At 12:55 AM 9/5/2003 -0400, the amazing Mr. Walter FrogRecord Knapp wrote:
> > Can anyone say why Li ion are so complicated to charge? I mean it is a
> > battery for gosh sake! I didn't think so. . .
>
>You can find discussions of this all over the place, here's a sample:
>
>"Li-Ion Charging: Li-Ion batteries commonly require a constant current,
>constant voltage (CCCV) type of charging algorithm. In other words, a
>Li-Ion battery should be charged at a set current level (typically from
>1 to 1.5 amperes) until it reaches its final voltage. At this point, the
>charger circuitry should switch over to constant voltage mode, and
>provide the current necessary to hold the battery at this final voltage
>(typically 4.2 V per cell).Thus, the charger must be capable of
>providing stable control loops for maintaining either current or voltage
>at a constant value,depending on the state of the battery."
>
>"The main challenge in charging a Li-Ion battery is to realize the
>battery's full capacity without overcharging it, which could result in
>catastrophic failure. There is little room for error, only =B11%.
>Overcharging by more than +1% could result in battery failure, but
>undercharging by more than 1% results in reduced capacity. For example,
>undercharging a Li-Ion battery by only 100 mV (-2.4% for a 4.2-V Li-Ion
>cell) results in about a 10% loss in capacity. Since the room for error
>is so small, high accuracy is required of the charging-control
>circuitry.To achieve this accuracy, the controller must have a precision
>voltage reference, a low-offset high-gain feedback amplifier,and an
>accurately matched resistance divider.The combined errors of all these
>components must result in an overall error less than =B11%."
>
>That's the idea anyway, now you know. The above was lifted from a ad
>blurb for a particular charger. I expect more research would show that
>if you charged it slow enough it might get easier. But for any
>reasonable time they are touchy.
>
>Walt
>
Once again, I have underestimated you. I should never have guessed in
advance that you didn't know. I now begin to understand the dilemma. But=
Sony seems to have solved it 10 years ago with all their cam-corders.
What about temperature of the battery inside its case, don't tell me that
fussy voltage rating has no nasty temperature coefficient!!?? If the
charger is in one case and the battery in another - - - how could the
battery temperature ever be figured into that 1% from inside the
charger? Maybe that is one reason all the Li ion batteries have so many
connections . . ?
And BTW ALL those connections had better be good ones. At one amp charge
rate obviously all it takes to get 100 mv is 0.1 ohm somewhere TOTAL
between the cell internals and the charger internals - easy to achieve
initially, but after several years of sloppy field use?? I think I'll go
scrub clean all my LI ion battery connections and chargers . . .
my best regards,
Marty Michener
MIST Software Associates PO Box 269, Hollis, NH 03049
EnjoyBirds.com - Software that migrates with you. http://www.EnjoyBirds=
.com
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