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"Generic" Cells - Are they any good?
#41
(06-23-2019, 11:19 AM)ozz93666 Wrote: I tend to agree , but this is a comparative test .. As long as same procedure was used throughout these are accurate results ...

As far as Cell A is compared to Cell B and C - yes, it's comparative and it's OK, but for checking datasheet's numbers you need absolute results. If the datasheet tells 2.5V cut-off, then you must discharge down to 2.5V. If it tells "10min pause after charge and 30min pause after discharge" - you must follow the instructions to compare your results with manufacturer's ones.

(06-23-2019, 11:19 AM)ozz93666 Wrote: Contact resistance due to cell not being held firmly won't effect capacity readings significantly

I'm talking about the material the contacts are made from, not the power of holding the cell. Compare the voltage drop from the cell to Opus' PCB with the same if the contacts were replaced with pure copper ones.
Yinlong LTO Lithium Titanate safety tests: https://youtu.be/eAUYbSDEy6I
Toshiba SCiB LTO Lithium Titanate safety tests: https://youtu.be/XsrRDZxEFQE

XTAR DRAGON 4-slot charger/discharger review: https://youtu.be/S6yVMsIuauE
Miboxer C4-12 4 slot x 3.0A charger review: https://youtu.be/X-ww1YALjvU
Miboxer C2-4000 smart charger/discharger review: https://youtu.be/jrbJceNXv1g

3600mAh Panasonic NCR18650G test: https://youtu.be/b_JqlQyyTM8
Samsung 33J for TESLA: https://youtu.be/7FMxgMmPeh4
Samsung 40T - a high drain 35A 21700 cellhttps://youtu.be/lxgKWiQ9580
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#42
Thunderheart, you are correct about the Opus, and we have gone over its shortcomings on the first page of this thread.

We respect your testing as reliable on this board - enough to give you a sticky for your testing thread. You have gone through great pains to make sure that you are testing cells most accurately to their data sheet.

This test, however, is a bit different. Its sole purpose is to track the degradation of 4 cells over a number of cycles. And 3 out of 4 of the cells in this test have no data sheet, and that was part of the inspiration for this test. The full testing method has been described in the Original Post of this thread. I've taken care to eliminate any sort of inaccuracies of the tester, even alternating the slots every 25 cycles.

So, for this test, consistency is more important than absolute capacity numbers.

With regard to the smooth versus jagged line, I believe manufacturers use some smoothing on their degradation curves, as well as testing multiple cells and averaging their plots. If I plotted the average of every 5 cycles (81 data points) instead of the results of 405 cycles (405 data points), it would be a lot smoother. Most of the variances come from the cell resting overnight, or possibly the IR of the cell, but it's never that extreme (besides Cycle 35 where I used an external fan to cool the cells and had like a 3% variance).

ozz93666, I've been testing these cells almost 5 months straight, and I'm only at 405 cycles. If I were to test these cells only 50 times a year, It would take me over 8 years to get to this point. I do think time does play some role, but mostly it's the time cells sit at full charge that makes the most difference. All of the cells in this test are about 8 years old, and I do have some 20 year old Sony's that I've tested that still hold 90%+ of their capacity with an unknown history. Since the cells internals are sealed, I can't see why the electrolyte would break down over time, but everything does have a shelf life.
ozz93666, stevelectric, thunderheart like this post
Formerly known as Dallski
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#43
(06-23-2019, 08:12 PM)Generic Wrote: This test, however, is a bit different. Its sole purpose is to track the degradation of 4 cells over a number of cycles

In that case everything is OK as all 4 cells are in equal conditions.

Once again, you've done a GREAT job and i can just imagine the time and other resources spent on it!
Yinlong LTO Lithium Titanate safety tests: https://youtu.be/eAUYbSDEy6I
Toshiba SCiB LTO Lithium Titanate safety tests: https://youtu.be/XsrRDZxEFQE

XTAR DRAGON 4-slot charger/discharger review: https://youtu.be/S6yVMsIuauE
Miboxer C4-12 4 slot x 3.0A charger review: https://youtu.be/X-ww1YALjvU
Miboxer C2-4000 smart charger/discharger review: https://youtu.be/jrbJceNXv1g

3600mAh Panasonic NCR18650G test: https://youtu.be/b_JqlQyyTM8
Samsung 33J for TESLA: https://youtu.be/7FMxgMmPeh4
Samsung 40T - a high drain 35A 21700 cellhttps://youtu.be/lxgKWiQ9580
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#44
(06-23-2019, 01:16 PM)thunderheart Wrote:
(06-23-2019, 11:19 AM)ozz93666 Wrote: I tend to agree , but this is a comparative test .. As long as same procedure was used throughout these are accurate results ...

