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Self Discharge on Powerwall Cells
#11
Thanks Rev0.
Batteries harvested: 802 / Usable batteries: 747 (93 %)

Cells tested: 747 (Average: 1878 mAh) / Cells in production: 0 (00 %)

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#12
Note that down to 4.1 or even 4.05V from 4.2 V will go alot faster than from 4.1 to 4.0. I charge all mine up and let sit for 1-3 weeks. I use all that are above 4.08 in powerwall.
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#13
Ok, can't be clearer. Thanks to both of you.
Batteries harvested: 802 / Usable batteries: 747 (93 %)

Cells tested: 747 (Average: 1878 mAh) / Cells in production: 0 (00 %)

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#14
I charge my cells, let them rest for 30mins then measure the voltage and write it on the cell.
Sometimes the cells only charge to 4.18 or 4.16 (tolerances or inaccuracies in the chargers). A month later I will re-measure them and write the new voltage on the cell too. If I had presumed they would all have been at 4.2 or 4.22 as thats what my chargers should do, then the ones that dropped to 4.12 or even 4.1 would have appeared to not be good.
So I check the level based on that.

Anything below 4.10 goes into a different pile for random use or whatever. 4-4.1 are spares and anything under 4 is seen as scrap.
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#15
(07-25-2018, 12:06 AM)rev0 Wrote: I would say 0.15-0.2V per month which is 5-6.6mV/day is my limit for good enough to use.

Would you say that limit applies for the larger parallel packs themselves or just the individual cells? One of my 100P packs has dropped 0.015V in about 10 days just sitting on the desk and it's kinda worrying me. All the others only dropped about 0.001V to 0.005V.
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#16
(05-31-2019, 08:17 PM)OhmGrown Wrote:
(07-25-2018, 12:06 AM)rev0 Wrote: I would say 0.15-0.2V per month which is 5-6.6mV/day is my limit for good enough to use.

Would you say that limit applies for the larger parallel packs themselves or just the individual cells? One of my 100P packs has dropped 0.015V in about 10 days just sitting on the desk and it's kinda worrying me. All the others only dropped about 0.001V to 0.005V.

Without knowing what test equipment you own, I would hazard a guess that the figures you mention are outwith the scope of your equipments accuracy, but almost certainly nothing to be concerned about.
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#17
(05-31-2019, 09:30 PM)Sean Wrote:
(05-31-2019, 08:17 PM)OhmGrown Wrote:
(07-25-2018, 12:06 AM)rev0 Wrote: I would say 0.15-0.2V per month which is 5-6.6mV/day is my limit for good enough to use.

Would you say that limit applies for the larger parallel packs themselves or just the individual cells? One of my 100P packs has dropped 0.015V in about 10 days just sitting on the desk and it's kinda worrying me. All the others only dropped about 0.001V to 0.005V.

Without knowing what test equipment you own, I would hazard a guess that the figures you mention are outwith the scope of your equipments accuracy, but almost certainly nothing to be concerned about.

So I was just literally connecting a fluke multimeter (can't remember the model but it's a decent starter one) to the busbars. Either way thank you, that makes me feel much better. Think I just got concerned cause they're such "big" packs and only one seemed to drop a hundredth of a volt.
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