Self Discharge LiCo low voltage question

[markass530]

Anyone know How much damage is happening with a LiPoly LiCO cell once it starts dipping below 2.6 via self discharge? anyone have a time frame on how long these cells would be good or a "Point of no return"

 

[Jeremy Harris]

My experience has been that the self-discharge rate of LiCoO2 is pretty low. I've had cells stored for around a year without touching them and they've all still been fine. I guess if you stored fairly well discharged cells you may have a problem, and getting down to 2.6V per cell is definitely getting into the irreversible damage area (I've had a cell go down to 2.5V and it just puffed when I tried to charge it). They are pretty variable though, some folk seem to have been able to get away with taking cells down to this sort of voltage and had them recover, although I suspect there may well be some impact on capacity and maybe internal resistance.

 

[pdf]

Hard to believe you would get a self-discharge rate of any significance. If it was truly a self-discharge, something might be wrong with the cells anyway. I had 3 bricks connected to a controller that slowly drained the cells over a period of a couple of weeks. They were probably below 2.5 though.

I think Jeremy is right; the results reported here are variable. Some people can recharge slowly and get quite a bit of use out of them. Some don't.

 

[dogman dan]

Uhh, wouldn't the point of no return be when they self discharge more than .1v or so? That is, from fully charged to whatever. Even my nearly worn out 2 year old lipo isn't that bad. More like no more than .05 lost overnight as lost surface charge.

If I have a cell that I charge to 4.1, and the next day it's at 3.95, I want that thing outta my house, off my bike. I might run it on the mower and charge outside some, but I don't want that thing on my bike no more.

They really shouldn't self discharge any, but if a device such as a bms, controller, cellog, was discharging it, I'd still be very very carefull with anything that went below 3v.

 

[markass530]

We're talking over a period of a year or so

 

[dogman dan]

Mmm. That makes some difference. But I still wouldn't trust em by now, if they got below the "lipo rules".

I was picturing it happenin in less time, but even if it took a year, truly self discharging would be real bad. I have some lipo on it's last few cycles, two years old, and it sure doesn't self discharge that much. Even though they are slightly puffy, low capacity, and now getting a lot warmer on discharge, they still hold at about .5 less than what you charged them at or better, for at least a few weeks.

If something discharged them, then they might be more savable for at least a few, "keep an eye on em" cycles. But self discharge that much sounds very bad to me.

 

[markass530]

ok, you connect any battery to a BMS, it's going to self discharge some, even after the BMS shuts down, it's not going to stay the same exact voltage forever. I didn't ask for a critique of a specific battery, just asking if anyone has any practical experience or theoretical knowledge dealing with LiCO cells ending up right around 2.6 volts , and then dipping below due to self discharge. I Can use google and figure out "Gee that doesn't sound good" myself, just wondering if anyone knows anything beyond the obvious

 

[Jeremy Harris]

ok, you connect any battery to a BMS, it's going to self discharge some, even after the BMS shuts down, it's not going to stay the same exact voltage forever. I didn't ask for a critique of a specific battery, just asking if anyone has any practical experience or theoretical knowledge dealing with LiCO cells ending up right around 2.6 volts , and then dipping below due to self discharge. I Can use google and figure out "Gee that doesn't sound good" myself, just wondering if anyone knows anything beyond the obvious

I think the answer you got from me in the first reply and the post after that by pdf pretty much sum up the situation for a cell down at below 2.6V. You may get lucky and have them recover, you may not in which case they will probably puff when you try and charge them. There's no real way of telling whether they'll recover or not from this sort of discharge, not even for cells from the same manufacturer.

When it comes to the BMS discharge rate then this should be pretty low, not more than around 50 µA from each cell as a rule. For a 5Ah cell that discharge rate is going to mean losing less than 10% of the cell capacity per year.

 

[markass530]

ok, you connect any battery to a BMS, it's going to self discharge some, even after the BMS shuts down, it's not going to stay the same exact voltage forever. I didn't ask for a critique of a specific battery, just asking if anyone has any practical experience or theoretical knowledge dealing with LiCO cells ending up right around 2.6 volts , and then dipping below due to self discharge. I Can use google and figure out "Gee that doesn't sound good" myself, just wondering if anyone knows anything beyond the obvious

I think the answer you got from me in the first reply and the post after that by pdf pretty much sum up the situation for a cell down at below 2.6V. You may get lucky and have them recover, you may not in which case they will probably puff when you try and charge them. There's no real way of telling whether they'll recover or not from this sort of discharge, not even for cells from the same manufacturer.

When it comes to the BMS discharge rate then this should be pretty low, not more than around 50 µA from each cell as a rule. For a 5Ah cell that discharge rate is going to mean losing less than 10% of the cell capacity per year.

Much appreciated as always jeremy, the previous comment wasn't directed at you