Power Over Ethernet

Power Over Ethernet

Power over ethernet lets you add a DC voltage source to the unused pairs in your ethernet cable. This power can be used to power devices that are poe compatible by just plugging the cable into them. Other devices can be powered by using a “tap” to break the DC pairs back out of the cable. POE is a good choice for powering devices in remote locations. A router can be placed on a roof right next to its high-gain antenna, reducing signal loss, without having to run a separate AC line. Plugging the DC “injector” into a UPS will keep dedicated VOIP phones functioning during a power outage. Terry Schmidt has written a nice guide covering the theory behind scratch building poe injectors and taps. It also has photos and descriptions of other peoples projects along with tips on how to keep from turning your router into a pile of plastic goo.

15 thoughts on “Power Over Ethernet

  1. hm…
    Well if i ever need a 250 ft power cord I know what to do now.

    Oh BTW, here is the definition of the word Hack from dictionary.com:

    v. tr.
    1. Informal. To alter (a computer program): hacked her text editor to read HTML.
    2. To gain access to (a computer file or network) illegally or without authorization: hacked the firm’s personnel database.

    v. intr.

    1. Informal.
    1. To write or refine computer programs skillfully.
    2. To use one’s skill in computer programming to gain illegal or unauthorized access to a file or network: hacked into the company’s intranet.

  2. spyingwind: wow, that’s neat. where ever did you learn how to do that? i’ve got one too.

    shut up:

    1. v. tr.
    to cause (a person) to stop talking

    2. v. intr.
    to cease writing or speaking

    now, wasn’t that fun fun? btw, see defintion number two.

    if you don’t like the hacks, then go away. just stop complaining about them; it’s not like anyone is forcing you to read this page.

  3. we all know dictionary.com is the formost leader in technology info.

    great article. i use these a lot at work and the thought of making my own for various purposes sounds cool.

  4. this is a very nice guide to making your own POE setup. even though POE is a pretty standard thing to do, making your own setup w/o the access point being originally made to use it is definitly a hack. nice one.

  5. PoE is standardized under IEEE P802.3af (Clause 33)

    Note that simply energizing the unused pairs in a typical Cat5 cable is -NOT- “PoE” and doing so risks inadvertent damage to devices corrected wrong.

    As one of the people who contributed to the spec, and as a person holding a related US Patent, I urge those interested in this spec (and the new high-power version coming out) to do appropriate Googling to get informed.

  6. “Note that simply energizing the unused pairs in a typical Cat5 cable is -NOT- “PoE” and doing so risks inadvertent damage to devices corrected wrong.”

    Actually I think that would be considered PoE, even if it’s not the traditional form. And yes, LOTS of things on this site will help you to inadvertently damage all kinds of devices, a little know-how is obvious before attempting such things.

  7. it seems to me that all this is not “Power-over-Ethernet” as in the specification but realy a simple “extension cord-over-ethernet” if you read the article they are not advocating that you power up all of the lines in your house with pseudo PoE but just allow yourself to put a Access Point or switch somewhere where power is not redily avalible or would be to diffcult to get to it.

    Use it for what it is: an __Extension cord__. That is what the big boys are doing with their APs. If you are trying to power a computer http://news.bbc.co.uk/2/hi/technology/4494899.stm from anywhere then you better hit the search engines up.

  8. reply to #2: nice, I just checked dict.org and realized that the standard definition of hack isn’t in the dictionary. A hack is a nonstandard is a solution to a problem that may or may not exist dervied from exploration of the surrounding topic (from hacking)

  9. You can get Power off of pretty mutch any
    Serial Port that comes Off the Mainboard
    BUS.I have a MSDOS Controlled AM/FM TV
    Broadcaster that only uses the Power off
    of a old 8pin Serial Interface.You can
    also get some off of the System Speaker
    as I once Demonstrated with a Crystoform
    LCD a while back, it’s just in Pulsating
    form cause it’s converting Bit Pipeline
    Data to Hz.

  10. Steve,

    What is your patent and does it only apply to P802.3af? If so please publish the patent number so we can avoid it.

    Personally I feel that standards that include proprietary patents are an obscene perversion of capitalism and should be avoided like the plague.


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