Continuous Charge Amp vs Continuous Discharge Amp

Batteries, Chargers, and Battery Management Systems.
eMark   100 W

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Continuous Charge Amp vs Continuous Discharge Amp

Post by eMark » Aug 27 2020 12:23pm

For the sake of this comparison we'll use a 12S6P (w/smart BMS) pack of LG HG2 3000mAh cells rated at 20A maximum continuous discharge, and a Charger quite capable of charging at a 6A rate without breaking into a sweat :thumb:

The HG2 Data Sheet ... https://www.18650batterystore.com/v/fil ... _sheet.pdf

Standard Charge ... 1.5A
Fast Charge ... 4.0
Max Charge ... 4.20 +|- 0.05v

Standard Discharge ... 0.6A (what i don't get is why it wouldn't be at least 1.5A, if not 3A)
Fast Discharge ... 10A
Max Continuous Discharge ... 20A

Question: What is it about a lithium cell chemistry (whether Lilo or Lipo) that you dare not charge a pack with the same energy that it's OK to discharge a pack? For example if discharging a 12S6P HG2 pack at a "Fast Discharge" of 10A, why not a "Fast Charge" at 10A (or 5A) instead of a max charge rate of only 4.25A ?

This was debated years ago in RC Lipo forums with the conclusion that you can actually charge at a higher rate than recommended, but it does shorten the cycle life. Well, if that's true than why would anyone want to discharge at 20A if you dare not charge higher than 4.25A with HG2 pack ?

So, any guesses as to the decreased number, if any, of useful charge/discharge cycles between these three 12S6P HG2 battery packs ...

A. Charged at 1.5A and Continuous Discharge at 15A (est. useful charge/discharge cycles?)
B. Charged at 4.0A and Continuous Discharge at 15A (est. useful charge/discharge cycles?)
C. Charged at 6.0A and Continuous Discharge at 15A (est. useful charge/discharge cycles?)

What i'm getting at is why 18650 lithium cells Should NOT Be charged at more than 1.33C, but can be discharged at 6.66C ? So in C. above why can't the pack be charged at 6A when it's OK to discharge it continuously at 20A ? OR another way of comparison is charging the pack at 6A and only discharging at 6A with the useful cycle life outliving both A. and B.

I'm in NO WAY suggesting that it's AOK to start charging at a higher rate than recommended. What i'm inquiring is why it's never OK to charge at the same rate that it is OK to continuously discharge at ? Is it basically because most charging is always done indoors (even though the chance of a fire is no greater than when discharging a pack). Shouldn't need a more expensive BMS when it's already oversized to handle continuous discharge of 20A.

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Re: Continuous Charge Amp vs Continuous Discharge Amp

Post by john61ct » Aug 27 2020 6:06pm

All such ratings are pretty arbitrary, in a good company the engineers have most say, but marketing is usually powerful as well and a lot depends on the expected use case / audience, their expectations and what the perceived competition is advertising with their data sheets.

Good longevity requires a low C-rate in both directions, certainly well below 1C. Charging usually the prospective customer will be OK with a few hours' cycle, so the maker can afford to be more realistic there.

The absolute maximum discharge rate is much more likely to be exaggerated in fact to the point to be quite destructive if held for more than a second or so.

Since LG is a great maker and HG2s are a top notch model, you can truly discharge at more than 3C continuously, with brief peaks up to 10C

in real life, as opposed to the fantasies published for most other units.

A 0.4C charge rate should be the norm for longevity if you have time. Going over 1C won't "damage" the cells per se, especially if they are hot, but you will lose life cycles off the back end the colder they are the more lost.

The key difference between charge vs discharge is, within propulsion use cases, the market accepts the loss of lifespan as inevitable, most users feel they have "no choice"

and with flying that is actually true

But with charging thete is always the choice of owning multiple packs and swapping them out to get longer range.

And wrt your BMS comment, using that to regulate current but having it all go through the BMS itself is always a choice.

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Re: Continuous Charge Amp vs Continuous Discharge Amp

Post by eMark » Aug 27 2020 7:47pm

If a HG2 pack can be discharged at a 'conservative' continuous discharge rate of say 6A then it can also be charged at a charge rate of 6A. In other words as far as the battery pack is concerned it should make no difference to the cells.

