ozz93666 said:
I've just had a look at your work Cherry , and to be honest I've no idea what you are doing...
You are measuring internal resistance ??? what for ??? For power walls the current is so low per cell , even with 300mOhm int reistance loses are still below 1% per cycle
Oz, thanks for your opinion, it forces me to clarify even mor what i am suggesting.
I will give the conclusion first, the reasoning second, to save you from reading too much babble of me.
I am NOT measuring IR for identifying the losses of a later use.
I measure IR because an IR of >300 mOhm will most probably (>90%) be a cell with Low capacity (<1500mA), or SD, or both. That knowledge can be achieved with a single measurement, even before charging.
If your situation is, that you need EVERY somehow usable cell, no care for the time spent on 10 Cells and only 1 of the good, then be it.
If you on the orther hand have rich resources and need a high success rate on your capacity cycling, then you might put this (>300mO) in a (seconds-)stock, and put your efforts in another one with betters prospects ( having a lower IR).
Means - I do not recommend to thrash a >300 mOhm cells on the IR alone. But, i predict that you (most probably) WILL Thrash it later, because it has not enough capacity left, or turns up as SD, or both. And you CAN Know that before you even start charging.
What you do with that knowledge, is totally up to you.
The other aspect of IR, being an issue on high current applications, has nothing to do with this.
I hope, that makes clear what i am publishing here.
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Ok, for the reasoning i promised:
It should be agreed knowledge that we all measure the capacity left in a cell to somehow thefine its Lifetime status, as i may call it for the moment. Cells are aging by time, by (high) temp, and by cycles, just to name the important ones. (Are there more ?)
Only a few days ago i realized ( someone talked about %capLeft as a factor) that 1900 - 2000 mAh is not a REAL good classification, given the fact it can be a type with 2000 for new, or 2800 for new. The difference should be obvious. Even More, there are cells which have 1800 as NEW. And they would end in the less preferred 1800-1900 class - just!
On the other hand, IR is (currently) only taken in consideration as a factor for usability in higher current applications, due to the losses you mention.
After my Investigation i am quite sure there is more hidden in the IR value, probably/hopefully a strong correlation of the lifetime status of the cell itself. From pure technical/chemical consideration, thats sounds very good, and the first try to put that in a sheet LOOKS very good.
Still, IR will probably not the the new classification of cells. But it may change the approach you do in qualifying your cells.
Minimum two people have said their statistical succes rate och checking cells is 30 %. Means they charge/discharge 3 cells to find a good one. That takes Apparatus and time.
When you get a prediction from IR, which cells have passed quite a good piece of their lifetime, and cocentrate on the other ones, you might increase that rate to a higher level. Getting more good cellls for the sane time/Equipment hours, with the price aof a Bine where are only 10 % good ones left in.
If that is something for depends just from the situation wher you are in.
Hope that again clarifies my reasoning.
Geek said:
camthecam said:
I think it is awesome. But for me - maybe a little complicated..
It does work.You can get the same results from measuring a cells voltage under load.
By measuring a cells internal resistance - if you have the equipment to do so accurately - can actually give you a reasonable estimate on capacity.
While Cherry's original post probably was beyond most users understanding, the theory and results are very helpful.
You are surely correct. When i write the whole process of thinking its the disadvantage that it is complicated to read and to follow. If i just post the result it is doubtful because it is not proven knowledge.
I did the top post of THIS thread exactly to get out of that dilemma.
My answer to oz hopefully does the first fix on that, thankfully he has given exactly what i needed to improve my reasoning for you all.
