[NSRCA-discussion] "Sick" Lipo Packs

Sun Dec 5 05:33:57 AKST 2010

Ron,

(The use of the word "you" in the following does not mean you personally 
Ron)

I think that the way we run the batteries, we will never get many 
hundreds or thousands of cycles from them.  If you put aside the 
marketing hype, no battery can supply what the typical r/c guy demands 
from it over many many hundreds of flights. We sometimes over discharge 
(at a high rate too), run them at sub optimal temps, charge improperly, 
etc. etc. etc.  With the advent of cheap batteries for our purposes, we 
treat the packs as utterly disposable and as a result get poor 
performance and life cycle life in return.  My first set of TP 5300 
Pro-lites cost me $650 for a set and believe me, I read the directions 
10 times and talked with lots of knowledgeable people before I attempted 
to run them the first time and then followed the instructions and 
suggestions to a "T".  Those packs made it to 175 useful cycles because 
due to the price, I treated them like gold.  Now, guys don't have that 
investment and don't use the same level of care but are still surprised 
when they don't last a long time. *Every single time* you over charge, 
over discharge, run a 50 degree battery right from your trunk, etc you 
damage the pack.  Period. It does not usually show up immediately so you 
think it's ok and keep doing things that damage the pack until at flight 
35 or 40, it starts to swell during a perfectly normal flight and the 
user thinks the packs just swelled up for no reason since they were not 
abusing it THAT flight, but the damage had already been done.

I am not saying at all that it's blame the user for all battery failures 
as there are some that are genuinely bad and have a defect of some sort, 
but you cannot abuse them over time and expect them to last. Again, 
these batteries are still very fragile and our usage of them is very, 
very extreme and the utmost care needs to be heeded to get maximum life 
and performance from them.  I am guilty too as I am not as diligent as I 
once was with the $650 set, and as a result sometimes get a reduced 
lifespan from a pack but we all justify it by saying that they were 
relatively cheap anyways.  I submit we can all get much better life and 
performance if we took better care of our packs, but that takes time and 
effort and diligence. There is a very good reason why some people get 
long life from their packs and others get much, much less from their 
identical brand packs.

