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"Generic" Cells - Are they any good?
#1
I'm going to be dedicating one of my Opus' to longevity testing some cells. It has 4 slots, so I am going to be testing 4 cells. Originally, I was going to only test generic cells, but I came up with the idea of testing a genuine cell as the 4th cell to act as a kind of "control." The "Generic" cells will be the ones that I have the most of: (1) CJ blue 2000mAh cells; (2) ASO purple 2000mAh cells; and (3) THLD blue 2000mAh cells. These are all new-old-stock cells from around 2011. The fourth cell will be a genuine one that was originally rated for 2200mAh and tested with almost new capacity. I was thinking of using either an LGAAS31865 from 2010; a Samsung ICR18650-22F from 2012; or a Sanyo UR18650A from 2015. I'd rather avoid using the Green Sony's or red heater Sanyos from before Sanyo was bought out by Panasonic. I'm leaning towards going with the Samsung, but let me know if you think some other cell would be a better representative of the "genuine" cells most people use for their power walls. 

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. 

I know that many people open up generic packs and are surprised that cells are testing at their rated capacity. I also know people question their longevity like in the article Mike/LithiumSolar cited posted by BatteryHookup. Also, I think hbpowerwall was longevity testing some Chinese cells, but I don't know what happened to that. So I'm hoping to, as scientifically as possible, give an answer to the age-old question: "Generic" Cells, are they ok to put in my powerwall?

Let me know if there is anything else I should consider before starting this test. Once I start cycling, I'm not going to make any changes.

EDIT: (1/30/19) I ended up going with the LG battery for the genuine cell. The Samsungs retested below 2000mAh and I want to keep the capacities as close as possible. Also, adding a picture of the cells being tested and their first capacity test. 



EDIT: (2/11/19) Started cycle 34 this morning and after breakfast came back to find the Opus fan not working. Before unplugging the Opus, I tested the cell temps. They were between 65 and 72*C! One spot on the back of the Opus was 85*C! I guess the overheat protection on this unit is not working because the cells were all still discharging at 1A! So I waited for everything to cool and when I plugged in the Opus, the fan kicked on again like normal. Anyway, I went ahead and discharged the cells and entered an asterisk in the log for cycle 34. Hope the high heat doesn't affect the test results.

EDIT: (2/12/19) For cycle 35, I ran a 120mm computer case fan blowing air over the cells from right to left. I was worried that the Opus fan might not come on, so this was mostly for backup. Well for this cycle, I thought either my Opus was toast, or the cells were permanently damaged, because Cycle 35's results, as compared to Cycle 33's results went like this: LG - 3.8% lower; CJ - 3.4% lower; ASO - 3.0% lower; and THLD 3.8% lower. Then for Cycle 36, I took the case fan away, and ran the test like normal. Results were back to normal ranges, and for Cycle 37, were almost identical to Cycle 33 (within 1mAh!). So looks like no permanent damage to either the cells or Opus. I'm carrying on with the test just like before. I'm just really shocked how much cell temperature can make a difference to the test results!

EDIT: (2/17/2019) Hit a milestone today, 50 cycles complete! Took a little longer than I'd like, but I'm making progress. Cells are changing slots again in the morning for Cycle 51. Nothing else new to report.

EDIT: (2/27/2019) Currently running my 79th cycle! That's like over a kilowatt of electricity put into and taken out of each cell :-D My new ETA for results of 100 cycles is Saturday, March 9th, 2019. Not really an update, but I did look at the LG datasheet, and turns out I'm testing it like they recommend, go figure! 1 Amp charge and 1 Amp discharge, but they do say to test at 500mA to get true capacity? The data sheet says that the LG Battery should have greater than or equal to 80% of its capacity after 300 cycles, not 500 like other name brand cells are good for. This was not a new cell, it had about 90% of its capacity left (2200mAh * 0.9 Opus correction factor = 1980mAh?). Based on that, it should lose about 6-7% of its capacity during this test by Cycle 100, and be at about 2070mAh. We will see!

