> Hi Olin, we have always trickled charged our NiCds
> at 10% C (constant current source).
> Usually overnight, often for a couple of days
> if we forget. We get excellent use from all our NiCd
> powered test equipment, for many years. My personal
> opinion is that this is the best charging method,
> provided you don't need a quick charge. :o)

This seems to be less clear for NiMH.  Here are two direct quotes from
Panasonic literature about their NiMH batteries:

"Trickle current: 0.033 to 0.05CmA.  When the trickle current is set higher,
the temperature rise of the batteries is increased, causing the battery
charactersistics to deteriorate."

"Total timer: 10 to 20 hours.  The overcharging of nickle-metal hydride
batteries, even by trickle charging, causes a deterioration in the
characteristics of the batteries.  To prevent overcharging by trickle
charging or any other charging method, the provision of a timer to regulate
the total charging time is recommended."

On the other hand, I've seen other manufacturers explicitly state that
trickle charging at .1C indefinitely causes no ill effects.  Perhaps there
are slightly different chemistries.

My conclusion is not to do long term trickle charging unless you know it's
OK for the particular batteries you have.


********************************************************************
Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 742-9014, olin@embedinc.com, http://www.embedinc.com

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