I have a 5S2P battery project and for this project I did tests to select the ones in good condition from the Samsung 30q batteries I have. Accordingly, I first measured the capacity of the batteries I selected. I measured the internal resistance of those between 2800-3000mah. I finally fully charged 10 batteries with an internal resistance of around 15mOhm (between 4.18-4.20V) and left them for 1 week. Seven of the batteries showed a value of 4.18, while three of them showed a value of around 4.02V when I measured them after 1 week. In this case, I wonder why these three batteries with low internal resistance and the same internal resistance self-discharged so much after 1 week of waiting? If anyone has any information and can share it, I would appreciate it.
Small IR 18650 doesn't hold charge
- Thread starter s3rkan
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harrisonpatm
10 kW
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Short answer: sometimes it just happens.
Long answer: You did a good job 1) checking for internal resistance, 2) measuring actual capacity, and 3) doing a self-discharge test. Because as you now see, just because a cell has good capacity left and good internal resistance, doesn't mean it has other hidden issues.
Some questions that can give you more things to check:
What tester did you use for individual cell capacity? Sometimes lower-quality testers may give you an inaccurate result, leading you to believe a cell has more capacity than it actually does.
What tester did you use to measure IR? There are some good ones, but there are a lot more bad/inaccurate ones.
Where did you get the cells, are they used? If they are used/reclaimed from something else, that would be more likely that you would find 3 self-dischargers.
How did you measure voltage, and was it consistent? I ask because if you used one of your testers to charge a cell up to 4.18-4.20v, and you assumed the tester was accurate when it told you it was 4.18-4.20v, but it was a poor quality tester that actually only charged up to 4.12-4.15v, then maybe it didn't discharge as much as you think it did.
I am currently testing 832 cells from the same make and manufacturer, that are supposed to be new. All are testing within 95% of their capacity, and all are testing below their IR specifications. But I am still finding 3-4 self-discharging cells so far. It's not unheard of.
Last thing. You said you're saving cells that are above 2800mah. That's 93% of their spec capacity. Which certainly isn't bad. But it is a definitive indicator of some level of aging. So it's not terribly surprising that you'd also find other signs of aging.
j bjork
1 MW
High self discharge is a known problem with 30q
docw009
1 MW
Just get rid of the cells that self discharged.
I've read about 30Q issues, but have Luna battery packs from 2015 and 2016 that still work well enough. Some capacity loss, but the packs hold voltage and are not ready to be recycled. I also built two batteries with new 30Q's in the past two years and they seem OK.
There are probably some bad 30Q lots that got into the retail channels. Also, I think people run them too high because of their rated 15A, and that's not good for longevity,
I've read about 30Q issues, but have Luna battery packs from 2015 and 2016 that still work well enough. Some capacity loss, but the packs hold voltage and are not ready to be recycled. I also built two batteries with new 30Q's in the past two years and they seem OK.
There are probably some bad 30Q lots that got into the retail channels. Also, I think people run them too high because of their rated 15A, and that's not good for longevity,
harrisonpatm
10 kW
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Or just set them aside for a future low-drain project. Flashlight, powerbank, 12v UPS, ect
999zip999
100 TW
Where did you get the cells ? History.
Hillhater
100 TW
Your tests are a good indicator for selecting matched cells but,..
* how much moore voltage drop is there after 2 weeks ?
* keeping cells at 4.2 v is not good for long life
* there is very little capacity between 4.2 and 4.0v
* most users tend to store cells at lower voltage (3.8-3.9v?), and only top charge just before use
* how much moore voltage drop is there after 2 weeks ?
* keeping cells at 4.2 v is not good for long life
* there is very little capacity between 4.2 and 4.0v
* most users tend to store cells at lower voltage (3.8-3.9v?), and only top charge just before use
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Though, if they self-discharge by a tenth of a volt in a week (see quote of OP below), they may not be something you can count on to still be charged when you need to use it, depending on the actual rate of self-discharge and the curve each follows.
Perhaps not an issue in a UPS that's always powered on and connected to the wall to keep them charged, but anything that has to just be charged when you need to use it, might be.
(assuming there are no other issues beyond SD).
Sorry guys for late response, I had a surgical operation and just recovered.
I am using YR1035 to measure the IR and using dso3d12 3 in 1 for measuring the voltage of the cells (really a consistent voltmeter). I have bought the batteries last summer from a local vendor here. Furthermore, I always keep them in storage voltage and never put them aside with fully charged.
During the test phase, when I tested the batteries as I mentioned above and did not use the batteries that failed the test, I observed that the battery packs I made maintained their inter-cell balance even in high charge-discharge processes.
My question above was mainly because I was wondering why the batteries were discharging despite their low internal resistance. I could not find any information on the internet on this subject. The reason for the self-discharge of the batteries that I knew before was their internal resistance. But in this case, I came to the conclusion that self-discharge may also be due to other reasons, and in this case, I realized that a protocol such as waiting for a while, while testing the batteries should be added to the test phase.
I am using YR1035 to measure the IR and using dso3d12 3 in 1 for measuring the voltage of the cells (really a consistent voltmeter). I have bought the batteries last summer from a local vendor here. Furthermore, I always keep them in storage voltage and never put them aside with fully charged.
During the test phase, when I tested the batteries as I mentioned above and did not use the batteries that failed the test, I observed that the battery packs I made maintained their inter-cell balance even in high charge-discharge processes.
My question above was mainly because I was wondering why the batteries were discharging despite their low internal resistance. I could not find any information on the internet on this subject. The reason for the self-discharge of the batteries that I knew before was their internal resistance. But in this case, I came to the conclusion that self-discharge may also be due to other reasons, and in this case, I realized that a protocol such as waiting for a while, while testing the batteries should be added to the test phase.
999zip999
100 TW
Did buy them brand new or is there weld marks from being removed from ?
Some cells just like to sit at their voltage. There is some room at the top. It differs with different chemistry.
Some cells just like to sit at their voltage. There is some room at the top. It differs with different chemistry.
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eMark
100 kW
More so with 30q than other high energy dense 18650 cells.
30Q cells for whatever reason were more prone to high self-discharge being leader among the high energy dense cells. This was true with 30Q 136, 138 and 141. The newer 30Q 6T and 30Q 6 150 T don't seem to suffer from high self-discharge
