Author Topic: EEVblog #393 - LiPo Battery Discharge Testing  (Read 27258 times)

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Offline EEVblog

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EEVblog #393 - LiPo Battery Discharge Testing
« on: December 02, 2012, 01:36:03 pm »


Dave.
 

Offline TriodeTiger

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #1 on: December 02, 2012, 01:37:54 pm »
Wowy, I was literally thinking about testing a few cells I've had with loads for the purpose of creating resistive heaters for the cold winter, and this appeared, literally seconds before I checked!

*curls up like a kitten to watch*
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Offline LEECH666

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #2 on: December 02, 2012, 02:44:47 pm »
I was literally about post questions in the beginner forum on how to characterize a Lipo, or well a Lipo powered USB power bank. Not sure if the claimed 12000 mAh are realistic. Especially since I found a little instruction manual paper card that says 4000-14000 mAh, but it doesn't say if this is model dependent or just a vague guess on the capacity.


Anyway, excellent video and timing Dave!
 

Offline baoshi

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #3 on: December 02, 2012, 03:12:12 pm »
Nice video Dave! Exactly something I'm waiting for.

Do you need to change the charging circuit to cater for the larger capacity battery?


Bob

PS: Notice the unpopulated footprint onboard. FT230XS is now stocking in farnell UK

PS2: The Turnigy Accucell 6 charger seems to be a good candidate for your next tear down  ;D
« Last Edit: December 03, 2012, 08:31:41 pm by baoshi »
 

Offline EEVblog

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #4 on: December 02, 2012, 03:59:04 pm »
Do you need to change the charging circuit to cater for the larger capacity battery?

No, it just takes longer.

Dave.
 

Offline Psi

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #5 on: December 02, 2012, 07:10:35 pm »
Nice video :)

There is an issue you may not be aware of, RC batteries, like the ones from hobby king, are a slightly different LiPo design to the kind you might get in a laptop or other device. They do not have any protection at all and will puff up/explode if shorted.

But their main difference is they take advantage of a battery characteristic which is normally undesirable (but dont matter with RC planes) in order to get their really high capacity.
High power RC LiPo batteries do not like to be fully charged for very long, it will shorten their live considerably. When you use one of these batteries for flying your RC plane you charge it up to 100% and then fly your plane in the next few days. When you get home all the batteries get put onto the charger in "storage mode" which will either charge or discharge them to a set voltage safe for storage.

I don't know just how significant this effect/damage is but its something that should be checked out as this kind of high discharge RC battery may not be very suitable for a usb powersupply where you want to keep it fully charged in your bag.

Here's a quote from http://www.rchelicopterfun.com/rc-lipo-batteries.html
Quote
You must store them charged, but not fully charged either – that will also degrade the cell matrix. Basically, the speed at which a LiPo pack ages (during storage) is based on both storage temperature and state of charge. You are likely ok to store a fully charged RC LiPo battery at room temperature for up to 4 days without doing much damage. Never store a LiPo in a hot car fully charged for an extended time, that will certainly cause damage as I explained earlier, but it worth repeating.

For optimum battery life, store your RC LiPo batteries at room temperature and at about 40-60% charged. That equates to around 3.85 volts per cell (open terminal resting voltage). The actual storage range is likely a little broader than this (I have heard some say numbers as high as 20-80% is fine, but since computerized chargers set the storage charge at 50% (3.85 volts per cell) that's what I recommend and what I follow myself.
« Last Edit: December 02, 2012, 08:03:36 pm by Psi »
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Offline T4P

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #6 on: December 02, 2012, 07:32:26 pm »
Yeah, trying to protect a battery capable of putting out 100A is not particularly easy with limited board space ^-^
The most powerful batteries are usually 26650 with possibly fake plate ratings @ 5000mAH (more likely 4000mAH) at 1C ratings for 26650 with a maximum of 2C for 18650 batteries so 900lm SSC-P7/XML-T6 blindlights are usually stretching the very cheap 18650s with only much less than rated faceplate probably about 1AH
 

