Li-Ion Cell/battery capacity

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#1
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Greets!

 

I was talking with a colleague about a project he is working on, specifically it's power supply...in this case a single Li-Ion cell.  he was telling me that Li-Ion cells only have about 60% of the rated capacity.  I completely disagree with this on so many levels as it is my understanding that you should store Li-Ion cells at 60% of their rated charge, but if one is getting only 60% of the rated capacity then one is buying defective, or mis-marked cells, and that it would be foolish for a manufacturer to mark a cell higher than it actually is.  My colleague seems un-deterred though.

 

Upon inspecting one of the cells he sent me it says "Tenergy" on the side and 1400mAh, and the heatshrink around the cell looks the same as what I see on the website, but a good copy can be hard to spot. 

 

http://www.tenergy.com/30036-1

 

I have not taken the time to do any testing on it, but I do wonder if the cell is an Ebay special.  I have been using "Turnigy" packs I purchased from Hobby King with a rating of 2.0Ah/3.7v and the runtime I am getting matched my calculations pretty well.

 

I am thinking the cell is defective, or counterfeit. 

 

So the question is what would be considered an acceptable tolerance for actual capacity compared to rated capacity on the cell?  I would say 10% to 95%, but I think that's being generous.

 

Thoughts on this welcome.

 

JIm

If you want a career with a known path - become an undertaker. Dead people don't sue! - Kartman

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB user

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Sounds like he found a bargain on used Samsung G S7 batteries!  smiley

I wouldn't want to charge those past 60% either.....

 

Jim

 

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jgmdesign: "I am thinking the cell is defective, or counterfeit."

 

By measuring the weight, it can be found that the batteries are counterfeit or not.

Last Edited: Fri. Aug 4, 2017 - 01:45 PM
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Goorman wrote:

jgmdesign: "I am thinking the cell is defective, or counterfeit."

 

By measuring the weight, it can be found that the batteries are counterfeit or not.

 

I have heard of this as well. 

 

ki0bk wrote:

Sounds like he found a bargain on used Samsung G S7 batteries!  smiley

I wouldn't want to charge those past 60% either.....

 

Jim

 

I don't think I follow you on this.....  Ahh..Upon a Google, I see what you mean about the battery.  I was referring to the cell itself.

 

Jim

If you want a career with a known path - become an undertaker. Dead people don't sue! - Kartman

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB user

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All LiIon batteries (well, in the small sizes, anyway), suffer a gradual loss of capacity with each recharging cycle. I am told that the manufacturers call "end of life" to be the point where the capacity has dropped to 60% (or some number like that) of the rated capacity. You, as the designer, need to take this drop in capacity into account, especially since the number of full charge/discharge cycles needed to reach it is only a few hundred. 

 

This might, or might not, be related to "new" batteries (that might not be so new) only having a fraction of their rated capacity.

 

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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I only have info as a "consumer", in that I got a game camera last year and did some Internet research.

 

I don't have any numbers to share.  All "Tenergy" are not created equal, right?

 

Is this AA sized?  1400 is pretty low.  I remember from my research that there were/are some tradoffs with the highest mAH offerings -- is it recharge count?

 

A quick educational search shows that there are different chemistries

http://batteryuniversity.com/lea...

and build structure -- some are "prismatic" and others are [I forget -- "stacked"?].

 

This person did fairly extensive tests with a variety of brands and capacities.  There are charts for size and weight along with capacity.  The 2010 set of data has a Tenergy model 

http://www.candlepowerforums.com...

but not the later and more extensive 2012 tests

http://lygte-info.dk/review/batt...

 

I didn't count them but there must be over 100 entries.  Scrolling down, indeed weight differences are seen.  But to get to what I think is the crux of the post:

jgmdesign wrote:
he was telling me that Li-Ion cells only have about 60% of the rated capacity.

 

So look at the discharge tests, done at several draw rates.  Indeed, some brand/model combinations do end up much lower than the nominal mAH.  But many of the models are very close.

 

Note also that the test result charts have several "trip points".  I think the first discharge is to 2.8V; others to 3.0 and 3.2.

 

In the excerpt below, some get quite close to rated; some not so much.

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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I fly 3D planes and helis where every last mAh matters because we generally get these batteries to dump their load at 10C, 20C or even more. For example if you have 550mAh then that should supply 550mA for an hour right? But 550mA is just "1C". In a plane you might use 10C (so a 5.5A discharge) or even 20C (a 11A discharge). Let's say you go for 10C (and maybe 2S so 7.2V) . So you are using 7.2V * 5.5A = 40W. 40W is enough to give a 100g..200g plane "sprightly"performance.(*) But the point here is that instead of 550mA for 60 minutes you are dumping the current at 10X the per hour rate so it will last 1/10th of an hour. So that means a 6 minute flight (and a 20C load will dump everything in 3 minutes). At these short flight times a minute either way is pretty noticeable. If the battery only gave 60% then your 6 minutes would be 3.6 minutes and you would notice!

