Author Topic: EEVblog #393 - LiPo Battery Discharge Testing  (Read 28523 times)

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Offline EEVblog

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #25 on: December 02, 2012, 11:29:25 am »
Given the above and the cost of the batteries and this application, is even a potential 20% reduction in capacity over the 1st year a significant concern?

Not a huge concern, if that's the actual figure.
Some people and places have mentioned dangers from doing this, which I doubt in practice is a huge deal, based on the massive size of the RC market.
But once again, I'd like to see definitive data from a reputable source?
If an extended capacity mobile phone battery is a similar cost, potentially less dangerous, and similar capacity (after not needing reduced storage) that might be a better solution?
I see some 10000mAh portable battery phone charger packs on ebay...

Dave.
 

Offline ecat

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #26 on: December 02, 2012, 11:37:55 am »
Not a huge concern, if that's the actual figure.

The Battery University has been recommended as a reliable source of information, though I cannot comment on the knowledge set of those providing the recommendations... <sigh> Why internet, why?

http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries

Some people and places have mentioned dangers from doing this, which I doubt in practice is a huge deal, based on the massive size of the RC market.
But once again, I'd like to see definitive data from a reputable source?
If an extended capacity mobile phone battery is a similar cost, potentially less dangerous, and similar capacity (after not needing reduced storage) that might be a better solution?
I see some 10000mAh portable battery phone charger packs on ebay...

Dave.

I guess the standard internet rule applies:
1) If 99.99% of random posters claim the same fact then accept it as a possibility but do your own research ;)
2) If 0.001% of random posters claim a fact and provide a link to research material then accept it as a possibility but investigate the source of the research and do some research of your own !
3) Do not believe anything you read on the internet.

Edit:
Do I think there is anything special  about the relevant chemistry of mobile phone batteries? No.
Do I think there is anything magical about the protection circuitry? No.
Do I think a cheap ebay battery marketed towards the general mobile phone buying public will be inherently better quality or more safe than a branded RC battery? No.

... but I am open to persuasion
« Last Edit: December 02, 2012, 11:56:16 am by ecat »
 

Offline Mikey

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #27 on: December 02, 2012, 11:47:49 am »
You got inverted text behind the buttons!!! I was almost losing my will to live while trying to get eagle to do that! :-\

Also Dave, I can make you some adabters for your load so you can put those plugs in, I just need the measurements...
« Last Edit: December 02, 2012, 11:49:52 am by Mikey »
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Offline EEVblog

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #28 on: December 02, 2012, 11:51:34 am »
Not a huge concern, if that's the actual figure.

The Battery University has been recommended as a reliable source of information, though I cannot comment on the knowledge set of those providing the recommendations... <sigh> Why internet, why?

http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries

Yes, I consider Battery University a reputable source.
But they don't mention these specific high discharge capacity LiPoly cells, which is what the issue supposedly is with.
With standard discharge capacity batteries I would not worry about this at all.

Dave.
 

Offline Baliszoft

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #29 on: December 02, 2012, 11:58:03 am »
Are those batteries bundled with a protection circuit of some kind (temperature e.t.c.). Can someone access the the data?

Are batteries for famous tablets/readers available and suitable for your needs?

Alexander.

na, RC batteries have no protection. It's almost impossible to have protection when you have legitimate loads of up to 200A.

And any protection would degrade performance big time. Noone would use a battery (or motor controller) with any kind of voltage drop caused by the protection circuit.
 

Offline Bloch

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #30 on: December 02, 2012, 12:41:38 pm »
How do you mount wires on the battery. Is it possible to solder direct to the "foil" ?
 

Offline king.oslo

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #31 on: December 02, 2012, 01:38:49 pm »
Thanks Dave! It is great to see some progress on the supplies. I have sometimes forgot my AC plugpack for something at home. They are often a couple of amps(, up to ~20V for laptops.) It would be great if this item could fill that void. So when you look at which regulators you can get, it would be nice if you keep my experience in mind. Thanks.M
 

Offline Kevin.D

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #32 on: December 02, 2012, 03:13:32 pm »
I dont like Lithium  based batteries at all now for things that are occasionally used, because of there bad loss of capacity with age even if they are not used,they work out much much more expensive than other  batteries . I discovered my li-ion batteries for my recharchable drill which doesnt get used very often (about once a month on average) had lost about 55% of it's capacity in two years  since i bought it .
In comparison I  have some rechargable hybrid NIMH  batteries (sanyo eneloop) that I have that have been used about twice  a month   now for over 3.5 years and they have hardly lost any of there original capacity as far as I can measure . Anyway  These look to win on cost  easily  over lithium based batteries ,they could potentially last many years ,I dont know.
« Last Edit: December 02, 2012, 03:44:57 pm by kevotronic »
 

