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Behaviour of cells in parallel take 2
#31
I actually picked those two at random from the cell database, but I was looking for 2 fairly common cells with similar capacity and different nominal voltages. I have no idea if they have similar IR ratings from the factory, so hopefully they do. I'm looking forward to your test results!
Check out my long-term capacity test of 18650s: https://secondlifestorage.com/showthread.php?tid=6868
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#32
Don't forget to consider this :

"With all batteries, SoC affects the internal resistance. Li-ion has higher resistance at full charge and at end of discharge with a big flat low resistance area in the middle."

https://batteryuniversity.com/learn/arti...resistance

With second life cells these variations in IR vs SoC may create other issues that single reading IR values miss...

Like the data and testing as it is this sort of work, experimentation and research that uncovers the reality... ++1
If you can't quantify how much they cost, it's a deal, I'll buy 5 of them for 3 lumps of rocking horse ......
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#33
(06-20-2020, 04:00 AM)Generic Wrote: I actually picked those two at random from the cell database, but I was looking for 2 fairly common cells with similar capacity and different nominal voltages. I have no idea if they have similar IR ratings from the factory, so hopefully they do. I'm looking forward to your test results!

Well here are the results of these cells tested.
Quite normal results of 2 reasonably decent batteries. I do not believe the Nom V had much influence on anything.
Wolf

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#34
Thank you Wolf!! During the discharge, right around 3.6V, cell 1 and 3 (3.6V cells) started to contribute more current than cells 2 and 4 (3.7V cells). However, the increase in current was not as dramatic as I expected. The 3.7V cells were around 0.9 Amps and the 3.6V cells were around 1.15 Amps. Likewise, on the recharge, the 3.6V cells took about 1.25 Amps each vs. the 3.7V cells 0.75 Amps each initially, before slowly reversing as more charge was absorbed.

So, nominal voltage makes a small difference, but not enough to cause concern when assembling packs, as long as there is about a 50-50 distribution within the packs.
Check out my long-term capacity test of 18650s: https://secondlifestorage.com/showthread.php?tid=6868
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