[volt-nuts] Ni-Cad vs. Ni-MH "Trickle Charging"

[Chuck Harris]

Hi Brooke,

Yes, I know.  I remember explaining it to you 5 or 6 years ago.

-Chuck Harris

Brooke Clarke wrote:
> Hi Chuck:
>
> There's a fundamental difference in the chemistry of these two batteries. The Ni-Cad
> is what's called endothermic so the temperature remains relatively constant during
> charge, but the Ni-MH is exothermic, meaning that the battery temperature is rising
> along with the state of charge. So you can leave a Ni-Cad on charge at a 0.1C rate
> and it will be charged in a half to full day and the temperature will be warm but not
> hot,. BUT, if you put a Ni-Cad on 0.1C charge it will get very hot and degrade the
..........................^NiMH^

> battery and might even catch fire or explode. Hence the constant rate recommendation
> of C/250 (or lower). It's not to charge the battery but to keep it from discharging.
> Some other charge mechanism needs to be used in addition to the constant rate for
> charging.
>
> Ref Handbook of Batteries, third edition, Linden & Reddy, pg. 29.22.
>
> Have Fun,
>
> Brooke Clarke
> http://www.PRC68.com
> http://www.End2PartyGovernment.com/