Recovering puffed cells

[dawrench]

Went to the Post Office today to pick up a new CellLog. Lost mine 3 weeks ago. I verified the cell voltages of my pack once home because the voltage felt saggy. Found one cell at 1.29 volts. Not Good. Opened the box to find the bricks puffed as in the photos. I don’t use a BMS and monitor cell balance manually every 2-3 cycles with a CellLog. Pack is 3x Turnigy 6S NanoTech 8.0 amp bricks in series. Things are usually extremely stable and I balance charge when I get a 20 mV spread or about every 55-65 cycles. For normal use, I bulk charge the string to 4.1 VPC. With this dud cell, I figure that exceeded 4.3 VPC on most cells and maybe even 4.4 on 2 cells.

I used an RC charger to cycle and balance the bricks. About 25% capacity loss but they didn’t get hot during charging. Internal resistance 1.8-2.0mV.
For now the whole pack is in it’s ammo can box in the back yard.

I don’t think I can recover the low cell or the 2 that went high but can the others be saved?

Will the cells continue to puff when charged?

How close am I to a fire?

Is it reasonable or feasible to puncture the cells to release the pressure and then reseal them?

Is there something I can do to reduce the puffing I have and prevent in the future?

I am curious to open up the low cell to see construction. Is there anything extremely poisonous or explosive inside? Really bad idea?

 

[D-Man]

De-puffing thread:
http://endless-sphere.com/forums/viewtopic.php?f=14&t=22650

 

[dawrench]

Here's a pic.

 

[Grinhill]

I haven't had success with de-puffed cells, I find that their capacity is significantly lower than their 'packmates'. Hmm, what a good word. :lol: They also are likely to leak, despite efforts to reseal.

I have however had more success with cutting out puffed cells, throwing them away and reconfiguring remaining cells into new packs.

Note, however that any packs or cells with such a history should be monitored more closely and treated with respect, such as your ammo can.

 

[dawrench]

Thanks for the de-puffing thread. I now have 3 cells that won't be going back in the pack I can experiment with. If they show any kid of capacity I'll keep them for starting the lawn mower.

 

[999zip999]

Sounds like cell for charging and storage in a barbaque outside. These packs are cheap to replace in a bike pack.

 

[dawrench]

I de-puffed and compressed 6 candidate cells last night. The cell that was at 1.29 volts had dropped to 0.03v so I did that one for practice. 20 minutes on a charger and the voltage didn't budge so it"s out back in the ammo can till I can carve it up. I thought that one a goner anyway. The 2 the went to 4.3v were cycled and show an IR of 2.1-2.3 mohms but at 25-30% reduced capacity. I hope a few light cycles will help that. The last three look better - only lost 1 amp/hr or so. 12v Booster pack now.