# AW IMR Cell Testing



## Battery Guy (Nov 2, 2011)

Greetings Everyone

I purchased a number of AW IMR cells a month or so ago for the purpose of doing similar tests but had not gotten around to it. Well, last Friday I found myself standing in front of my Maccor battery tester and inspired by DFiorentino's recent post showing his test results on a variety of IMR cells. So I grabbed my box of AW IMR cells and went to work. I know that this is somewhat of a duplication of DFiorentino's efforts, but I already had the cells, so I figured I might as well run the tests.

Here are the cells that were tested:

14500 (rated 600 mAh)
16340 (rated 550 mAh)
18350 (rated 700 mAh)
18490 (rated 1100 mAh)
18650 (rated 1600 mAh)
26500 (rated 2300 mAh)

Here are some of the test details.

*Test Setup*

All tests were performed on a Maccor Seriers 4300 battery tester. The Maccor has separate leads for voltage sensing. If connected to a cell properly, this eliminates voltage errors due to contact and lead resistance. All cells had two nickel tabs spot welded to each lead. One tab was connected to the voltage sense lead and the other to the current leads. In this way even the resistance of the spot welded nickel tab should not affect the results. 

*Test Procedure*

All cells were subjected to one initial "break-in" cycle where they were charged at a C/2 rate to a C/20 cut-off, allowed to rest for 1 hour then discharged at C/2 to 2.5 V. This first break-in cycle is not reported in any of the curves below.

Following the break-in cycle, all tests were performed with the following procedure:

1.) charge at C/2 to 4.2 V with a current cut-off of C/20
2.) rest for 1 hour
3.) discharge at specified rate to 2.5 V
4.) rest for one hour
5.) repeat steps 1-4 with a different discharge current

*Limitations*

One cell is hardly what I would call a statistically significant sample. There is certainly going to be variability in cell performance, so please recognize this limitation. Unfortunately, I do not have the time to repeat this work on multiple samples. These results are what you might expect for new cells. Exactly how the cells degrade will depend on the cell design, manufacturing quality and your use/abuse pattern. 

In other words, your mileage may vary.

*Presentation of the data*

It is always difficult to figure out how to present a lot of data so that it is useful for a broad audience. In an attempt to cover my bases and provide something for everyone, I am presenting Ragone plots and discharge curves. I decided to present the discharge curves in two ways. The first series of plots represents one cell size per graph and shows discharge curves for the following conditions:

0.5 A, 1 A, 2 A and 4 A (14500, 16340 and 18350)
0.5 A, 1 A, 2 A, 4 A and 6 A (18490)
0.5 A, 1 A, 2 A, 4 A, 6 A and 8 A (18650)
0.5 A, 1 A, 2 A, 4 A, 6 A, 8 A, 10 A and 15 A (26500)

The second series of plots is an attempt to compare the performance of the cells in a normalized way. These plots show the C/2, 1C, 2C, 3C, 4C and 5C discharge performance normalized to the rated capacity of the cell. 

*Ragone Plots*

If you are unfamiliar with Ragone plots, see my Intro to Ragone Plots thread.

Ragone plots are great ways to represent a lot of information in a compact form. If you have a regulated light, then Ragone plots are going to probably provide you with all of the information you need. I discuss how to use these Ragone plots in post #24 further down in this thread.

The first plot below shows the actual power vs energy response for all of the cells. The second plot is normalized to cell volume.

_Please note that these plots are currently incomplete. I still need to test the 18650 and 16340 cells, and I need to run the 18490 and 26500 cells at higher discharge power to establish their power limits. I will update these plots as additional data is collected._












*Constant Current Discharge Results per Cell Size*

































*Constant C-Rate Discharge Results Normalized to Rated Capacity*































I find this last plot showing the 5C rate comparison very interesting. It is clear that the 16340 cell does not hold up as well as the others. You also see that performance of the 14500 and 18490 are very similar, as are the 18350 and the 26500. It might mean that these similarly performing cells are made by the same supplier, or it might mean nothing at all.

I hope that you guys find this useful. If there are any additional discharge conditions you would like to see, let me know and I will do my best to add them to these plots.