So, in effect it's a trade-off between having a lower charge rate with a higher discharge rate to get the most number of usable charge/discharge cycles. What i don't understand is why LG has a Standard Discharge rate of only 0.6A instead of at least 1.5A, if not 3A. Doubt it's a typo misprint? Would a Standard Discharge of 1.5A or even 3A have that much of an adverse effect on cycle life longevity ?
Standard Discharge ... 0.6A (what i don't get is why it wouldn't be at least 1.5A, if not 3A)
Fast Discharge ... 10A
Max Continuous Discharge ... 20A
If the Standard Discharge is truly 0.6A then it would seem both the Fast Discharge and Max Continuous Discharge are actually overrated (for cycle life longevity). On one hand (0.6A) may be too conservative and on the other hand 20A may be too optimistic.

Is it the old proverbial go-around ... Figures don't lie, but liars can figure (when it comes to these data sheets and cycle life longevity). Is the real reason the Standard Discharge is only 0.6A (instead of 1.5A) is so LG can justify what is claims is their cycle life of HG2
Last edited by eMark on Aug 27 2020 8:00pm, edited 1 time in total.

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Re: Continuous Charge Amp vs Continuous Discharge Amp

Post by john61ct » Aug 27 2020 7:59pm


eMark wrote:If a HG2 pack can be discharged at a 'conservative' continuous discharge rate of say 6A then it can also be charged at a charge rate of 6A. In other words as far as the battery pack is concerned it should make no difference to the cells.
Why would you think so?

Again, you are killing off potential lifetime every time you go to high current.

If you have no choice, then so be it, just accept you need to replace the pack more frequently.

But what is the scenario for needing to charge over 1C? Every cycle?

> What i don't understand is why LG has a Standard Discharge rate of only 0.6A instead of at least 1.5A, if not 3A. Doubt it's a typo misprint?

Again, **all these numbers are arbitrary**, there is no magic hard "black and white" threshold, all the variables are grey-scale tradeoffs.

I think outside of high-current propulsion use cases, most people would expect a "standard" cycle to last at least 4-5 hours.

Don't you?

Maybe the just decided to highlight the lifespan tradeoff of high current rates

or wanted support for quoting (e.g.) 800 cycles to 80% EoL rather than 200.


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Re: Continuous Charge Amp vs Continuous Discharge Amp

Post by serious_sam » Aug 28 2020 5:06am

eMark wrote:
Aug 27 2020 7:47pm
If a HG2 pack can be discharged at a 'conservative' continuous discharge rate of say 6A then it can also be charged at a charge rate of 6A. In other words as far as the battery pack is concerned it should make no difference to the cells.
No.

Even though the chemical reaction is reversible, it isn't symmetrical. Charging and discharging put different stresses on the materials.

They're purposefully optimised for the discharge process, so the recharging process is compromised as a result.

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Re: Continuous Charge Amp vs Continuous Discharge Amp

Post by eMark » Aug 28 2020 1:09pm

john61ct wrote:
Aug 27 2020 6:06pm
All such ratings are pretty arbitrary, in a good company the engineers have most say, but marketing is usually powerful as well and a lot depends on the expected use case / audience, their expectations and what the perceived competition is advertising with their data sheets.
john should know better than trying to run that explanation ("arbitrary" meaning random, chance, hit-or-miss) past us for why "Standard Discharge" is only 0.2C. Here's the 18650 industry definition (non-arbitrary) of "Standard Discharge" when used in data specs by the major brands (e.g. LG Chem, Sony/Murata, Samsung) ...
“Standard Discharge” shall consist of discharging at a constant current of 0.2C to 2.5V. Discharging is to be performed at 23 °Celsius (73.4F) plus or minus 2 °C
So, my original question which john skirted is why such a low "Standard Discharge" rate (0.2C) when according to Serious_Sam's explanation logic should then say it should be higher than the standard charge rate of 0.4C-0.5C for 18650 lithium cells.
serious_sam wrote:
Aug 28 2020 5:06am
They're purposefully optimised for the discharge process, so the recharging process is compromised as a result.
If that's really true (i'm not saying it isn't) than why wouldn't the "Standard Discharge" spec used by the 18650 industry (0.2C) be even higher that the standard charge rate of 0.4C-0.5C (legitimate question)? If as Serious_Sam says that 18650 cells are optimized for the discharge process and the recharging process is compromised then why is the 18650 industry "Standard Discharge" at only 0.2C. However, being that the standard charge rate is higher than the standard discharge rate calls into question Serious_Sam's explanation.

