robert nanzig wrote:
>
> Any guesses as to why my car battery exploded yesterday when I
> turned the ignition key . It left a nice inverted dent in my hood.
I gather this battery was not in your Alpine?
Batteries can "blow up" when the pressure in the cells exceeds the
ability of the case to contain that pressure. I can think of two
reasons why a battery might explode.
It doesn't sound like had just charged the battery, so maybe it was not
caused by hydrogen gas igniting ?
Another possibility is an internal short in one of the cells. The
battery cells have conductive plates, between the conductive plates are
seperators (sp?) - a non conductive "plate", which is porus to allow the
electrolyte to interact with the conductive plates. Shorts can and due
develop between the plates, maybe at the edges of the plates, maybe
through the seperators. A high impedance (relatively speaking) short can
cause the battery to self discharge, without other effects.
A "hard" short within the cell can cause a battery to blow up. The
short, due to high localized heating, can be self feeding in that it
causes the plates to warp and increase the short, or it might cause the
generation of burn marks, which is composed of carbon, which is a
conductor. The point of this is that the chemical energy in that cell is
suddenly trying to discharge via a relatively small short in a short
time. Very quickly what can happen is:
small short - high local heating - short gets stronger - pressure builds
- may or may not produce flammable gas - heating continues - electolyte
goes into vapor - pressure builds - cell ruptures maybe with flame.
Thankfully catastrophic failures of this type are rare.
-Roger
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