Peri Hartman via EV wrote:
To take this to a traction pack, I would want to try a similar design
where strings of cells are spot welded in parallel for the desired
current load. As I understand it, you can put as many in parallel as you
want and control them with a single BMS unit.
Well... There are those that believe this, and it is certainly done.
However, think about failure modes: Sooner or later, a cell will fail.
What happens if one of the cells in parallel shorts? All the rest will
dump all their stored energy into that one shorted cell. That is very
likely to result in a burst cell or even a fire. And packed like this,
once one cell starts burning, it can set the rest on fire.
When laptop manufacturers connected their cells directly in parallel,
there were some dramatic failures and fires. Since then, reputable
manufacturers are using cells with *internal* fuses and safety devices.
Hobbyists and el-cheapo manufacturers aren't likely to use such cells.
--
The principal defect in a storage battery is its modesty. It does not
spark, creak, groan, nor slow down under overload. It does not rotate.
It works where it is, and will silently work up to the point of
destruction without making any audible or visible signs of distress.
-- Electrical Review, 1902
--
Lee Hart's EV projects are at http://www.sunrise-ev.com/LeesEVs.htm
_______________________________________________
UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
http://lists.evdl.org/listinfo.cgi/ev-evdl.org
For EV drag racing discussion, please use NEDRA
(http://groups.yahoo.com/group/NEDRA)
