Redpacket said:
Curious: with the IR readings, do you tend to measure at a know SoC or maybe after a charge?
The IR readings in the chart are after a charge as you can see by the V to the left of the IR reading. Most of the time the cells have been pre charged and are sitting at this SoC for at least2 to 3 hrs before the IR measurement but more likely a day or 2. The 3.6* cells you see in the chart if you look at the datesit was early in my IR testing and experimenting. That was the V they came out of the pack with.
I now take an initial IR reading no matter what the Voltage is,before I go through the trouble of cleaning up the cell, to determine if they are worthy.
If the cellpasses my criteria then it gets charged by whatever method the cell can handle. Right now anything ~3V or below gets the CC/CV 4.2V, 50mA treatment.
>3V cells get300mA.
I do notice there is some change in IR at different SoC'es for cells. Most good performing cells whether at 1.5V or 4.2V will have an IR where the delta is pretty tight as in <10%. So lets say I have a Sanyo UR18650FM with 1.5V and an IR of 55.2m? this is a good candidate to charge. After charge and a restthe V is 4.15V and the IR is 51.3m?, then after the norm test C/D/C the V is 4.2 and the IR is 54.5m?. Subsequent tests have show that the IR does not change very much(~ 10% if that)on a good cell between different percentages of SoC.
On low performing cells it seems that the IR goes up by more than 10% from the initial "wakeup charge". With over 4000 cells recorded the amount of data is interesting to study. But also time consuming to data mine and find correlations between all these criteria IR, V, mAh, manufacturer, and model#.
I try to collect as much data as I can. The problem is that it seems each cell manufacturer and each part number have different criteria when considering good VS bad. So the search continues. But I will have"some" answers with some concrete measurement criteria for certain cell types in the not to distant future as there is irrefutable evidence piling up that has to be disclosed.
Wondering if the SoC, voltage or a few "wake cell chemistry up" charge cycles makes any difference to the IR reading?
Funny you should mention that. I am doing an experiment on some curious cells that have a reasonablecapacity outcome 75% to 80%but have a quite high IR
I am cycling them an my SKYRC at manufactures spec and they seem to hold and if nothing else increase their mAh results slightly every time. I will run them a couple more times and see what their IR is at the end.
Till then
Wolf