[NSRCA-discussion] "Sick" Lipo Packs

[Ron Van Putte]

I'm still trying to figure out what is happening that makes the cells  
"puff".  I know it's not good, but since I'm an aeronautical engineer  
and not an "electro-chemical" engineer (whatever that is), I don't  
know what is going on.  Is there a chemical change that results in  
the production of a gas?  If so, what is it?  Where does the gas go  
when you charge the pack? If not, just what is going on?

Ron VP

On Dec 4, 2010, at 7:23 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 not 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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>
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