

Can recharging from lowlevels be aided by pressurizing the cells, for example with boards and clamps, while trickle charging up 'from the-point-of-no-return'? I don't see how that would actually aid the necessary chemical reactions on the right path. But you could rule out any gas in the cells I suppose.

I sent a pm to lfp but since I don't fully understand the chemistry behind these questions, I'll search the web to better understand too.

Also, I never expected powersupplies to drain down like that. The controller caps do, but soooo slowly.
A big 'mybad' I guess. A word to the wise (Why do they say that, shouldn't it be 'a word to the stupid' lol?)

If you're only wise from hearing the word, that means the word is really to the stupid imo. Dumb sayings

 

[whatever]

I"ve had some success with very low voltage lithium cobalt oxide cells, I just recharge them very slowly individually, I use 500ma or lower for many hours.

 

[nutnspecial]

Thanks whatever, that was my thinking too, somehow rated charge ends up in a runaway reaction at very low cell levels. I suppose it's because of extremely low capacity at that level.

Hey dmun, (demon? just got that- oh my bad dnmun)
cells *theoretically* were lower man, and a bms was not mentioned. A supply style charger was though.
Wanna get into an argument about them being '''''''totally'''''' discharged @ 0v?
Just kidding, I think I know what you mean. Or do I? Makes no difference I guess.

That damn bms was actually drinkin a beer and typin on the forum as a matter of fact lol. It left the MW PS charger plugged in but turned off. Apparently the bms didn't know that was bad.

 

[dnmun]

the RC charger has a BMS built into it. that is how the cells are balanced.

the output on most high power chargers is isolated by a relay that is only turned on when the charger is charging with the correct polarity. the RC balancing chargers have a mosfet on the output that disconnects the terminals of the pack from the output caps.

the drain down resistor across the output caps is usually about 5600R. 5mA?

 

[nutnspecial]

So how would 20s 5.8ah go from 3.65 nominal below 2.5v in less than 24 hours when they were only connected to an unplugged set of 3x mw hrp 24v 300w in series? I can only guess they were drainin off their caps.

So far the cells are responding well to 1/2%c (.05a for 10ah) charge until 3v (goes surprisingly fast).
Then conservatively at 1%c probably until 3.3 or so just to attempt to maintain saving this lil' f'ers.
I have clamped the cells too, but have no idea if that helps proper energy retention or just hides the symptomatic puffing.

 

[dogman dan]

I would mark a pack that had cells that went to 2.4v, and then treat it as a potential hazard from then on.

It would never come inside again. But I would not hesitate to charge it outside, or use it on a bike provided I could get it off the bike fast if needed. In my case, that would become the pack I use on my mower.

I'd put it on the RC charger, and bring it back at a slow rate to above 2.8v, then charge normally. Normal being not that darn fast anyway, on my chargers.

I never leave my lipo plugged into anything overnight. Since I take it off the bike and put it in safe storage, it always gets unplugged.

 

[John in CR]

Thanks whatever, that was my thinking too, somehow rated charge ends up in a runaway reaction at very low cell levels. I suppose it's because of extremely low capacity at that level.

Hey dmun, (demon? just got that- oh my bad dnmun)
cells *theoretically* were lower man, and a bms was not mentioned. A supply style charger was though.
Wanna get into an argument about them being '''''''totally'''''' discharged @ 0v?
Just kidding, I think I know what you mean. Or do I? Makes no difference I guess.

That damn bms was actually drinkin a beer and typin on the forum as a matter of fact lol. It left the MW PS charger plugged in but turned off. Apparently the bms didn't know that was bad.

As far as useful energy goes it was fully discharged, however, the little trickle down to that at rest voltage would do little damage compared to riding and drawing max current through the cell at low voltage which bounced back to that at rest voltage.

 

[nutnspecial]

I'm curious what potential malfunction warrants the caution- what would it look like?
=cells in question are charging with the rest, then suddenly they go way out of balance past limit into runaway, then taking all the rest with it?
It seems like lipo looses balance more and more as the pack gets lower, but then naturally seeks level on charge like water receding from and then covering back up imperfect coral?

Thanks guys, yeah they were low, but trickle down and back up might be okay. You're right John, probably big differences in trickling over high current whether it be discharge or charge when the cells near dead.
Mark the packs now for sure!
I literally charged @ 1/2%c from 2.2- 2.7v and 1%c rate for 3more hours to bring up tp 3.4v.
The cells went from about .4 out of balance to just .04 by 3.45v.

Hoping for some more 'been there done that' and input on if and how pressure is beneficial when charging back up from dead. Also, has anyone particularly trickled down their batteries with a supply charger?

 

[dnmun]

i thought he said he had a balancing charger. kinda impossible to analyze stuff when the facts are not there. i thought this was a 6S lipo pack on a balancing charger but is instead 20S of lipo and it is left attached to the power supply. not a charger.

so 84V/5600R is what?

 

[nutnspecial]

Are you talkin to me? Are you talkkkinnn to me? :lol:

so 84V/5600R is what?

Please tell me.

I've heard of the 'golden' lipo rule. Do unto others. . . Hmmm no that wasn't it. Minimum cell levels.

