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Will this circuit work to make a solar powered USB charger? Answered

Would this work? It's supposed to charge both the batteries and whatever is in the USB, and then when there is no light the batteries will charge the USB. IN914 is to prevent battery discharge, LM7805 is to change voltage to 5V. The question mark is for a a resistor i heard you need to bridge the white and green connections so it works on iphones/itouches. Anyone know which it is?

Link to better image of circuit: http://i27.tinypic.com/n4xq4x.jpg
Using this solar panel: http://www.adafruit.com/index.php?main_page=product_info&cPath=44&products_id=262

EDIT: I realized that I need two solar panels in series to get 12V, because 6V won't be enough because the LM7805 takes 2V. Am I right? In that case, wouldn't it make more sense to put the batteries in series with the USB



Best Answer 8 years ago

If you go with 12 volts put the battery on the right side of the regulator so that you are getting only 5 volts to it, and 5 volts might not charge the battery to max. 12 v. would be too much. And no, don't put it inseries with the usb port. It must be in parallel with it.

You've show 4x AA, which probably exceeds 5V or is very close to. I doubt that 5V is enough. Especially if you're running through a regulator (and why as the USB is regulated anyway)?


The solar panel is 6V, and the battery and usb are in parallel so they each should get 6V, no? And 4 AA batteries make 6V no? What happens if I send 6v to the usb(aka without the lm7805)?

That's clearer. Go with Steve' on this as he knows what he's talking about better than I do past this point.


You could use a "Low drop out regulator", instead of the 7805