Why is Opus never finish charging some cells?

[harrisonpatm]

As I am doing my primary charging of salvaged laptop cells, I have had about 4-8 cells in the past week that my Opus charger is trying to overcharge. These have almost exclusively been the red Sanyo cells. They have passed my first voltage check, being recovered at above 3V, meaning none of these are 0V or very low voltage cells that I'm trying to recover. So I rotate them into the Opus charger at set it to 300mA current. What happens is, the voltage will increase to somewhere between 4.10V or 4.15V in 2-4 hours, depending on the cells starting voltage. Then the charger will go off into it decreasing current, which is to be expected. Except it doesn't end. I pay attention to the accumulated mAh, and it gets up to 3500-4500 mAh (which is obviously ridiculous) when I pull it, while never going above 4.15V. They get warm, not hot; around 30-40 degreees C. I also use Liitokala chargers, and they never exhibit this behavior, despite putting similar "questionable" cells through them. I also process other red Sanyos that don't exhibit this problem.

I will of course not be using these cells, set them aside to discard, but I was wondering if anyone else has seen this behavior and know why this is happening. On one of these occasions, I wasn't paying as much attention as I should have and the accumulated mAh got up to 5500! Clearly this is either a bad cell or a charger glitch. I know the Opus chargers aren't supposed to be dead accurate, and I have gathered from this forum that the red Sanyos can be glitchy. Just want to understand what's the specific issue here. .

 

[OffGridInTheCity]

This sounds like bad/self-discharging cells. As they get close to 4.1v or 4.15v and the OPUS charge current drops to 100ma or 50ma or 27ma... the cells discharge faster than the charge current, get hot, never get to 'full charge' or it takes twice as much ah as the capacity of the cells. These should be discarded!

I find the chances of this very high on 0v cells that you try to recover. There has been much discussion, but cells that pull all the way down to 0v (or even go negative in their history when in series with others) are likely damaged. The few that do charge up? - they are usually below my minimum acceptable % of original capacity - e.g. 85%.

 

[harrisonpatm]

This sounds like bad/self-discharging cells. As they get close to 4.1v or 4.15v and the OPUS charge current drops to 100ma or 50ma or 27ma... the cells discharge faster than the charge current, get hot, never get to 'full charge' or it takes twice as much ah as the capacity of the cells. These should be discarded!

Good thought, that as they reach full charge, they are self discharging faster than Opus can top them off with it's final charge.

I find the chances of this very high on 0v cells that you try to recover. There has been much discussion, but cells that pull all the way down to 0v (or even go negative in their history when in series with others) are likely damaged. The few that do charge up? - they are usually below my minimum acceptable % of original capacity - e.g. 85%.

Point taken, but as I had mentioned, these are cells from my sorted stash of above 3.0V recovered. They have been sitting at this charge 3 months-1year, and the first sort checked them at 3V or above. Granted, still likely self-dischargers, but is there something else that might be going on, given that these weren't 0V cells?

 

[OffGridInTheCity]

Point taken, but as I had mentioned, these are cells from my sorted stash of above 3.0V recovered. They have been sitting at this charge 3 months-1year, and the first sort checked them at 3V or above. Granted, still likely self-dischargers, but is there something else that might be going on, given that these weren't 0V cells?

They can still be self-dischargers as they reach full charge - if they accept more charge than they are specified for then that's the most likely explanation rather than some kind of OPUS (or similar) failure

 

[Wolf]

but is there something else that might be going on, given that these weren't 0V cells?

Is there a way you can check the IR of theses cells other than from the Opus?
My guess is that the AC IR measured with an RC3563 or YR1035+ will be >80mΩ and more than likely>100mΩ
Which basically tells you the cells are at end of life.
I have tested many cells with this higerer IR and have found many with low capacity and charge time exceeded issues.
My SKYRC MC3000 and MegaCell Chargers allow me to set a time limit on how long a cell is allowed to charge before it is deemed N/G
Since I test all my cells at 1A and the largest cells I have are 3500mAh my charge limit is set to 4 hrs if any cell doesn't charge to full at that time limit it is deemed obviously no good. Additionally all my chargers have a 50°C temp limit if that is reached the cell is also deemed N/G.

All in all IR is the key and once you use it to prequalify your cells the rest will come easy.

Wolf

 

[Korishan]

these are cells from my sorted stash of above 3.0V recovered. They have been sitting at this charge 3 months-1year, and the first sort checked them at 3V or above.

Just because they sit at this stage just fine, doesn't mean they aren't SD's.

In your OP, you describe the classic situation where the cells have probably started growing dendrites. These punch holes through the electrolyte separation barrier. However, they aren't far enough to cause a dead short, but close enough that when there's enough voltage potential, current can start to arc between layers, causing heat.

This effect can sorta go away over several charge cycles. If you charge them at a full 500mA to full charge, you'll notice they get very hot, closing in on 120-130F. Then discharge them down to about 50% SoC, and then charge again. This sometimes destroys the dendrites, or at least knocks them back a bit.
However, IF you do something like this, those cells should be closely monitored because if they go over 130F, they are in extreme risk of becoming a rocket. ALSO, never ever ever use these in a large build. Especially with high drain. They may be fine for something like a single cell flashlight or such.
But I would highly recommend to toss them to be on the safe side. Or discharge them down to 0V and use them for spot-welding/soldering practice.

 

[Korishan]

btw, updated thread title to more accurately reflect what your question is so it's easier for others to search

 

[harrisonpatm]

Just because they sit at this stage just fine, doesn't mean they aren't SD's.

In your OP, you describe the classic situation where the cells have probably started growing dendrites. These punch holes through the electrolyte separation barrier. However, they aren't far enough to cause a dead short, but close enough that when there's enough voltage potential, current can start to arc between layers, causing heat.

This effect can sorta go away over several charge cycles. If you charge them at a full 500mA to full charge, you'll notice they get very hot, closing in on 120-130F. Then discharge them down to about 50% SoC, and then charge again. This sometimes destroys the dendrites, or at least knocks them back a bit.
However, IF you do something like this, those cells should be closely monitored because if they go over 130F, they are in extreme risk of becoming a rocket. ALSO, never ever ever use these in a large build. Especially with high drain. They may be fine for something like a single cell flashlight or such.
But I would highly recommend to toss them to be on the safe side. Or discharge them down to 0V and use them for spot-welding/soldering practice.

They're definitely discarded already, just wanted to learn why. Thanks.

Wolf, my IR meter is still in the mail.

 

[Wolf]

Wolf, my IR meter is still in the mail.

Ah yes @harrisonpatm we did have a discussion in another thread about that didn't we.
I find some cells esp. the older Sanyo UR18650A , UR18650F, FB, FJ, FK,FM, and some of the UR18650Y to be very susceptible to being S/D's or "Vamp cell" ( being a cell that never completes a charge but just continuously soaks up power yet never getting excessively hot).
Whereas a S/D will actually complete a charge cycle but over the course of a couple of weeks will settle in at a lower than acceptable voltage.
Usually <4.1V.
Of course there are the "heaters" and you know my position on those.
I am not trying to single out Sanyo as Panasonic's CGR series and and some others also have this issue just not as prevalent.
Wolf