Subject:
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Re: RCX as programmable battery charger
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Newsgroups:
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lugnet.robotics
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Date:
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Mon, 14 Oct 2002 19:52:50 GMT
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Viewed:
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954 times
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In article <NGBBLFNPCLBPEJNIJPOEKEIJCCAA.camp0s@libero.it>, lego-
robotics@crynwr.com says...
> I was looking at my 1 years old cell phone, its battery is deteriorationg so
This could be done... I think. Learning how it all works is
enough of a reason to make a $100 microcontroller charge $10 batteries...
The Rcx outputs current limit at about 350 Ma, as I recall
(Info is on the WWW - search on "Rcx Internals" ).
The output voltage is about
1.5 volts LESS than the supply. I assume you'd run
this off a plug-in power supply.
So, let's say you want to charge 3 nicads, putting out
up to 1.5 volts into them. Decide what MAXIMUM current
you want to limit to, as use a series resistor to
limit the current. MAybe that would be something
like 100 Ma. So, figure it out, like this:
3 Nicads max voltage= 4.5
9Volts (Into Rcx) minus about 1.5 equals 7.5 out of Rcx
So you want a voltage drop of 7.5 - 4.5 = 3 volts at .1 Amps (100Ma)
R = Voltage Over Current R = E / I so R = 3 / .1 = 30 ohms.
A standard resistor value is 27 ohms. Ooops, how much POWER ??
P = E * I so Power (Watts) = 3 * .1 = .3 watts so you need at least
a 1/2 watt resistor.
Now, the Rcx has pulse width "speed" control, from full-on down
to on 1/8th of the time. It's fine to charge batteries with a pulse.
So you can set the current lower than your maximum by setting the
"speed". Oh, some Nicad and alkaline charges actually put a short
NEGATIVE (Opposite polarity) pulse thru the battery when charging.
Search on "Pulse Battery Charging" on Google.com
So, you can control charging current, possible negative-pulses,
and time. If you want to make a fast-charger, you may want to
measure temperature of the battery too.
There's plenty to start experimenting with!
--
Regards, Terry King ...In The Woods In Vermont
tking@waitsriver.k12.vt.us
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Message has 2 Replies:
 | | Vision Comand
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| I recently bought a vision comand. I was unable to install it. I have Windows XP. Can anyone help me? Is there a patch? thank you scott (22 years ago, 14-Oct-02, to lugnet.robotics)
| | | R: RCX as programmable battery charger
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| Thanks for that info, i also searched with google about maximum output power, but the only thingh i got was 10 mA from the the microcontroller chip and a lot about firmware, programming and other stuffs. What i'm whising to do, is not just a (...) (22 years ago, 14-Oct-02, to lugnet.robotics)
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Message is in Reply To:
| | RCX as programmable battery charger
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| I was looking at my 1 years old cell phone, its battery is deteriorationg so fast cause of a bad recharger. I wondered about building a "hardware" charger, but i never found a design without a IC with good features: without an IC its quite difficult (...) (22 years ago, 7-Oct-02, to lugnet.robotics)
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