LG HG2
Standard Discharge = only 600mA
Sony/Muriata VT6C
Standard Discharge = only 600mA
Samsung 30Q
Standard Discharge = only 550mA

Hopefully, Serious_Sam will explain what is different about an 18650 cell that it's more optimized to accept a higher discharge rate than a charge rate when the standard charge rate is 0.4C-0.5C while the standard discharge rate is only 0.2C

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Re: Continuous Charge Amp vs Continuous Discharge Amp

Post by Balmorhea » Aug 28 2020 3:42pm

I think the very low “standard discharge” rate is the one at which the battery displays the greatest mAh capacity and by which its claimed capacity is derived. If you really need it to deliver a full 3000mAh or more, that’s how fast you get to discharge it. For our purposes, this value is irrelevant.
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Re: Continuous Charge Amp vs Continuous Discharge Amp

Post by larsb » Aug 28 2020 4:01pm

@balmorhea :thumb:
Nailed it.

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Re: Continuous Charge Amp vs Continuous Discharge Amp

Post by john61ct » Aug 28 2020 7:56pm


eMark wrote:
john61ct wrote:
Aug 27 2020 6:06pm
All such ratings are pretty arbitrary, in a good company the engineers have most say, but marketing is usually powerful as well and a lot depends on the expected use case / audience, their expectations and what the perceived competition is advertising with their data sheets.
john should know better than trying to run that explanation ("arbitrary" meaning random, chance, hit-or-miss)
Not the meaning of arbitrary as I am using it.

I mean, there is no standard basis between makers that defines these numbers objectively. The company is free to choose a given rate spec over a wide range, without disclosing the parameters that affected their choice.
“Standard Discharge” shall consist of discharging at a constant current of 0.2C to 2.5V. Discharging is to be performed at 23 °Celsius (73.4F) plus or minus 2 °C
If you accept that definition then every battery with the same mAh capacity will have exactly the same discharge rating. Of course that gives you the answer to the question "where did LG get that number?"

But then you are acknowledging the number is irrelevant in trying to determine whether one battery model actually performs better than another.

A perfect example of exactly the meaning of "arbitrary" I meant, in the sense "they pulled the number out of their X", if it were "standardized" on 0.1C or 0.4C it would be just as useful.

In other words you got your answer, but the upshot is that spec can be ignored in comparing cells

> why wouldn't the "Standard Discharge" spec used by the 18650 industry (0.2C) be even higher that the standard charge rate of 0.4C-0.5C (legitimate question)?

Because it is an arbitrary spec, will always be proportional to energy capacity no matter how crappy the cell, IOW that spec has nothing to do with power capacity.

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Re: Continuous Charge Amp vs Continuous Discharge Amp

Post by john61ct » Aug 28 2020 8:08pm

In fact in the objective real-world performance tests conducted by expert members, it is very common for **much lower** (slower) discharge rates to be required in order to actually reach the vendor's claimed capacity number.

There is an inherent tradeoff in cell design, physical construction differences, between optimizing for high **energy** capacity and seeking a high power discharge rate.

In many cases "within 80-90%" of rated mAh capacity is considered "good enough" even for top performing cells in use cases where power is the factor considered top priority.
LG-HG2-3000mAh.jpg
LG-HG2-3000mAh.jpg (75.7 KiB) Viewed 488 times

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Re: Continuous Charge Amp vs Continuous Discharge Amp

Post by eMark » Aug 29 2020 1:10pm

Balmorhea wrote:
Aug 28 2020 3:42pm
I think the very low “standard discharge” rate is the one at which the battery displays the greatest mAh capacity and by which its claimed capacity is derived.
Isn't the greatest mAh capacity potential because the cell is drained as low as 2.0V, and not the rate of discharge whether 0.2C or say 0.5C ?
Balmorhea wrote:
Aug 28 2020 3:42pm
If you really need it to deliver a full 3000mAh or more, that’s how fast you get to discharge it.
Don't you mean how low you discharge the cells (2.0V vs 3.0V or 3.4V) instead of the rate of discharge (0.2C or 0.5C) ?
Balmorhea wrote:
Aug 28 2020 3:42pm
For our purposes, this value is irrelevant
For the purpose of this thread it's NOT irrelevant as no one discharges the cells in their pack as low as 2.0V or discharges at a rate as low as 0.2C (600mA - HG2). The whole purpose of docware's "ageing tests" ... viewtopic.php?f=14&t=103092 ... was to establish what docware felt was a more realistic/practical "Standard Charge" and "Standard Discharge" parameter for extending cycle life longevity before reaching 60% of a cell's mAh capacity ...
docware's parameter

charge 1A to 4.1V, 5 minutes wait, discharge 2.5A to 3.4V, 5 minutes wait. For "middle energy“ cells PF and 29E were discharge modified to 3.3V to keep the same DOD. In the hindsight discharge could be lower, maybe 2.2A .
What was docware's rationale for lowering (not faster, but slower) from 2.5A to 2.2A? How realistic is his "Standard Discharge" for cycle life longevity when ebikers "Standard Discharge" average is more likely somewhere between 5A to 10A (depending on amount of pedal assist)