Cheers,
BG


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## Kestrel (Nov 2, 2011)

Very nice, thank you. 



Battery Guy said:


> I find this last plot showing the 5C rate comparison very interesting. It is clear that the 16340 cell does not hold up as well as the others. You also see that performance of the 14500 and 18490 are very similar, as are the 18350 and the 26500. It might mean that these similarly performing cells are made by the same supplier, or it might mean nothing at all.


Any similarity/differences in appearance regarding the positive nipples? :thinking:


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## Battery Guy (Nov 2, 2011)

Kestrel said:


> Very nice, thank you.
> 
> 
> Any similarity/differences in appearance regarding the positive nipples? :thinking:



I did not look close. When I get a chance I will take some photos and post them.


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## kiely23+ (Nov 2, 2011)

very good!
thank you... :thumbsup:


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## badtziscool (Nov 2, 2011)

thanks for this very informative post. I think the most interesting thing is the comparison between 16340 and 18350. There's been quite a few legos put together that is using a 16340 to power triple and quad xp-g dropins and it's clear from the graphs that pushing the cell at 4A is just too much. Of course some of these dropins are capable of going well over 4A.


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## 45/70 (Nov 2, 2011)

Nice job, BG.:thumbsup:

I've been using LiCo cells for quite a few years, but only recently have acquired four of AW's 18650 IMR cells. I have just never needed what these cells are best at, offering good performance at high current rates (1C+). It will be interesting to see how the IMR 18650 cells perform.

In the meantime, I am now also in need of IMR 16340 and 14500 cells. Unfortunately for this particular application (Jetbeam RRT-0, which can utilize either size cell), they have to have at least a "button top", if not an actual "nipple". This kind of narrows the choices down quite a bit.

I'm torn between using AW's "protected" LiCo cells, or using IMR cells. The LiCo cells work great, but I really don't like running them at 1.7A. On the other hand, in addition to this light incorporating the "cheap" solution to polarity protection (a recessed positive contact, instead of a diode), it also offers no over discharge protection, as most of my other lights do. These two "features" are unbecoming of a $100 pocket light, IMO.

Anyway, thanks for performing all the work involved and providing the resultant information. I will keep an eye out for the 18650 update. From experience, I'm expecting they will also perform well. I'll also add, that considering the size of a 16340 cell, I'm not too surprised they falter a bit at high current.

Dave


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## Battery Guy (Nov 3, 2011)

45/70 said:


> In the meantime, I am now also in need of IMR 16340 and 14500 cells. Unfortunately for this particular application (Jetbeam RRT-0, which can utilize either size cell), they have to have at least a "button top", if not an actual "nipple". This kind of narrows the choices down quite a bit.



With the exception of the 26500 cell, all of the AW IMR cells that I tested had a relatively small button top for the positive terminal. I remember this clearly because it was very challenging to spot weld two separate leads to positive terminal for voltage sensing.

Lighthound now has AW IMR 18650 cells in stock. I ordered two yesterday for testing, and hope to have the results posted in a week or so.

Also, when I purchased the IMR cells I also purchased samples of the rest of AW's line of LCO cells. I hope to perform similar tests on these and post the results in a new thread in a few weeks. 

Cheers,
BG


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## 45/70 (Nov 3, 2011)

Battery Guy said:


> With the exception of the 26500 cell, all of the AW IMR cells that I tested had a relatively small button top for the positive terminal. I remember this clearly because it was very challenging to spot weld two separate leads to positive terminal for voltage sensing.



Yeah, as I said, the selection of 16340 or 14500 IMR cells with nipples, is pretty much limited to either AW's, or AW's. I believe there may be some "CrapiFire" type cells available, but more and more have pretty much given up on cells of this type. I've sure bought and used enough of them to determine their quality, ie. low.

I did check into shao's cells in the MarketPlace, but unfortunately, the only cells that have nipples are a few of the 16340 cells, and this seems rather random, as most do not seem to have them. On top of that, the 16340 cells don't seem to perform very well. All of his other cells are flat tops, or minimal button tops.

