Samsung 40T and other cells like it?

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flippy   1 MW

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Re: Samsung 40T and other cells like it?

Post by flippy » Oct 14 2019 12:42am

rg12 wrote:
Oct 13 2019 6:57pm
It's pretty hard to calculate as it's so random, for me it's about 5 second long bursts that come let's say every 20-30 seconds but still super hard to estimate...
mount a analog ammeter. just a regular "ye olde" meter. the needle with even out the readings.
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Re: Samsung 40T and other cells like it?

Post by docware » Oct 14 2019 1:45am

rg12 wrote:
Oct 13 2019 5:22pm

Now#2, pulling about 120A from a 17.5Ah 25R pack is abusing it as I've seen 25R packs being totaled after 10 month of use (not even daily) at 110A 20Ah which is bursts of 5.5C.
So I'm abusing my poor 7P 25R pack.
Yes, we agree with you. And you already know it : you are abusing your pack by high current draw. You have slim sporty looking electric 5 kW motorcycle which is feed by small battery pack. No wonder that you pay price for that. There is no free lunch.
If you don´t want to use Lipo for your hobby, than you need bigger pack. Or pay the price.

viewtopic.php?f=14&t=102682&p=1502617#p1502617

Spending time on higher temperatures is not sole degradation mode. There are much more possibilities how to abuse cell. High discharge is one of them, especially at lower temperatures, high charge currents, high DOD (depth of discharge), …….. We just don´t know what all you and your colleagues are using from this spectrum.

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Re: Samsung 40T and other cells like it?

Post by rg12 » Oct 14 2019 6:40am

Hillhater wrote:
Oct 13 2019 8:12pm
I am trying to imagine in rg12’s “real world” pack of many 18650s, how some of those “internal” cells with no exposure to external cooling, but infact surrounded by other “Hot” cells ..what their temperature build profile is like when the pack is subjected to bursts of 120+ amps (8C) ?
Do those internal cells have any chance of shedding heat between bursts ? Or does each burst just jack the temp up further ?
A temp probe inside the pack on those inner cells would be a useful data source.
No need to be sarcastic.
120A is devided by 7P so it's about 17A per 20A rated cell.
Of course it's not a lab with a single cell in an air conditioned room but it's funny that in the real world a 17A burst of 5 seconds from a 20A "constant" current rated cell is considered abuse.
docware wrote:
Oct 14 2019 1:45am
rg12 wrote:
Oct 13 2019 5:22pm

Now#2, pulling about 120A from a 17.5Ah 25R pack is abusing it as I've seen 25R packs being totaled after 10 month of use (not even daily) at 110A 20Ah which is bursts of 5.5C.
So I'm abusing my poor 7P 25R pack.
Yes, we agree with you. And you already know it : you are abusing your pack by high current draw. You have slim sporty looking electric 5 kW motorcycle which is feed by small battery pack. No wonder that you pay price for that. There is no free lunch.
If you don´t want to use Lipo for your hobby, than you need bigger pack. Or pay the price.

viewtopic.php?f=14&t=102682&p=1502617#p1502617

Spending time on higher temperatures is not sole degradation mode. There are much more possibilities how to abuse cell. High discharge is one of them, especially at lower temperatures, high charge currents, high DOD (depth of discharge), …….. We just don´t know what all you and your colleagues are using from this spectrum.
I'm aware of that and mentioned before that I don't care since I ride only every few month so screw it, plus I'm building the battery packs so have only the cost of the cells and BMS so I can go through 3 packs a year if I wanted and it will still cost me like one pack retail.

About the 110A example that killed the pack within 10 month it was of a colleague's of mine and that guy never went below 72V on his 20S pack, he doesn't go full throttle like a guy making a motorcycle out of it, mostly weekends riding in dirt.
Was surprised how much these brand cells are crap in the real world, using them so much below their max constant rating for bursts that use 75% of their max rating and they all go 400% IR raise in less than a year.

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Re: Samsung 40T and other cells like it?

