Since becoming a student at UC Davis, I have realized the importance of knowing where power outlets are so that I can plug my phone in... I spend a lot of time on my phone and it drains the battery rather fast.. I have since decided to build a solar cellphone charger. Now I know I could just go out and buy one, but: A: whats the fun in that & B: I have a problem with the chargers that are out there. They mainly charge your cellphone (or other USB peripheral device) from the internal battery.. which in turn gets charged from the solar cell. The problem with this is that you are required to leave the solar charger unit out in the sun sometimes for 6 or more hours. Now I don't know about you, but I think the sun gets pretty hot right? The internal battery of the solar chargers are lithium ion/lithium polymer batteries which are not supposed to be left in the heat of the sun or they can be destroyed (I made the mistake of leaving my ipod on the seat of my car... needless to say I killed that battery and it would only hold a charge for 20 minutes after that). Besides, the solar cells are small and charge the internal batteries up slowly...
So my theory is this: 3.5W solar cell connected to a boost/buck converter with voltage regulation and a USB output. The converter is capable of taking 3-30V and regulating it to a stable 5V which happens to be the voltage of the USB (notice I didn't say bus, because that would then be universal serial bus.. bus ;) ) The beauty of this is that as sun exposure changes and the voltage from the cell (actually an array, or panel) will drop, but the output on the USB will remain at 5V, just at a lower current. This bare bones charger will be housed inside a custom acrylic enclosure. Pictures will come once all the parts have come in the mail.
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