Chris Moon

On 12/5/2010 12:00 AM, Ron Van Putte wrote:
> Yeah.  Now my head feels like my belly felt on Thanksgiving afternoon.
>
> However, it begs the question of what over discharging or discharging 
> too quickly actually is.  I can understand going past the mah rating 
> as over discharging.  Can discharging to 75%, 85% or 95% of the mah 
> rating be considered over discharging, if the rate of discharge is 
> under the C rating?
>
> Ron VP
>
> On Dec 4, 2010, at 8:21 PM, John Fuqua wrote:
>
>> First good explanation of why Lipos swell that I have seen.  Thanks 
>> for the insight.
>>
>>
>>
>> From: nsrca-discussion-bounces at lists.nsrca.org 
>> [mailto:nsrca-discussion-bounces at lists.nsrca.org] On Behalf Of Chris
>> Sent: Saturday, December 04, 2010 7:37 PM
>> To: General pattern discussion
>> Subject: Re: [NSRCA-discussion] "Sick" Lipo Packs
>>
>>
>>
>> Stu is right, all cells in the pack were subjected to the same 
>> overcharge or over discharge and will also fail as the first cell 
>> did.  One event will probably not show up as a swelled cell but it is 
>> the overcharge / over discharge over many cycles that will result in 
>> swelling. Notice the article says that max voltage is temp related, 
>> and most chargers don't make this adjustment so even with a "good" 
>> balance charger, you can still overcharge.
>>
>> Chris
>>
>> Part of a good article:
>>
>> This was the common problem with many cheap Chinese LiPos of around 
>> 2005-2008. Most are better now, but it's the #1 cause of premature 
>> LiPo failure: water contamination in the plant. Many of China's LiPo 
>> factories are on the coast, where the altitude is very low and the 
>> humidity is high. You can't run the humidity too low on the assembly 
>> floor, because you're working with volatile chemicals that could 
>> explode in the presence of a spark, and you can't run it too high 
>> because then you end up with a worthless LiPo that swells on first use.
>>
>> Here's the science. You have three ingredients that are functional in 
>> a LiPo battery. The rest is wrapping and wiring attachments.
>>
>> Cathode: LiCoO2 or LiMn2O4
>> Separator: Conducting polymer electrolyte
>> Anode: Li or carbon-Li intercalation compound
>> I'm going to be a little vague in my language here. The chemicals 
>> involved vary according to manufacturers, so I don't want to make any 
>> assumptions.
>>
>> Remember your chemistry class? Note the absolute lack of any hydrogen 
>> atoms in the reaction. None, zero, zip, nada. If you have water 
>> inside your battery -- and virtually all batteries have a little bit 
>> -- you've got problems. When the chemical bond of H20 is broken by 
>> electrolysis and heat, you end up with free oxygen. You also have 
>> free-roaming hydrogen that typically ends up bound to your anode or 
>> cathode, whichever side of the reaction it's on and depending on the 
>> state of charge of your battery.
>>
>> Now, this is a pretty unstable situation that's exacerbated by any 
>> over-discharge or over-charge condition creating metallic lithium in 
>> your cell. The end result is Lithium Hydroxide: 1 atom of lithium, 
>> one atom of hydrogen, and one atom of oxygen.
>>
>> But you still have a free oxygen atom floating around inside the 
>> battery casing, that typically combines with one other oxygen atom -- 
>> O2, or what we sometimes think of as "air" -- or two other oxygen 
>> atoms, to form a characteristic tangy, metallic-smelling substance 
>> called "ozone", or O3. Gases expand with heat and contract with cold. 
>> Chuck a swollen battery in the freezer and it might come out 
>> rock-hard again... until it heats up. It's not frozen, it just got 
>> cold enough that the gases inside didn't take up much space at all.
>>
>> And that free O2 or ozone is just waiting to pounce and oxidize some 
>> lithium on the slightest miscalculation on your part. The modest 
>> over-discharge during a punch-out, or running the battery a little 
>> too low or letting it get a little too hot, or running the voltage up 
>> to 4.235v/cell on a cold day when the actual voltage limit per cell 
>> is more like 4.1v. All of these create the perfect storm for a puffy 
>> battery to quickly turn itself into a ruined battery or an in-flight 
>> fire.
>>
>> Understanding the role of free oxygen in your battery, from water and 
>> other causes, is CRUCIAL to understanding why batteries fail, and why 
>> sometimes you can get by with flying a puffy battery, and sometimes 
>> you can't.
>>
>> If a Lithium battery is overcharged or charged too quickly, you end 
>> up with LOTS of excess free lithium on the anode (metallic lithium 
>> plating), and free oxygen on the cathode. A free oxygen atom is small 
>> enough to freely traverse the separator without carrying an electric 
>> charge, resulting in lithium OXIDE on the anode. Lithium "rust", in 
>> reality. Useless to us at this point, just dead weight being carted 
>> around inside your battery's wrapper.
>>
>> But lithium oxide uses fewer oxygen atoms than existed in the ionized 
>> state, so you end up with, again, FREE OXYGEN. And people wonder why 
>> if you over-charge a LiPo underwater, it still ignites despite the 
>> lack of open air...
>>
>> If it's over-discharged or discharged too quickly, the reverse is 
>> true, but you end up with Lithium Oxide on the cathode, but at a 
>> lower rate because there's simply less there. Basically, an abused 
>> battery quickly develops corrosion on both poles of the battery 
>> inside the wrapper. And the more it's abused, the worse it gets as 
>> the resistance goes up and it still gets driven hard.
>>
>> This, by the way, is the most common cause of swelling today for our 
>> aircraft when flown with a high-quality pack (not knock-off eBay 
>> leftovers from expensive Chinese mistakes of 2004-2009). The reality 
>> is, these kinds of cells, regardless of their 'C' rating, are built 
>> for use where they last for several hours... not several minutes. 
>> While the chemistry if used as designed is good for thousands of 
>> cycles, we're driving them so far out of spec that we're lucky to get 
>> hundreds of cycles out of them.
>>
>> In most cases, too, our batteries are under-specced. If slow-charged 
>> and slow-discharged, many of these packs would often hold 
>> considerably more mAh than we think they do. That's one of the 
>> reasons we get the performance we do from them. Higher-C-rated packs 
>> also often introduce gelled electrolyte into the separator, and 
>> carbon or phosphorous nano-structures on the anode and cathode 
>> mixtures rather than the "pound it out thin and hope it's mixed 
>> right" approach used with sheets of anodes & cathodes today.
>>
>>
>>
>> On 12/4/2010 8:23 PM, Stuart Chale wrote:
>>
>> Been there done that but my experience is that before long additional 
>> cells will fail and the cycle will continue.   With the cost of the 
>> lower priced packs, ie: Zippy's I would no longer bother :)
>>
>> On 12/4/2010 6:45 PM, Ron Van Putte wrote:
>>
>>
>> Those of you who use lithium polymer battery packs to power their 
>> competition airplanes are familiar with "puffed" packs.  I recently 
>> had four elderly 5S packs "puff".  We all know that's not good, but 
>> what I'd like to know is what's actually happening.
>>
>> I know it's probably not wise for consumers to take lithium polymer 
>> packs apart, but that's exactly what I did with four packs.  I 
>> discovered that in three of the "puffed" packs, only a single cell 
>> was "puffed".  In the last pack, there were two "puffed cells.  I did 
>> a little arithmetic and quickly discovered that I could make three 
>> "unpuffed" packs from the good cells I had.  So, I unsoldered the 
>> "puffed" cells from the four packs and cannibalized one pack to make 
>> three 5S packs from what I had left.  This process is obviously for 
>> the timid or the careless.  I was careful and had no mishaps.  
>> However, I would suggest that anyone who says "Oops" a lot should not 
>> attempt doing this.
>>
>> The three 5S packs I have left are "rock solid".  Experienced 
>> electric-pilots will know just what I mean.
>>
>> I have flown these packs and they seem to perform just as they did in 
>> their "youth".
>>
>> My questions are:  Why do lithium polymer cells "puff"?  What is the 
>> likely future of my recovered 5S packs?
>>
>> Ron VP
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