Most dedicated chargers shut off or trickle upon full charge. This is
particularly true of Lithium Ion; you can't overcharge those even a
little or they become mini-bombs. For that reason, they have regulators
built into each cell to prevent overcharging.
Smart NiMH chargers also shut off before damaging the batteries.
Good NiCad chargers do the same. Bad ones don't. My Black and Decker
drill's charger warns against charging longer than 24 hours. It doesn't
regulate the charge apparently.
There is a (cheap) form of charger commonly used with low-end NiCad
applications, and in a larger form, with low end lead-acid battery
chargers (automotive). The principle of this sort of charger is this:
power flows from higher-voltage sources to lower-voltage destinations.
...just like water flows downhill. A depleated 12v automotive battery,
for example, might be dead at around 11 volts. It's fully charged at
12.5 volts, and "floats" at 13.5 volts or less. So the idea of a taper
charger is to charge at a constant 13.4 volts (approximately). If the
battery is at 11 volts, it takes on a charge rapidly. As it begins to
reach capacity, its internal voltage increases, and thus the charge rate
declines. When the battery's charge state reaches 13.4 volts, there is
no differential between the source (the charger) and the destination
(the battery). Current stops flowing (or slows down to the trickle
rate) simply by virtue of the fact that there is no appreciable voltage
differential. The charger self-regulates this way, but the charge times
are slower than chargers which have multiple phases.
[EMAIL PROTECTED] wrote:
In a message dated 9/2/2005 11:27:16 PM Pacific Standard Time,
[EMAIL PROTECTED] writes:
Think of it more this way...
If you heat water toward boiling point, you will get hot water, but if
you heat it hotter than boiling point, you will get gas (steam). Water
can only accept so much heat before it vaporizes.
A battery can only accept so much energy before its physical properties
also begin to change for the worse. A lead acid battery will boil off
its electrolite. A NiCad will overheat, expand, explode. A LiIon will
suddenly ignite. The chemistry is affected by charge state. Push it
past a certain point, and its composition changes in an undesirable way.
============
Hmmm, I leave the charger on my Canon batteries on a long time. For hours,
usually longer than it takes to actually charge them. Go away, busy, etc.
I THINK the charger shuts off when the battery is full. It appears to. But
maybe I should double-check this. I do the same thing actually, with everything
I charge. Cell phone battery, PDA battery, etc. Leave it there over night
sometimes.
However, in those situations the charger is battery specific, designed for
that specific battery. And they all appear to shut off.
But even so I may be losing some battery power, huh? Maybe they overcharge a
tiny little bit each time. This needs more thought.
Marnie Or more helpful people with answers.
