After studying how to make a simple solar charger, I decide to make a fast prototype to test. I got one solar panel a long time ago, the ratings of this solar panel is unknown. The solar panel will output different voltage and current under different lighting condition, so we have to measure it before use. I measured this solar panel would output maximum 3V under bright sunlight, and output 2V under my table lamp.
Everyone got a table lamp when working in front of the computer, and the light condition will remain considerably constant when compare to the outdoor sunlight condition. It would be easy to make one simple table lamp charger.
The above diagram is my setup, I used the schottky diode (IN5819) to prevent back current flow to solar panel when the lamp is off. The diode is placed between the solar panel and the the battery holder with two AAA batteries loaded. When charging, I measured the forward voltage across the diode is 0.14V which is small when compare to a normal diode.
Initially, the voltage across 2 batteries are 1.7V, after a while the voltage is 1.81V, so it is charging right now. The charge current measured is only 0.12mA.
The current is too small, and not so sure how long it will charge up to 2V:)
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