So it doesn't hurt to first take another look at 18650 (and 21700) datasheets. A most extensive list is found at ... https://secondlifestorage.com/celldatabase.php ... however, even their figures aren't always the same as the manufactures datasheet. For example this website's extensive list shows the Sony/Murata VTC6 as having a "Standard Discharge" of 3000mA (1C), same as the "Standard Charge" of 3000mA (1C) ... https://secondlifestorage.com/showthread.php?tid=1698

Whereas, the actual Chinese VTC6 datasheet shows 0.2C for both (600mA) the "Standard Charge" and "Standard Discharge" (see 2.1) ... https://www.imrbatteries.com/content/so ... vtc6-2.pdf ... as also does ... this website's VTC6 datasheet ... https://lygte-info.dk/review/batteries2 ... %20UK.html ... indicating 0.2C (600mA) for both the "Standard Charge" and "Standard Discharge" for VTC6. ... but how practical is this when power tool cells are both fast charged (which i assume is above 1C) and fast discharged (which I assume is above 1C).

Its become evident that an ebiking "Standard Discharge" should be based on a more realistic/practical "SD" than 0.2C with "SC" of 0.5C and "SD" of 0.2C being somewhat of an 18650 industry norm. However, we all can agree 0.2C is not a realistic/practical ebiking "SD" as evident by our own ebiking and docware's own "ageing tests" parameter ... viewtopic.php?f=14&t=103092

So, getting back to LG Chem's HG2 (docware's "ageing" 3000mA winner) and two different HG2's datasheets ... https://secondlifestorage.com/showthread.php?tid=8388 (600mA "SD") and https://www.18650batterystore.com/v/fil ... _sheet.pdf (600mA "SD")

Charging: 4.2V Maximum
1500mA Standard Charge
4000mA Maximum Charge
Discharging: 2.00V Cutoff
600mA Standard Discharge
20000mA Maximum Discharge

NOTE: Maybe, Balmorhea can explain/justify why LG's HG2 Chinese datasheet shows a "SC" of only 0.2C ? There must be some logical reason ... it just can't be arbitrary.

My best guess as to why HG2's "SD" is less than half of the "SC" (600mA vs 1500mA) is because the "Cutoff" is at 2.00V. If the industry norm "Cutoff" were at 3.00V (or better yet 3.30V) wouldn't the "SD" be closer, if not the same, as the "SC" (0.5C or better yet 1C) ?

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Re: Continuous Charge Amp vs Continuous Discharge Amp

Post by Pajda » Aug 29 2020 2:01pm

eMark I hope you finally find the dependency or law what you looking for. I gave up this search a long time ago simply because I cannot find any generel rule.

Maybe you noticed common policy that in "product specifications" from all manufacturers there are very few information. I think that this is the exactly minimum amount of informations which is mandated by the authorities. Only if you are a big customer you can get the full "datasheet" from manufactuer with much more informations and test results.

And just small remark to the LG HG2. In its oficial product specification there is specified standard discharge also down to common value of 2.5V. The lower value of 2.0V is used for high discharge test with 20A. This is actualy safe because you are only compensating the HG2 cell DC internal resistance which is about 25mR, so at 20A it gives you DCIR voltage drop of 0.5V and so you are able to use 100% DoD as when discharging at standard rate of 600mA, where the DCIR voltage drop is negligible 0.015V. Also in cold conditions you can go even lower down to 1.5V.

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Re: Continuous Charge Amp vs Continuous Discharge Amp

Post by Balmorhea » Aug 29 2020 2:08pm

eMark wrote:
Aug 29 2020 1:10pm
NOTE: Maybe, Balmorhea can explain/justify why LG's HG2 Chinese datasheet shows a "SC" of only 0.2C ? There must be some logical reason ... it just can't be arbitrary.
The faster you discharge a cell, the less Ah capacity it delivers. Since the manufacturer rates a cell for capacity, they have to define the conditions under which it delivers that rated capacity. These conditions include fully charged voltage, end of discharge voltage, and discharge rate. My guess is that 0.2C is the fastest you can discharge that cell and still yield its maximum capacity.

This is the same reason why lead-acid batteries are specified for their capacity at C/20 or C/24 discharge rates. If you discharge them faster, they deliver much less energy.
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Re: Continuous Charge Amp vs Continuous Discharge Amp

Post by john61ct » Aug 29 2020 7:05pm

Is this the same guy with the "meandering strings" thread? Demanding tone rings a bell. . .