 

I use "quality" cells from the likes of Hobby King ("Turnigy" etc) and on the whole these things live up to published performance or even exceed it. So, no, on the whole you would expect 100% of stated capacity.

 

(flying planes is a fun way to test battery capacities very quickly).

 

I usually take 6 .. 10 packs along with me which is enough to keep things going for an hour or more. The downside is that you can't charge at the same 10C..20C high rates as discharge so what comes out in 6 minutes can take the best part of 30mins to an hour to put back if you only charge at 1C .. 2C.

 

(*) 100W/lb is considered a "sweet spot" so that is 100W / 454g which 40W / 181g. I try to fly about 140..160g in fact using 550mAh packs. The battery pack alone is about 30g of that.

Last Edited: Fri. Aug 4, 2017 - 03:22 PM
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BTW the link in #1 is a LiIon "cell". I think it could be different for LiPo which I believe are "more efficient" and "energy dense".

 

I just checked the packs I use and they are actually Turnigy "nano-tech" 460mAh (25C-40C discharge), 2 cell 7.4V:

 

https://hobbyking.com/en_us/turn...

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I've seen sand filled "power banks" on youtube to upp the weight. I think it was from the entertaining BigClive.

Personally I've had bad experiences with Ai Specials. They work reasonably when new but loose almost all capacity after half a year.

 

For tolerances on capacity and reccomende charge / discharge levels etc.

Well, you're an engineer. Get a datasheet. Batteries have datasheets, just like uC's, transistors, resistors and anythink else electronic.

Shove the datasheet in the face of your colleage and if he refuses to believe that I proclaim him to be an idiot and you should ignore him for at least a week.

 

Paul van der Hoeven.
Bunch of old projects with AVR's:
http://www.hoevendesign.com

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Paulvdh wrote:
Well, you're an engineer. Get a datasheet. Batteries have datasheets, just like uC's, transistors, resistors and anythink else electronic.

 

I have and I have also shown my colleague, who I think just does not want to admit he was/is wrong. wink

 

clawson wrote:
I fly 3D planes and helis where every last mAh matters because we generally get these batteries to dump their load at 10C, 20C or even more.

My son and I run R/C trucks and the difference in the draw on the cells between a T-20 motor, and a T18 is very noticeable.  Cannot wait to see what happens with a T-12!

 

clawson wrote:
So, no, on the whole you would expect 100% of stated capacity.

I would expect 100% on a brand new cell, but I usually assume 95% but in a few cases a little lower.

 

ka7ehk wrote:
All LiIon batteries (well, in the small sizes, anyway), suffer a gradual loss of capacity with each recharging cycle.

I would say that to be true of any rechargeable.  But not as large a loss per recharge for the Li-Ion

 

ka7ehk wrote:
I am told that the manufacturers call "end of life" to be the point where the capacity has dropped to 60% (or some number like that) of the rated capacity.

Thats a pretty big loss to consider a cell/pack EOL.  But hey, it's their spec.

 

theusch wrote:
Is this AA sized? 1400 is pretty low.

No, I posted a link to the cell in the OP.

 

Some good information in those links Lee, I will forward them on, Thanks!

 

Jim

If you want a career with a known path - become an undertaker. Dead people don't sue! - Kartman

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB user

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clawson wrote:
But 550mA is just "1C".

In my poking around I thought I saw a 1C limit somewhere for lions.  Your tigers may be different.  Can't remember which page it was on...

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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ka7ehk wrote:
... especially since the number of full charge/discharge cycles needed to reach it is only a few hundred.
An order of magnitude greater and can be recharged below freezing :

Tadiran Batteries

TLI SERIES 
Industrial Grade Rechargeable Lithium-ion (Li-ion) Batteries

http://www.tadiran.com/tli-rechargable.html

 

"Dare to be naïve." - Buckminster Fuller

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Paulvdh wrote:
Batteries have datasheets

Indeed.

 

And the datasheet will be very specific on how, exactly, they define "capacity" - and the conditions of its measurement.

 

If you try to test "capacity" under significantly different conditions & limits from the datasheet, it is quite likely that you will get a different answer ...

 

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Paulvdh wrote:
Shove the datasheet in the face of your colleage

and, conversely, get him to show his sources for his allegation!

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69

Paul van der Hoeven.
Bunch of old projects with AVR's:
http://www.hoevendesign.com

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 ... or a 'g'