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Lipo storage

Why, oh why, do we do it?

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Erfolg05/02/2010 11:56:51
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For some time I have been troubled about the storage of Lipo packs not being immediately used.
 
I think most or all of us modellers are aware of the general treatise to put our Lipos into storage mode if not going to be used imminently. Indeed many chargers have as standard a Lipo storage charging regime.
 
Again we all seem to be aware of the general justification, that this process will improve life and or reliability.
 
What I have never seen printed is what the process is, in scientific terms, that makes this a good thing to do. Why not drop the cell voltage to say 3.7v.
 
The other thing that has bothered me is, when the cell is manufactured, it probably has a voltage of close to zero (or has it). So why if the voltage drops below 3v, does the cell become unusable?
 
Are Lipos suitable devices to use for application such as Lap Top Computers, Power Tools, Mobile Phones, stand by lighting systems etc.  If they should not be charged to 4.2v per cell unless being used immediately?
 
Erfolg
Myron Beaumont05/02/2010 12:21:10
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Erfolg
You're not the only one confused .I too have read this that and the other since I got involved with having purchased 3 Lipos & lost one already .I'm sticking to Timbos chart about what voltage to leave them at when not in use & it seems to work.  I do a bit of topping up occasionally & keep them at room temperature .As you say  we need a chemist to explain just what is going on in that funny floppy pack.(or is it a secret!)
G-umpy
Keith Simmons05/02/2010 13:01:41
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Here is a thought,  How are Lipos stored in a shop ? and what is the "shelf life".  I must admit that I don't charge them up when I buy them, Only when ready for the lipos first flight and than maintained afterwards. 
How many of us buy lipos during the build of their model so to build in a battery tray etc., (Not an ARTF one)
Ian Regan05/02/2010 13:57:02
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when i come back from flying i always charge the lipos that i have used on the day so they r ready for next time, i,am i doing wrong by doing so.
ken anderson.05/02/2010 14:03:16
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ian-same here-i've been doing the same for 3 year's now-no problem's----you'll hear all sort's of do's and dont's.....but i fly all the time weather permitting....long time storage is a killer if they are put away fully charged...so they say.....it's like the 'memory effect' with nicad's----in theory ok-in reality..hard to prove......
 
    ken anderson....... 
Bruce Richards05/02/2010 14:06:08
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Me too. Fly then charge so they are ready for next time. Life is to short for all this faffing about.

Edited By Bruce Richards - Moderator on 05/02/2010 14:06:51

Ian Regan05/02/2010 14:11:39
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ok thanks,ken; bruce, i will carry on as i do, they say dont fix it if it aint broke. how often do u balance ur lipos??
ken anderson.05/02/2010 14:39:16
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ian....high season(summer)..maybe once a week...low season(winter)once a month......i used to bal charge them all the time till i read on the forum the 'great one's'(timbo) word's that it wasn't reqd...........
 
  ken anderson........
ericrw05/02/2010 15:00:11
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I've just bought a 2 cell 2000mah Lipo from my LMS.  I've just had it on charge and I had to put in 1017 mah to top it up ready for the week-end.   So that would indicate it had had approx 51% charge in the battery.   Eric.
Tim Mackey05/02/2010 15:51:25
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Thats about right - they should be charged ( and stored by distributors / retailers ) at approx 50 -60% charged.
In a nutshell "best practice" is....
 
Store partially charged, and in a cool to very cold place.
 
I normally keep all mine partially charged, and then bring into room temperature environment the night before flying, and fill 'em up, but as Bruce says so eloquently, sometimes I dont bother with all this "faffing about"
Erfolg05/02/2010 15:55:22
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But Why! Timbo. Other than it ensures best life, practice.
 
For me the issue is, what is or is not happening?
 
Erfolg
Tim Mackey05/02/2010 16:07:22
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Simply ( I only do simple Erfolg ) its because storing LiPolys fully charged increases their IR which reduce their ability to deliver the punch. Being stored fully charged, especially in a fluctuating ambient environment will also cause the voltage to fluctuate, possibly going over the maximum allowable 4.2V which causes further damage.
Its reckoned by many that every hour a cell is stored higher than 4v is doing damage.
Here is a link to some more data which i did use as reference material for my article on batteries a couple of years back.
If you want more chemical and technical info, then I dont have it. Sorry.