Post by john61ct » Oct 14 2019 7:50am

If by "20C rated" you mean mfg specs, yes that is guaranteed to not work, those are 100% pure fiction.

Anywhere above 4-5C even on much better (actual tested by users) rated cells, will mean a very short lifespan if a high duty cycle.

Abuse is not a black and white issue, nor disparaging, just something to try your best to avoid.

But sometimes necessary, just do it with open eyes and replace your packs more frequently.

Kind of silly to come to experts in a forum to ask advice and then just dispute it.

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Re: Samsung 40T and other cells like it?

Post by rg12 » Oct 14 2019 8:11am

john61ct wrote:
Oct 14 2019 7:50am
If by "20C rated" you mean mfg specs, yes that is guaranteed to not work, those are 100% pure fiction.

Anywhere above 4-5C even on much better (actual tested by users) rated cells, will mean a very short lifespan if a high duty cycle.

Abuse is not a black and white issue, nor disparaging, just something to try your best to avoid.

But sometimes necessary, just do it with open eyes and replace your packs more frequently.

Kind of silly to come to experts in a forum to ask advice and then just dispute it.
By 20C you mean 20A (8C), and yes, it has been along time since I found out specs are all BS but it's annoying that it's off by so much.

What cells in the area of 8C do you recommend due to testing other than 25R? (I mean better than 25R)

When did I dispute your advice?

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Re: Samsung 40T and other cells like it?

Post by john61ct » Oct 14 2019 8:15am

I am a total noob, so no advice to offer.

But the past threads repeat advice from the real experts over and over, it seems every month.

Most cells rated as 30C by the maker should not even be used at 5C for more than a few seconds.

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Re: Samsung 40T and other cells like it?

Post by j bjork » Oct 14 2019 8:36am

rg12 wrote:
Oct 14 2019 8:11am


What cells in the area of 8C do you recommend due to testing other than 25R? (I mean better than 25R)

I think sony vtc5A and molicell p26a is a lot better, I will wait to see what the experts say :)

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Re: Samsung 40T and other cells like it?

Post by rg12 » Oct 14 2019 8:55am

john61ct wrote:
Oct 14 2019 8:15am
I am a total noob, so no advice to offer.

But the past threads repeat advice from the real experts over and over, it seems every month.

Most cells rated as 30C by the maker should not even be used at 5C for more than a few seconds.
Every month you say I'm given an advice and I don't take it?
I'm happy that you keep track but I really have no idea what you are talking about, I do appreciate the help I get here a ton and take it in account and usually to tell you the truth I don't think I ever found myself not agreeing.
People for some reason get upset that I abuse my 7P pack with huge currents but that's choice and not something that I stand behind and say "this is the best pack on the planet for my use", I have a 90mm wide frame so that's what I chose to go with.

As for 30C rated cells, don't confuse C with A, many people call 25R a 20C cell when it's a 20A cell with 8C.
Cylindrical max I've seen is 15C but with about 1500mAh capacity and when you go to 2500mAh area you will see a max of 8-10C
If you are talking about all those efire fakes then you will see an 18650 with 6000mAh and 20C but that works only when in China :lol:

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Re: Samsung 40T and other cells like it?

Post by Hillhater » Oct 14 2019 5:43pm

rg12 wrote:
Oct 14 2019 6:40am
Hillhater wrote:
Oct 13 2019 8:12pm
I am trying to imagine in rg12’s “real world” pack of many 18650s, how some of those “internal” cells with no exposure to external cooling, but infact surrounded by other “Hot” cells ..what their temperature build profile is like when the pack is subjected to bursts of 120+ amps (8C) ?
Do those internal cells have any chance of shedding heat between bursts ? Or does each burst just jack the temp up further ?
A temp probe inside the pack on those inner cells would be a useful data source.
No need to be sarcastic.
120A is devided by 7P so it's about 17A per 20A rated cell.
Of course it's not a lab with a single cell in an air conditioned room but it's funny that in the real world a 17A burst of 5 seconds from a 20A "constant" current rated cell is considered abuse.
I didnt intend it to be sarcastic ?..what did you read that way ?
I was genuinely trying to say we do not know the environment around those cells enclosed by others in the pack.
And i did not say you are abusing those cells, infact all the “data” suggests you are within the normal parameters for use. On the Ecig test site, they run the 25r cell through repeated bursts of 20, 40 and 60 amps ( 5 sec on, 30 sec off) and record the temp increase,
.. also temp monitoring at constant discharge of 20A (76deg C)..so all looks normal..
...BUT.. as you say, that is lab conditions, not burried inside a bunch of other heated cells..very different conditions. as you know, it only needs a few cells in a pack to “weaken” , for the whole pack performance to suffer dramatically.
Why dont you put a cheap temp probe inside one of your packs ?
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Re: Samsung 40T and other cells like it?