I always appreciate tests of new cells. There are many to research that help with making a decision when purchasing cells for specific applications. On the other hand, there are very few tests of used cells, some, but not many. It is my opinion that these tests better reveal the true ability and performance of any chemistry cell.

I don't now whether you've seen this thread that I started a while back. It involves testing some older used AW cells and, in most cases, some used, but not as much, or as old "CrapiFire" cell types. The results are typical of what I've experienced in my nearly 7 years, using LiCo cells in flashlights/torches. As I state in the thread, considering both the number of cycles, and the age of the cells tested, one could easily come to the conclusion that the AW cells would last _at least_ four times as long as the competitors presented.

Dave


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## xul (Nov 3, 2011)

In the first graph, 
note that discharge current, I, is not a linear function of measured capacity 
so to predict capacity C from I 
take the log of I to make the relationship linear 


Measured ....discharge ........log of I
capacity, C ....current, I .........LI
0.35 ............2 .................. 0.301029996
0.25 ...........4 ...................0.602059991


Have Excel calculate the slope and intercept 
-0.332192809 =slope 
0.45 =intercept 


So C should equal 
-0.332192809 times Log(I) + 
0.45 


confirm 
I LI ................C
2 0.301029996 0.35
4 0.602059991 0.25


so for a discharge current, I, of 
3 
take the log 
0.477121255 =log I 

then the capacity should be C = 
-0.332192809 times 
0.477121255 plus 
0.45 
equals
0.29150375 

and not 
0.3 
as you would expect from a linear relationship 
between C and I 

In this case the difference is only 
2.8 percent but this may be 
larger with other batteries


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## Battery Guy (Nov 3, 2011)

xul

Sorry buddy, but you totally lost me. What exactly are you trying to point out in the first graph?

Cheers,
BG


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## xul (Nov 4, 2011)

Battery Guy said:


> xul
> 
> Sorry buddy, but you totally lost me. What exactly are you trying to point out in the first graph?
> 
> ...


Sorry. 
I need to take a writing course.


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## Battery Guy (Nov 4, 2011)

xul said:


> Sorry.
> I need to take a writing course.



I doubt that very much. I just did not understand what the calculations were for. Looks interesting. Please explain.

Cheers,
BG


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## xul (Nov 5, 2011)

Well, battery testing graphs may show current levels of 0.1, 1 and 10A. This much variation, two orders of magnitude, is better understood using a log scale rather than a linear scale.

The trouble comes if you want to know performance for an intermediate value of current. If you linearly interpolate between values you will be significantly off, i.e., halfway between the 1A line and the 10A line is 3A, logarithmically speaking, not ~5A.

My spreadsheet is for doing this tedious calculation, back and forth between linear and log scales.

Nailing down battery performance can be really difficult, at least for the reason of the exponential relationships between almost everything. 
And we all think linear.

Too bad the sliderule people are out of business. These things have a one-for-one correspondence between linear and log scales.


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## Battery Guy (Nov 5, 2011)

xul said:


> Well, battery testing graphs may show current levels of 0.1, 1 and 10A. This much variation, two orders of magnitude, is better understood using a log scale rather than a linear scale.



Ah, I understand now. I was thinking about testing these under constant power conditions and plotting Ragone plots, which are log Power versus log Energy. Maybe I should do that.


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## xul (Nov 5, 2011)

Battery Guy said:


> Ah, I understand now. I was thinking about testing these under constant power conditions and plotting Ragone plots, which are log Power versus log Energy. Maybe I should do that.


With switch-mode regulators constant power is an option and it's generally different than constant resistance or constant current.

Decide what the goal of your testing is and then design your test around that goal. If constant power regulators are commonly used then test results that relate to this mode will be useful for many people.


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## Justin Case (Nov 5, 2011)

xul said:


> Well, battery testing graphs may show current levels of 0.1, 1 and 10A. This much variation, two orders of magnitude, is better understood using a log scale rather than a linear scale.
> 
> The trouble comes if you want to know performance for an intermediate value of current. If you linearly interpolate between values you will be significantly off, i.e., halfway between the 1A line and the 10A line is 3A, logarithmically speaking, not ~5A.
> 
> ...



