I'm new to the forum and a newb when it comes to electronics. I have built a few hobby boards from Ramsey electronics and have decent soldering abilities but as far as component selection I'm a little stuck at the moment.
I am basically trying to build a circuit identical to this
http://forums.vwvortex.com/showthread.php?6983041-DIY-Built-in-USB-Charging-Ports
Now i will be running the 5v converter off of a 12v DC source and the converter is rated at 5v DC @ 3 amps. For anyone using the search function, most smartphones use the d+ and d- contacts on a USB port to communicate to the device which amount of current to draw. In the previously posted link they were trying to charge at 2000 mah. To get 2000 mah an iphone needs to see 2.75v on d+ and 2v on d- . I am only trying to pull 900 mah by using 2v at d+ and 2.75v on d-. I know that this voltage orientation will work for 900 mah based on this sites listed information
https://www.voltaicsystems.com/blog/choosing-usb-pin-voltages-for-iphones-and-ipads/
So to sum all of this up, my intentions are to use the listed 47k ohm, 51k ohm and 75k ohm resistors but wire them in opposite to the way the original link listed to get the voltages on the pins I need. This should work with most smart phones.
So the problem I'm having is resistor selection. I've tried to use the online resistor calculators and formulas both to find what wattage resistors to buy so that they can handle the heat. Also the type of resistors needed. Also looking at mousers site they list heat ranges in their selection. I'm just trying to find common parts but if it needs to be anything special I have no problem with going that route. Any help or direction would be greatly appreciated.
Btw I'm going with USB ports rather than the common charger for a specific reason, so please don't refer me to the thousands of typical chargers. I simply need direction on resistor selection
Thanks for your time
I am basically trying to build a circuit identical to this
http://forums.vwvortex.com/showthread.php?6983041-DIY-Built-in-USB-Charging-Ports
Now i will be running the 5v converter off of a 12v DC source and the converter is rated at 5v DC @ 3 amps. For anyone using the search function, most smartphones use the d+ and d- contacts on a USB port to communicate to the device which amount of current to draw. In the previously posted link they were trying to charge at 2000 mah. To get 2000 mah an iphone needs to see 2.75v on d+ and 2v on d- . I am only trying to pull 900 mah by using 2v at d+ and 2.75v on d-. I know that this voltage orientation will work for 900 mah based on this sites listed information
https://www.voltaicsystems.com/blog/choosing-usb-pin-voltages-for-iphones-and-ipads/
So to sum all of this up, my intentions are to use the listed 47k ohm, 51k ohm and 75k ohm resistors but wire them in opposite to the way the original link listed to get the voltages on the pins I need. This should work with most smart phones.
So the problem I'm having is resistor selection. I've tried to use the online resistor calculators and formulas both to find what wattage resistors to buy so that they can handle the heat. Also the type of resistors needed. Also looking at mousers site they list heat ranges in their selection. I'm just trying to find common parts but if it needs to be anything special I have no problem with going that route. Any help or direction would be greatly appreciated.
Btw I'm going with USB ports rather than the common charger for a specific reason, so please don't refer me to the thousands of typical chargers. I simply need direction on resistor selection
Thanks for your time