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Results of Capacity Testing 18650s for 1,600+ Cycles
#61
Congratulations to Generic for the testing and sharing the results.
I know that this takes a lot of commitment to do manually.
I am only at 140 tests between 2 cells, and while each test is fairly quick, it still adds up.

(09-10-2019, 10:18 PM)rev0 Wrote: Wow, you did all these cycles manually? If you're interested in continuing this sort of testing I could send you an 18650 cycle tester I've been working on (would be an older version of which I have several), details are here: http://rev0.net/index.php?title=CCR It sure seems easier than manually restarting a cycle on these cells and taking down the data.

That is a lovely offer.
It is nice to see someone else supporting generics testing and contributions to the community. I offered to provide an opus tester earlier on, so his device is not tied up.

I have had a quick look at your project and this looks very interesting to me as I also would like to do some repeated testing of cells.

I have started already with a single zb206 and tp4056 and have done 140 tests across 2 cells, so only 70 cycles for each cell.
I do have a bunch of questions that would be answered by being able to automate this testing. From the manual testing I have already done, I have determined that it would really not be feasible for me to do without automation.

I have many cells that are exactly the same type, and the packs have date codes.

I would like to observe how cells behave over many cycles where
-cells are different ages based on manufacture date
-cells that have had very little use
-cells that have had lots of use
-cells have been at zero volts and recovered
-1A charge and discharge
-0.5A charge and discharge
-reduced voltage range

I believe low use vs lots of use could be reasonably estimated based on the state of the packs and devices my cells come from.

I think the 1A vs 0.5A comparison would be a nice contribution to the second life storage community.
In theory the reduced currents and voltage range extend cell life, but being able to show the size of the effect in real life would be great.
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#62
Oz -Well, the newest Samsungs that Thunderheart has been reviewing quote cycle life to 70%, so I think the actual percentage is a bit arbitrary. After 70 cycles on each cell, are you seeing any degradation?

rev0 - Wow, you've done some very interesting research! Another member mentioned about the ReVolt cells only getting 340 cycles before nosediving, and I couldn't find the results until I clicked your link! I may be interested in your offer, I'll send you a PM.
Check out my long-term capacity test of 18650s: https://secondlifestorage.com/showthread.php?tid=6868
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#63
(09-11-2019, 05:32 AM)Generic Wrote: After 70 cycles on each cell, are you seeing any degradation?

I don't think I have seen any degradation yet, certainly not that I can spot without analysis of the results.
I just got the lowest result yet, but also the highest result yet a couple of days ago.
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#64
(01-31-2019, 01:02 PM)Overmind Wrote: I agree with Dallski here, these home testers are good enough for general use but not good enough for professional use.

If I cannot set the exact discharge max current and the minimum voltage specified by the manufacturer, the test is not professionally relevant. Also, none of the testers I have encountered support high discharge currents. That makes most of the tests of high power cells irrelevant. They will test fine at 1A discharge and instant die at 10 or 20A.
I'm going to use the Charge Test function at 1000mAh and record the capacity for each of the cells after each cycle. These will all be full cycle 4.2V to 2.8V discharges, so it's a lot more abuse than a typical powerwall will give these cells, but it will also help speed up the results. I'm going to aim for at least 100 full cycles.
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#65
Update time! 705 cycles. Chart is self-explanatory. We are now past the 70 or 80% that every datasheet I have ever seen usually stops at. I am also re-uploading the degradation numbers at each 100 cycle interval. I was doing the math with the Wolf method, but was getting over 100% degradation, so I'm reverting to how we all do state of health: tested capacity over initial capacity. I'm starting to wonder if the THLD cell will make it to 805 cycles? I'm also considering changing the Title of this thread to "Long Term Capacity Testing Cells." I think a lot of people who would benefit from this information are skipping over this thread because they have an uninformed negative bias toward generic cells (I used to be one of those people). 





jdeadman, Oz18650, BatteryMooch And 2 others like this post
Check out my long-term capacity test of 18650s: https://secondlifestorage.com/showthread.php?tid=6868
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#66
 

First cell to be completely degraded: CJ! It has been testing under 100 mAh since Cycle 776, but it is still putting out about 64 mAh for 30 straight cycles. I think I'm done testing this cell at 1000mA, so now that I have an official number for Cycles 801-805 for my data, I'm going to run the cell at 500mA discharge for Cycle 806 to see what capacity it has at a lower discharge rate. And maybe 300mA for Cycle 807 and 200mA for Cycle 808 if it doesn't take forever. Then after Cycle 808, I'm going to fully charge it at a 200mA charge rate, and test its voltage at weekly intervals to see if it self discharges. The THLD cell looks like it's going to be fully degraded pretty soon, too, so I think I will do the same thing to it after 5 or 10 sub-100mAh cycles. 

 

 


You may notice that the ASO and LG cells seem to be dipping quicker than before, but I don't think they are degrading any faster. I think they are showing lower capacities because the CJ and THLD cells are not generating heat next to them like they did before. I wish I had temperature correction like rev0's equipment, but I don't, and this is one of the downsides of the Opus. 

Also, like any true research, data creates more questions than it answers. For instance, the THLD cell started dropping capacity much earlier than the CJ cell, but the rate of decline was flatter. The CJ dropped like a rock, from about 1000mAh to <100mAh in just 75 cycles. Could it be the chemistry? Electrolyte? Cobalt content? Age? 



I also wanted to post this chart. It shows how much energy each cell has stored in its lifetime. The CJ cell was able to store 5 kilowatts of energy in its lifetime!

Lastly, I just want to mention that I have received the cell cycler from rev0 and am excited to start another long-term test after I do some other testing like high-drain generics and possibly some end-of-life (50% of original capacity) genuine cells to see their degradation much more quickly than with new cells. We'll see. Stay tuned?
100kwh-hunter, bogptrsn, stevelectric like this post
Check out my long-term capacity test of 18650s: https://secondlifestorage.com/showthread.php?tid=6868
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#67
Congratulations! You finally wore a cell out.

Glad you are going to be able to have another round. Especially with some level of automation.
Crimp Daddy and Generic like this post
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#68
Great work, that's all i can say, cheers mate and thanks
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#69
Great work!
I wonder how much the current being drawn compared to the capacity of the cell contributes to the accelerated drop in capacity?
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#70
Great question, Oz. I do believe if I did this test at 500mA instead of 1000mA, I would have gotten more cycles. Most likely due to a slower chemical reaction within the cell and reduced heat from the slower reaction (and less heat from the Opus). But I can't say for sure because I don't have any proof.

What I can say, though is that I did test the CJ cell at 500mA, 300mA, and 200mA, like I said I would:
66 mAh @1,000mA
330 mAh @500mA
505 mAh @ 300mA
679 mAh @ 200mA

So, I got 10x the capacity by reducing the discharge rate 5x on a "dead" cell. Interesting. So if I had a 50kW powerwall, and ran a coffee maker, toaster oven, microwave, and a window AC all at the same time for a 5kW load, the cell would be doing 200mA and get 679mAh useable. I'd have to be drawing 25kW from the powerwall to only get 66mAh from the "dead" cell.
100kwh-hunter and Ibiza like this post
Check out my long-term capacity test of 18650s: https://secondlifestorage.com/showthread.php?tid=6868
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