I’ve got a couple of Raspberry Pi’s kicking around. One of the limitations that I didn’t quite like was that I needed to have an outlet nearby since the voltage drop over long extended USB runs can be too much when you’re pushing the Pi.
I found this TP-Link Power Over Ethernet Adapter Kit and saw that it had optional 5/9/12V DC power output. Since the Pi requires 5v, I thought I’d give it a try. I also had to pick up a StarTech.com USB2TYPEM2M 2m USB to Type M Barrel Cable, USB to 5.5mm 5V DC Cable
I added in a Micro USB OTG to USB 2.0 Adapter to connect the USB-barrel connector to the Pi.
I tested it out in with a 50 foot ethernet cable, and no issues running wifi+pi camera+usb thumbdrive steady for 1 week!
You do also get fully functioning 100M ethernet cable on the other side, but I added the wifi usb adapter that I had just to make sure that this adapter was up to the job. According to the manual of the PoE adapter, it’ll push out 2.1a at 5v, which is plenty of power for the Pi. Note that this solution that I used is NOT 802.3af compliant, so the splitter won’t work with a typical PoE switch. I didn’t realize this until after I had purchased this TP-Link kit, but there are similar options available.
If you’ve already got a PoE switch or injector, you can get the Tp-Link TL-POE10R Splitter. If you need an injector as well, you could also couple it with the TP-Link TL-POE150S Poe Injector. I haven’t tried the 802.3af solution, but it appears that it puts out the same amount of power.
I’ve seen people out there splice in USB power using the unused pairs of a cat5 cable, and I know you can buy “passive” adapters that do the same thing, but in my experience with the Raspberry Pi, voltage drop is the enemy.