Post by rg12 » Oct 14 2019 6:24pm

I should do that actually but it's packed so nice (my 7P) to tare apart right now but I may do it if I find myself mega motivated with not much work around me...

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Re: Samsung 40T and other cells like it?

Post by john61ct » Oct 14 2019 6:45pm

LiPo packs are routinely rated 30C and higher.

Some are fine at 8C or even 10C.

Really good way to go for maximum power density.

My point was, it seems likely your problem is caused by your overestimating the ability of your pack to support your C-rate needs.

Better quality cells and/or bigger Ah capacity would be required to do so.

You "cannot do that" can be objective fact, and is different from "you should not do that".

Obviously as long as you know your packs will need replacing quickly, do what you like.

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Re: Samsung 40T and other cells like it?

Post by john61ct » Oct 14 2019 6:48pm

rg12 wrote:Every month you say I'm given an advice and I don't take it?
No, I mean you can learn a lot by reading past threads by others with the same issues and misunderstandings.

You are wasting members' valuable time arguing known facts with experts (not me)


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Re: Samsung 40T and other cells like it?

Post by leffex » Oct 14 2019 7:50pm

rg12 wrote:
Oct 14 2019 8:55am
As for 30C rated cells, don't confuse C with A, many people call 25R a 20C cell when it's a 20A cell with 8C...
Hey RG

I have some cool info. I tried 10a rated cells, Panasonic 2900pf cells at 24p. Build with copper wire on the series connections. In comparison to some old turnigy multistar 12C 20ah (10ah2p) it turned out the PF's were "better than" them. That is pretty strong! The sag was however worse than some other turnigy old 20C cells at 20ah (5ah4p). OLD = 500 cycles. I also made a comparison and calculated that a theoretical old 28ah lipo was as good as 24p Panasonic at 66ah. Not directly compared by the AH but something.

My battery module thread if you like to know more about it.
viewtopic.php?f=14&t=101122

I sure would like to try out some 21700 40T cells. I was once liking the idea of high capacity 50E but 20p of 50E is just too much if you want 20-22 series. That's 26-29 kg of weight and only 200A than a 10p 40T with 300-350A performance at half the weight and volume. :banana:
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Re: Samsung 40T and other cells like it?

Post by docware » Oct 15 2019 2:52am

The rate at which a battery or cell can be charged or discharged is limited by the rate at which the active chemicals in the cells can be transformed.
Forcing high currents through the battery results in incomplete transformation of the active chemicals reducing the battery’s effective charge capacity and it also causes unwanted, irreversible chemical reactions to occur because the chemical transformations cannot keep up with the current demands.
The unwanted chemical transformations consume some of the active chemicals causing the battery to lose capacity and thus age prematurely.

From the above we can expect that with each charge/discharge cycle the accumulated irreversible capacity loss will increase. Although this may be imperceptible, ultimately the capacity reduction will result in the cell being unable to store the energy required by the specification. In other words it reaches the end of its useful life and since the capacity loss is brought on by high current operation, we can expect that he cycle life of the cell will be shorter, the higher the current it carries.

A.jpg
A.jpg (78.73 KiB) Viewed 1295 times
The capacity reduction at high discharge rates occurs because the transformation of the active chemicals cannot keep pace with the current drawn. The result is incomplete chemical reactions and an associated reduction in capacity. This may be accompanied by changes in the morphology of the electrode crystals such as cracking or crystal growth which adversely affect the internal impedance of the cell.