As far as Cell A is compared to Cell B and C - yes, it's comparative and it's OK, but for checking datasheet's numbers you need absolute results. If the datasheet tells 2.5V cut-off, then you must discharge down to 2.5V. If it tells "10min pause after charge and 30min pause after discharge" - you must follow the instructions to compare your results with manufacturer's ones.

(06-23-2019, 11:19 AM)ozz93666 Wrote: Contact resistance due to cell not being held firmly won't effect capacity readings significantly

I'm talking about the material the contacts are made from, not the power of holding the cell. Compare the voltage drop from the cell to Opus' PCB with the same if the contacts were replaced with pure copper ones.
 This test is all about measuring reduction in capacity over cell life , measuring the % drop , so using opus will not effect things too much , particularly at low discharge currents  ....

My instinct tells me the material the contacts are made from will not have a significant effect ...
Lets do the calculation just to check .... your terminals are 10mm x 0.5mm thick so that's 5mm2 of copper  

Each 1 cm has a resistance of 0.134 mOhm ... 

but that is not where the resistance is , you  connect onto these buss bars with crocodile clips ... Danger High resistance (a few mOhm ) ... much better to solder (Zero mOhm ) , and then thick  wires connecting to your apparatus , probably around 5mm2 ,same as bus bar  but total length looks about 60cm so resistance of wire is 8m Ohm ... 

You have about 10mOhm between battery and measuring device ... How will this effect readings ... it will effect high current discharge much more ...@ 5 A ...   I x  I x r  =  0.25W    So @ 5A  the connectors are disappearing 0.25W over a 1/2 Hr discharge resulting in a 0.125WHr error in capacity measurement ......  at 1A discharge the error will be 5 times lower 0.025WHrs . these losses are totally predictable , perhaps the measuring device has already adjusted readings??

Compared to opus , lets suppose their contact terminals are 10 time more resistive than yours , still that will not have much effect on things because they are very short , connecting wires will be much thinner , but also much shorter ... the killer lies in the weak springs and type of contacts  used to force connection  onto the cell this can cause many 10's mOhm resistance.
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#45
Thanks for your input Thunderheart! Honestly, if I added up all the actual time I spent on this, it wouldn't be more than a few hours. It's just writing down the results every cycle, taking a picture of those results, and resetting the Opus. If all that took a minute, that's 6.75 hours for 405 cycles. Not bad. And its just 1 Opus, so not much material cost either.

oz93666, I know that the Opus overstates the results. The three generic cells are all 2000mAh cells and the Opus was showing almost 2200mAh when the test started. The point is, like you mentioned, that the contact resistance in the cell holders does not change. Whatever that resistance is, does not matter as long as it stays the same throughout the whole test. The only variable I'm testing for here is degradation.
Formerly known as Dallski
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#46
2.5V cut-off does not mean you should normally discharge the cell down to that value. That's the red-alert-emergency-shutdown value. I would never recommend discharging any cell under 3V if you want some life out of them. I always try to keep them above 3.3V as per the original Li-Ion specs.

Yes, some manufactures consider that discharge value when stating capacity, which is not really fair, but this forces you to indeed consider it when testing.
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#47
I did my own amateur comparative testing with my Opus BT-C3100 v2.2 on my haul of dead laptop batteries. Of the 150 cells I pre-tested so far, the LG batteries are consistently worse than others in terms of internal resistance at max charge. (To me it's a quick rough indication of capacity because it's inversely correlated to IR)

Therefore, I'd be much interested if your control test used a Panasonic or Samsung instead Big Grin. Either way, thank you for the rigorous tests! I also get some ASOs in my haul and those are also quite promising in my prelim max-charge IR tests.
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#48
Awesome test Generic! I'm happy to see cells degrade indeed a bit slower then I thought they would.

Do we have some idea as to how much not fully charging/discharging is prolonging there live? And what limits do most people use?
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