Edited By Timbo - Administrator on 05/02/2010 16:16:20

Tim Kearsley06/02/2010 08:34:05
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I think another facet of this which is often overlooked is that if you charge your LiPos fully, i.e. to 4.2V/cell, which is of course what the vast majority of chargers will do, then at temperatures below about 10 degrees C you have overcharged them and risk damaging them!  The Cellpro chargers have a temperature sensor built in and will only charge a pack to around 85% of full charge if the temperature is below this value.  It's worth considering, if you charge your LiPos in an unheated out-building.  I do much the same as Timbo in that my LiPos are stored outside and then brought in well before charging and allowed to warm up.  It is "faffing around" I agree, but LiPos are not cheap and I want 'em to last as long as possible!  I also insulate them well when I take them up to the filed, to try and keep them as warm as possible - LiPos don't like the cold when asked to deliver tens of Amps!
 
Cheers,
 
Tim.
 
Erfolg06/02/2010 15:59:52
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Tim
 
I had assumed that storing Lipos, posed a possible issue if the storage environment varied in temperature. The issues as you described.
 
I charged my Lipos sometime on arriving home, before my next outing. All seemed well, in my world, all was light and happiness.
 
Then came the atrocious weather, where as I had believed the Met Office, "It will be milder winter than would be deemed usual"".  I did not fly for over 6 weeks. Struggled to do my "tenny bobper sitting" as the UK became impassable. Then there was a one day window of just freezing weather.
 
I rushed to the field, (avoiding the giant pot holes). launched my first model, which struggled. Battery dying I thought. I then prepared the second model and found more issues.
 
Checks at home seem to confirm two dead batteries.
 
This caused me to question the validity of storing the batteries even for short periods at 4.2v. On reflection it could be that the batteries were on there way to exhaustion due to age, they were 3 years old, used approximately 200 cycles each. But the sudden death seems to have been triggered by the +6 weeks storage.
 
All of this reminds me of a lecture on hardening steel. For centuries Japanese Monks produced some of the best sword and knives in the world. The method involved elaborate ritual interwoven with processes. It took months to make each piece. The monks thought that the whole process was essential. Who was to argue, the whole system produced the goods. Now it is known, that the iron requires a certain amount of carbon and trace elements, by processing methods the disposition and orientation of the carbon and grain structures are controlled, the hardening is achieved by a phase change in the melt (Face bodied cubic and body centred cubic),and  by manipulating the cooling velocity of the steel the hardness and toughness can be controlled.
 
This knowledge enables knives and other artifacts to be produced at a low cost and time, with high quality. This has  enabled us all to afford what was once the province of the rich and privileged.
 
I believe at present we could be in the position of the Japanese Monks. Having a lot of ritual to try and  keep our Lipos well and useful. 
 
Some of the things we do could be bizarre, keeping our batteries at the bottom of the garden in a nuclear bunker, as the chemistry could be that on Nitro Glycerine. Where as my Mobile phone which appears to have a lipo, is kept in my pocket, charged when it is charged etc.
 
Knowledge is very powerful
 
Erfolg
 
Tim Mackey06/02/2010 16:14:47
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Your mobile phone almost certainly uses a lithium ion batttery, complete with hard case, and built in PCM ( protection circuit modules ) - this is also the case for things like laptops and ipods etc.
ken anderson.06/02/2010 17:02:11
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hello erfolg-the mobile phone batt's dont get discharged in a matter of min's--throwing out the limit of there design/function in life-----------i take my hat off(if i had one) to lipo's for the transformation of model aircraft flying...and also the brushless motor's..
 
 
     ken anderson............
Erfolg06/02/2010 17:13:53
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Timbo
 
For me it is all about, understanding what I am doing, particularly if there are risks and benefits. I would be surprised if we modellers are the only users of Lipos, yet we may be.
 
There are many other high energy density electrical storage batteries, are they intrinsically different to our Lipos?
 
I can and do accept that the internal resistance changes with time with our Lipos. As most chemical reactions tend to occur at a faster rate with higher temperatures, could cooler storage be beneficial? In the case of the Lipo at a lower voltage. I do not know, only wonder.
 
Erfolg
Myron Beaumont06/02/2010 17:52:05
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I havn't heard of one single use for lipos except us weight concious modelling  lot . Is this maybe the result of a "failed or superceded" technology so to speak & that if the weight consideration is a main factor then we have fallen for it ? Li ion rules OK ? I know of lots of applications for them in an ever developing field .for their use . 
Myron Beaumont06/02/2010 17:57:13
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I was just thinking ! Their voltages aren't exactly what we want either are they ?-so we have to buy more gizzmos to sort that out as well !
Erfolg06/02/2010 18:19:44
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There does seem to be a number of high discharge uses for Li-ion applications. The most obvious are portable power tools.
 
I must try and establish how a Li-ion battery is configured. Primarily to try and understand the differences in there construction and electrochemistry

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