Obviously capacity is lower at higher current discharge! Peukert's Law. . .

Much more pronounced with lead chemistries, where they publish the various Ah capacities at multiple rates, the 20-hr one being the apples to apples standard. Same principle with LI though.

The **battery** industry is hardly going to go to any special "standards" efforts just for the teentsie tiny eBikes niche.

Certainly 99.99% of their usage cases are going to be much lower rates than 0.2C

And of course their marketing materials will go to a lower than usual definition of 0% to make capacity look bigger.

As I said, arbitrary.

Look to the gods like Pajda for more objective information, thank you sir for all your work for the community!

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Re: Continuous Charge Amp vs Continuous Discharge Amp

Post by eMark » Aug 30 2020 11:38am

Like Padja and john61ct have stated/implied it's just too complex other than to say that as a general rule the 18650 industry norm of 0.5C (Standard Charge) and 0.2C (Standard Discharge) is what manufacturer's use for determining a cell's "typical nominal" capacity ...
The capacity of a cell depends on the charge-discharge current if the testing is done galvanostatically. Therefore, you will not get the same value if you test the cell at different current values. First of all, you have to calculate the theoretical specific capacity of the cathode material. Then you will be able to calculate the theoretical specific capacity of your cell (this is dependent on the amount of the cathode material you use in your cell). This will give the theoretical current value to charge or discharge the cell in 1 h which means to say that this is the amount of current to use if you want to charge-discharge the cell at 1 C rate.
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Serious_Sam previously indicated that the inherent nature of any 18650 pack (e.g. 12S6P HG2) favors a higher rate of discharge than it does a higher rate of charge when it comes to cycle life longevity maintaining as much capacity as possible until finally reaching 60% of useful capacity ...
serious_sam wrote:
Aug 28 2020 5:06am
Even though the chemical reaction is reversible, it isn't symmetrical. Charging and discharging put different stresses on the materials.

They're purposefully optimised for the discharge process, so the recharging process is compromised as a result.
However, Balmorhea's reasoning seems more justified for why the general 18650 (and 21700) industry norm is: 0.5C (Standard Charge) and 0.2C (Standard Discharge) ... seemingly favoring the charge side (0.5C) over the discharge side (0.2C) ...
Balmorhea wrote:
Aug 29 2020 2:08pm
The faster you discharge a cell, the less Ah capacity it delivers. Since the manufacturer rates a cell for capacity, they have to define the conditions under which it delivers that rated capacity. These conditions include fully charged voltage, end of discharge voltage, and discharge rate. My guess is that 0.2C is the fastest you can discharge that cell and still yield its maximum capacity.
OK, guys here's what's still puzzling about the physics of it all. Assuming that Balmorhea's explanation is true (and we have no reason to think otherwise) then it would seem the physics of it all is purposefully optimized more for charge side than the discharge side for obtaining the rated mAh capacity (3000mAh) whether HG2, VTC6, 30Q ("Standard Charge" 0.5C and "Standard Discharge" 0.2C). As Padja says trying to explain the 18650 industry's reasoning why they favor a higher "SC" of 0.5C than they do a lower "SD" of 0.2C is next to "Mission Impossible" using a higher charge side (0.5C) norm when determining the "typical nominal" cell capacity. You'd think both sides would be the same "SC" 0.2C and "SD" 0.2C, but then what do i know.

Is it really beyond our understanding or even interest in this "Battery Technology" forum composed of some of the brightest most inquisitive minds in any Battery Technology forum on planet earth?

Would be interested in docware's take. Does anyone remember a thread where docware might have expressed his opinion why the industry norm of "Standard Charge" is higher (0.5C) than the "Standard Discharge" (0.2C) for arriving at a cell's "typical nominal" capacity?

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Re: Continuous Charge Amp vs Continuous Discharge Amp

Post by john61ct » Aug 30 2020 1:36pm

I do not think anything here is that complex. Just do not rely on data sheets for your care parameters, simple.

A capacity test rate of 0.2C will always yield a lower mAh number than say 0.02C, but with the latter, prospective buyers will complain it is an "artificially" low rate, as if the vendor is "cheating" to get closer to their rating.

So an industry defined "standard" of 0.2C is just to give a reasonable apples-to-apples comparison between brands

there is no "objective" reason to choose that number, compared to say 0.1C or 0.3C

which is my meaning when I say it's an "arbitrary" choice.

eMark wrote:You'd think both sides would be the same "SC" 0.2C and "SD" 0.2C, but then what do i know?
No, I would never have thought that, not sure where you got that notion.