Assuming an exponential relationship, such as Arrhenius, then it seems you ought to take natural logs, not base 10 logs. Using base 10 vice base e results in a constant shift error. Also, if different mechanisms operate at low vs high discharge current, then you will also have different activation energies, which can cause further problems with the interpolation, since it really becomes an extrapolation. I don't know if this is actually the case, but unless you have knowledge of operative mechanisms behind the exponential relationships, it is a risk. If I were to assume the same mechanism across the board, then I might use something like Lagrange interpolation or divided differences, and take advantage of the other data points available to me, not just the two adjacent ones.

Your check that the slope and intercept values are correct also seems unusual. Of course the back check will give you exact results. You conducted a linear regression using two data points. Well, any two points define a straight line so of course you'll get back the same x,y points.


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## xul (Nov 6, 2011)

If I had the software I'd do more sophisticated analyses. 
I tried to download a free program, I think it was 'R', but something went wrong. Computers are great when they actually work.


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## Battery Guy (Nov 7, 2011)

I just started the tests on the AW IMR 18650 cells today, and hope to post results by Friday. I also started constant power discharge tests on the other cells, so I hope to post a partial Ragone plot on Friday as well.

Cheers,
BG


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## xul (Nov 8, 2011)

Check the variation between several identical cells. 
If you see a +/- 5% variation between cells and a +/- 5% variation between brands, the cell variation may be masking the brand variation.


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## Battery Guy (Nov 8, 2011)

xul said:


> Check the variation between several identical cells.
> If you see a +/- 5% variation between cells and a +/- 5% variation between brands, the cell variation may be masking the brand variation.



As stated in the limitation section in the original post, I acknowledge that a sample of one is far from being statistically significant. Unfortunately, I do not have the time or resources to do testing on multiple cells. 

Cheers,
BG


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## Battery Guy (Nov 11, 2011)

Greetings Everyone

I have added data for the AW IMR18650 cell to the first post. 

Cheers,
BG


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## jasonck08 (Nov 11, 2011)

You should also try some higher discharge currents, after all most of these cells are rated 8-10C.


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## Battery Guy (Nov 11, 2011)

jasonck08 said:


> You should also try some higher discharge currents, after all most of these cells are rated 8-10C.



I am planning on it. I will be running constant current tests at higher discharge currents to add to the above tests, and I am presently doing constant power tests so that I can construct Ragone plots for these cells. 

It is a lot of testing and takes a lot of time, so be patient.

Of course, I probably won't be running the 16340 any higher. At 5C it is already a pretty poor performer.

Cheers,
BG


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## Battery Guy (Nov 12, 2011)

Greetings Everyone

I have added Ragone plots to the first post in this thread. They are not complete yet, but I will update them as more data is collected.

I thought that I would take a moment to talk about how to use a Ragone plot to select an appropriate cell, or determine how fast a particular cell should be discharged.

Let's consider the Ragone plot below:







At this point, only the curves for the 14500 and 18340 cells are complete, so we will only consider those cells for the purposes of this discussion.

Every cell has a characteristic Ragone plot that has the following similar features:

1.) a relatively vertical, straight zone at low power where the amount of energy available is relatively insensitive to discharge power
2.) a relatively flat, horizontal zone at high power where the amount of energy is very sensitive to discharge power
3.) a transition zone between these zones

_*The important point to remember is that you only want to use the battery in the first section, i.e. the vertical, straight zone where the amount of energy available is relatively insensitive to discharge power. *_ There are two reasons for this:

1.) The difference between the total energy available and your actual discharge energy is dissipated as heat. The bigger the difference, the hotter the cell will get during discharge and the fewer cycles you will get out of it.
2.) As cells age, the total capacity available decreases and the internal resistance increases. The result is that the Ragone plot shifts down and to the left. If you are operating a new cell in the transition zone or above, you will see a big decrease in performance as the cell ages. 