Ageing Accelerators
The previous paragraph indicated some of the basic ageing factors inherent in the battery chemistry. From this we can see that certain external environmental and usage factors, such as those following, can be considered as ageing accelerators.

High and very low temperatures
High energy throughput rate (Charge and discharge rates)
Mechanical stress or vibration which can give rise to open or short circuits or seal failures.

Operating Environment
In addition to the ageing accelerators noted above there are some less obvious environmental factors which can influence battery life.

A temperature gradient across the battery can increase the rate of battery ageing. From Arrhenius we know that, with a 10°C difference in temperature across the battery, some cells will age at twice the rate of others giving rise to unbalanced stresses on the cells resulting in premature failure. High pressure or cyclic pressure changes can cause mechanical failures of the cells.
High humidity can give rise to corrosion causing increased contact resistance at the battery terminals.



Source : THE ELECTROPAEDIA https://www.mpoweruk.com/

https://www.mpoweruk.com/Software_Confi ... attery.htm
https://www.mpoweruk.com/failure_modes.htm
https://www.mpoweruk.com/life.htm
https://www.mpoweruk.com/lithium_failures.htm
https://www.mpoweruk.com/reliability.htm
https://www.mpoweruk.com/chemistries.htm
Last edited by docware on Oct 15 2019 6:18am, edited 2 times in total.

rg12   100 kW

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Re: Samsung 40T and other cells like it?

Post by rg12 » Oct 15 2019 4:27am

john61ct wrote:
Oct 14 2019 6:45pm
LiPo packs are routinely rated 30C and higher.

Some are fine at 8C or even 10C.

Really good way to go for maximum power density.

My point was, it seems likely your problem is caused by your overestimating the ability of your pack to support your C-rate needs.

Better quality cells and/or bigger Ah capacity would be required to do so.

You "cannot do that" can be objective fact, and is different from "you should not do that".

Obviously as long as you know your packs will need replacing quickly, do what you like.
We were talking about cylindrical, I know that lipos go up to these C rates but it seems you changed what you meant between messages, nevermind.
john61ct wrote:
Oct 14 2019 6:48pm
rg12 wrote:Every month you say I'm given an advice and I don't take it?
No, I mean you can learn a lot by reading past threads by others with the same issues and misunderstandings.

You are wasting members' valuable time arguing known facts with experts (not me)
I don't know what you are talking about again, this is my thread with my specific question about the 40T and if I feel like asking someone a question since he did some tests that are relevant to me then I don't need your permission to ask in order to not come out as wasting everyone's time.
Meanwhile you are wasting my time by having me replying to the terrible stuff you write in a public forum on me and in my thread.
If I'm wasting your time then don't reply like an internet troll.
leffex wrote:
Oct 14 2019 7:50pm
rg12 wrote:
Oct 14 2019 8:55am
As for 30C rated cells, don't confuse C with A, many people call 25R a 20C cell when it's a 20A cell with 8C...
Hey RG

I have some cool info. I tried 10a rated cells, Panasonic 2900pf cells at 24p. Build with copper wire on the series connections. In comparison to some old turnigy multistar 12C 20ah (10ah2p) it turned out the PF's were "better than" them. That is pretty strong! The sag was however worse than some other turnigy old 20C cells at 20ah (5ah4p). OLD = 500 cycles. I also made a comparison and calculated that a theoretical old 28ah lipo was as good as 24p Panasonic at 66ah. Not directly compared by the AH but something.

My battery module thread if you like to know more about it.
viewtopic.php?f=14&t=101122

I sure would like to try out some 21700 40T cells. I was once liking the idea of high capacity 50E but 20p of 50E is just too much if you want 20-22 series. That's 26-29 kg of weight and only 200A than a 10p 40T with 300-350A performance at half the weight and volume. :banana:
Thanks for the info man, but it's kind of hard doing a comparison with old packs as there are so many factors that change.
and yeah, the 40T seem awesome as they have great energy density while being rated for high discharge although that I'm not really sure about since I heard they have a short life span so this is the reason of this thread, to find out if there is any truth in that or maybe it was just someone who beat it to max C all the time while that would kill any brand cell.