> why the industry norm of "Standard Charge" is higher (0.5C) than the "Standard Discharge" (0.2C) for arriving at a cell's "typical nominal" capacity

Charging is not used to arrive at a capacity number, only discharge is relevant to determining that.

> Is it really beyond our understanding or even interest in this "Battery Technology" forum composed of some of the brightest most inquisitive minds in any Battery Technology forum on planet earth?

Pretty grandiose for an abstract question, just theoretical, not that relevant to IRL battery care and IMO not interesting.

Nominal capacity to three digit accuracy is not important IRL, you're overthinking all these "spec issues", what is actually important is very simple:

if you prioritize longevity, stay well away from the "maximum stress" voltages used in the specs, and keep current C-rates as low as is practical (by increasing pack Ah capacity) for your use case.

Nothing "favors a higher rate of discharge", unless you are now acknowledging that proper care means slower C-rates in general, and especially in charging, where going to high rates is usually not as necessary.

But if you are **required by your use case** to discharge at say 5C rates or higher for more than a few second bursts,

then if slow charging is inconvenient for you (need to own more packs),

then don't go to that trouble, you probably aren't extending lifespan much anyway.

If your use case allows nice low discharge rates, then also charging slowly will have a much greater relative impact on longevity.

Same with capacity utilization, high-current abuse will greatly reduce the positive impact of going to 4.15V stop-charge compared to 4.2






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Re: Continuous Charge Amp vs Continuous Discharge Amp

Post by Pajda » Aug 30 2020 1:44pm

eMark it is good to realize that the information given in the datasheet may not be directly related to the theoretical laws of operation of the cells. So as was previously mentioned, it is very likely that the value of 0.2C for standard discharge was historically "shot from the side". The 0.2C SD value is in use for lithium cells more than 10 years and I think that it was used for direct comparison with the latest industrial NiMh cells. However, the point is that any value could be chosen (eg. 0.1C or 1C) but the most valuable thing is that the choses value is respected across the manufacturers! Also there is a simple commercial view. Yes new lithium cells can easily handle 1C as SD but what do you choose to advertise 3000mAh at 0.2C or 2950mAh at 1C discharge rate? So even if you have cell with low DCIR you still lose some mAh at higher discharge rate.

But the standard charge rate is different story! Firstly, the 0.5C value is not standardized at all, many cells have 0.3C value and you can find cells with higher value like 1C as well. The practical issue is that if cell is capable of faster charging, you will not lose any mAh, you just lose some efficiency (nobody cares) and so we are back at the simple commercial view, where you are shortening the charging time without any loss.

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Re: Continuous Charge Amp vs Continuous Discharge Amp

Post by eMark » Aug 30 2020 6:59pm

Pajda wrote:
Aug 30 2020 1:44pm
eMark it is good to realize that the information given in the datasheet may not be directly related to the theoretical laws of operation of the cells. So as was previously mentioned, it is very likely that the value of 0.2C for standard discharge was historically "shot from the side".
What i'm getting at in all this is that instead of "theoretical (manufacturer's) laws of operation of the cells" i'm coming from the angle of "practical use (ebiking) of operation of the cells" when attempting to estimate the approximate "compromised" nominal capacity of a new pack without having to use a watt meter when ebiking (which i've done for curiosity).

First let's use docware's "ageing test" parameter for energy cells like HG2 and 29E that's a more practical parameter than the aforementioned manufacturers SC/SD (e.g. SC 0.5C / SD 0.2C with 2.0V to 2.5V Cutoff) ...
docware's parameter:
charge 1A to 4.1V and discharge 2.5A to 3.4V. For "middle energy“ cells PF and 29E were discharge modified to 3.3V to keep the same DOD. In the hindsight discharge could be lower, maybe 2.2A.

Note: IMO, this charge and discharge parameter is not realistic for ebikers; especially the discharge parameter. As another member stated ebikes need 4A discharge just to get traction.
Here's a more realistic ebiking charge/discharge parameter ...
charge 2.0A to 4.1V / discharge 5.0A to 3.4V-3.3V Cutoff
Can you copy and paste a graph from docware's "ageing tests" ... viewtopic.php?f=14&t=103092 ... that shows the "compromised nominal capacity" (first few cycles with new cell) of LG Chem HG2 (3000mAh rated) and that of Samsung 29E (2900mAh rated) ?