So let's take a look at the 14500 and 18340 cells in the Ragone plot above. For the 14500 cell, it looks to me like the first zone extends up to ~14 W, or just above the 6C discharge rate. So I would recommend that the 14500 cell be used for applications up to, but no more than about 12 W or 6C. For the 18340 cell, the first zone extends up to ~10 W, or just above the 3.3 C discharge rate. So I would recommend that this cell be used for applications up to, but no more than about 8 W or 3C.

"But wait a minute, these cells are rated to 8C maximum continuous discharge!" I hear you cry. Well, you can see from the Ragone plot that both cells are indeed capable of 8C continuous discharge. However, you are going to take a pretty big hit on available discharge energy, you will be heating the cells up a lot, and you will likely notice pretty rapid performance degradation with continuous use at 8C, especially for the 18340 cell.

Hope you find this useful. Let me know if you have any questions.

Cheers,
BG


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## Battery Guy (Nov 12, 2011)

I thought some of you might find it interesting to compare the AW IMR cells to a couple other commonly used cells, so I have added a conventional Eneloop AA and a Sanyo 2600 mAh 18650 lithium-ion (typical laptop cell) to the Ragone plot below:






Note that the Sanyo 18650 cell has a relatively small transition zone. This is because the cell has a PTC that kicks on at discharge rates of ~3C.

Cheers,
BG


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## 45/70 (Nov 13, 2011)

Battery Guy said:


> Note that the Sanyo 18650 cell has a relatively small transition zone. This is because the cell has a PTC that kicks on at discharge rates of ~3C.



Heh, I was wandering what the "crook" in the Sanyo's plot was. I sometimes observe similar anomalies when my cat jumps up on the testing area, LOL!

Looks like the AW IMR 18650 performed as expected. I'm preferring these to my Samsung 30A cells, even though they don't run as long overall.

With download's Pocket Rocket, the IMR cells will run down pretty much until discharged (3.60-3.70 Volts OC) on "high" (~3A), before the voltage warning kicks in, which is at ~3 Volts. The Samsung's start to fail at around 3.80 Volts OC, so the runtime actually works out to being close to the same, on high. While at lower levels (150 and 600mA) the Samsung's definitely offer superior runtime, I can't help but think that the 30A cells are not going to last as long with frequent 3A loading, as the IMR cells will.

Thanks for adding the Ragone plots, BG. I find these very interesting, if not useful, as well. I have an offline collection of all of your Ragone plots for reference.

Dave


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## Battery Guy (Nov 13, 2011)

45/70 said:


> Thanks for adding the Ragone plots, BG. I find these very interesting, if not useful, as well. I have an offline collection of all of your Ragone plots for reference.



I am really glad somebody finds them useful because they are a bit of a pain to put together! There is A LOT of test data summarized in one Ragone plot. 

I think Ragone plots are absolutely fantastic tools. For a single cell, you can see very clearly what the performance limits are and where you should be operating. They are also great for comparing different cells. 

One shortcoming of Ragone plots is that they don't tell you operating voltage of a cell during discharge, and this is important for a lot of hotwire and similar unregulated mods. Therefore, the humble constant current discharge curves still have their place.

Cheers,
BG


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## 45/70 (Nov 13, 2011)

Battery Guy said:


> I am really glad somebody finds them useful because they are a bit of a pain to put together! There is A LOT of test data summarized in one Ragone plot.



Absolutely, and I understand that there is a lot of work that goes into making them!:thumbsup:



> One shortcoming of Ragone plots is that they don't tell you operating voltage of a cell during discharge, and this is important for a lot of hotwire and similar unregulated mods. Therefore, the humble constant current discharge curves still have their place.



Yeah, well, I have a lot of the simple constant current discharge plots from many sources, as well. Fortunately, I am able to custom make my own, for the cells that I have, with my CBA.

Dave


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## Battery Guy (Nov 13, 2011)

45/70 said:


> Yeah, well, I have a lot of the simple constant current discharge plots from many sources, as well. Fortunately, I am able to custom make my own, for the cells that I have, with my CBA.



I was looking into getting a CBA, but it seems that a major shortcoming is that it does not have separate voltage sense leads. This was a killer issue for me, especially for high current testing. When I contacted the manufacturer, they told me that their software takes care of voltage errors caused by connection resistance, but I remain skeptical. Any thoughts on that?


