[NSRCA-discussion] "Sick" Lipo Packs

[Stuart Chale]

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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