DIYbanter - View Single Post - Lithium Ion or NiMH power tool "systems": Which one?

Jim Yanik

(Chris Lewis) wrote in
:

According to ransley :

Chris I did look at that site, I still believe even from what they
said heat is being generated, and damaging the cell, since the
dustbuster is not being trickle charged

Heat is always produced if current is going through it. The
question is how much, and how much the cell can tolerate it.

Or, in other words, is a continuous .01C trickle charge when
the place where it is at 20C going to do as much damage as
letting the battery sit on a window sill at 35C? No.

That seems sarcastic, but it's not intended to be, just pointing
out that the fact you do put a little heat in the battery via
trickle charge, it's not going to be any different than the same
amount of heat introduced any other way.

Unless the trickle charger makes the battery noticably warm,
it's going to make relatively little difference. At least with
Nicds.

Continuous trickle charge matters more with NiMH and Lithium (note
the remarks about hydrogen generation on NiMH).

yet 1-hour fast chargers make NiCd packs quite warm,and those packs last
far longer than trickle charged packs. The heat only builds up in the last
part of the charge,BTW.That is how many chargers decide when to cut off the
charge.Other fast chargers use the "knee" voltage to detect a full charge
for NiCds.
NiMH fast chargers must use the deltaV/deltaT method of charge
detection,there's no voltage "knee" in NiMH cells.

trickle chargers are just simple wallwart transformers and not IC charge
controlled,simply X ma for Y time(usually at or less than 1/10C
rate),allowing for under or over charging of the pack,shortening it's life.

--
Jim Yanik
jyanik
at
kua.net