Puffy cells and stuff, the root cause
Excessive cell case flexing due to either overcharging or reduced external pressure cycling will cause internal shorting of the electrodes, fatigue of the aluminum and copper current collector fingers, etc. This is the root cause.
When a Lithium cell is "puffy" it typically has a reduced capacity and is an indication of over-charging. i.e. it is damaged goods.
But what else can puff out a cell?
How about the 3 psi differential pressure between the inner volume of the cell case (@14.7) and the reduced pressure of the E/E bay at 6000' (@11.8 psi) -- the deflection of the 5" x 7" sheet of 0.031" thick 304 stainless steel that is the S1 and S3 cell case will experience plastic deformation. You can see it in the CT scans of the Main, Fig 22. That expansion creates voids in the windings and separates the poly separator from the foils--it is now damaged goods and its charging profile will no longer follow the sinc and exponential model assumed by the Battery Charging Unit software as described in the patent.
Is it possible that three 45-second 450Amp APU starts with 60 seconds rest in-between would pull the pack down below the 15% capacity lock-out of the BMU.
What is the 15 % lock-out? That is the condition when the BMU energizes the contactor to open-circuit the battery and render it useless unless returned to the vendor for reset/recharge.
Last edited by kenneth house; 16th Mar 2013 at 13:59.