What's your best guess from docware's graphs as to the approximate loss (compromised nominal capacity vs manufacturer's ideal nominal capacity) of a new cell using docware's SC/SD parameter?
  • The datasheet SC for HG2 is 0.50C (1500mA) to 4.20V and SD is 0.2C (600mA) to 2.0V Cutoff to achieve manufacturer's "typical (ideal) nominal capacity" of 3000mAh.
  • The datasheet SC for 29E is 0.47C (1375mA) to 4.20V and SD is 0.19C (550mA) to 2.5V Cutoff to achieve manufacturer's "typical (ideal) nominal capacity" of 2900mAh.
What's your best guesstimate as to the even greater compromised (diminished) nominal capacity of these two cells after say 400 cycles (HG2 and 29E) using the following more realistic ebiking parameter compared to docware's charge/discharge parameter ...
Charge 2A to 4.1V and Discharge 5.0A to 3.4V
In your best guesstimate would both these packs (12S6P) have already reached 60% of what's considered useful capacity with the above parameter before even reaching 400 charge/discharge cycles (assuming no pack abuse). Another best guesstimate question: Would a 12S6P (either HG2 or 29E) have a better chance of getting 400 usable cycles than a 12S3P pack with the above parameter or is the size of the pack irrelevant ?

larsb   1 MW

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Re: Continuous Charge Amp vs Continuous Discharge Amp

Post by larsb » Aug 31 2020 1:43am

@emark: It seems to me you think you are on to a great discovery, and your tone is annoyingly demanding.

You’re not in any way breaking new ground and the cell manufacturers are not deceiving you. The truth is simple: you can charge at higher charge rate since normally datasheets doesn’t show the charging efficiency. The added RI2 losses from higher charge amps therefore doesn’t show. It will cost some lifetime. (Saw now that Pajda already stated this)

On the discharge side of things it’s the opposite, the shown nominal capacity is heavily affected by current in RI2 losses. I can’t be bothered to see if it’s been mentioned already in the thread since i'm on my phone but you can check https://lygte-info.dk/ where any test will show the effect of higher current on capacity.

Then for the lifetime: i’ve seen a lot of lifetime graphs in datasheets for higher discharge than 0.2c
Some cells have it, some cells don’t. Bottom line is that they all suffer from shortened lifetime at higher current.

Moving on..

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Re: Continuous Charge Amp vs Continuous Discharge Amp

Post by eMark » Sep 01 2020 5:49pm

larsb wrote:
Aug 31 2020 1:43am
You’re not in any way breaking new ground and the cell manufacturers are not deceiving you.
Never implied I was. No they're not deceiving me or you, but that's not to say they aren't misleading others, both newcomers and others that have been around the block a few times.

It's been put forth in this thread by others that the reason the Standard Discharge is so low at .2C with a Cut-off as low as 2.5V is to achieve the manufacturer's nominal rated Ah capacity when charging, or at least achieve the minimal rated Ah capacity. Think you might agree the datasheet "Standard Discharge" of .2C with 2.5V Cut-off is not realistic/practical for ebiking. At least VTC6 has both "Standard Charge" and "Standard Discharge" at 1C (3 amps). A "Standard Discharge" of only 3 amps with a 2.5V Cut-off isn't realistic for ebiking. Maybe Ok for a bike light :wink:

Of the ten ageing tests by docware nine of them were the Standard Charge of .5C and Standard Discharge of .2C with Cut off at 2.5V . The only exception was VTC6 with 1C for both SC & SD. HG2 and 30Q datasheets are SC .5C & SD .2C that is an industry norm of sorts for the majority of 18650 cells. Docware's ageing test parameter of only charging to 4.1V and discharging to 3.3V-3.4V is common sense for prolonging the manufacturer's minimal Ah capacity rating before reaching 60% of its capacity.

Yes, there may be some deception if Standard Discharge has to be as low as .2C with Cut- off as low as 2.5V in order to achieve the manufacturer's rated nominal cell capacity when charging ... AND ... obtain the manufacturer's suggested charge/discharge cycle life with a SC of .5C and SD of .2C with Cut-off as low as 2.50V. How many ebikers do you know charge discharge their pack no higher than 1C or charge at .5C from the time the battery is new.

I've balance charged my 10S3P pack at .5C ever since it was new. Figuring 8.4Ah with 10S3P-30Q when new (2800mAh cell instead of 3000mAh cell) with SC .5C to 4.1V with average SD 2C to 3.4V). After 120 charge/discharge cycles currently at 7.5Ah = 89% capacity figuring 8.4Ah when new (10S3P-30Q). My 10S Controller Cut-off is at 32.25V with bounce back to 33-34V.
larsb wrote:
Aug 31 2020 1:43am
Then for the lifetime: i’ve seen a lot of lifetime graphs in datasheets for higher discharge than 0.2c
Have you ever seen a Panasonic, Sanyo, Samsung, or LG Chem datasheet with a Standard Discharge higher than 1C ? What is misleading (and deceiving) is the word "Standard" when referring to discharge rate whether for ebiking or a power tool.