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Re: Samsung 40T and other cells like it?

Post by john61ct » Oct 15 2019 8:16am


rg12 wrote: this is my thread with my specific question about the 40T

the 40T seem awesome as they have great energy density while being rated for high discharge although that I'm not really sure about since I heard they have a short life span so this is the reason of this thread, to find out if there is any truth in that or maybe it was just someone who beat it to max C all the time while that would kill any brand cell.
This was answered in the first three replies.

They may be fine for low discharge usage, but their high C-rate performance only lasts for a short time.

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Re: Samsung 40T and other cells like it?

Post by john61ct » Oct 15 2019 8:17am

For the third time:

If you want high power density (high C-rate performance) you must accept lower energy density.

A battery that gives better than usual combination of these two opposing factors, will have lower cycle lifespan.

So pick **the one** factor that is most important to you and make a short list

then choose your second more important factor and look for a cell where that factor is "not too bad", do not expect much for that aspect

And accept that the third performance factor will be bad, only able to choose the "least worst".

Rather than asking for good ratings in all three factors, when they each oppose each other.

And of course then a fourth factor, e.g. cost, comes into the picture. . .


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Re: Samsung 40T and other cells like it?

Post by rg12 » Oct 15 2019 8:40am

john61ct wrote:
Oct 15 2019 8:16am
rg12 wrote: this is my thread with my specific question about the 40T

the 40T seem awesome as they have great energy density while being rated for high discharge although that I'm not really sure about since I heard they have a short life span so this is the reason of this thread, to find out if there is any truth in that or maybe it was just someone who beat it to max C all the time while that would kill any brand cell.
This was answered in the first three replies.

They may be fine for low discharge usage, but their high C-rate performance only lasts for a short time.
Ughh again...
Nobody but yourself complains here about what has been answer and what's not.
john61ct wrote:
Oct 15 2019 8:17am
For the third time:

If you want high power density (high C-rate performance) you must accept lower energy density.

A battery that gives better than usual combination of these two opposing factors, will have lower cycle lifespan.

So pick **the one** factor that is most important to you and make a short list

then choose your second more important factor and look for a cell where that factor is "not too bad", do not expect much for that aspect

And accept that the third performance factor will be bad, only able to choose the "least worst".

Rather than asking for good ratings in all three factors, when they each oppose each other.

And of course then a fourth factor, e.g. cost, comes into the picture. . .
I'm aware of all of that but when a respected manufacturer comes out with such a rating for high C rate with high capacity then I look into it and even though it's Samsung I'm still suspicious because I know how stuff works in the real world and that's why I opened this thread.
Seems like Samsung did nothing new here as they just took a 10A cell and rated it at 30A and raised the temperature in the datasheet to a whopping 80C which is obvious this thing ain't gonna last.
I'm still surprised by the super low IR it has out of the box (7 milliohm) but I still wander if I use it at half it's discharge rate for bursts just like I limit customers with the 25R which is my main cell that it will last just as long.

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Re: Samsung 40T and other cells like it?

Post by KWS Seuren » Oct 15 2019 1:30pm

I'm still surprised by the super low IR it has out of the box (7 milliohm) but I still wander if I use it at half it's discharge rate for bursts just like I limit customers with the 25R which is my main cell that it will last just as long.
Hi rg,

What do you think about the 25R against other cells, are they the best power/capacity/price cells?

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Re: Samsung 40T and other cells like it?

Post by rg12 » Oct 15 2019 3:56pm

KWS Seuren wrote:
Oct 15 2019 1:30pm
I'm still surprised by the super low IR it has out of the box (7 milliohm) but I still wander if I use it at half it's discharge rate for bursts just like I limit customers with the 25R which is my main cell that it will last just as long.
Hi rg,

What do you think about the 25R against other cells, are they the best power/capacity/price cells?
I never really looked at other cells for high discharge as I'm a business and cells that are claimed to be better (by a bit) cost at least 50% more than the 25R so it's the most affordable for sure.
Just know that you shouldn't go over 50% of their C rate if you want it to have a decent life span and that you need to know how to build for high current like enough nickel thickness, busbars and tons of other stuff that's related to safety.

