Ampster
Renewable Energy Hobbyist
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?But without the absorption, it will settle.
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?But without the absorption, it will settle.
3.32 usuallyCells 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?
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?3.32 usually
With zero absorption
It applies to LiFePo4 also. It's the reason for the CV setting.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.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?
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.It applies to LiFePo4 also
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.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.
Yes, they will settle.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.
How they were charged? Do you mean C rate or the slope of that current taper during CV stage?How far they settle, depends on how they were charged
In the upper knee, the voltage climbs fast.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 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.Actually, it should have given them a lot of useful information about why they are seeing that voltage after charging.Gu
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.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.
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/70% rested, along with the other values I stated.
Are the SOC values.
It's only an approximation, through the flat part of the voltage curve. Once you get into the knees, it's very accurate.But even those are approximations and the only accurate way to measure capacity is to track Amphours in and out.