Making a universal USB charging port? Is it possible to reduce a DC current's AMPs without affecting its voltage?
so i came with an idea to create a universal port that will charge all my devices so i got to thinking
First i would buy a AC/DC power plug(I live in Australia) to reduce the current to 5V @ 2.5Amps,
Link : http://bit.ly/L89ez5
I was planning to strip the end port so i'd have a positive and negative wire, which would eventually lead to the + and - power wires on a female USB port.
However i came to 2 problems with this.
1. Power Amperage/Voltage
Since it supplys 2.5Amps i found out this would be too much for some of my devices, after researching on the internet(Correct me if i'm wrong) I'm led to believe that with the way DC currents work, devices will only draw the amount needed, however my concern is that some devices sometimes make use of the extra amps and allow themselves to charge faster at the expense of a shorter battery life. To combat this i thought up of using a rotary switch linked with different amounts of resistors to allow me to select how many amps the port will give.
However my first problem is that after more researching that i can't simply use normal resistors to reduce the amps without affecting the Voltage. My aim amps choices are:
1000mA(Mobile Wifi device)
2000mA(Just in case)
How would i achieve this? what resistors would i need to buy/how many? I read something about some forumla but couldn't find what exactly it is.
2. The Data Pins
During my research i found out my PSVita is picky with its USB Port choice, its one of many few devices that like to be charged using a dummy port, In which i found out a Dummy port has the Data pins shorted, if they arn't shorted then the device will refuse to charge from the port. At first i thought it would be simple, i'd just have a switch that would short pins when i needed it. But then i realized what about my normal devices? What would i have to put between the the data pins to allow normal devices to charge normally.
Any and all advice would be appreciated.
This is what i had planned: