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POE question

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  • 03-02-2014 6:54pm
    #1
    aidanki
    Registered Users Posts: 1,277 ✭✭✭


    Im new to POE, and am going to be powering up a 12v IP cam soon,

    ill prob get the POE adaptor online,

    question does it have to be a specific 12V POE adaptor or are they all the same ?


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    #2
    Alun
    Registered Users Posts: 21,466 ✭✭✭✭Alun


    As long as the camera and the PoE injector both conform to the IEEE 802.3af standard that's about it really

    PoE devices actually deliver a maximum of 48VDC and it's up to the receiving device, i.e. the camera, to negotiate with the injector as to what power requirements it has via the 8023.af protocol. The PoE electronics inside the camera will convert what is left of that 48VDC after losses to what it needs internally.

    By "after losses" I mean that due to the cable lengths and the relatively high resistance of the thin Ethernet cable wires, with a cable run of any length the voltage drop will be considerable so actually delivering 48VDC to a device would be almost impossible.

    BTW The bit in the spec sheet for your camera that specifies "12V DC, PoE" means 12VDC if supplying it via a normal mains adapter.


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    #3
    White Heart Loon
    Closed Accounts Posts: 1,788 ✭✭✭White Heart Loon


    Yeah, but most IP cameras aren't 802.11af compatible, but they usually come with their own injector.


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    #4
    Alun
    Registered Users Posts: 21,466 ✭✭✭✭Alun


    White Heart Loon wrote: »
    Yeah, but most IP cameras aren't 802.11af compatible, but they usually come with their own injector.
    The one he has is (as mentioned in another thread he has) ...

    http://www.irishwireless.net/cctv/surveillance_cameras/ds-2cd2012-i

    See the PDF datasheet, it specifically mentions 802.3af.

    EDIT: I've also checked a random selection of IP cameras from D-Link and Axis and they all seem to support it too.


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