Offline T4P

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #33 on: December 02, 2012, 03:30:24 pm »
"Hybrid" There's such thing as a hybrid battery  :o
Anyway, lithium batteries have shelf lifes and NiMH have short service lifes if brought above 42C which is quite common in drills due to having lower discharge ratings  :-+
 

Offline Kevin.D

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #34 on: December 02, 2012, 04:00:30 pm »
"Hybrid" There's such thing as a hybrid battery  :o

Well "hybrid" NiMH is  what the inventors Sanyo marketed them as  ,others companies are marketing them also now,  some as low self discharge or "LSD NIMH" , (which are mostly sanyo's batteries rebranded, according to some websites).
 

Offline free_electron

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #35 on: December 02, 2012, 05:18:49 pm »
keep the display horizontal

Code: [Select]
   
USB  | disp |     rotary encoder    | pushbutton   | terminals

rotary encoder : push to toggle between current and voltage. spin to alter.
single pushbutton : output on/off

having a long horizontal stick allows you to put it sidewayson the bench. you can stack mulitple ones. vertical is not so handy.. it'll topple over.
Professional Electron Wrangler.
Any comments, or points of view expressed, are my own and not endorsed , induced or compensated by my employer(s).
 

Offline muvideo

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #36 on: December 02, 2012, 07:41:04 pm »
Hello Dave, now I want to see the 5Ah cell tested to full 20C  specs ;)

As for the storage, I have read about the problem somewhere,
but now I cannot find any reliable source, but also I could not
find any reliable info about the real difference betweeen the high
rate RC so-called li-po and the low rate normal li-ion cells.

What could be a decent protocol if one would try to make own
aging tests?

I was thinking something like n groups for n test voltages,
each group will be maintained at the test voltage, periodically
part of the cells in group will be tested with a pair of
charge-discharge cycles, and restored to the voltage it had
before the last test. Each group could be 2 or more cells.

A possible scenario could be:
Initial stabilization of 20 cycles to full capacity,
3 groups 2 cells each, 3 voltages: 4.2 4.05 3.9V
every month one cell per group will be tested for residual
capacity and full capacity, and then recharged to the same
voltage it had before the last test.
In one year, half of the cells will experience 24 cyles and
half will be tested only in the beginning and in the end of
the test, so we could try to separate the cycling effects
from the plain aging effects.

Minimum requirements: 6 cells, and one year of time :)

Fabio.

edit:
Dave, reading the comments on youtube, big
single cell Li-iron cells can be found around,
cylindrical and prismatic, in eu there is ev-power.eu
« Last Edit: December 02, 2012, 07:48:19 pm by muvideo »
Fabio Eboli.
 

Offline EEVblog

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #37 on: December 02, 2012, 09:56:18 pm »
Dave, reading the comments on youtube, big
single cell Li-iron cells can be found around,
cylindrical and prismatic, in eu there is ev-power.eu

LiFePO4 would be nice, but the charger chips are not cheap and plentiful like LiIon/LiPoly

Dave.
 

Offline NickS

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #38 on: December 02, 2012, 11:23:33 pm »
But they don't mention these specific high discharge capacity LiPoly cells, which is what the issue supposedly is with.
With standard discharge capacity batteries I would not worry about this at all.
I was actually under the impression that all LiPo batteries preferred 40 - 70% charge while in storage, even mobile phone and laptop batteries.
No one does it for mobile phones and laptops however because that kind of defeats the purpose of having a mobile device.
 

Offline muvideo

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #39 on: December 03, 2012, 12:38:45 am »
I did a quick search on the net, apart from batteryuniversity I found few references,
for example these:
http://www.rathboneenergy.com/articles/sanyo_lionT_E.pdf pag.8
http://chglib.icp.ac.ru/subjex/2012/pdf05/ElectrochActa-2010-55(3)927.PDF
http://www.che.sc.edu/faculty/popov/drbnp/WebSite/publications_pdfs/web21.pdf

Seem that the aging is mainly determined by the storage temperature,
and less by SOC (voltage), the effect is there but less than temperature.

