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Testing large amounts of cells quickly

Posted: Jul 19 2019 7:35pm
by BYqSXt8Z
Hi, I got some second hand batteries (a123 26650) that I need to sort by capacity... 28850 of them. Does anyone know of a tool that can extrapolate battery capacity from things like ir, voltage sag, and such in a few seconds or even minutes?

Thank you

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Re: Testing large amounts of cells quickly

Posted: Jul 19 2019 7:54pm
by flat tire
No. You have to individually test each battery.

Re: Testing large amounts of cells quickly

Posted: Jul 19 2019 8:48pm
by Matador
I wish... But to do so in such short time, you'd need to use supercapacitor rather than lithium cells. The bottleneck is the discharge rate for measuring discharge capacity...
DCIR can be measured in seconds however... You can thus extrapolate voltage sag by ohm law and knowing how much load you wanna pull: Sag (aka delta V) = DCIR (in ohms) x load (in amps).

Matador

Re: Testing large amounts of cells quickly

Posted: Aug 31 2019 5:30am
by Bison_69
Hi guys,

Battery University came up with a quick way to analyze lithium cells using pulse frequencies...

If someone could reproduice this electronic device to adapt to many individual channels (multiplexing circuit)
then many cells could be checked in a very short time.
https://batteryuniversity.com/learn/art ... _batteries

They actually have the tool (technology) but not made for large scale testing, may be one day
someone could reverse ingineering it and build a version for the hobbyist.
https://www.cadex.com/en/technology/our ... /quicksort

Re: Testing large amounts of cells quickly

Posted: Aug 31 2019 8:07am
by BYqSXt8Z
Bison_69 wrote:Hi guys,

Battery University came up with a quick way to analyze lithium cells using pulse frequencies...

If someone could reproduice this electronic device to adapt to many individual channels (multiplexing circuit)
then many cells could be checked in a very short time.
https://batteryuniversity.com/learn/art ... _batteries

They actually have the tool (technology) but not made for large scale testing, may be one day
someone could reverse ingineering it and build a version for the hobbyist.
https://www.cadex.com/en/technology/our ... /quicksort
I don't know if I'm misunderstanding, but it seems like they are talking about testing impedence.

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Re: Testing large amounts of cells quickly

Posted: Aug 31 2019 9:43am
by fechter
By measuring cell IR and voltage you can get a pretty good idea if a cell is bad or not, but the only way I know of to check capacity is to do a full charge/discharge test.

You might try doing the fast tests on a sample of cells and see how it correlates to the actual capacity.

If the cells were not used much, their capacity should be pretty close to spec if they are not damaged. You can tell a lot about A123 cells from their resting voltage. Anything below 2v is bad for sure. Good ones tend to stabilize around 3.3v. Bad ones also tend to have accelerated self-discharge, so that is one more fairly easy test to do. Charge a bunch of them to 3.65v and let them sit for a few days, then measure voltage.

28850 is a mountain of cells. How did you get that many?

Re: Testing large amounts of cells quickly

Posted: Aug 31 2019 10:57am
by BYqSXt8Z
fechter wrote:By measuring cell IR and voltage you can get a pretty good idea if a cell is bad or not, but the only way I know of to check capacity is to do a full charge/discharge test.

You might try doing the fast tests on a sample of cells and see how it correlates to the actual capacity.

If the cells were not used much, their capacity should be pretty close to spec if they are not damaged. You can tell a lot about A123 cells from their resting voltage. Anything below 2v is bad for sure. Good ones tend to stabilize around 3.3v. Bad ones also tend to have accelerated self-discharge, so that is one more fairly easy test to do. Charge a bunch of them to 3.65v and let them sit for a few days, then measure voltage.

28850 is a mountain of cells. How did you get that many?
I settled on a methodology not that far off from that + a little bit. I'll stay quiet on that until I can test a few hypotheses as there I no point in spreading misinformation... Just some hunches I want to explore for now.


