OK on a lighter note I have some interesting information regarding AC vs DC IR.
I have tested 226 cells so far with varying degrees of SOH.
Some of these cells where pulled out of newly acquired packs, some have been siting in my storage area because they were cells I wouldn't use in my power wall as they were less than my 2250mAh criteria.
All voltages were recorded as the cell was found. AC IR was tested and DC IR was also tested if there was enough V in the battery.
Out of all of the cells 4 were below 0.5V and 2 had no V at all with a tripped CID suspected as the AC IR was ∞.
The 4 cells that were < 0.5V had a respectable AC IR hence were gently recovery charged to 3V at 20mA and then finish charged and tested at full 1A on the OPUS. No Explosion, No rupture, No fire.
Some pictures of the various packs these cells came from.
I also pulled some selected cells from my close by stock to try to round out the selection. I am committed to testing 1000 cells with this study so I guess I will have to go to my cell stock in my storage trailer this week to get some more.
So now to the good part.
The whole procedure for each cell is as follows:
Note: checked" implies recorded
AC IR checked, Voltage checked, DC IR checked, Cells inserted into Charger/Testers and the IR that the Tester showed checked, C/D/C at 1A except for the Vapecell which only does 1A charge and .5A discharge. The mAh results checked, the post C/D/C V and AC IR checked, and the post DC IR checked twice.
All this info can be found on this sheet
hereor downloaded below as an attachment.
So far, the only correlation I see between AC IR and DC IR (of cells I would consider using because the AC IR was acceptable) is that DC IR is somewhat higher.
In the filtered graph of cells, I would use, you will notice that the precharge DC IR is very high on some of the cells. That is because they are < 2.8V and the DC IR is high due to the V drop. The cells recover to a respectable DC IR after their charge.
Here is a graph of all the cells with precharge and postcharge voltage.
If you notice the AC IR does not change much at all and the DC IR follows it in a more exaggerated fashion depending on the voltage of the cell.
The current observation is that AC IR so far has been a very good indicator of a cells SOH with DC IR confirming it.
AC IR can indicate a cells SOH even at low V i.e. a cells cutoff V of ≈2.8V to 2.5V and even below that, where DC IR needs the cell to be at least ≈3.2V to get a reasonably respectable reading.
Here is a chart of the SOH compared to AC and DC IR.
These are just preliminary findings and by no means support a conclusion yet.
If someone wants to dig into the data on the sheet and extrapolate more info that would be great.
Stay tuned
Wolf
Excel Sheet of 246 cells tested with AC IR and DC IR
Harvest Data Date,Cell Number,As-Found Condition,Part Number,Manufacture,Wrap Color,Insulator Color,mAh Rating,Nom V,Max V,Cut off V,Standard Charging,Standard Dis charging,Charge Cutout mA,Manufacturer IR (mΩ AC 1kHz) ,My Personal Prefered IR (mΩ AC 1kHz) ,My Pedrsonal Max IR (mΩ AC 1kHz) ,...
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