Setup: I have a portable solar panel (for camping, etc) that outputs to two USB ports (2 amp). I want to use this to power a small Li-ion charger. I know that there are products/adapters I can buy to achieve this but I am fascinated by the science of it and want to know *how* all this works. So I want to build the circuit myself. Specs: - My solar panel is 19.5 watts (in sunlight) and has two 2 amp USB ports for output. - My charger requires input of 12v 1amp. So, if I under stand this right, I only need 12 watts to power the charger and my solar panel *can* output up to 20 watts (5v 2amp x 2). So I think I have enough watts to work with but I don't know how to physically achieve the conversions I need. Should I wire the USB outputs in series (and double the voltage) or should I wire them in parallel (and double the amps)? Either way I will need to convert both for my output to match the input for the charger but I guess, I just don't know which approach is best and why. Which devices do I want to use in my circuit to convert voltage/amps? I am pretty sure that a transformer would do the trick for AC but I don't know how to change voltage on DC? And are amps as simple as resistors/ohms law? Is there a generally accepted "better" way to solve this problem - ie, is there a rule of thumb or something that says its always "better" to wire them in series and do your conversions working with high voltages or/rather go parallel and convert working with higher amps? And why? Do I need to worry about my current not being entirely stable? I know that the output of solar panels can vary, should I be thinking about capacitors? Or? So those are my questions - thank you so much for your time. And I really do what to learn "why" so if you have any links that would explain these solutions in beginner terms, that would be fantastic! Thanks!