Also, we should keep in mind that the high rate RC cells after all are
low cost-high performance cells, this should come at a cost and the
cost probably is aging performace. I'm telling this because
I'm also interested in Li chemistry for long term use,
recently I made some tests and in one it was easy to spot the cycle
by cycle aging of the RC cells, I made also a post about it somewhere
here.

Reading the marketing material of the "big" li-ion manufacturers seem
to suggest that they are working on the cycle life, and the latest cells
are charged to 4.35V, instead of the usual 4.2. To me this sort of
confirms that the li-ion chemistry is damaged by high voltages, and
the manufacturers are trying to solve also this problem
(higher voltages means also higher capacities):
http://samsungsdi.com/battery/cylindrical-rechargeable-battery.jsp

I hope we can find more info because the li-ion costs are coming
down to the point we will use them more frequently than Pb or Ni chemistries.

Fabio.
Fabio Eboli.
 

alm

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #40 on: December 03, 2012, 12:43:50 am »
I would also be worried about self discharge, since this is another spec that is not very relevant for RC use.
 

Offline johnnyfp

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #41 on: December 03, 2012, 05:17:34 am »
If you want real power, stop fannying around with small fry get a  batteryspace.com/LiFePO4-Prismatic-Module-3.2V-200-Ah-10C-Rate-640-wh-60.0.aspx  mohooo ha ha!!! >:D
 

Offline DL5TOR

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #42 on: December 03, 2012, 09:34:53 am »
If you want real power, stop fannying around with small fry get a  batteryspace.com/LiFePO4-Prismatic-Module-3.2V-200-Ah-10C-Rate-640-wh-60.0.aspx  mohooo ha ha!!! >:D


[irony]
Or just pop in a AGM deepcycle Lead battery with 100Ah. ONLY has 20Kg but lasts very long
[/Irony] :-/O

73
 

Offline opablo

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #43 on: December 03, 2012, 01:06:15 pm »
Dave, about that PS you are designing...

if the user will be able to customize and improve the firmware... (I understand that it is OpenHW and Arduino based?)

Can you add to the pcb maybe 6 extra soldering pads ? going to unused lines of the microcontroller (maybe 4 digital pwm + 2 analog input)

So the users will be encouraged to easily create their own crazy mods.

 

Offline LaurenceW

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #44 on: December 03, 2012, 07:55:25 pm »
A tad off message, maybe, but 3.7V is so, well, "not enough".

Question - is it safe to string two or three same size LiPo cells in series and them treat them as one 7.4 or 11.1V battery, with charging profiles just 3 x (volts, not amps!!) higher?

Are there any off-the-shelf charging chips that do this? the ones I've found so far all appear to be for single cells.

Go on, Dave, show us what a 20C cell will do, shorted >:D
If you don't measure, you don't get.
 

Offline xani

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #45 on: December 03, 2012, 07:55:55 pm »
What really bothers me about that design is setting up voltage/current by using buttons instead of rotary encoder, it's just not very fast and tiring, especially if doing some kind of voltage testing like checking how circuit reacts on different voltages.
 

Offline SeanB

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #46 on: December 03, 2012, 08:06:56 pm »
Simple answer is not, you need to charge each cell to the same voltage. Overcharge and they tend to go out in a flambé as so many laptop owners have found out.
 

Offline NickS

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #47 on: December 03, 2012, 08:09:20 pm »
Question - is it safe to string two or three same size LiPo cells in series and them treat them as one 7.4 or 11.1V battery, with charging profiles just 3 x (volts, not amps!!) higher?
You should always charge each cell separately. Chargers for larger packs have multiple pin charging plugs.

Or just use a boost converter to get the voltage you need without introducing additional charging complexity.
 

Offline johnmx

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #48 on: December 03, 2012, 08:38:50 pm »
How do you mount wires on the battery. Is it possible to solder direct to the "foil" ?
I think not. I tried to solder but without success. In cell phone batteries I only see spot welding.

If someone knows the best way to connect a wire please let us know. The crocodile clips are not a good option…
Best regards,
johnmx
 

Offline peter.mitchell

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #49 on: December 04, 2012, 12:46:25 am »
With a VERY hot iron you can quickly tin the tabs, once they're tinned they are  very easy to solder to, or you could drill small hole in the tab and nut&bolt it to appropriately provided pads on your board?
 


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