Weird LiPo puffing?..
 

...it looks like I just waved goodbye to a lump of £150 LiPo:

http://img.photobucket.com/albums/v6...9294453308.jpg
http://img.photobucket.com/albums/v6...9294470688.jpg

But...it seems a bit strange to me exactly why, and how it puffed. I only discovered the puffed cell the other day when I'd taken the Havoc out for a run, and bought it back in to pack away for a while as I was going on holiday. The truck had been running great...no performance issues. The LiPo itself ran cool as always, only getting lukewarm (I never bother to temp the pack now during a run), and it charged fine as usual.

The pack is a 5S Elite 35C 5000, running a CC-Neu 2200 in a RWD truck that's geard for about 60. Gearing is a little high, but the motor never gets more than around 150 and I can't brintg the ratio down further...so it's not stress. I did accidently, and very briefly short the pack out a few weeks ago (literally a few milliseconds, as the fuse on my balancer blew instantly), but I checked the pack over carefully afterwards; no puffing.

The only thing I can think of is that, ever since I've had it, one cell has always charged up to exactly 4.214V - a little higher than the others which are always around 4.206 - 4.208. Maybe that's caused the puffing over time? Also, the puff seems to be along the bottom of the cell, which seems odd. It's been like it now for over a week.

Was just wondering if you guys had any thoughts on this? :neutral:

maybe when it was shorted out, some of the soldering that held the balance wire to the lipo tab was burnt off?... And you are using a LVC/LVA right...? I know a fast way to puff up lipo is to over discharge them...

The balance lead wasn't even plugged in when the short happened, and the pack continued to charge and balance as normal afterwards. And yep, I always run a 3.3v per cell cutoff, but I usually stop running before that.

make it into a 4s pack. all the other cells look fine except for cell 5

Looks like possible impact damage. What does your battery tray look like?

I doubt that the short caused this for two reasons:

1) I assume you are using the LBA10, right? That's the only one I know with a fuse. If so, it's rated for 10A. Our setups draw FAR more than that, so that's not it.

2) From experience, Elite cells are awesome. I've pulled more than 30C on my 3.3Ah cells (more like 40C bursts), and they held up fine.

What it looks like is that a cell puffed (for whatever reason), but the battery tray was holding in that section of the puff (the top part in your pic) making it look lopsided.

As to why it puffed in the first place: Your setup must either pull a very hefty current, the cells got too hot, that one cell got charged too high over 4.2v, or, like Linc said, physical damage.

I have seen the elite cells puff without physical damage. I put it down to cq or mfg issues. Your setup may be drawing more than you think, and that cell may be a little weaker than the others, and it is always the weakest link that goes first...

I still think physical damage though.

is the whole 5th cell puffed, or just the corner.... if it is the corner, it could be physical damage...

Thanks for the input guys. The balancer I use isn't an LBA10, but a Robbe 12S balancer (http://store.modelpower.co.uk/robbe-...ncer-286-p.asp). It does use a 10A fuse like the LBA10 though, which blew on the moment of the short (I wasn't paying enough attention, and brushed the balancer's banana plugs together when plugging them in to the charger).
The Elites do perform great though as you say, Brian, and I usually just check pack temp with my hand every 5 or 10 mins; it's never been more than slighly warm (certainly no more than 110, tops), and the voltage always stays good under load until the very end of the run. It was the same low temp at the end of the last run. My transmitter warns me if it ever hits 3.3V per cell, even if only for a moment. The pack usually maintains at least 3.8V per cell for about 80% of the run, under high throttle.

The weird thing is though, that the pack sits in the tray the way up it is in the pic - with the bulge at the bottom, which is why I didn't notice it before. It uses a custom RC-M battery tray. The truck does do some pretty large jumps though, so I guess that could have contributed somehow. Then again, when I look closely, it does look like it might be the fourth cell that's puffed, pushing out the cell on the end. The pack's always secured in pretty well.

Aqwut, it's just the bottom "half" of the cell, which is mainly why I was curious (and decided to tap the font of experience that you guys are).

From what y'all saying then, sounds like physical trauma, or the slight overvoltage to that one cell during the charge. I'm kinda hesitant to try and break the pack up though (I know it's technically fine to do, but I don't trust myself to not mess up).

Lincpimp, that's interesting...how often have you seen it happen?

That's a neat balancer! Kinda looks like two LBA's in one package, minus the port to network another balancer. Don't know the US $$ exchange rate, but it would be expensive!

About $90, yikes.

Weird issue, but I agree with the others- reassemble it into a 4s pack, Im sure Linc can guide you through the process :yes:

Yeah, it is an unusual balancer. I wouldn't buy it myself at that price lol, but it came bundled with my "Mega Power 960SR" charger - which is identical to the Robbe Infinity III, but rebadged (not a Chinese knock-off though...they're made in the same factory). The balancer is accurate too, so appears to use the same quality components...even though the whole bundle was $200 from HobbyCity. :yes:

Good point though, SuicideNeil. LincPimp, you might find a PM from me in your inbox at some point (if you don't mind?). Thanks for all your help by the way, everyone. :yes:

If it was puffed, the cell would be sort of mushy.