> >
> > Interestingly airlines are happier with lithium batteries inside
> > equipment than with batteries packed seperately. Presumablly because
> > there is less risk of getting a large concentration of batteries
> > stacked together that way.
> >
>=20
> Also less chance of the batteries being shorted - otherwise with pretty m=
uch
> any battery I've come across you have exposed terminals. I'm still wonder=
ing
> what actually resulted in the LiPo causing that (if indeed it
> did) as I understood the danger is in charging or shorting out a battery,=
 which
> doesn't seem all that likely with a battery installed in a RC model - the=
 only
> high current pathway even if stuff malfunctions should be via the motor,
> which would limit the peak current (any other pathway should be via thin
> traces which would act as fuses - they certainly do in my personal
> experience!) Don't see why it should be an issue leaving batteries instal=
led in
> things.

I wouldn't be surprised at something  like this happening with an installed=
 battery, especially if the battery has no short circuit protection circuit=
ry inside it.=20

Consider the emergency beacon that caught fire in a Boeing Dreamliner while=
 it was sitting on the tarmac at Heathrow Airport in London. My pick for th=
e cause of the fire is a tantalum or ceramic capacitor going short circuit,=
 a well-known failure mode for both classes of component, and I have had mu=
ltiple examples of it happening within my experience. My pick would be that=
 this is what happened in this toy, causing the battery to catch fire.

These days you can get tantalum capacitors with a built in fuse for use in =
critical positions, see the Kemet 04053/T496 series ...

http://www.kemet.com/kemet/web/homepage/kechome.nsf/file/KEM_T2010_T496.pdf=
/$file/KEM_T2010_T496.pdf

I believe Tantalum-Polymer versions mitigate against the short circuit fail=
ure mode, but that still leaves ceramic capacitors as a weak point  ...


--=20
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