This is a method for building cheap power over ethernet (PoE) converters using two easily available Dual RJ45 jacks from Radio Shack. I figured this out, and you can send email to jna@retina.net, if you have questions.
The best part about this is that there is very little wiring involved. Since the dual jacks already have all 8 wires connected together within the RJ45 jack, your job is more or less a cut and splice job. No punching down wires, but some soldering is involved.
Our Method closely resembles the NycWireless PoE method.
First, Purchase Two Dual RJ45 Surface Mount Jacks from Radio Shack (cat# 273-453)
Open them up. Designate one as your input (ground floor), and the other as the output (roof box/attic/whatever.)
You'll see wires coming from the metal terminal screws going to the jack, and then wires coming from the jack going to the second jack. All cuts are made to the wires going <i>inbetween the jacks</i>. All soldering and attaching goes to the wires that now go to the metal terminal screws.
Let's go!
1. Cut the GREEN, RED, BROWN, and WHITE leads between the two jacks. This prevents power from going into the ethernet while preserving the other wires for Ethernet TX/RX.
2. Cut the jack off the power supply. Figure out the polarity, and be sure to remember it.
3. Strip wires and Solder (or screw down) the GREEN and RED wires to the Negative (-) power supply wire. I did this by cutting off the metal (terminal screw clip) ends of the wires, twisting them together, stripping, and then soldering. Use Heat Shrink tubing or electrical tape when you're done.
4. Repeat for the Positive power supply wire and the BROWN and WHITE wires.
5. Make the same cuts on the wires inside the second jack.
6. Maintaining polarity, solder the GREEN and RED wires on the second jack to the negative power supply wire going to the power supply jack that you cut off earlier.
7. Repeat for the BROWN and WHITE wires, to the positive wire of the power supply jack. Note for the Linksys WAP11, the BROWN and WHITE Wires go to the center pin of the jack (on my power supply this was the wire without words printed on it.)
You're done. Within each jack, the individual RJ45 connector that has only a single set of wires going into it is where your ethernet goes. The RJ45 connector that has wires going in and out is where the PoE cable goes. Label the outside of the jack case with a Sharpie.
Remember that for long runs there will be a voltage drop, heat increases in the wire itself due to dissipation, and resistance to overcome. You may need a larger transformer (we did!) For the Linksys WAP11, we've found that using RadioShack's 2Amp DC "Travel" Adapter (Cat#??) works really well. We're using it now for a run of 148 feet, with the Travel Adapter set to 9VDC.
There's more information about handling voltage drops at NycWireless.
Good luck, and be sure to use a Multimeter to verify your work.
