H. Dziardziel wrote in
:

On Thu, 25 Aug 2005 18:55:43 -0400, Darmok
wrote:



Charging in only 20 minutes is a 3C charge rate ie, three times
the cell mAh capacity. Shaver NiCads would be in the 500m-1000Ah
range. NiMh 2000-2600mAh AAs can handle that 1500-2000mA charge
rate but must not go over full charge or will be destroyed.

The question is: is that a timed 20 minutes or a "smart" 20
minutes? If timed and one starts with fully discharged cells
then all is well. NiMh have no memory effect so can be charged
and dicharged from-to any level But, if a smart charger is used,
it may not properly detect the NiMh charge state and keep charging
past fully charged.

For say, 1500mAh cells, that would take about one hour however so
manul timing would suffice. Monitoring the cell temperature is a
good idea. Some heating while charging is normal for NiMh but
after full charge is reached it quickly ruins the cells.



According to what I've read here and there,cell temperature is NOT a good
way to detect full charge for NiMH cells. For NiCd,its OK.
By the time the temp changes the NiMH cell is overcharged.

--
Jim Yanik
jyanik
at
kua.net