LiPo pack dented corner

[dawrench]

So, I've been using these Turnigy Nano tech 6s 8.0 Ah packs in a 18s pack for almost year now. On the bike, they are in a steel Hammo can from the army navy store with 3/8 inch+ foam padding all around. For charging I remove them and charge separately with a RC balance charger and then put them back in the steel can. It's less than convienent but it works until I buy a high voltage bulk charger.

So last nite I was putting them back in the steel can fully charged and I dropped one about 20". It landed more or less on one corner. The blue shrink wrap split and there is a small dent in the corner of one cell. Seriously freaked out, I grabbed it, laid it in another steel can I have for this purpose and got it outside for the night. No smoke show and all cells still in balance. I charge to 4.1 v per cell.

Is this pack still safe to use or should I break it down to it's cells and save the undamaged ones as spares? I see dnmun's pack has several with worse dents in corners.

 

[dawrench]

32 hours after the fall the cell voltages are:
cell 1 4.097
cell 2 4.107
cell 3 4.101
cell 4 4.100
cell 5 4.094
cell 6 4.100 -- measured several times - sometimes I get 4.103

I think the damaged cell is number 6.

 

[zombiess]

It doesn't look too bad, but I would watch an monitor it if I was using it just like you should do with all LiPo packs. I caught a bad nanotech cell I had after storing them for about 6 months, the cell actually split it's foil and leaked, it read 0V, all the other cells were fine, no smoke/fire or anything. I disassembled that pack and have spares now. I have 1 or two packs I've done the same to after dropping them... oops. Over a year later they are fine electrically, no difference so I believe the damage was pretty much cosmetic. If it starts to become unbalanced, then the cell is bad and should be disposed of. Some more experienced guys can chime in.

If you aren't comfortable, just pitch it and buy a new one, they aren't expensive for what they are and worrying sucks.

 

[dogman dan]

If it stinks and is leaking, dump it. If it won't hold a charge, dump. Anything funny looking, dump.

Otherwise, it's possible you dodged a bullet. I wouldn't advise trusting your "good" lipo so much that you'd be much different trusting a dinged, but otherwise looking ok pack.

Some I dropped got damaged enough to chuck, others seemed ok, and got used 3 years with no problem.

 

[dnmun]

that was an old ping pack which had lived inside a pelican box for a long time and it had distorted in the corner from 'creep' as the pack swelled with age. the two distorted ends of the pack were inverted and placed into the middle of the pack so i could get the flat, previously inner, middle of the pack, pouches out to the ends of the pack where i used the 1/4" plywood endplates.

what happens in your case where the corner has real structural changes is that the electrodes and separator layers are now damaged so eventually i would expect them to short out on the edge so i think it would be a good candidate to become a future pouch donor when the other packs end up losing a cell here and there.

i have less anxiety about the ping pouches shorting than i do with the lipo pouches. but i really do not know if the pouch will fail by creating a lotta heat when it shorts or just slowly drain to 0V.

but this is one of the reasons i think rebuilding them into regular packs with endplates to protect them physically on the outer corners is worthwhile, but i am most concerned that the constant distortion of the shrink wrap in the corners does the same thing to the lipo pouches as what happened to the ping pouches. they are essentially the same imo.

 

[Ykick]

Disect one and you'll better understand the 100's-1000's layers of thin film windings that comprise these cell. A minor dent by itself probably isn't fatal but it is cause for concern and should be capacity, IR tested and monitored closely.

 

[dawrench]

OK, I'll run a couple of charge discharge cycles out in the back yard just to see before beginning dissection. Cell voltages are still stable - no change from last night. Shrink wrap removal and building a solid pack is in the near future. Thanks.

 

[dnmun]

if you get it out of the shrink wrap where you can see it better you might feel more confident if it is not as bad as it looks on edge.

maybe it can be squeezed back flat with your fingers but i think you can learn a lot by just monitoring it every time you charge.

if you see the voltage start to drop rapidly over time when measured before the charge it would be reasonable to remove it then.

i think a lot of them get damaged this way and most times people don't notice it. you only saw how bad because you removed the shrink wrap in that corner. most never do that.

 

[dawrench]

It's now about 56 hours since it dropped. Voltages are still the same - no change.

When compressing the pack with woodworking clamps before wrapping with filament tape, how much pressure should I use?