Offline IanB

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #7 on: December 02, 2012, 07:46:56 pm »
I have to say I was slightly surprised when the capacity measurement came out bang on spec like that. Some low cost batteries are notorious for having vastly inflated capacity numbers on the label. Thumbs up for the vendor in this case  :-+
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Offline EEVblog

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #8 on: December 02, 2012, 07:48:37 pm »
Yeah, trying to protect a battery capable of putting out 100A is not particularly easy with limited board space ^-^

If you don't need the 100A, not at all!
A 5A polyswitch or something in series will do nicely.
But of course once the battery is installed and connected to the correct charging circuitry, it doesn't need protection. As a) the terminals aren't going to spontaneously short out, and b) the charger circuitry isn't going to try and mysteriously overcharge charge.

Maybe I could just leave the power on all the time to prevent full charge ;D

Dave.
 

Offline EEVblog

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #9 on: December 02, 2012, 07:50:13 pm »
I have to say I was slightly surprised when the capacity measurement came out bang on spec like that. Some low cost batteries are notorious for having vastly inflated capacity numbers on the label. Thumbs up for the vendor in this case  :-+

Yes, Hobby King have a big rep, and a review comments system. So if a product doesn't meet spec, everyone would soon know about it!

Dave.
 

Offline Psi

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #10 on: December 02, 2012, 07:56:05 pm »
Yeah, trying to protect a battery capable of putting out 100A is not particularly easy with limited board space ^-^
A 5A polyswitch or something in series will do nicely.

I think a typical polyswitch is rated for 50-100A maximum input and you'd get far more than that if the battery did get shorted, probably 1kA or so.

Although i guess the PCB tracks to the polyswitch will limited the current somewhat. So it might be fine.
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Offline EEVblog

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #11 on: December 02, 2012, 08:02:56 pm »
I think a typical polyswitch is rated for 50-100A maximum input and you'd get far more than that if the battery did get shorted, probably 1kA or so.
Although i guess the PCB tracks to the polyswitch will limited the current somewhat. So it might be fine.

That's the tick isn't it. How is the battery going to get magically (solidly) shorted when it's in the case.
The polyswitch would be almost token.

Dave.
 

Offline EEVblog

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #12 on: December 02, 2012, 08:20:12 pm »
I don't know just how significant this effect/damage is but its something that should be checked out as this kind of high discharge RC battery may not be very suitable for a usb powersupply where you want to keep it fully charged in your bag.

The micro can sense the battery voltage and also switch the unit off. So it's possible for the firmware to go into a "storage" mode if you say, try and switch it off when the voltage is above 4.xV or something.

Dave.
 

Offline ejeffrey

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #13 on: December 02, 2012, 08:35:50 pm »
I would expect that the cold resistance of the polyswitch would limit the current to considerably less than 1000 amp.  Even if it doesn't, the battery won't care a bit about the brief overload while the switch heats up.

In this case, a polyswitch wouldn't be so much to protect the battery as to protect the PCB tracks/wiring from the battery.
 

Offline Psi

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #14 on: December 02, 2012, 08:53:04 pm »
I don't know just how significant this effect/damage is but its something that should be checked out as this kind of high discharge RC battery may not be very suitable for a usb powersupply where you want to keep it fully charged in your bag.

The micro can sense the battery voltage and also switch the unit off. So it's possible for the firmware to go into a "storage" mode if you say, try and switch it off when the voltage is above 4.xV or something.

Dave.

Yeah, it would need to have a built in dummy load though.

When plugged into a usb port it would charge to 100% then start a counter which would begin an automatic discharge to 3.8V after 4 days.

« Last Edit: December 02, 2012, 08:54:40 pm by Psi »
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Offline EEVblog

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #15 on: December 02, 2012, 08:56:17 pm »
Yeah, it would need to have a built in dummy load though.
When plugged into a usb port it would charge to 100% then start a counter which would begin an automatic discharge to 3.8V after 4 days.

