DogDipstick said:
Charging from sub 4.2v..? it would continue to fill the cell with capacity until reaching an equilibrium, at 4.2.. where the CV stage would begin...
However, if it has reached 4.2v, and CV stage is in application, it takes me longer than the (3) hours to taper on some (large) cells. Current does not, has not dropped within 3 hours.
This is the scenario you present. Correct? I do run into this, on some cells, that are usually beat degraded, used, cells: Not reaching the specified termination current (set in charger) whithin the time period you mention.
i asked for this specifc cell. not any others. lets keep it simple and focused.
DogDipstick said:
Hypothesis: Cell is not full of capacity, and will be, if tapering is allowed to continue ( over your 3hrs). Until full, when the cells will be metered discharged and proven for the input capacity in mAh.
its not my 3 hours, its the datasheets stated 3 hours that a charge should take. the manufacturer has concluded that in their testing that if you charge the cell by its reference parameters (As stated in chapter 6 and 7) should it take longer then 3 hours to reach this state then the cell does not meet specifications. it does not say it is bad or worn, just that it does not meet the datasheet specifications. more on this below.
DogDipstick said:
The current continues, never reaches C/20 as per your scenario.
the same thing applies as above. the cell no longer meets specifications as stated in the datasheet. it does not tell you anything more then that at this point.
DogDipstick said:
and cell is heated slightly and lifespan is detriment. My hypothesis. The (loss) from the cells charge efficiency is greater than the current provided.. never reaching termination current taper for the cell,.... was never charged to full voltage. Is that what it means?
yes, mostly correct.
heating is a byproduct of any battery charge but heating does not mean bad things, many cells operate better at higher temperatures. this is why the datasheet mentions testing temnperature specifically in chapter 6. any testing done outside the range stated in the datasheet is invalid if you want to know the state of the cell. so far you only concluded that the cell has a high self discharge that exeeds the cells capacity to absorb current at that specific voltage. in order to make a assessment to understand what is going on you will need to do a charging and discharging test as stated in the datasheet of the cell.
but that datasheet only tells you the state of a NEW cell. not a used one.
DogDipstick said:
Like the "overtapering" term I made up earlier,.... Some cells will benefit from a charge termination. If they are allowed to taper to minuscule amounts, they will have a detrimental lifespan for the long taper will heat the cell up in the long run.. This is my hypothesis.
"hypothesis" would be the correct word. that is a word you use when you dont know but have an idea. lets correct this and turn in into fact. but the "taper" is speak of is the CV portion of the charge so i will use that term. taper is just clouding the subject.
few ground rules we shall no longer debate and you will have to accept these as simple fact, if you dont understand these concepts you can ask for clarification on them if needed on how it exactly works:
1: the CV section of a charging process can happen at ANY voltage.
2: the voltage of the charging process is dictated by the charger/power source.
3: every single CC/CV charger/power source will NOT increase its voltage beyond what is set.
4: every single CC/CV charger/power source will NOT increase its current beyond what is set.
many cells (basically none) have a linear relationship between their float voltage and capacity. generally most capacity is between the 3.5 and 3.8 range. the higher you go beyond 4V or so you get less and less capacity relative to its voltage. so charging at lower voltages means it takes longer to saturate the cell at that voltage relative to charging at higher voltage. its basically like filling a colander but with less and less holes the further up you go. eventually the cell will ber actually filled. but this process will take many hours, especially on lower voltages where most of the capacity is. so even stopping at the 1/20C will take frocking ages if you do that at 3.8V for example.
so, the CV section is completly and utterly dependant on what the cell wants to do by the design of the chemistry. the charger has ZERO influience on the CV section. it only caps the current during the CC portion (hence the name) as the cell will abosrb all the currents it can in relation to its IR. so you need to protect the cell from itself during this stage. but once you reach your set voltage the current will naturally lower as the IR increases and the cell fills up to your set voltage (whatever that might be).
lets be clear: the cell does not give a frock about what voltage you charge it to. that is a lifespan/capacity question you need to make when making your product. lower is better in this regard. but you will need more cells to compensate for any consession you make in this regard wich will add cost and all that jazz. so lets stay away from that part as far as we can and just discuss that you can charge to different voltages. the reason behind it is not relevant for this moment.
you are VERY focused on the last bit of the charging process and stopping it there. lest see what happens when you do.
if a cell is not saturated at the voltage were it is being charged at (aka: still taking in current) it means that as soon as you cut the charge the voltage of the cell will drop. especially on a 4.2V charge level this drop can be quite noticable. 4.15V float or even a tad lower is not uncommon. this voltage WILL drop the more wear the cell has.
so what did you actually do by doing this? you charged the cell to 4.15V. not 4.2V. that is it. once you let the battery rest the voltage simply drops to its -actual- charge level.
so knowing this, why not just charge to 4.15V and just hold the cell there? for the cell it does not matter, its a 4.15V so nothing is different.
here is the important bit i think you misread in all this:
yes, there is some studies done in keeping the cell floating but these studies have shown that the damage that is being done is nothing compared to just charging to a high SoC. so if you were to charge a cell to 4.15V for example and kept it floating there will do the exact same "damage" to the cell as just charging to 4.2V and cutting the charge off a 1/20C as stated in the datasheet and the cell will drop back down to 4.15V anyway.
if i were to charge a cell to 4.05V and just hold it there it would do the same "damage" then charging to 4.1V and just cutting off the charge as the cell will naturally already drop down to 4.05V. so in the end you do the same thing, just with a lot more expensive tool.
DogDipstick said:
I dont know haw a big vs small cell would react differently from this scenario, if any difference.
cell size is not a factor. its the chemstry that decides what happens.
DogDipstick said:
Small cells have high IR, and I suppose the heat created fro the collumbic in-efficency would be detrimental to the cell, moreso, with small currents, than a low IR large cell, with identical currents... .
IR is a result of size and chemestry. there is a natural balance that dictate their use case. using a high IR laptop/phone battery in a cordless tool will yield "interesting" results. using low IR power tools in a phone will do as well, as you walk from charger to charger as the capacity is utter shit. its just a question of remaining within the specs and preferably under them. cooking any cell regardsless of its size is detrimental.
DogDipstick said:
Is that what it means? I honestly dont know what the specified "3hrs" has to do with it.
hopfully you begin to understand that the 3 hours have nothing to do with normal operation/usage. just testing the cell according to the manufacuters specs.
DogDipstick said:
However, it WILL reach that when the IR is raised at the end of the charge ( cell takes no more).
so the cell terminates the charging process naturally by itself without any input from the charger. you can just hook up a CC/CV supply to a cell and once the cell has reached its steady state at the set voltage nothing more will happen, just like communicating vessels do. at some point the level (voltage) is equal and nothing more will happen. it REALLY is that simple. so "terminating a charge" is completly unnessesary unless you are TESTING the cell.
ps: running those tests is fine, but several people here already have done a LOT more testing then you will probably ever do. i have litteraly spent over 10k euro in test equipment over the years and have tested hunderds of cells to their breaking point.
that is why i am telling you that terminating the charge does basically nothing you need to concern yourself about. just dial the voltage a tad down to 4.1V or so on your dumb CC/CV power supply and you will also enjoy a battery that will live a happy long life. at least one that lives longer then one you keep topped up tat 4.2V with your expensive charger...