On Thu, 27 Oct 2005, Olin Lathrop wrote:

> Brooke Clarke wrote:
> > Yes, but it's a matter of how hot.  The Ni-Cad chemistry is what's
> > called endothermic and the Ni-MH is what's called exothermic.  This
> > means more heat is produced at the end of charge with the Ni-MH battery
> > and amounts to about 30 degrees C more than the Ni-Cad (100 F vs 150
> > F).
> 
> No matter what chemistry goes on inside, you can't escape basic conservation
> of energy:
> 
>  HeatOut = PowerIn - PowerStored
> 
> Perhaps power is stored/released under different conditions for NiMH than
> for NiCd, but the above equation has to still be true.

Yes but "PowerStored" could be in the form of unwanted products (e.g. 
hydrogen gas) so although you are not seeing any more useable stored 
electrical energy it would be possible (depending on battery chemistry) 
NOT to see an increase in heat output (or a disproportionately small 
increase). I can also imagine conditions where unwanted products cause 
changes in the thermal system of the battery (e.g. complexes with higher 
latent heat of solution or fussion).


Regards
Sergio Masci

http://www.xcprod.com/titan/XCSB - optimising PIC compiler
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