18650 Pack - Self-dishcharge wait time?

1xAA

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Sep 27, 2020
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I have all 392 cells tested/rated/sorted and recharged...how long do I let them sit and retest for self-discharge?
 

Korishan

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Generally, the longer the better, within reason. But most let the sit for at least 2 weeks. Another bunch will go about a month.
 

1xAA

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Sep 27, 2020
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Thanks...after 2 weeks where should I draw the line on voltage?
 

Korishan

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Usually you don't want fully charged cells (assuming Lithium Ions) to drop from 4.2 to 4.1V within a couple weeks. They should stabilize around 4.1-4.12V. They will continue to self discharge, but the speed at which they do drastically slows down, or it should. So after a couple months, they shouldn't be below 4.08V, for example.

I have some cells that have sat for almost 2 years and are still around 4.05V.

So basically if they drop below 4.1V after 2 weeks, they would be considered self dischargers and not used in powerwall/brick applications. They would be fine, probably, in small devices like toys, remotes, small tools, lights/torches, etc. Nothing were you'd be reliant on them.
 

jonyjoe505

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Feb 28, 2018
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did you do an IR test on the cells?
I had cells that pass the self discharge test but once I put all the cells in a pack I get balance problems. Since I got a IR tester (yr1035), I always find 1 or 2 cells from the packs that I took apart that had high IR (in the 100's) .
I wouldn't build a pack without first checking the IR. It's too much work taking a pack apart.




image_pwinpl.jpg
 

100kwh-hunter

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Mar 2, 2019
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i put them away for two weeks, if they where above 4.11v keep.... below 4.09: discharge to 0.00v and throw away.
Indeed ir is a very good thing to know also.
I had a yr1035 ir tester, very good piece of equipment...once you bought it, you will ask your self: how the heck i could test cells without this...
Buy it with the "full options"

It is so much quicker but you wont have perfect numbers on soh or degradation of your cells, but perfect cells.
For testing the whole pack i did not come this far with the yr ir meter, so i dont know.
My pack testing was after 4 weeks to see if there was a voltage drop(100 cells), also incl balacing.
my two cents, i wish you good luck in your endevours....never ever sell your cells!
NEVER!
With best regards Igor
 

1xAA

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Sep 27, 2020
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Lost 12 cells over the two weeks. Mostly 4.16v Lowest I kept was 4.12v.
 
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