VTC6 3000mAh capacity with 1C Standard Discharge of 3 amps. There is nothing "standard" about even 1C (3amp) discharge when it comes to ebiking (or a power tool), and as far as a .2C discharge that's laughable. So, yes there is datasheet deception because ebikers won't get the rated datasheet nominal Ah capacity even with a SC of 4.2V, and 3.4V Cut-off. Yeh, there are always exceptions, but for how long?

Which is better: SC of 4.20V and 2.50V Cut-off ... OR ... SC of 4.11V and 3.20V Cut-off

larsb   1 MW

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Re: Continuous Charge Amp vs Continuous Discharge Amp

Post by larsb » Sep 02 2020 12:25am

..when it comes to ebiking
That’s why there are tons of specific use tests going on, like pajda here, mooch in the vape community or users at budgetlightforum, lygte-info and all others

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Re: Continuous Charge Amp vs Continuous Discharge Amp

Post by john61ct » Sep 02 2020 2:19am

Just forget "standard" in your vocabulary Mark

Nobody cares about these "standards" once they have selected their cell, and neither should you, all this overthinking about a non issue is just a waste of time.

The data sheets are not intended to have anything to do with ebikes, the makers do not know nor care about the eBike market.

It is up to each of us to decide what **our** standards are. So you decide on your priorities, and set your Ah capacity according to the C-rates you consider appropriate for your use case.
eMark wrote:Which is better: SC of 4.20V and 2.50V Cut-off ... OR ... SC of 4.11V and 3.20V Cut-off
Take the SC out, meaningless here.

Yes there is some longevity benefit to going to 4.10V or 4.15V rather than 4.2

But not nearly as much as a lower avg DoD%, leaving in an extra 5-10% can double / triple cycle lifespans.

And **how long you sit** at high SoC is more important than the charge termination point, shorter the better.

2.5V is just stupid crazy way too low, unless the discharge rate has to be so stupid crazy high, that you see a bounceback all the way to 3.2V or higher at rest.

LVC cutoff point is meaningless without the discharge C rate, or benchmarking against the recovered resting voltage after an hour isolated.


eMark   100 W

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Re: Continuous Charge Amp vs Continuous Discharge Amp

Post by eMark » Sep 02 2020 2:04pm

larsb wrote:
Sep 02 2020 12:25am
...when it comes to ebiking
That's my point larsb. It's obvious to me that these 18650 datasheets are aimed more at the medical field than DIY ebikers. I thought my now one of you guys would have made mention. Even the high energy cells like VTC6 and others for power tools will show a higher Standard Charge of 1.36C and higher Standard Discharge of 5C (A123). It's possible these are also more realistic when it comes to ebikers more demanding use (e.g 3C discharge), than even VTC6's modest spec with only 1C for both Standard Charge (SC) and Standard Discharge (SD) .
larsb wrote:
Sep 02 2020 12:25am
There are tons of specific use tests going on, like pajda here, mooch in the vape community or users at budgetlightforum, lygte-info and all others
You can add my 10S3P 30Q (141 cell) specific :wink: test pack that can be easily split into two 5S3P packs and paralleled for balance charging with my old 2S-6S (i balance charge at .5C with P-groups variance of 4mV). Maybe, Pan, Sam and LG are just too conservative for the realistic/practical demands of most ebikers (e.g. 1.3C charge & 3C discharge). IF only ...

... maybe why some DIY ebikers use Lipo pouches is they like what they see on the label :wink: ... better yet buy ten Venom Fly 30C 3S 3200mAh 11.1V LiPo $38.99 ea :wink: :wink: :wink:
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john61ct   100 GW

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Re: Continuous Charge Amp vs Continuous Discharge Amp

Post by john61ct » Sep 02 2020 2:53pm

Again you insist on obsessing about "standard" discharge

when that is a useless spec for your context and NOTHING TO DO WITH the cell's ability to handle usage at higher rates!

They are not targeting medical applications any more than flashlights or solar powerwalls

batteries are general purpose.

eMark   100 W

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Re: Continuous Charge Amp vs Continuous Discharge Amp

Post by eMark » Sep 02 2020 7:57pm

maybe write letters to Samsung, LG Chem, Sony/Murata, Panasonic and other manufacturers of 18650's telling them to remove Standard Charge and Standard Discharge from their 18650 datasheets as it's "arbitrary" :wink: ... just list maximum charge and maximum discharge :lowbatt: ... but then that's also "arbitrary" :lol: :lol: :lol:

... moving on :thumb:

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