Charging 0 Volt 26650 Cells

[DENWA]

Bought a bunch of 26650 LiFePO4 packs for my son and I to play with.

$75 shipping included for 135 (3.3Ah) cells in low voltage packs so I figured what the heck.

3 different manufactures of cells but in general
~80 have voltages between 2.0-3.3V-- all successfully charged to 3.6V at 250mA now monitoring cell voltages looking for bad cells
~25 have voltages between 1.5-2.5V--all successfully charged to 3.6V at 250mA now monitoring cell voltages looking for bad cells

~15 have voltages 0.5-0.9V--Charging these now really slowly at 50mA fingers crossed looks like they are charging
~15 have 0.0V and 6 of these have evidence of cell leakages/rust on the cans.

For giggles I tried to charge one of the 0.0V cells at 250mA and it surprisingly it charged to 3.6V but it did get warm and stayed warm and after removing the power supply discharged back down to 0V overnight.

My experience with Lithium Ion 18650 tells me the 0V cells have dissolved the anode off the substrate and these are a short internally.

I may continue to mess with a few of these to see if I can revive them but overall got more than what I paid for and my son is having a great time with me.

FYI--We got a HF plastic ammo can and realized we can easily fit a 4s 16p stack of cells inside with 120A BMS making a cool little jump box for ATV's etc.

 

[sunshine_eggo]

I recovered several dozen LFP prismatic cells sitting at 0.6V. 0% fall out.

I have never attempted to recover 0V LFP, but your efforts describe my results with 0V NCA.

 

[DENWA]

I recovered several dozen LFP prismatic cells sitting at 0.6V. 0% fall out.

I have never attempted to recover 0V LFP, but your efforts describe my results with 0V NCA.

NMC and NCA seem to be more forgiving than the straight Cobalt cells of years ago. My buddy at MoliCel says they have a "ceramic-like" coating on the cathode that keeps them much more tolerant to low voltage abuse and dendrite growth.

 

[Substrate]

Yikes - if you want to play, then perhaps let something smarter do all the work for you, and instantly bin those unsafe, or possibly bring them back much smarter and safely - which is designed to do this job in the first place.

A small amperage Tecmate-Optimate TM-471 0.8A analyzer and charger. Designed for 4S (nominal 12v) LFP batts. Your little 3a cylindricals are typical for these types of motorcycle LFP banks.

https://www.amazon.com/OptiMATE-Lithium-TM-471-Battery-Charger-Tester-maintainer/dp/B00Y38X7WI/ref=sr_1_7

The blinky lights make it fun for the kids. Safely. The manual makes it fun for you, albeit one can just clamp and walk away (well, not abandoned, but near). You indicate that you are monitoring them, so that is a good sign. You would do the same here, even with the Optimate.

 

[DENWA]

Yikes - if you want to play, then perhaps let something smarter do all the work for you, and instantly bin those unsafe, or possibly bring them back much smarter and safely - which is designed to do this job in the first place.

Sorry, I don't think a 4s smart charger could be more safe than a current regulated power supply and power resistor bank.

Cells are either short and cannot store energy, (so ~50mA into a short no big deal) or they are a resistor that dissipates stored energy as heat at the same rate which it did while storing it...

 

[Sverige]

This is a very timely thread, as in the last few days I’ve been playing with some 26650 size 2200mAh A123 LiFePO4 cells which i have been resoldering into 4S packs, hoping to put them in parallel with my 272 and 100Ah LiFePo4 prismatics.

All of them had been discharged down to 0V through my own carelessness of leaving them unloved and discarded for many years. I used to fly them in model RC planes and must’ve bought them 15 years ago at least. I charged them on a NiMH program at 800mA up to around 2.7V then switched over to LiFe charge profile at 1.5A.

Out of 12 cells, 4 are showing excessive self discharge, the others seem to have somehow survived and after being charged and balanced yesterday the packs have held their voltage overnight. I’ll give them a week to make sure they’re stable before putting them in parallel with my larger cells.

I suppose there’s nothing to be done to revive / recondition the self discharging ones? I did wonder about a high current charge (5C?) to see if I could wake them, but maybe that would just cause an incendiary reaction and wake the neighbours instead? ?

 

[Substrate]

Sorry, I don't think a 4s smart charger could be more safe than a current regulated power supply and power resistor bank.

The Optimate is, and part of the name is Ampmatic. The current is constantly monitored and adjusted, even though small, to look out for common problems that bad cells initiate that fall outside of the normal charge curve for LFP, given both rapid voltage and current monitoring.

If un-normal response is detected and the poor charge behavior continues - it will stop and immediately warn you. Other chargers just blindly plow ahead with simple low current - and maybe adopt only a timeout. Killing what might have been recoverable.

And end user might do the same with his own programmable supply, but cannot manually adjust both voltage and current, and watch for cells that might fall out of the norms fast enough. Hence their attempt at recovery renders a dead battery, whereas the speed and smarts of the Optimate can bring them back safely.

Problems like these are exacerbated by their major demographic - those using $300 LFP motorcycle starting batteries that in older days, had no bms or balancers at all. Driving these to zero volts was common, and since replacing $300 motorcycle LFP start batteries all the time isn't a good option, the engineers at Optimate relied on their decades-long experience of reviving expensive powersports AGM sla batteries that have also been driven to zero, to recover them safely.

