Intro: Solder USB Power Cable to Raspberry Pi
Micro USB plugs are rare in my household, but a bunch of USB cables have been lying around. So maybe it is possible to solder a USB cable directly to the Raspberry PI? Yes it is, Paul Bealing describes it very well here: http://www2.pmb.co.nz/blog/?p=1767.
Step 1: Cut the USB Cable, Remove the Data Lines
We just need the red and black power wires from the USB cable. Remove about 5cm of isolation and cut the white and green data wires.
Step 2: Wrap the Strain-relief
To avoid the wires to be torn away, the cable is wrapped once around the video out. Please keep the orientation as shown in the image to avoid unwrapping. Then plunge the two wires through the hole in the middle of the board.
Step 3: Solder the Supply
Finally solder the wires to the board. Red (+5V / Vcc) is connected to the polyfuse F3 and black (0V / Gnd) to the protection diode D17. - Enjoy.