PV Gap

Adrian Said:

I want to make a very small small solar garden light.....?

We Answered:

The 1.5V panel can probably charge a single nicad cell, though how long it will take is not known unless the current rating of the panel is known. The nicad cell needs to be connected the right way around or it will destroy the solar panel. Better to have a 3V panel and a single cell. This will deliver its full current to charge the battery.

The voltage of a single cell is insufficient to operate an led directly, though an led is what you need. The normal torch bulb uses far too much current for this, even the smallest types.

If you look up "Joule Thief" you will find a way to increase the voltage of a single cell enough to operate an LED, or you can have extra panels and cells in series to get a higher voltage. An LED needs a series ballast resistor. The joule thief achieves that in its own way. The links below shows circuits. Yes it may be cheaper to buy one ready made, but the battery and the solar cell are the expensive parts, the electronic components are just peanuts. And good to try anyway. Learning. The Joule Thief type of circuit uses so little current to drive an LED it is probably unnecessary to turn it off. The system could "know" it is dark from the solar cell itself too, but you need some sort of control device to turn the lamp on and off. Can't avoid some electronics in this unit. And it saves money, it just needs one cell instead of 3 or 4 with a 6V solar panel to drive even an led directly.
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