Especially for the non-savvy consumer. Being able to do this without them having to adjust *anything*, and get those settings wrong defeating the purpose, is an additional smart move. Truthfully, being a battery-nerd, I wanted to play with settings. They took that away from me. But the walk-away results were totally worth it.

So not a Johnnie-come-lately charger, with hobby type engineering. It's the real stuff.

Forgot: It's not just a matter of recovery either. Those that have been recovered are tested afterwards. Also giving you the "yes, we recovered it, but is it healthy or on it's last legs anyway?" That test procedure is more accurate than we can do at a hobby level. Just because a recovered battery holds voltage for a day or two doesn't mean it's good. So hate to say it, but it outsmarts even the best of us nerds.

 

[Substrate]

Note too that the optimate is designed for 4S. In this project, even if 4S isn't a desired final configuration, just temporarily wire them up in 4S, get the cells off the floor safely with this charger, and then do whatever the heck you want to do later with your final configuration, top balance etc with other gear.

Quite frequently, it's the revival process we aren't slick enough to do with mere low-current trickle charging and a safety timer. This thing is humiliating to nerds like me.

 

[Substrate]

Just to have fun - I took a 4S well-top balanced battery, and purposely discharged one of the cells to 50% capacity.

Without any bms or lvd, I let it run my load until that cell hit the floor at zero volts, and the load started to chatter on and off as the cell repeatedly recovered and died. For about 30 minutes.

Pulled the load, and within 2 hours of rest, the cell recovered by itself to 2.9v. Fortunately it didn't go into reverse-polarity.

Put the Optimate 5 Lithium on it. Oh it noticed. After going into the save mode, it came out quite quickly actually at 1.5A.

A minute later, it is freaking out with current going up and down all over the place trying to see what's up. It noticed all right.

 

[Substrate]

Just an update - the Optimate brought the cell in that 4S back just fine, although lets say top-balance was no longer perfect.

I prematurely aged that poor cell like a fine-cheddar!

 

[Sverige]

Out of my 12 A123 26650 cells, 6 have now revealed themselves to be unable to hold a charge longer than about 2 days, so they are junk unless anyone knows of something which could be done to revive them?

The others appear fine and I’m wondering if the ones which survived had not been discharged fully down to zero volts (even though they were close) and the ones which are now self-discharging were the ones which made it all the way down to zero.

 

[Substrate]

Hemm. Do an IR measurement.

Also know that A123 cells are not sold to the consumer directly, so as in the past, they were among the highest targets of counterfeiters - even with their special terminals. Sometimes cannibalized A123 caps placed upon junk cells and rewrapped.

Just be safe.

 

[Sverige]

Hemm. Do an IR measurement.

Also know that A123 cells are not sold to the consumer directly, so as in the past, they were among the highest targets of counterfeiters - even with their special terminals. Sometimes cannibalized A123 caps placed upon junk cells and rewrapped.

Just be safe.

Ok I’ll try measuring IR. Mine are genuine A123s and were bought when they were newly available back in (I forget which year) but perhaps 2009. They may not be sold directly to the public now, but when LiFePO4 was a new technology, they were being marketed and sold as alternatives to LiPo batteries for RC model planes, which is why I bought some.

 

[Substrate]

The only thing I can think of is that if those that did make it down to zero, and were brought out of the discharge knee with too much normal charge current, didn't just outright fail, but got aged prematurely. Tough cells, but they noticed.

Like only recharging with 50-100ma until they get up out of the knee, like above 2.8v or so, and then use normal charge currents again. I got tired of doing that, so that's why I go into my Optimate schpiel ..

The one I just hammered got recovered, still pulls full capacity, and has a normal IR roughly the same as the others. BUT, I took a sharpie and wrote a zero on it, so I know right where to go to if the battery goes wonky a few years from now. It's like the cells hold a grudge against you for going to zero.

 

[Sverige]

The only thing I can think of is that if those that did make it down to zero, and were brought out of the discharge knee with too much normal charge current, didn't just outright fail, but got aged prematurely. Tough cells, but they noticed.

Like only recharging with 50-100ma until they get up out of the knee, like above 2.8v or so, and then use normal charge currents again. I got tired of doing that, so that's why I go into my Optimate schpiel ..

The one I just hammered got recovered, still pulls full capacity, and has a normal IR roughly the same as the others. BUT, I took a sharpie and wrote a zero on it, so I know right where to go to if the battery goes wonky a few years from now. It's like the cells hold a grudge against you for going to zero.

Yeah. I remember the buzz around these cells when they first came out. After dealing with fussy LiPos for so many years, A123s seemed unbreakable. People were intentionally abusing them and reporting no negative consequences. I mean guys flying RC model planes were landing with probably under 3V/cell then recharging by connecting a 4S pack directly in parallel with a 12V car starter battery then flying again 5 mins later.

Over time we have all learned a bit more about how to keep LiFePO4 happy and preserve the lifespan, thankfully.

 

[Substrate]

I remember those times well. Prior to that, we used pure-lead little hawker/enersys Cyclon agm's to hammer on. Oh baby! But not for RC planes, that's for sure!

Cyclon

Featuring Thin Plate Pure Lead (TPPL) technology, Cyclon batteries provide longer service life. Safe enough for installations in offices or hospitals.

www.enersys.com