On Sun, 10 Sep 2000 23:34:27 -0700 Mark Willis <[EMAIL PROTECTED]> wrote:
> Samuel W. Heywood wrote:
>> 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.
> Yep <G> I planned on that (Remove old batt. from cordless phone, snip
> wires, solder, install replacement battery in cordless phone <EG>
> Since then I've found that the local Radio Shack will let me check their
> NiCad recycle box for connectors and possibly batteries; Well, mostly
> connectors <G>
>> > 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've had less luck with long term storage; I grok BIOS settings pretty
> well so this isn't a bad problem, and learned long ago to do everything
> the same on EVERY computer, and to write HDD parameters where they can
> be seen on older machines <G>
> Scary numbers: With 6mA charging a 360mAh NiCad pack, it'd take about
> 60 hours for a full charge. Probably longer, all things considered.
> <G>
That is correct for a 360 mAh battery pack.
My calculation is for a 60mAh NiCad pack, as originally stated, not a
360mAh NiCad pack. Only 10 hours for a 60 mAh battery pack.
>> > 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.
> Nope. Your number's right for a resistor directly across 5V - you're
> forgetting the voltages across all the parts here. The resistor's
> actually across about 0.7V; I do this for a living - so I'm glad I
> didn't mess up:
I was making the calculation for the simple installation of a
current-limiting resistor connected between the 5V source and the 3.6 V
NiCad pack. I don't see the need for the diode if you simply disconnect
your 5V source after your 3.6 V NiCad pack is fully charged. IMHO, a NiCad
pack should be charged, then discharged almost completely, and then charged
again. I don't think it is a good idea to keep a NiCad pack on continuous
trickle charge all the time.
<snip>
> (For those not knowing: The diode's pretty mandatory, it's so you don't
> discharge the battery to all the 5V powered stuff when the power supply
> on your computer's turned off! That'd be "bad". <G>)
I agree; however, in my circuit I would simply disconnect the 5V powered
stuff when the computer is powered off. Then no problem.
All the best,
Sam Heywood
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