Yes, it assumes of course that the USB wouldn't be connected permanently.

Dave.
 

Offline EEVblog

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #16 on: December 02, 2012, 09:32:20 pm »
Well, it seems that many places recommend storing these high C batteries at much reduced capacity, but I have yet to find any actual definitive data on it.
In which case that kinda sucks, and it's probably better to go with a regular low-c type, like an extended capacity mobile phone battery or something. But of course fakes in that market are rife.
It would have to be universally available too.
Suggestions?

Dave.
 

Offline SeanB

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #17 on: December 02, 2012, 09:44:32 pm »
Then just charge it to 4.05V and accept the battery will never be fully charged, and compromise on life slightly. If charging on USB that would be the likely case, as it will take 4 days to fully charge the 5AH cell from a standard high power USB current of 500mA. It would probably be good to have an external 12-19V input to a separate charger chip, which will enable it to be charged from a laptop PSU easily, and will satisfy most users. Charge time on that would be under 2 hours, and it would be usable while charging ( though at the expense of higher output noise though) without killing USB power delivery, allowing use on a unpowered hub ( common laptop limited ports).
 

Offline Psi

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #18 on: December 02, 2012, 10:01:34 pm »
yeah, i agree. just have a default max charge volts that's lower than spec.

People can hack the firmware to use 100% charge if they want, or make it a menu option.
« Last Edit: December 02, 2012, 10:07:20 pm by Psi »
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Offline EEVblog

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #19 on: December 02, 2012, 10:09:28 pm »
yeah, i agree. just have a default max charge volts that's lower than spec.
People can hack the firmware to use 100% charge if they want, or make it a menu option.

The micro does not control the charge rate, it's a Microchip charger IC.

Dave.
 

Offline Psi

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #20 on: December 02, 2012, 10:12:01 pm »
ah. i figured the charge IC would have SPI and be programmable for the charge specs of the battery used.
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Offline ecat

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #21 on: December 02, 2012, 10:14:45 pm »
Well, it seems that many places recommend storing these high C batteries at much reduced capacity, but I have yet to find any actual definitive data on it.

See the table on page 1
http://ozarkmountainbarnstormers.com/pdf%20files/Lipo%20Storage%20Tips.pdf

It's something I want to know too.

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?
 

Offline firewalker

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #22 on: December 02, 2012, 10:17:12 pm »
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.
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Offline Psi

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #23 on: December 02, 2012, 10:21:43 pm »
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.
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Offline EEVblog

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #24 on: December 02, 2012, 10:22:56 pm »
Then just charge it to 4.05V and accept the battery will never be fully charged, and compromise on life slightly. If charging on USB that would be the likely case, as it will take 4 days to fully charge the 5AH cell from a standard high power USB current of 500mA.

How do you figure 4 days?
at 1/10th C it takes only 10 hours to get to 85% capacity in the constant current mode.

Dave.
 

Offline EEVblog

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #25 on: December 02, 2012, 10:29:25 pm »
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, 10:37:55 pm »
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, 10:56:16 pm by ecat »
 

Offline Mikey

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #27 on: December 02, 2012, 10:47:49 pm »
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, 10:49:52 pm 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, 10:51:34 pm »
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, 10:58:03 pm »
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, 11:41:38 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 03, 2012, 12:38:49 am »
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 03, 2012, 02:13:32 am »
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 03, 2012, 02:44:57 am by kevotronic »
 

Offline T4P

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #33 on: December 03, 2012, 02:30:24 am »
"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 03, 2012, 03:00:30 am »
"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 03, 2012, 04:18:49 am »
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.
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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 03, 2012, 06:41:04 am »
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 03, 2012, 06:48:19 am by muvideo »
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Offline EEVblog

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #37 on: December 03, 2012, 08:56:18 am »
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 03, 2012, 10:23:33 am »
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, 11:38:45 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, 11:43:50 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, 04:17:34 pm »
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, 08:34:53 pm »
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 04, 2012, 12:06:15 am »
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 04, 2012, 06:55:25 am »
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 04, 2012, 06:55:55 am »
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 04, 2012, 07:06:56 am »
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 04, 2012, 07:09:20 am »
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.
 