EDIT: (3/9/2019) As promised, here are the results!! I have run 105 cycles, 5 more than the 100 set in my goal. The reason for that was to get an average of the first 5 cycles and the last 5 cycles, and compare those. Because I was switching slots every 25 cycles, the heat on the right 2 cells was affecting the results a little. Cells have more capacity at higher temperatures, and a few degrees Celsius seemed to make a little difference. That's why I used the averages of Cycles 101-105 in comparison to Cycles 1-5, as those cycles were all in the same slots. Ok, here are the results:

 

 

And the degredation:
 

So with that, obviously, I have to run this test to at least 205 cycles or until I get bored of it. And it seems like I have more questions than answers at this point. To me, I'm not surprised the LG lost the most capacity. It started this test at about 90% capacity when you factor in the tester correction factor. Also, according to the data sheet, it is one of those 300 cycle rated cells, not a 500 cycle one. I was expecting 6% degradation to be honest, so it did better than I thought it would. Now onto the generics. Why did they do so good? Is my Opus wearing out or something? It was surprisingly consistent throughout this whole test. The jagged lines on the charts are only because my resolution is between 2100 and 2220. If it was 0-2200, it would appear very smooth. I have some theories about why generics and regular laptop cells die fairly quickly. Mainly (1) keeping them at full charge most of the time, which I have seen in other tests that it absolutely kills the cells quickly; (2) temperature in a laptop is usually pretty warm as there is usually no active cooling for batteries and computers are known to generate heat; and (3) especially in generics, the BMS's are terrible. Almost every generic pack I have opened uses thin gauge aluminum wiring, nickel-plated steel for nickel strips, some lack a thermister for temperature monitoring, and the spot welds are usually really easy to remove and countless packs have a disconnected cell in them. Bad quality control might be why people avoid generic packs. But the cells seem to be well manufactured. Time will tell. I will have to keep this test going to see if capacities will fall off a cliff. Or maybe, just maybe, generic cells are actually good. P.S. I did take pictures of every cycle's results and I have the results of every test written down, if anyone is interested, I can upload that as well.
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#2
Its 1000mA not mAh Smile

What you need to take into account is that the Opus is not consistent. Not between cells nor between the slots and you can get different results each time. For instance the contact surface do create some issues. So when testing for getting a result you need to remove the variation Smile

So for doing the test I highly recommend to first test all cells atleast 3-5 test on a high end tester to know their baseline and then do same on each slot to know the slots baseline.

If you skip this the variation or what you need to remove from the end-result will be bigger Wink

Hope you get the information above.
Good luck!
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#3
I'm not sure the OPUS is that faulty I have done repeated tests with it just to satisfy my curiosity.
The biggest fault the OPUS has is its IR measurement that is way off but as far as capacity measurement consistency per slot and per battery I don't find that much of a problem here. The BT3100 V2.2 correlated with my tester results of before and the min max difference is almost negligible.
Here is my sheet of results. Again the proof is in the documentation not in the conversation.

Now maybe I got the testers that were built in the middle of the week not on Monday (hangover day) or on Friday (can't wait to get out for the weekend)
but these are the results I am getting.

Don't let the numbers get in the way of the facts. Tongue

Wolf
If 18 X 650 = 2200+mAh then we have power! 
May all your Cells have an IR of 70mΩ or less Smile
Last count as of 3/22/2019
Total Number of Cells           3679
Cells  >80% of Capacity        2389
Cells <80% of Capacity         1265
Cells ≥2200mAh & ≥ 80%     1653
Google Drive for info https://drive.google.com/drive/folders/1...sp=sharing
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#4
The Opus is manufactured on soooo many places and in so many variants and I have seen sooo many different results... Once again it depends on what you compare to. I would say it can diff up to 10% or so easily. In your document you have atleast 5% or something I think? (Without checking)

Im not going to show something up here but you can never trust a source into its decimal part like 1mAh that the opus show and then think its accurate down to that. Thats what im trying to say... You Always need to build in a variance like in your test you have 5% then you need to scale away everything that doesnt fit into that.

The more itterations you run your numbers the larger the error is every time so if you start with 5% error and you then redo the test with another factor you have another 5% added... And so forth Smile

Does it make any difference in the end? Depends... For instance testing 2.2Ah cell and you get a result out that is 2150mAh.. Does it state it degraded? No it doesnt if you have a 5% variance. Its just within the limits and perfectly fine. Thats the deviation line you need to set Wink

The only reason i sort based on 100mAh is because I have not established a baseline and deviation. The 100mAh deviation policy have prove to work great as long as you random the cells Smile The end result have been below like 3-4% deviation between each built pack and thats better than i have seen on the Opus itself. Luck perhaps?