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## HKJ (Nov 13, 2011)

Battery Guy said:


> I was looking into getting a CBA, but it seems that a major shortcoming is that it does not have separate voltage sense leads. This was a killer issue for me, especially for high current testing. When I contacted the manufacturer, they told me that their software takes care of voltage errors caused by connection resistance, but I remain skeptical. Any thoughts on that?



In the pro version of the software you can add a resistive compensation, but it does not solve problems with varying contact resistance in the connector.
Another issue it the voltage resolution, it is 10 mV. I believe this is a bit coarse when making graphs.


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## samgab (Nov 13, 2011)

Battery Guy said:


> I was looking into getting a CBA, but it seems that a major shortcoming is that it does not have separate voltage sense leads. This was a killer issue for me, especially for high current testing. When I contacted the manufacturer, they told me that their software takes care of voltage errors caused by connection resistance, but I remain skeptical. Any thoughts on that?



Considering from your other graphs and posts that you have access to some really high end gear (Maccor) at work... Compared to what you have access to the CBA would be like a toy.


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## 45/70 (Nov 13, 2011)

Battery Guy said:


> I was looking into getting a CBA, but it seems that a major shortcoming is that it does not have separate voltage sense leads. This was a killer issue for me, especially for high current testing. When I contacted the manufacturer, they told me that their software takes care of voltage errors caused by connection resistance, but I remain skeptical. Any thoughts on that?



Yeah, the CBA's are not really precision instruments. Add to that, they are way overpriced, IMO. That said, they are quite useful. I don't really need all that much precision, or accuracy to make a valid comparison, as a hobbyist. The important part is the interpretation of the results, not the equipment used. Unfortunately, this is where many users fail.

Dave


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## Mr Happy (Nov 13, 2011)

I've never quite seen the appeal of the CBA. It seems to be closed proprietary hardware and software, and for a device like that I would really want it to be open and modifiable.

I think I would rather spend the time building something equivalent with some MOSFETS, some big heat sinks, and an Arduino. I would be able to fine tune it to my needs and would get far more educational value out of it.


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## Mr Happy (Nov 13, 2011)

Those graphs are surely full of valuable information :thumbsup:, but one thing they don't do is give a feel for the raw power in some of those cells. This is not a criticism by any means (far from it), but just a mention of another dimension that affects people intending to actually use these cells as power sources.

What prompts this comment is that the K2 LFP26650E (energy) cells I thought I had are actually LFP26650P (power) cells. And I've suddenly found that in the process of fitting them to a prospective hotwire mod, I'm scared witless of accidentally shorting them out. I briefly scratched a wire between the terminals to get a measure of what would happen and it was like letting a dragon out of a cage. Cells like this are *bad*.


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## jasonck08 (Nov 13, 2011)

Battery Guy said:


> I was looking into getting a CBA, but it seems that a major shortcoming is that it does not have separate voltage sense leads. This was a killer issue for me, especially for high current testing. When I contacted the manufacturer, they told me that their software takes care of voltage errors caused by connection resistance, but I remain skeptical. Any thoughts on that?



That is definitely my biggest complaint, is the fact that its measuring voltage on the same wires that are carrying current. Very poor design IMO. I don't have the Pro software, and don't really want to spend the extra $100 for this simple feature, but I find myself usually measuring the @ the cell voltage underload with a DMM, recording it, then later dumping the results into excel and adjusting the voltage... Usually about +0.05 or 0.06v.

Another thing I could do to get very accurate voltage readings is to use my datalogging Agilent DMM to measure voltage @ the cell during the discharge.



45/70 said:


> Heh, I was wandering what the "crook" in the Sanyo's plot was. I sometimes observe similar anomalies when my cat jumps up on the testing area, LOL!
> 
> Looks like the AW IMR 18650 performed as expected. I'm preferring these to my Samsung 30A cells, even though they don't run as long overall.


