Puffy LiPo's

[Pilot Ben 28]

What are the problem and dangers of a puffy lipo? Will it die on me in the air or is it just performance that is affected?

 

B

[Bravedan 106]

No simple one line answer!

While the obvious safety advice is that if its swollen, its finished, a LiPo is generally OK if:-

1. When charged each cell sits between 4.17v and 4.21v such that the max difference between highest and lowest passes a balance checker test.
2. The internal resistance of the pack allows the current needed to be drawn for a normal calculated duration.  Bench test run.

Minor swelling of the outer cells or cell packaging in the stack is a sign that the pack has been stressed. The swelling might be serious in the sense that the pack paste structure has been affected, or minor in the sense that the sealed pack has been expanded by heated air, often during an over use run at high drain current, which may or may not still be trapped, keeping the swollen shape.

If you can detect that ALL the cells are no longer normal DITCH THE PACK IMMEDIATELY.

Put a slightly swollen pack in the freezer for 20 mins, and if the swelling disappears (and lots will) the problem is not necessarily fatal.

Treat all swollen packs with suspicion, charge them outdoors away from anything flammable, store them outside the main house in a LiPo bag, and you may well get years more use.

I have somewhat swollen packs that have been that way for five YEARS further use to no noticeable effect (notably Tipple). I have packs that have not swollen yet have without being stressed suffered a chemical composition change causing excessive internal resistance and a load giving duration in seconds, though sit happily at 4.19-4.20 volts per cell (Gens-Ace..........YUK!!).

Duration and power have no direct relationship to minor swelling.

[Pilot Ben 28]

Thanks Dave. They haven't had easy lives. They are only 25c yet they've powered edf's and hotliners! 

For £10 a pop from hobbyking I think tomorrow is the last time I will trust them in a decent plane. From then they'll be consigned to shockies and smaller stuff.

 

B