I am going on a camping trip and want to build a 12v charger for my cell phone for emergency as I will be on a island I want to use Small Solar Panel 3V 20mA I was wondering how many I would need to make 12v so I can wire them to a car charger also how would I wire them thanks

You may be better off buying one of those units already wired up. First you need to wire enough panels to give you more than 12V.. something like 15V or more. This would ensure you get 12V due to cloudy days, different angles to the sun, and other conditions. Then, if you are lucky enough to get some decent sun, you need some electronics to knock it down to the 12V you are looking for and not burn up your cellphone charger due to excessive voltage. Oh, don't forget you have to mount all this stuff into something that is sturdy, protective, and still allow the sun in.

Like I said, you may be better off buying a pre built unit.

thanks sin bad i was thinking of buy in this http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=44768 and wiring it to a cigerate lighter socket and simpling plugining my car charger in it

How about this charger, even comes with the cords for various cell phones
http://www.goldengadgets.com/product_info.php?products_id=396

Even a better assortment of solar and emergency chargers for phones.
http://www.21st-century-goods.com/page/21st/CTGY/CELL1

I was actually think of those on that exact site i was just trying to maybr make it my self thanks mark