On Tue, 29 Aug 2000 03:00:29 -0700 Mark Willis <[EMAIL PROTECTED]> wrote:
> Hi, all. In talking with some people about replacing Real Time / CMOS
> batteries, I have had some ideas on "Improving" these.
> Wanted to ask: Has anyone here soldered a Cordless Telephone battery
> pack in place, to replace the standard 3V/60R NiCad battery pack?
> (Disadvantage: It'd take "forever" to charge off the motherboard.
> Advantage: It'd run your CMOS / Real Time Clock, for a LONG time.)
I've done that. It works. I charged the battery *before* soldering
it onto the motherboard.
> Just a semi-random thought, that I may try (Sometimes can get 3-AA NiCad
> packs for $2 or so, this'd be interesting for some machines that are
> normally powered off, though I may have to add a power charging circuit
> to charge this quicker when the machine's powered on!) So many machines
> here are usually off, only occasionally powered up for a few hours, and
> that's rough on CMOS batteries. I've thought of putting a 117V to 5V
> trickle charger in those machines.
I know from personal experience and observation that a machine can be
shut down, powered off, and remain unplugged for a couple of years and
usually still conserve the CMOS settings and the correct time/date. It
only takes a few micro-amperes to hold the time and CMOS settings. That is
not at all rough on the batteries. Installing a trickle-charger would be a
waste of time and money.
> I am imagining a quite slow voltage-limited, current-limited trickle
> charge for these batteries (Probably just a diode from 5V then a 120 ohm
> resistor to current limit this to about 6mA so a 60mAh pack charges at
> 1/10C or so?)
If you should decide to build a trickle charger for a 60mAh battery pack,
then I agree that the current should be limited to about 6mA. However, I
disagree with the value you have calculated for your resistor. Using the
Ohm's Law formula,
R = E / I, and substituting we get R = 5 / .006 or 833 ohms.
All the best,
Sam Heywood
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