Online johnmx

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #48 on: December 04, 2012, 07:38:50 am »
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, 11:46:25 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?
 

Offline baoshi

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #50 on: December 04, 2012, 03:21:47 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…

I have been using some special Chinese solder which contains acid in the flux core. These are useful to solder nickel plate onto 18650 battery case if you do not have spot welding machine. It also corrodes iron tip badly :-\
I also heard that goot makes special flux for this purpose, but never test myself though...

 

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #51 on: December 04, 2012, 05:00:44 pm »
Quote
It would probably be good to have an external 12-19V input to a separate charger chip, which will enable it to be charged from a laptop PSU easily, and will satisfy most users. Charge time on that would be under 2 hours, and it would be usable while charging ( though at the expense of higher output noise though) without killing USB power delivery, allowing use on a unpowered hub ( common laptop limited ports).
2A USB power supplies are very common nowadays given that a lot of tablets use them. Also, 900mA USB 3.0 ports are becoming more common, along with high current (1A or more) USB ports on some new motherboards.
Quote
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).
That's a NiMH chemistry tweaked for hybrid vehicles and other high peak current, low self discharge applications. It is more expensive than regular NiMH for the same capacity.
Quote
LiFePO4 would be nice, but the charger chips are not cheap and plentiful like LiIon/LiPoly
LiFePO4 is much more forgiving than common Li-ion (overcharge would just greatly shorten the life instead of causing thermal runaway), so you can implement the charging and discharge cut off in software. Back it up with the watchdog timer and it should work quite well.
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Offline baoshi

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #52 on: December 04, 2012, 06:33:00 pm »
2A USB power supplies are very common nowadays given that a lot of tablets use them. Also, 900mA USB 3.0 ports are becoming more common, along with high current (1A or more) USB ports on some new motherboards.

I ran into the same dilemma when doing another project a while ago. The issue here is to allow detection of dedicated charging port (DCP) to enable higher charging current (as opposed to normal <500mA). Otherwise the charging circuit will blow USB port on a normal desktop/laptop. FT230X has battery charger detection function but I'm still waiting for the new chip to be shipped to test if it is compatible with Android or Apple adaptors. Even if does so, more circuitry will be needed to isolate BCD (maybe even PWREN#/SLEEP#) signal, which could significantly increase cost.



 

Offline jnissen

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #53 on: December 05, 2012, 05:51:59 am »
Feedback on the video.

Why mess with soldering the batteries at all? Just use an accepted hobby standard plug and you can take advantage of the huge variety of packs offered. It makes very little sense to hard tie this pack in place when there are literally 1000's of different pack options with connectors already installed.

The display is totally inadequate for what your trying to convey. I agree with ditching the buttons and use a rotary encoder or knob. A lot more intuitive and easier to set. 2X8 is fine if all you want to provide is minimal feedback. Your trying to make the display do way to much. Fail!!!!
 

Online NiHaoMike

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #54 on: December 05, 2012, 03:42:34 pm »
I ran into the same dilemma when doing another project a while ago. The issue here is to allow detection of dedicated charging port (DCP) to enable higher charging current (as opposed to normal <500mA). Otherwise the charging circuit will blow USB port on a normal desktop/laptop. FT230X has battery charger detection function but I'm still waiting for the new chip to be shipped to test if it is compatible with Android or Apple adaptors. Even if does so, more circuitry will be needed to isolate BCD (maybe even PWREN#/SLEEP#) signal, which could significantly increase cost.
It should be pretty easy to just use a microcontroller with USB. When input power is valid, try to establish communication. If that fails, use some GPIOs and resistors to detect if the data lines are shorted to each other. Then just have a GPIO set the current limit on the primary side. And detecting a USB 3.0 port can be as simple as checking if the USB 3 ground is connected.
Cryptocurrency has taught me to love math and at the same time be baffled by it.

