how should i be making an USB solar charger?

i have a 12V solar panel lying around, and want to make an USB charger with it.
i've looked around, but i cant find anything with the same specs as i have...

anyway, i want something that i can put indoors overday, that charges something (batteries?) and then that something charges my MP3 player overnight.
what is the best way/instructable to use?

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Re-design8 years ago
I've never seen one.

You could change several 9 volt batteries in parallel then switch and have them charge your usb thingie.  You'll need to use a voltage regulator to get the 12 v's down to 10 to charge the batteries.  THen another voltage regulator to get the 9 v's down to 5 for the use.

You can use a dpdt on off on switch to do the change over.  The center is off with battery charge on one side and usb charge on the other.

It's a lot of work just to charge something that you can charge in an hour just by plugging into your computer but it's good experience and there's not a better way to learn electronics than designing and building something.

You can get voltage regulator info by googeling it and the pinout for the usb port also.

Good luck.
godofal (author)  Re-design8 years ago
its also for becouse its better, and partly becouse i have to much spare time :D
but ur saying i need 10V to charge 9V batteries?

anyway, is it safe to charge rechargable batteries straight off a solar panel? (no li-ion ofcourse)

if so, il just place enough AA's for 12V, charge those off the panel and then just use a 5V regulator and a switch for charging my MP3 player...
godofal (author)  godofal8 years ago
oh, and in case u wanted 2 ask, yes im going to documentate and make an instructable out of it if it works out ok :)
Unless it's a large panel it's only going to slow charge so it shouldn't be a problem.

And you do need a little higher voltage than you're charging since you loose some in the charging due to restances.

Documenting it for instructables is an understood.
godofal (author)  Re-design8 years ago
but its not a problem to charge 8 batteries(1.5V) in series with 12 V?

I don't think 12 v. would get 8 batteries to full voltage.  But some 1.5 v. rechargeables are only 1.2 volts.
godofal (author)  Re-design8 years ago
so use 7 batteries then?
godofal (author)  godofal8 years ago
just found some 1.2V AA's, so i can use 8 of them and then it charges OK?