How to make a "USB fast charge cable" for your phone

I have USB adapters in the "power ports" (cigarette lighter sockets) of my car and motorcycle and a wall wart with USB ports for use in the house. When I use standard USB cables, my phone, iPod, GPS, and other gadgets charge at only the standard USB rate -- about half an amp (500ma). Often this is ok. 500ma is enough to charge most things overnight. However, 500ma is not enough to power my phone and charge the battery at the same time. In fact, it's not even enough to just power the phone when it is busy -- such as when it is running Google Maps Navigation and has the screen on. My Nexus S battery will slowly go dead during road trips even though it is plugged into the USB power port. Clearly I need to supply the phone with more juice.

USB devices like your phone will draw only 500ma from devices that they recognize as USB hosts, such as your computer (sometimes there are special drivers you can install to boost the power output for charging USB devices, but I never install them). Dedicated USB chargers will supply more than 500ma -- usually 1 amp but sometimes more. How does your phone know the difference between a dedicated charger and your computer?

Pick up any USB cable. Look inside the end that you plug into the computer and you will notice that there are 4 metal tabs. The outer two carry power and the inner two carry data. USB gadgets like your phone look at those two data pins to see if there is a computer on the other end of the cable. If there is, the gadget will draw only 500ma. If there is not, the gadget will draw more, and thus charge faster. Or in the case of my Nexus S, not go dead while I use it for navigation.

The way you fool the phone into thinking it is on "AC power" rather than "USB power" is to short the two data pins together. When the phone probes the data pins, it will see that the pins are connected together, decide that it is on "AC power", and will draw more current. You should take care, however, to short the pins in such a way that the phone sees the short, but whatever you plug the cable into doesn't see the pins at all. Shorting the data pins on your computer may damage it. You've been warned! I should note here that I never plug a modified cable into an actual computer -- only into USB power ports. If you follow these instructions and your computer or phone catches fire or otherwise gets damaged, it's your fault, not mine. No one made you do this. Moving on...

Materials needed:
* Aluminum foil
* Scotch tape
* Scissors
* USB cable

I am modifying an Apple USB extension cable, since I have one handy and it lets me plug other "real" USB cables into it, saving me the trouble of modifying more than one cable. You can use whatever USB cables you have handy. The Apple USB extension cables have an annoying ridge in them that prevents insertion of ordinary USB cables, but that is easily fixed with a pair of needle-nose pliers; simply smash the little ridge and the Apple USB extension cable will be converted into an ordinary one.

Look in the computer end of your USB cable again to see how far apart the middle two metal tabs are. Cut a small rectangle from a sheet of aluminum foil, just wide enough to cover the middle two pins. Stick the rectangle onto a piece of scotch tape. Trim the piece of tape+foil so that it will cover the middle two pins but not the outer two. Make sure the tape is a little wider than the foil. The foil will short the pins from the point of view of the phone, and the tape will hide the pins from the point of view of the cigarette lighter/wall wart USB port. Insert the strip of tape+foil into the USB plug to cover the middle two pins, aluminum foil side down. Rub the tape+foil down over the pins (using a toothpick or whatever), making sure it is flat and stuck well. Stick the rest of the tape around the outside of the metal housing. Leaving the extra tape wrapped around like this means there will not be a tape edge to scrape when you insert the USB plug into a port.

Plug the modified cable into a USB power port and into your phone. It should show that it is charging. But at what rate? On a Nexus S, you can dial *#*#4636#*#* (star-pound-star-pound INFO pound-star-pound-star) to get to a special "phone information" menu that will show you whether the phone is on AC power or USB power. After applying the tape and foil, I accessed that menu and saw that the Nexus believes that it is on AC power -- success!
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