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solar powered clock

xeroshady

Oct 5, 2012
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Hey guys, I'm a college freshman, and a total newbie when it comes to electronics. I'm working on a project, the gist of which is as follows:

I want to use a solar panel to power an ordinary clock. The solar panel also recharges a set of rechargeable batteries, as long as it receives optimal sunlight. When the Earth rotates and the solar panel no longer receives direct sunlight, the rechargeable batteries take over and power the clock, as well as a motor, which makes the whole setup rotate, until the solar panel receives direct sunlight once again. Now, the solar panel takes over, and the batteries stop supplying power to the motor, and the cycles continues. By the evening, the rechargeable batteries should have stored enough energy to power the clock throughout the night, until the next morning, when the solar panel takes over.

Basically, when the voltage produced by the solar panel is high,current should flow from panel to clock. When the voltage produced by the solar panel is low, current should flow from rechargeable batteries to motor and clock.

How should I go about this? What components will I need? (capacitors? transistors? relays?)
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Jan 21, 2010
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My first suggestion would be to get a solar garden light and hack it so it didn't light the LED, and use the battery to power the clock.

These things mistreat the battery, but a rechargeable battery should last almost as long as the battery in a regular clock, so you won't have to replace it often.
 

donkey

Feb 26, 2011
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the easiest way to do this is to hook your solar panel to the batteries using a diode to stop voltage feedback. they will charge the batteries as long as there is sunlight. so no matter what happens your batteries will still recieve some sort of charging from the panels. then run your clock of the batteries. no need for complicated circuits unless you want to put in a charge controller (at 1.5volts I doubt it would be the best idea)
 

xeroshady

Oct 5, 2012
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ok, I found this:

http://www.evilmadscientist.com/2008/simple-solar-circuits/

so all I have to do is replace the LED by a motor and clock. Now I've got a few questions.

1) what's the resistance of a clock powered by a 1.5V AA battery? (or how much current is required to power it?)

2) what values of solar panel voltage, current and rechargeable battery voltage, current should I use?

3) incase I decide to use a motor, will the motor from a laptop CD tray suffice to rotate the solar panel (which might be 50 grams max)?
 

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BobK

Jan 5, 2010
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That circuit is designed to turn the LED off when the sun is shining. Not a good idea for your clock.

Bob
 

xeroshady

Oct 5, 2012
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Argh, that was stupid of me.

So, will something like this (image in attachment) work? (disregarding component values)
 

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(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Find a solar garden lamp that contains a single battery.
 

donkey

Feb 26, 2011
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stupid question here, but why in your diagram do you have a clock and a motor?
 

BobK

Jan 5, 2010
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When the Earth rotates and the solar panel no longer receives direct sunlight, the rechargeable batteries take over and power the clock, as well as a motor, which makes the whole setup rotate, until the solar panel receives direct sunlight once again.
Not sure how that is going to work, unless the motor is driving the clock on a car going east to west, at about 1000MPH (depending on latitude.).

Bob
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Not sure how that is going to work, unless the motor is driving the clock on a car going east to west, at about 1000MPH (depending on latitude.).

Hahaha, yeah.

The power required by the clock is so small that there is no need to steer the panel to point at the sun.

The difference in power you get may not even be as much as the motor requires!

And there's a whole lot of other reliability and practicality issues that do not need to be considered if you omit this.
 
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