Sorry for the ramble Tongue Im just making sure that noone get burned hoping the opus does 0.5% variance results Big Grin
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#5
Daromer
OH believe you me I know exactly what you are talking about.  Big Grin
As you know I have done a bunch of testing with these testers and have come to the conclusion with the results we get there is always going to be a certain deviation with the testers themselves. No matter which one is used . I am now testing the iCharger x6 and will have the results in the near future.
I no longer test with the Zanflair as you know because it has really inflated results. I am going through all my previously tested cells and the Zanflair is definitely way off. Foxnovo is slowly becoming my favorite. Simple does the job and accurate. If anything it's a little (very little) on the low side.

Dallski
I am looking forward to your test and hope you will record and share the results with all of us.
Just for a baseline on your OPUS that you are going to use run 1 cell through all 4 slots and see how much difference you get. I am curious as my deviation between slots was less than 5%.

Onward forward never straight.

Wolf
If 18 X 650 = 2200+mAh then we have power! 
May all your Cells have an IR of 70mΩ or less Smile
Last count as of 3/22/2019
Total Number of Cells           3679
Cells  >80% of Capacity        2389
Cells <80% of Capacity         1265
Cells ≥2200mAh & ≥ 80%     1653
Google Drive for info https://drive.google.com/drive/folders/1...sp=sharing
Not your average Wolf       
            Cool



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#6
(01-28-2019, 03:03 PM)Wolf Wrote: As you know I have done a bunch of testing with these testers and have come to the conclusion....

Not good enough! Do all the tests over again to make absolutely sure without a hint of doubt that the previous results could possibly be somewhat as accurate as perhaps the second somewhat inconclusive or sub-conclusive random results. We need repeatable data here!


Tongue
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#7
(01-28-2019, 07:01 PM)Korishan Wrote:
(01-28-2019, 03:03 PM)Wolf Wrote: As you know I have done a bunch of testing with these testers and have come to the conclusion....

Not good enough! Do all the tests over again to make absolutely sure without a hint of doubt that the previous results could possibly be somewhat as accurate as perhaps the second somewhat inconclusive or sub-conclusive random results. We need repeatable data here!  


Tongue

LOL I will never get my powerwall built if all I do is test the testers. Oh wait a minute I am testing the testers or is it the batteries I'm so confused.

Wolf
Korishan and LEDSchlucker like this post
If 18 X 650 = 2200+mAh then we have power! 
May all your Cells have an IR of 70mΩ or less Smile
Last count as of 3/22/2019
Total Number of Cells           3679
Cells  >80% of Capacity        2389
Cells <80% of Capacity         1265
Cells ≥2200mAh & ≥ 80%     1653
Google Drive for info https://drive.google.com/drive/folders/1...sp=sharing
Not your average Wolf       
            Cool



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#8
Smile We should not OT this thread any more. As long as we all agree that there are a deviation on the cheap testers for instance the pressure or corrosion will cause different values Im happy. That will make sure that we have the proper info we want and people doesn't get dissapointed when tests are done.
Wolf, LEDSchlucker, Korishan like this post
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Current: 10kW Mpp Hybrid | 4kW PIP4048 | 2x PCM60x | 83kWh LiFePo4 | 10kWh 14s 18650 |  66*260W Poly
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#9
Glad I inspired a good discussion on testing equipment! I've read through a lot of threads on accuracy and Opus hacks and have come to a simple conclusion that I think we can all agree on: these testers are "good enough" for us. If we were all doing 1P packs without balancing, accuracy would be paramount. But with so many cells in parallel, it is only important to get close. Especially since all the cells we use are at different stages in their lifetimes, pack capacity can literally change in a few cycles.

With that being said, I was going to test each cell in the same slot, which would negate any slot-to-slot variance.

I'm not really looking at absolute numbers, but a capacity curve. Kind of like a 100 day moving average in investing. You dont look at the day to day ups and downs, just a larger overall trend.

Also, I'm testing in a climate controlled room, so temperature should not play any factor, or if it does, it will affect all the cells equally.

Again the whole point of this test is to see if generic cells are really junk or if they can be useful in powerwall applications. I'm testing 3 different brands of generics, but manufacturing could vary day-to-day even within the same brand. I would have to test a much larger sample with more accurate testing equipment to get a definitive answer. But I'm just going for "good enough." Thank you for all your input!
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#10
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.
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