Powering a wired `LAN port

Discussion in 'DIY PC' started by Man-wai Chang, Dec 4, 2011.

  1. How much current and/or maybe power does a typical gigabit LAN port use?
    500mA like USB 2 port?

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    Man-wai Chang, Dec 4, 2011
    #1
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  2. Man-wai Chang

    Paul Guest

    Man-wai Chang wrote:
    >
    > How much current and/or maybe power does a typical gigabit LAN port use?
    > 500mA like USB 2 port?
    >


    I'm not sure I understand the question.

    *******

    There is a standard called Power over Ethernet. It's used by a
    central piece of equipment, to power Ethernet peripherals. It
    might provide more power, than the Ethernet chip inside the
    peripheral might need.

    http://en.wikipedia.org/wiki/Power_over_ethernet

    "The original IEEE 802.3af-2003 PoE standard provides up
    to 15.4 W of DC power (minimum 44 V DC and 350 mA) to each device."

    Not every piece of Ethernet equipment, pumps DC power down
    the Ethernet cable. My little $39.95 four port router,
    does not power the Ethernet cables. Plugging in a peripheral
    which runs off PoE into my router, would result in the
    peripheral being un-powered and non-operational.

    You might find things like some Cisco router, with a
    PoE power source on each Ethernet port. It's more
    likely to be some expensive equipment which provides power.

    It is possible to buy devices that pump "phantom" power down
    an Ethernet cable. For example, this device set.

    ftp://ftp10.dlink.com/pdfs/products/DWL-P200/DWL-P200_ds.pdf

    What that does, is allow ordinary ethernet data to travel through
    the cable, while at the same time, adding PoE. One adapter box,
    inserts 48V @ 400mA into the Ethernet cable. Now, if you did that,
    I presume *any* PoE device at the other end would work.

    The second adapter they provide, pulls off the PoE power, and converts
    it to a more useful lower voltage potential. For example, 12V DC is
    used by a lot of surveillance cameras. And other things might benefit
    from a 5V DC supply. And so on. Using that kit, means you could
    power a surveillance camera, packet based, outside your house and
    away from an AC outlet.

    But a proper PoE compatible peripheral, wouldn't need the adapter
    at the end, but would just draw in the 44V or 48V DC or whatever,
    and do internal conversion to a lower DC voltage. Not many silicon
    chips could deal directly with the 44V directly.

    So the total available power on the PoE cable, is higher than USB, but
    it's not directly useful. You could even get a nasty shock from it!

    Paul
     
    Paul, Dec 4, 2011
    #2
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  3. >> How much current and/or maybe power does a typical gigabit LAN port
    >> use? 500mA like USB 2 port?

    >
    > I'm not sure I understand the question.


    Pardon my English. I meant how much current/power is needed to drive a
    typical gigabit ethernet port in a hub/switch/router?

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    Man-wai Chang, Dec 5, 2011
    #3
  4. Man-wai Chang

    Paul Guest

    Man-wai Chang wrote:
    >>> How much current and/or maybe power does a typical gigabit LAN port
    >>> use? 500mA like USB 2 port?

    >>
    >> I'm not sure I understand the question.

    >
    > Pardon my English. I meant how much current/power is needed to drive a
    > typical gigabit ethernet port in a hub/switch/router?
    >


    I looked up 82547GI on the Intel site, and it says

    Power dissipation 1.0W (typical)

    When I look up the number for a dual port chip (two RJ45 connectors),
    the 82571EB product overview says

    Active link state 2.8W @ D0 1000 Mbps

    So you could say the power might be in the 1 to 1.4W range,
    per Ethernet port.

    Those numbers are just for NIC chips. If you have an
    ADSL modem, cable modem, four port router, switch or hub,
    the power could be quite a bit higher on one of those.
    For example, my ADSL2+ modem draws enough power, the
    wall adapter for it actually runs hot. That means not
    only does the modem waste power, but even the wall
    adapter isn't very efficient. That modem is in the 10 watt
    range, and it would appear the adapter is wasting another
    couple watts on top of that. Most of my other wall adapters
    run cooler than that.

    Paul
     
    Paul, Dec 5, 2011
    #4
  5. Thanks!


    > So you could say the power might be in the 1 to 1.4W range,
    > per Ethernet port.
    >
    > Those numbers are just for NIC chips. If you have an
    > ADSL modem, cable modem, four port router, switch or hub,
    > the power could be quite a bit higher on one of those.


    --
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    / v \ Simplicity is Beauty! May the Force and farces be with you!
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    ^ ^ 17:10:02 up 7 days 16:10 0 users load average: 0.00 0.01 0.05
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    Man-wai Chang, Dec 5, 2011
    #5
  6. Man-wai Chang

    Guest

    On Dec 5, 4:37 am, Man-wai Chang <> wrote:
    > Thanks!
    >
    > > So you could say the power might be in the 1 to 1.4W range,
    > > per Ethernet port.

    >
    > > Those numbers are just for NIC chips. If you have an
    > > ADSL modem, cable modem, four port router, switch or hub,
    > > the power could be quite a bit higher on one of those.


    Note that when no activity is occurring, you will get near zero watts
    on the port. That's the nature of transmission protocols; no activity
    means no transmission means no power on the wires.
    --
    // T.Hsu
     
    , Dec 5, 2011
    #6
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