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Offline crispus

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #55 on: December 05, 2012, 07:28:20 pm »
Hi Dave,

Where did you get those batteries?

Thanks
I know I'm numskull, but I look around me and I feel better.
 

Offline T4P

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #56 on: December 05, 2012, 07:44:52 pm »
Feedback on the video.
The display is totally inadequate for what your trying to convey. I agree with ditching the buttons and use a rotary encoder or knob. A lot more intuitive and easier to set. 2X8 is fine if all you want to provide is minimal feedback. Your trying to make the display do way to much. Fail!!!!
Okay. I have never seen a small rotary encoder and he did want it to be SMALLER not being totally unable to shove it inside a bag or something without fearing for damaged encoders or broken shafts
The display is doing too much? Like? He's not trying to do an entire UI and seriously that is quite INTUITIVE already, being above to shove that much UI is a good thing and not a FAIL!!! What do you when you're limited for space?
 

Offline aargee

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #57 on: December 06, 2012, 08:06:40 am »
Dave, watch those bare terminals and your wedding ring.

100A (or more) will automatically spot weld the terminals to your ring and heat it up white hot and your finger....
Not easy, not hard, just need to be incentivised.
 

Offline crispus

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #58 on: December 07, 2012, 10:06:52 am »
It is from HobbyKing. I didn't remembered.
I know I'm numskull, but I look around me and I feel better.
 

Offline peter.mitchell

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #59 on: December 07, 2012, 03:55:07 pm »
It is from HobbyKing. I didn't remembered.

Single 5000mAh cell:
http://www.hobbyking.com/hobbyking/store/__18560__Turnigy_5000mAh_1S_20C_Lipoly_Single_Cell_.html
2 Cell pack made from the above single cells:
http://www.hobbyking.com/hobbyking/store/__21001__Turnigy_5000mAh_2S1P_20C_hardcase_pack_ROAR_APPROVED_.html
4 Cell pack made from the above single cells:
http://www.hobbyking.com/hobbyking/store/__15521__Turnigy_5000mAh_4S1P_14_8v_20C_hardcase_pack.html

Buying the 4 cell packs and de-soldering them is better value for money, but a fair amount more work, also the tabs have been trimmed, so they may be a little more difficult to solder/attach.
 

Offline amyk

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #60 on: December 07, 2012, 05:43:58 pm »
Single 5000mAh cell:
http://www.hobbyking.com/hobbyking/store/__18560__Turnigy_5000mAh_1S_20C_Lipoly_Single_Cell_.html
For a second I thought that said 18650 and wondered how that could be true... the highest (real) capacity 18650 are currently around 3Ah.
 

Offline peter.mitchell

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #61 on: December 07, 2012, 06:54:10 pm »
Single 5000mAh cell:
http://www.hobbyking.com/hobbyking/store/__18560__Turnigy_5000mAh_1S_20C_Lipoly_Single_Cell_.html
For a second I thought that said 18650 and wondered how that could be true... the highest (real) capacity 18650 are currently around 3Ah.

Best place to look at 18650s http://lygte-info.dk/review/batteries2012/Common18650Summary%20UK.html
 

Offline Otatiaro

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #62 on: December 10, 2012, 09:35:57 pm »
Hi,

I'm working on a prototype that needs built in battery too and was thinking about using these (that I use in helicopters / planes for years).

But I don't have any 2200mAh 20C in stock, would it be possible to have the dimensions of the battery itself and the dimensions of the solder pads (I'm designing a footprint for direct solder on the bottom of the board) ?

Thomas.
 

Offline diablo248

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #63 on: February 19, 2013, 09:54:40 am »
Maybe somebody have datasheet for this battery?
 

Offline diablo248

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Re: EEVblog #393 - LiPo Battery Discharge Testing
« Reply #64 on: February 21, 2013, 08:20:19 am »
Ok I cannot find any datasheet but maybe You know that this single cell battery has got same protection circuit built-in? If not could you recommend me which IC can I use?
 


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