 

Slightly OT, but I'm curious as to how those Samsung 30A cells are holding up for you. I got some samples about 18 months ago, when I tested them for a few cycles they did well. When I tested a cell 1 year later that had zero cycles on it and had been stored at about 3.7v in a cool dry place, the increase in internal resistance was evident. For example the cell should have a 3.78v nominal voltage @ 0.2C when charged at 4.35v during the CV stage. However, with this cell I was getting like 3.65 nominal voltage, which is unacceptable for a brand new cell sitting in storage for 1 year. Same problem with the Samsung 28A too. I'm wondering if these cells were from a bad batch or if other people have noticed this problem too.


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## Battery Guy (Nov 14, 2011)

Mr Happy said:


> Those graphs are surely full of valuable information :thumbsup:, but one thing they don't do is give a feel for the raw power in some of those cells. This is not a criticism by any means (far from it), but just a mention of another dimension that affects people intending to actually use these cells as power sources.
> 
> What prompts this comment is that the K2 LFP26650E (energy) cells I thought I had are actually LFP26650P (power) cells. And I've suddenly found that in the process of fitting them to a prospective hotwire mod, I'm scared witless of accidentally shorting them out. I briefly scratched a wire between the terminals to get a measure of what would happen and it was like letting a dragon out of a cage. Cells like this are *bad*.



Yeah, the Ragone plots really don't tell you about how much energy can be dumped in a short circuit event. These power cells seldom if ever have a PTC built in, and combined with the low internal resistance, you can get a whole lot of power for a short period of time out of the cell if you have a short circuit. People talk about IMR cells being "safer", but not too many people talk about this aspect of their usage.


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## Battery Guy (Nov 14, 2011)

samgab said:


> Considering from your other graphs and posts that you have access to some really high end gear (Maccor) at work... Compared to what you have access to the CBA would be like a toy.



True, but I have a limited number of Maccor channels. I was thinking of augmenting the Maccor with something like a CBA, which is far less expensive. But the way it measures voltage is a killer issue for me.


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## Mr Happy (Nov 14, 2011)

Battery Guy said:


> Yeah, the Ragone plots really don't tell you about how much energy can be dumped in a short circuit event. These power cells seldom if ever have a PTC built in, and combined with the low internal resistance, you can get a whole lot of power for a short period of time out of the cell if you have a short circuit. People talk about IMR cells being "safer", but not too many people talk about this aspect of their usage.



I did a quick calculation with the LFP26650P cells. The datasheet estimates the internal resistance at less than 9 milliohms, so that might produce a short circuit current of up to 3.2 / 0.009 = 350 A. That would give a power dissipation of 350^2 * 0.009 = 1.1 kW. With a cell capacity of 2.6 Ah, this power could be produced for 10-20 seconds or more. There's a definite case for handling this kind of cell with a great deal of caution.


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## 45/70 (Nov 14, 2011)

jasonck08 said:


> Slightly OT, but I'm curious as to how those Samsung 30A cells are holding up for you.



Hi Jason. I haven't had the cells long enough to really comment, only a month or so. They do hold voltage under load better than any other LiCo cells that I have. That was my main interest, as once the Pocket Rocket's cell voltage drops to ~3 Volts, it's pretty much all over. This performance comes as no surprise though, as I had studied many discharge graphs before I purchased the cells.

So anyway so far, so good. I might add that these cells would work a bit better if I could charge them with a 4.35 Volt CV. My iCharger is limited to 4.30 Volts maximum CV. I just figure the cells will last a bit longer this way, and don't fret over it. I might charge them on a regulated PS sometime, just to see if it really makes any significant difference. I doubt that it will though.

