On 27 Aug 2005 05:04:45 GMT, Jim Yanik . wrote:

For say, 1500mAh cells

A typo, "1500mAh cells" should read "1500mA."

, 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.

My post was poorly worded thanks. My "monitoring the cell
temperature" along with "some heating" was to imply hand sensing
as a very simple check of what's going on in the cells if they
have charged for more than 20 minutes or from an unknown charge
state..

The assumption was the shaver does not use temperature sensing
except for catastrophic shutoff and if a smart 20 minute charger
it is of course designed for NiCad characteristics so may not ever
shut off.

Unlike NiCads, NiMh are exothermic while charging so will get
warm, especially at this rather high charge rate.. Once fully
charged however the temperature (T) rises sharply after the very
small voltage drop that indicate full charge . The problem is
this short delay and the electronics and packaging usually getting
warm along with ambient variations. So, as you say, it's not
usually used since difficult to detect reliably.

NiCads, being endothermic are more reliably temperature end of
charge detected since the T change is sharper. In either case,
_hot_ cells indicate overcharging

Regards..