Understanding Relationship of Battery SOH: Original to Used


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Festus

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Aug 26, 2022
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19
Nope, at least not me. I want to know the initial voltage and AC IR of every cell that gets pulled from anything. After charging and testing the SOH I again check IR and voltage. Again after at least a 25 day rest, and finally at the last moment when building the pack I test IR and voltage again. If I am going to invest this amount of time in building a powerwall I want to know the SOH of every cell and leave nothing to chance. All it takes is 1 cell to ruin your whole pack and potentially your battery.

Wolf

Got it- better safe than sorry. No cutting corners. Thanks for the input.

I'm using the flow chart and I think it's your spreadsheet, but it has testing voltage after 14 days. I can go with 25days, that seems a bit more cautious. I just got an IR tester RC3563 and have started testing IR. Those M26 cells tend to be on the higher side of the range you mentioned e.g. some are creeping up to 37, although they are still in spec of less than or equal to 60mOhms.

BTW, I read through your thread on the DIYBMS. I think I'm going to give it a shot.
 

Wolf

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Sep 25, 2018
Messages
1,784
Those M26 cells tend to be on the higher side of the range you mentioned e.g. some are creeping up to 37, although they are still in spec of less than or equal to 60mOhms.
If they are the gray LGFBM261865 You should be OK with an initial IR in the mid 40s. After charging them however the IR should drop to <40mΩ.
On the other hand if they are the purple LGBBM261865, LGEBM261865, or LGGBM261865 they should initially be <40mΩ and after charging preferably reside in the low to mid 30s with a max of 38mΩ. The max spec of 60mΩ is in my view a cell just hanging on to its last gasp.
Anything above 45mΩ in that series of LG cells is not to be used in my book.

BTW, I read through your thread on the DIYBMS. I think I'm going to give it a shot.
Great, I will be posting soon how to do the initial test on the controller and get it set up, Then how to program the modules.
if you have any questions let me know.

Wolf
 

Festus

New member
Joined
Aug 26, 2022
Messages
19
If they are the gray LGFBM261865 You should be OK with an initial IR in the mid 40s. After charging them however the IR should drop to <40mΩ.
On the other hand if they are the purple LGBBM261865, LGEBM261865, or LGGBM261865 they should initially be <40mΩ and after charging preferably reside in the low to mid 30s with a max of 38mΩ. The max spec of 60mΩ is in my view a cell just hanging on to its last gasp.
Anything above 45mΩ in that series of LG cells is not to be used in my book.


Great, I will be posting soon how to do the initial test on the controller and get it set up, Then how to program the modules.
if you have any questions let me know.

Wolf
That's a huge help. Exactly what I needed to know on those cells. I just found some last night that are over 38mΩ. Hopefully I don't have to toss too many. So far the batch hasn't been too bad, as in the majority are at or below 36mΩ.

Also, really appreciate the work on the DIYBMS. I've been trying to start the ordering process but haven't had time. Not in too big of a hurry as it will take some time to test all the batteries and figure out how to design the packs.
 
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