Parallel testing (Because I’m lazy)

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J_Mack58

Member
Joined
Apr 7, 2021
Messages
93
I was breaking down some 26650 packs when I decided to goof off a little. The packs are 4s5p, so when I got to the 5 in parallel I decided to capacity test them as is. The result from 3 cause one lost contact are 17.55ah, 16.29ah and 15.73ah. For 3200 mAh cells the expected is 16ah which two exceeded and one was close enough. I would use these cells with no further testing but what about IR? Well I tested them in parallel too. Results are 9.36, 9.45 and 8.97 mohms. Parallel resistance looked liked it was going to be good but after doing the math and assuming all cells equal or very close the calculated valve of the 9.36 mohms parallel pack is 46.8 mohms/cell, the 9.44 ohms pack is 47.25 mohms/cell and 8.97 pack is 44.85 mohms/cell. That sucks!!! These cells suppose to be under 30 mohms. check my math:
for the 9.36 mohms I do 1/9.36=.1068 divide that by 5 and I get .0214 1/x that and I get 46.8
1/rt = 1/r1+1/r2 …… +1/r5. You all remember.
Anyway my cells IR results can’t be bad, time to take them apart and confirm they suck!
Results 27, 28, 24.6, 24.9 and 27.1 mohms They are good!
With these results my IR tester should have read 5.250 mohms when it read 9.36 mohms. Where did the extra 4.11 mohms come from? Peep the last 4 pictures. Damn nickel strip. It did not add 8 mohms because they are in parallel too. (Hope that is right, hell it sounds good anyway. Hope you enjoyed and for a final thought… Do our Nickle strip rob us of some power? Ohms Law says it does.
 

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Oberfail

Member
Joined
Jun 22, 2021
Messages
110
Thats a very interesting way to test them. I hope it will work out for you ^^
I did that aswell with some lower-end 18650's that were supposed to be put into a hand vacuum cleaner.
 

J_Mack58

Member
Joined
Apr 7, 2021
Messages
93
Thats a very interesting way to test them. I hope it will work out for you ^^
I did that aswell with some lower-end 18650's that were supposed to be put into a hand vacuum cleaner.
Since I had to split them to get the true IR, I’m redoing the capacity test as I sleep.
 

floydR

Member
Joined
Aug 23, 2017
Messages
1,330
Altho safer because they are LFP cells accepted practice is to only test cells while you are awake,. unless in a a fire safe building outside of living quarters. Might even be the accepted practice on LFP cells. I suspect many people testing 18650/26650 cells have fallen asleep at some point while testing cells, I know I have a couple times.
later floyd
 
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