I got some 3500 cells XD


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Re: Testing large amounts of cells quickly

Posted: Sep 02 2019 10:29am
by BYqSXt8Z
So to get the correlations down I'll be doing some endurance testing on some sacrificial cells (1000 cycles). The issue I'll have is it takes around a month to run a single cell. That means I need to test with many cheap testing rigs, so I've designed one from jellybean components and modules, controlled by an arduino. Purchasing in volume will be difficult financially, but would bring the cost down considerably so I can run 100+ cells at a time. If anyone is interested in a 1s cell cycler, please let me know, I'd like to sell some to help pay for the construction of the large setup. It is possible to do more than 1s, but voltage resolution goes down to 0.025v instead of 0.005v

By the way, I've attached some pictures of my current more manual setup for larger packs to show I'm serious about getting this done, and I've also already invested in a precision impedence tester.

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ImageImage

Re: Testing large amounts of cells quickly

Posted: Sep 03 2019 7:58am
by fechter
Wow, that's a setup. Bet it generates a lot of heat at times. I like the load resistors. The "big guys" use synchronous inverters as a load to dump the energy back into the grid. Not that it saves that much money but it greatly reduces the heat generation.

I've messed with cell impedance and found it doesn't really tell you much unless the cell is completely toast. Readings were all over the map depending on SOC and temp. Cell IR is a much more reliable indicator. I guess it will depend on what frequency the impedance is measured at.

Re: Testing large amounts of cells quickly

Posted: Sep 03 2019 8:08am
by BYqSXt8Z
Thanks :) I'm not super happy with the reliability of those b6 but no surprise there. They are still very helpful for bulk processing to ready everything for the precision tests or for regular use though. V1 of the arduino prototype will be tested today when I get my high current 22650 holder in :)

Isn't cell impedence just a fancy word for cell IR? From what I read the spec provided by mfg is not just resistance but impedance. I find the best tests are at around 80% soc for the lifepo4. I'm doing 1kh tasting, from what I've found that is suppose to be the standard, but the readings fluctuate non stop is my biggest issue. I might have to build an arduino split voltage tester for proper IR measurement.

In the winter that heat will be nice with the -40 temps we get here ;) Eventually I want to use the power to charge batteries on the opposite part of the cycle, but one thing at a time!



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Re: Testing large amounts of cells quickly

Posted: Sep 03 2019 9:47am
by fechter
Impedance measured at 1kHz won't tell you the same thing as IR measured at DC, but it's easier to make the tester. DCIR measurements can be done by watching the voltage sag and recovery from a high load placed on the cell for a few seconds. There are some testers out there that do this.

Re: Testing large amounts of cells quickly

Posted: Sep 03 2019 10:02am
by BYqSXt8Z
fechter wrote:Impedance measured at 1kHz won't tell you the same thing as IR measured at DC, but it's easier to make the tester. DCIR measurements can be done by watching the voltage sag and recovery from a high load placed on the cell for a few seconds. There are some testers out there that do this.
Ummmm I went about it back wards, I though they used 1khz impedence for the spec sheets and I was trying to compare to nominal. Making a high current tester with arduino is a piece of cake... Darn.

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Re: Testing large amounts of cells quickly

Posted: Sep 06 2019 6:48am
by BYqSXt8Z
I just confirmed, the a123 data sheet specifies ac testing at 1khz... I'll have to compare usefulness!

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Re: Testing large amounts of cells quickly

Posted: Sep 06 2019 1:00pm
by BYqSXt8Z
Battery cycler prototype built! Now custom pcb coming to clean it all up.

Ps since there was a comment about the resistor board, it's super simple but here I the design anyways. I use jumpers to make any combination from 1 - 15 p resistors to get a bunch of different values. It's based on putting 5w resistors in the board, all 15 identical resistance at 2/3 ohm per v of battery you plan on testing (so I rounded to 2.2 ohm for testing 1s lifepo4 for example)

https://easyeda.com/editor#id=|189505d6 ... d7c43e32f7
Image

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Re: Testing large amounts of cells quickly

Posted: Sep 06 2019 3:35pm
by fechter
What is the little display unit you're holding? Arduino, but I don't think I've seen that display...

Re: Testing large amounts of cells quickly

Posted: Sep 06 2019 4:10pm
by BYqSXt8Z
Oled 0.91" display

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Re: Testing large amounts of cells quickly

Posted: Sep 08 2019 2:54pm
by BYqSXt8Z
If you're going to use it, the SSD1306ASCII library is amazingly small and efficient.

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