Steve wrote:
Which brings me to another question..
As I have stated, I have had a very good experience with the NiMH AA
batteries and a 'smart charger' from Maha..
I have just been looking at replacement battery packs for my two Skil
Proffesional cordless drill. These drills came with two each 12 volt Ni-Cad
battery packs and one each Ni-Cad charger.
After 10 years of heavy and faithful service in building my 38 ft boat, it's
time to replace the batteries..
The replacement batteries for these drills are now only available in NiMH
and cost $82 each. (2.5 ah)..
What will happen if I use these new batteries in the Skill OEM 'dumb' Ni-Cad
charger??
The battery vendor doesn't mention or recommend any battery chargers for
these batteries.
I wish someone would reveal the smart circuit so I could modify my existing
chargers. Were it not for the microprocessor involved, a clever (not me) guy
could reverse engineer it from one of the AA chargers.
You can use existing NiCd chargers to charge NiMH. The difference is - it
will take about twice longer because older chargers use constant current
and NiMH is about twice larger capacity then NiCd.
Another issue is termination once it is charged. At low current (which will
be the case with NiCd charger) it is not as critical as other poster mentioned -
there is just not enough heat development at low current to cause any problems
(not to be mistaken with LiIon battery, where overcharge will _kill_ the battery).
It is indeed better if you terminate charging when full using smart methods
(such as negative voltage drop) as battery will live a litle longer.
But for small currents this methods are not applicable anyway, because
at low current there is no negative voltage drop... so you are back to
the timer.
Terminate charging after batteries get hot, or after time
passed, calculated using formula: cap. of new NiMH * 12 hr / capacity of original NiCd
and you will be OK.
Regards,
Evgenij
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