The drop in nominal voltage you observed with your sample cells, may be normal for these. I have no idea. I'm sure in a years time, any Li-Ion cell will suffer some internal resistance increase. This is the nature of lithium-ion cells, they degrade whether you use them or not. All that can be done is to store them properly, as you did, and hope for the best. That does seem to be a bit more performance loss than I would have expected. On the other hand, I would think, at least some new 4.20 Volt LiCo cells would fall short of a 3.65 Volt nominal voltage, as most are rated either 3.6 or 3.7 Volts. So, after a year in storage, maybe 3.65 volts, really isn't too bad.:shrug:

I store unused cells at 35-40F in the Fridge. That may have helped some. B.U. shows a 50% reduction in degradation, when storing cells at *EDIT* *0*C* vs. 25*C** *EDIT*, over a period of one year. I don't know how cool the place you stored the cells in was, but temperature may have been a factor.
Oops, sorry BG, I believe I carried us even further OT.:candle:

Dave


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## Battery Guy (Nov 14, 2011)

Mr Happy said:


> I did a quick calculation with the LFP26650P cells. The datasheet estimates the internal resistance at less than 9 milliohms, so that might produce a short circuit current of up to 3.2 / 0.009 = 350 A. That would give a power dissipation of 350^2 * 0.009 = 1.1 kW. With a cell capacity of 2.6 Ah, this power could be produced for 10-20 seconds or more. There's a definite case for handling this kind of cell with a great deal of caution.



Agreed. In this way these cells are not unlike large capacitors. The safety issues are pretty significant if you get the voltage up by putting four or more cells in series.

That being said, the same is true for large lead acid, NiCd and NiMH batteries. I think that the difference is that the power density of a lithium-ion can be so much higher, so people are deceived by the relatively small size.


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## Battery Guy (Nov 17, 2011)

Greetings Everyone

I have updated the Ragone plots in the original post. This is the best I can do for right now. I am having problems with my test equipment and I cannot go over 50 W for discharge. So for the time being, this is all I can do. 

But I think that we do see quite a bit from these Ragone plots. Based on the data collected so far, I would say that the maximum discharge rate for the 16340 and 18350 cells should be 3C-4C. The 14500 can be taken has high as 6C. The 23500 cell is good to at least 6C, and might possibly go higher but I have no data yet. The 18650 and 18490 cells are good to at least 10C, and might possibly go higher, but again I need more data to confirm.

You can certainly use these cells at higher rates, but you are likely going to see faster performance fade with time. Remember that as cells are used, these Ragone plots tend to shift down and to the left as both power capability and energy (and capacity) decrease. In general, the plots shift down faster than they shift to the left, so loss of power capability tends to happen much faster than loss of energy. 

Cheers,
BG


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## 45/70 (Nov 17, 2011)

Battery Guy said:


> ......Remember that as cells are used, these Ragone plots tend to shift down and to the left as both power capability and energy (and capacity) decrease. * In general, the plots shift down faster than they shift to the left, so loss of power capability tends to happen much faster than loss of energy*.



Good point, BG. This is something that I have noticed in the last few years and seems to apply to all cell chemistries.

I just ran my yearly (actually longer than that) "Break-In" of my first 20 eneloop AA cells (the only AA eneloops I have) on my three Maha C9000's. These cells are dated 8/06 and I purchased them, I think in 2008, so anyway, they are about 6 years old. Last time I checked, they were holding voltage under load quite well, not as good as when "new" (actually at the time, 2 years old), but still adequate. This time however, I noticed that during the 0.2C discharge, the cells spent most of the discharge below 1.20 volts. As you noted, the capacity is still respectable (1700-1800mAh), but the voltage under load, or power, is down considerably this time around. Time for replacement, or at least to augment them with some fresh, higher performing, new cells.

Dave


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## vvvoland (Dec 23, 2013)

Battery Guy said:


> Greetings Everyone
> 
> I have updated the Ragone plots in the original post. This is the best I can do for right now. I am having problems with my test equipment and I cannot go over 50 W for discharge. So for the time being, this is all I can do.
> 
> ...



Thank you for your tests. These were the first tests AW IMR that I found, thank you could not tell without registering 
Did you manage overcome 50 watts ?


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## HKJ (Dec 23, 2013)

vvvoland said:


> Thank you for your tests. These were the first tests AW IMR that I found, thank you could not tell without registering
> Did you manage overcome 50 watts ?



You have not looked much, I have also tested AW batteries and I did go above 50 watt.

Index of AW tests: http://lygte-info.dk/review/batteries2012/batteryIndexAW UK.html
You can also find all the tests here on CPF.


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