PPRuNe Forums - View Single Post - 787 Batteries and Chargers - Part 1
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Old 6th Feb 2013, 09:19
  #494 (permalink)  
saptzae
 
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@hetfield
Let's say one cell out of six in one of the eight "cells" goes short.
The remaining 5 cells will deliver max current in that short until they are dead or the short cell is on fire. The BMS CAN'T stop this. It's an internal process out of reach for the BMS/Charger.
Fully concur, and I believe this is what actually happened to both ANA and JAL batteries.

I try to focus on what happened and want to stay away from what to change until failure is understood.

- There is no indication as of yet that the cells were bad ex GS Yuasa.
- To short, cell(s) must have deteriorated quickly
- What caused this deterioration
- Was deterioration during integration
- Was deterioration during operation (BMS)

- When a sub-cell@cell shorts, the BMS _must_ detect this and take the battery off-line. That did not work either. Clarify: The BMS must detect a cell short, which, at the initial event, will be a sub-cell short. How: By detecting cell voltage transients.

However, I can see merit in parallelizing 24 standard 3Ah cells via a (30A) fuse per cell. A single cell short would simply remove the shorted cell from the others, with much less energy dissipation and collateral damage.

Edit: A123 went broke after several batteries, consisting of small cells, went up in flames... A123 Replacing Batteries That Led to Fisker Karma Shutdown - Bloomberg

Last edited by Jetdriver; 7th Feb 2013 at 11:43.
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