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EVE 280 Ah from Shenzen Basen are not "brand new" as advertised

Cells normally settle. A voltage of 3.3 is pretty normal voltage that my cells settle at. What do your cells settle at after the surface charge dissipates?
3.32 usually
With zero absorption
Charged to 3.56
 
Mine settle to the same voltage whether they spend time at constant voltage or not. Absorb is a Lead Acid term. Are you applying Lead Acid concepts to Lithium charging?
It applies to LiFePo4 also. It's the reason for the CV setting.
It's really only important for top balancing.
 
Mine settle to the same voltage whether they spend time at constant voltage or not. Absorb is a Lead Acid term. Are you applying Lead Acid concepts to Lithium charging?
It is not the time spent above 3.4V it is the charge they have absorbed to achieve 100%SOC. A slow constant 3.4V or above as long as the cells will take it achieves 100%SOC 3.55V for a shorter time can also achieve 100% but it isn't the voltage reached, it is the charge accepted.
If the cell is settling below 3.3 in a short time, it likely hasn't reached 100% yet.
Calculate the total Wh the cell can accept and be certain that amount has reached the cell. If it has, and the cell STILL drops below 3.3 in a short time, then the cell is suspect.
 
It applies to LiFePo4 also
What applies to LFP? Earlier you implied that LFP will settle if not given Absorb time. As I said earlier, LFP settle regardless where the are stopped charging. Lead Acid batteries are not full, if not given sufficient Absorb time and that can lead to sulfation. That is a different chemical process which is entirely different with Lithium chemistry.
 
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Calculate the total Wh the cell can accept and be certain that amount has reached the cell. If it has, and the cell STILL drops below 3.3 in a short time, then the cell is suspect.
I agree that is a good diagnostic to tell if a cell has gone bad if it self discharges at a significant rate. Since the curve is so flat below 3.3 it might take a while. Most cells that degrade lose capacity, but I am sure there are those that also self discharges more than others.
 
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What applies to LFP? Earlier you implied that LFP will settle if not given Absorb time. As I said earlier, LFP settle regardless where the are stopped charging. Lead Acid batteries are not full if not given sufficient Absorb time but that is a different chemical process.
Yes, they will settle.
How far they settle, depends on how they were charged.
 
How far they settle, depends on how they were charged
How they were charged? Do you mean C rate or the slope of that current taper during CV stage?
I have charged a lot of LFPs a lot of ways and maybe It have not paid attention enough. 3.3 volts is what I have seen routinely. Are you talking millivolts in terms of the voltage they settle at? My meters do not record that degree of resolution. I think it can be misleading to other readers to suggest that the resting voltage can be used as a diagnostic or that it bears any coorelation to how a cell has been charged. I have read no academic papers that suggest anything different.
 
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How they were charged? Do you mean C rate or the slope of that current taper during CV stage¿?
I have charged a lot of LFPs a lot of ways and maybe It have not paid attention enough. 3.3 volts is what I have seen routinely. Are you talking millivolts in terms of the voltage they settle at? My meters do not record that degree of resolution.
In the upper knee, the voltage climbs fast.
If you charge at a higher voltage, or for a longer time.
The SOC is higher. And the resting voltage.
3.40v is 100% rested
3.35v is 99% rested
3.33v is 90% rested
3.30v is 70% rested
There's only 0.10v difference between 70% and 100% SOC.
If you stop charging as soon as you hit a target voltage, it will settle to a lower rested voltage and SOC.
 
@timselectric , we have gotten sidetracked from trying to help @guidecca figure out whether he has a bad cell or not. All we know is that his cell discharged and now he his charging it again. We do not know how many Amphours he put back in so we have no idea what the capacity is and whether it has lost capacity. None of our recent discussion has shed any light on his issue.
 
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Actually, it should have given them a lot of useful information about why they are seeing that voltage after charging.
 
Actually, it should have given them a lot of useful information about why they are seeing that voltage after charging.Gu
I respectfully disagree. I can't make sense of a lot of what you are saying. For example I have never heard the term 70 percent rested. It can take a while for some cells to reach resting voltage or a simple load will get them there quickly. The surface charge disappears quickly and is insignificant in terms of Amphours.
I do agree that there can be a 0.1 volt difference between 100 percent SOC and 70 percent SOC but that does not help @guidecca figure out if his cell has the stated capacity or not. The only way to do that is to track the Amphours going in and out of the battery for several cycles to get a good approximation of the capacity.
 
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I respectfully disagree. I can't make sense of a lot of what you are saying. I have never heard the term 70 percent rested,
I do agree that there can be a 0.1 volt difference between 100 percent SOC and 70 percent SOC but that does not help @guidecca figure out if his cell has the stated capacity or not. The only way to do that is to track the Amphours going in and out of the battery for several cycles to get a good approximation of the capacity.
The rested voltage, or Rested SOC. Is the voltage of the cell, after charging is removed. And the cell has been given time to rest. And settle to the actual voltage or SOC.
70% rested, along with the other values I stated.
Are the SOC values.
 
70% rested, along with the other values I stated.
Are the SOC values.
But even those are approximations and the only accurate way to measure capacity is to track Amphours in and out. 70% rested is a meaningless statement. It is impossible to tell when a cell is 70% rested. Even using voltage to predict 70% SOC is only an approximation because the voltage curve is so flat at that point for LFP/
 
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But even those are approximations and the only accurate way to measure capacity is to track Amphours in and out.
It's only an approximation, through the flat part of the voltage curve. Once you get into the knees, it's very accurate.
 
If he understood it, it definitely does.
Now he should know what to do, to test it completely.
All of this information, was for his benefit. And hopefully helps others who find it here.
 
If he understands? I have been messing around with Lithium batteries for 10 years and your statements are hard for me to understand. I know you are trying to be helpful but I am concerned that your vague statements could be misunderstood by some readers.
My view is the most useful information about a cell is it's current capacity compared to it's original or stated capacity. I hope @guidecca can get the answer to that question.
 
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