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Modifications: Power Over Ethernet (POE) 1

I wanted to improve the range and reception quality of my wifi hotspot for my neighbors, because it wasn’t very good with the router inside the house. There are basically two options for improving reception outdoors: an expensive extension antenna at the end of an *incredibly* expensive cable, or mounting the whole router in a weatherproof box and running a much cheaper ethernet cable up to it.

I did not want to run an additional wire to the router for power, so I decided to build a POE kit for it. Basically, the ethernet cable has two unused twisted pairs of wire. A pair of adapters are built which allow power to be run between them over these wires. The wires are kind of thin for this purpose, and some voltage is lost over large distances, but usually a whole twisted pair is used for each polarity (-) (+). The shorter, connecting cables that are not between the adapters should not be energised, since you don’t know if your hub is supplying POE in an incompatible way, or if one or more devices is built to ground or short-circuit these terminals.

These instructions told me how to quickly and safely open the case. This will void your warranty, but remember that if you bought your router from FON, they have sold it to you *without* a warranty:


I was going to build a *pair* of POE adapters out of ethernet cable connectors (the kind to make one long cable out of two), but there was only one left in the store. Looking at the back of the circuit board of my Linksys WRT54GL router, I saw that the necessary terminals were left unconnected, not grounded nor shorted with other terminals. This would make it easy to simply solder a pair of wires onto the back of the router circuit board.

This diagram shows the actual choice of wiring polarity I used, and is the most used standard, “New Cisco POE”:

And finally, here are the actual pictures of my own completed Frankenstein:

My soldering skills could use some improvement!

NAKED ROUTER, WOO-HOO!!! (You can barely tell, but yes, the LED lights are on)

I should have put a power receptacle on the adapter, but I was impatient so I just cut the power cord. After stripping the wires and resoldering them, I chose to reattach the plug so I can still use it directly. I marked the “energised” side with the red dot. The POE is only connected to the jack on the left leading to the router’s WAN port, not the one on the right leading to my cable modem.

Here is one of the world’s best tutorials on building your own POE kit:

The next stage is building a weatherproof enclosure. I’m looking for a plastic food storage container (“Tupperware”) as a temporary solution.

0 Responses to Modifications: Power Over Ethernet (POE) 1

  1. Oooo.

    Almost makes me want to resurrect my old (Fon-supplied!) WRT54G in a new power-over-ethernet incarnation and give this a go, except it’s currently nestled in a mess of network cables powering my home network in its second career. I might have to scavenge another WRT54G and give this a go 😉

  2. Florin says:

    Guys, by doing this there is a great risk to have interferences from the dc power intro your LAN an being slowed down a lot 🙂

  3. austintx says:

    And… if i’m unable to pump a full 100MBits through that cable, it’s no big deal, since my Internet connection is only 5MBits (and it looks like they’ve actually throttled my neighborhood down to 3MBits since a recent outage).

  4. carl says:

    I have read the article on the POE system. Well I’m sort of in the similar situation. Here it is, I have a linksys wrt54gl router that has a third party firmware in replacement to the retail firmware. The router is being used for pre-paid hotspot in my town. I purchased a POE injector from a vender online, and the POE is IEEE802.3af compliant. the output is 48v @0.32amps.

    Now the problem:
    The rj45 connection path, here is how I have the connection. Oh I’ve conttacted the router vender and they mentioned that the router is POE compliant. Ok, I have the cable modem connected to the in port of the POE, than the out port of the POE to the in port of the router. Please correct me if I’m wrong, so after that I’m guessing the POE should detect the devices and it required voltage, right. Well I’ve installed these systems in the past, so it’s puzzling to me that it’s not working here. Well reply to my email and shed some light for the issue. maybe missing something there. Thnak you Carl

  5. austintx says:

    Carl: I’m skeptical that your 48v .32A POE injector is right for this project. The router is built for 12v 1A, though it doesn’t require that much to operate, unless it is booting up or otherwise very busy. 48v is going to FRY IT, unless you have a ridiculously long Ethernet cable which drops 75% of the voltage, or you actually have a transformer at the router end to fix it.

    The Linksys WRT54GL doesn’t facilitate POE; It does not come from the factory prepared to accept power through an Ethernet port. My article is about modifying one so that it can. Perhaps Linksys meant that it would work with passive POE; which anything will.

    Ordinarilly, a passive POE system involves an “injector” close to the power transformer and an “extractor” close to the router. These devices place the voltage onto unused wires in the Ethernet cable, keeping it isolated from the wires used for data. You can buy them pre-made, build your own, or do it the lazy way like I did. I didn’t need an “extractor” because I soldered a couple of wires on the router’s circuit board.

    You would be better off using a passive injector/extractor pair, and the original transformer supplied by Linksys. I’ve had no problems powering my Linksys WRT54GL over 100′ of Ethernet cable this way.