Anyway, I think it could be a bad idea to leave your power wires plugged to charger when charger is off. Some power supplies/chargers probably will drain down their capacitors, and thus your battery overtime.
Not noticible in an hour or two. But almost 24hr on a sub midlevel pack probably wouldn't be good.

So lets say -theoretically- or maybe not hehe, you did this and are aghast when the cell checkers don't even read the cells. Measuring pack voltage hints of average cell levels sub 3v- uhoh.

The first thing (besides preparing for some fiery excitement) I would think is parallel all like celled packs to help level any low cells.
Next step start a balance charge on parallel packs equalling less than .1c
So If I were trying to bring up 6s2p 1c charge =10ah from 2.4v cell average, .05a might still even be daring. Is someone making popcorn?

First post.
12s1p drained by supply charger, changed to 6s2p and trickle charged on balance charger.
I think it's all there.

**EDIT Thanks for the input guys! In case anyone already guessed, to me this is just as much real life as it could be theoretical or hypothetical.

Extremely low parallel recharge and clamping cells brought cells from sub 2.2v with .4v imbalances into natural balance of .01v by about 3.6v/cell. This is exactly how they have acted on previous cycles. Sub 3.5v= imbalance.

I proceded to go back to 12s1p and 'fire em up' across the bulk of they're power range @ a 2-3c charge. Stopped at 3.89- 3.9v (still in balance)

I will let them @ storage voltage for a while, see what happens, and report back.


I'm pleasantly surprised to say the least, my lipos are a friendly beast.

15c draws soon will delight, break-in like you expect to run,
right?

 

[dogman dan]

What warrants the caution? Extreme caution is warranted with Hobby RC lico packs when they are brand new, and just tested good!!!

Once you violated the golden rule, irreversible damage happened inside. Sure, they may revive and be useful again for a time. Don't expect the cycle life packs from the same batch will give. Don't trust em again.

Lyens, (if I recall correct) revived an over discharged battery, and one day when he drew it down very low again, it burst into smoke and stink, if not actual flames. I would not trust that pack again for shit, not charging , discharging, or storing it. Stuff like that I use on my mower. If it starts to smoke, I'll just flip the mower and dump the flaming piece of crap on the grass. So far, never happened. But I try hard not to discharge old ruined packs very deep.

 

[nutnspecial]

What warrants the caution? Extreme caution is warranted with Hobby RC lico packs when they are brand new, and just tested good!!!

Oh course! I didn't mean to mislead any people. To me there shouldn't be anything mystical about it. I am trying to understand the how and the why on a more technical level.
I agree possibly lost cycles, but will need to do some study if I'm to understand how the chemistry reacts and can be expected to act with my particular experiences so far.

I really have heard or learnt nothing to logically convince me on a technical basis, that the these cells won't perform just as they have previously. But yes, don't put lipo on your morning toast. lol

Cells have maintained balance, and I will put the back in service soon.

PS, no comments on my poem above? I mean, who writes a freakin poem about lipo?

 

[dnmun]

that is only because you have not read much of the available information. if you wish to learn then you need to invest the time in educating yourself and not expect others to explain everything in detail to save you the trouble of learning it from reading.

if you cannot calculate the drain down rate then you have a long slog ahead.

 

[nutnspecial]

that is only because you have not read much of the available information

Ever so helpful. . . Your post serves no purpose other than to instigate and inflame when it's @ someone who is being responsible, and is reading and trying to learn. Which I am, and most people that post are to the best of their ability.

If you don't like me, that's fine, you don't have to comment on my thread (and at this point I'd prefer you didn't actually), [strike]because I don't think you've been helpful or gracious in the least.[/strike] EDIT Naw, that's not true, after rereading all your posts I do think you were making an attempt. My apologies.
What I want to say is that some gracious humbleness and a spirit to help is the best thing to have backing our posts.
I try hard to help and not pass judgement on people that may not know what I know. Golden rule.

Besides sharing new experiences and knowledge, Isn't that what this forum is about?

Regards,
Jay

 

[liveforphysics]

If you have an interest in learning about the mechanisms of abuse induced cell failures, this page has surprisingly high quality content (as opposed to sites like battery university). Just going to 2.4V/cell at a low C-rate isn't super devastating, but often when a pack gets to that low of an SOC, some cells have been driven down to 0V and/or reversed, which can/does cause real problems.

http://www.mpoweruk.com/lithium_failures.htm

 

[cal3thousand]

If you have an interest in learning about the mechanisms of abuse induced cell failures, this page has surprisingly high quality content (as opposed to sites like battery university). Just going to 2.4V/cell at a low C-rate isn't super devastating, but often when a pack gets to that low of an SOC, some cells have been driven down to 0V and/or reversed, which can/does cause real problems.

http://www.mpoweruk.com/lithium_failures.htm

Nice! going to read up on this Luke-approved source.

 

[nutnspecial]

Thanks man! 8)

 

[nutnspecial]

Excellent reading, alot of greek. The article offers some great explanation on lithium. A little scary to have it spelled out, but understanding leads to better care in practice imo.

I'll be reporting my hypothesis on my experience so far once I can figure out how to properly present it. Right now it would be wrought with technical errors.