IR threshold between cells that should not be paired anymore?

[klrman]

That's not normal. Typically you should see only a few milliohms variation whether rotated in-slot or between slots. The MC3000 should serve better for tracking health because - unlike the AC 1kHz test - it will incorporate some of the resistance components with longer time constants (but not all of them since the test duration is too short).

It would be interesting to see how the AC test compares to the MC3K pulse test on a wide variety of cells. For example, what's the largest difference between the two that you've encountered?

When I get back home tonight, I will do an extensive test with the MC3 and the SM8124A on all my cells, which is not that much really, just 21 at the moment and another 12 on the way and will post back here the largest difference between the two readings. Going to test all my 26650's as well and see if everyone has a stable reading in the mc3 and what's going on with the 18650's why they don't.

 

[klrman]

Tested all my cells and after taking the lowest readings of any cell in the MC3000, which consisted of rotating the batteries in their bays and swapping them in other bays, the results have been always consistent. All batteries have shown IR readings to be 60 to 62 % higher in the MC3000 vs the SM8124A tester. As I get more cells and as they age, I will continue to do this test to see if it still remains the same. If so, then I could just add 60% to the sm8124a figures to get a fairly accurate reading of how the batteries are wearing, or at lest it could be useful for cross checking to identify if there is a problem with either the meter or the charger.

 

[Gauss163]

Tested all my cells and after taking the lowest readings of any cell in the MC3000, which consisted of rotating the batteries in their bays and swapping them in other bays, the results have been always consistent. All batteries have shown IR readings to be 60 to 62 % higher in the MC3000 vs the SM8124A tester [...]

Most likely as the cells age that 60% excess will increase since - as I explained above - the AC test typically does not include the IR components that increase the most during aging (e.g. charge transfer resistance), but the MC3000 does include (some of) these. I've seen reports of much higher differences between these types of IR tests. You might try some old/unhealthy cells to see such.

To get consistent IR measurements in the MC3000 (or similar cylindrical cell chargers) it helps to verify that the batteries aren't loose (with high contact resistance) by ensuring that they don't rotate if you run a finger across them with very slight touch (if they do rotate then adjust them to get a tighter fit).

 

[klrman]

Thanks for the info. Yes, the cells were tight and hard to rotate. Unfortunately, I only have newer cells at the most a year since I purchased them. Not a great reference but as time goes by I can record what is going on and post back here. Will ask some of my friends if they have any real old cells that I could test as well to compare. That would be a good start I think. Again, thanks for all the help Gauss, I learned a lot in the last week or so, very helpful.

 

[Gauss163]

^^^ A good source of old/unhealthy cells are older laptop batteries (there are threads here about how to safely harvest cells from laptop batteries).

It would be interesting to collect further data showing the differences between the AC and DC IR tests on common testers. Currently there is little data available - probably because few people have access to both. Such data would prove useful for comparative analysis when making purchasing decisions. Iirc HKJ has some of the AC testers so maybe he'll post some data in the near future.

 

[klrman]

Good idea. Just called a local computer shop and he said he has a box of old laptop pulls, so I'm going to pick a couple and see what readings we can get out of them.

Should I attempt to revive and charge then first before testing for final IR with the mc3000 and sm8124a?