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Re: Samsung 40T and other cells like it?

Post by john61ct » Oct 15 2019 6:40pm


rg12 wrote:I never really looked at other cells for high discharge as I'm a business and cells that are claimed to be better (by a bit) cost at least 50% more than the 25R so it's the most affordable for sure.

Just know that you shouldn't go over 50% of their C rate if you want it to have a decent life span and that you need to know how to build for high current like enough nickel thickness, busbars and tons of other stuff that's related to safety.
Say you have a 20Ah pack, the comprising cells rated by the mfg at 30C but in reality (forum expert testing consensus) they are actually only good for 5-7C for 2-4min bursts.

So what rate are you recommending by "shouldn't go over 50% of their C rate"?

0.5C
1.5C ?

15C?
45C ?

2-4C
or 8-10C ?

Not being a smart-ass, genuine question about your approach.



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Re: Samsung 40T and other cells like it?

Post by Matador » Oct 15 2019 9:15pm

[/quote]
In fact most of informations about cell life which you find on internet are only "old wives' advice" based on rules which actually did not works in significant amount of cases :?

Many people forget when evaluating cell EOL, that there are two major conditions. Capacity fade and DCIR rise, where the DCIR rise is important particularly in applications with more than 0.2C (rated capacity) discharge load. Also there is of course no general rule about dependency between this two parameters. So you can find many cells with high capacity fade but with relative stable DCIR and also cells with relative low capacity drop but significant DCIR rise, which make some cell almost unusable just at ca 85% of remaining capacity.
[/quote]

Best quote ever. Especially the old wives advice. I laugh so hard... And it's true... The strategy kind of reminds me of old dead battery cars which might show good voltage but once you put it on a load tester with significant load, DCIR make the voltage drop so much that voltage becomes unusable for anything practical (like starting you car in winter). So yeah, what good is it if a cell has 85% remaining capacity after 250 cycle but if you run it at just 5A voltage drops by a full volt. For my personal need, preserving a decent DCIR with cycling-aging is better than preserving capacity with aging. Don't want my cells cooking.... High capacity/low discharge cells will be good to power a clock... or a one ton powerbank.

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Re: Samsung 40T and other cells like it?

Post by rg12 » Oct 16 2019 4:33am

john61ct wrote:
Oct 15 2019 6:40pm
rg12 wrote:I never really looked at other cells for high discharge as I'm a business and cells that are claimed to be better (by a bit) cost at least 50% more than the 25R so it's the most affordable for sure.

Just know that you shouldn't go over 50% of their C rate if you want it to have a decent life span and that you need to know how to build for high current like enough nickel thickness, busbars and tons of other stuff that's related to safety.
Say you have a 20Ah pack, the comprising cells rated by the mfg at 30C but in reality (forum expert testing consensus) they are actually only good for 5-7C for 2-4min bursts.

So what rate are you recommending by "shouldn't go over 50% of their C rate"?

0.5C
1.5C ?

15C?
45C ?

2-4C
or 8-10C ?

Not being a smart-ass, genuine question about your approach.
My approach works with most known brand cells for keeping them from heating and having IR rising issues over time.
If 25R is advertised as 8C then max 4C, not that hard.
Mostly we are talking about ebikes here so the 4C is for bursts, never constant 4C from full to LVC.

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Re: Samsung 40T and other cells like it?

Post by john61ct » Oct 16 2019 7:13am

I think the best rule of thumb for general applicability is to ignore the fictional advertised C-rate completely.

Rely on objective standardised testing only, if high C-rate is important to your use case.

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Re: Samsung 40T and other cells like it?

Post by docware » Oct 16 2019 7:37am

I have peak load 0,9 C = 3A per cell on my ebike 8)

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