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Wireless Networks Thread, Power Injector Switch in Technical; POE switches are intelligent they only push current if the device requests it as it talks about it, so if ...
  1. #16

    john's Avatar
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    POE switches are intelligent they only push current if the device requests it as it talks about it, so if its non-POE it won't send it and thus turns the POE off on that port.

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    I have used the D-Link PoE adaptors with IP security cameras, but have now switched to these passive power injector leads as they are cheaper, use the PSU that comes with the kit and avoid the need for the D-Link receiver to be mounted near to the item to be powered:

    LinITX.com - Passive PoE Injector/Splitter Set

    The only issue may be that you need to do a simple soldering job if the built-in DC plug is not the right size for the device to be powered.

    There's some other useful stuff on the site too - for example, I carry round a tiny PS2 USB keyboard for testing and connecting to remote servers that spend most of their time without a keyboard:

    LinITX.com - USB Tiny Thumbpad Keyboard

  3. #18

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    Quote Originally Posted by john View Post
    POE switches are intelligent they only push current if the device requests it as it talks about it, so if its non-POE it won't send it and thus turns the POE off on that port.
    The Dlink thing is POE so it will get it's power, unless it's turned off (manually).

  4. #19

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    Bear in mind that the POE standard specifies a DC supply of 48V. Using a passive splitter with the AP's bundled PSU will probably result in only 5V or 12V on the line. This means there will be higher current in the wire and subsequently greater resistive losses. The upshot of this is that trying to power an AP over the anything like the maximum 100m of cat5 will be hit-or-miss.

  5. #20

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    Quote Originally Posted by linker3000 View Post
    I have used the D-Link PoE adaptors with IP security cameras, but have now switched to these passive power injector leads as they are cheaper, use the PSU that comes with the kit and avoid the need for the D-Link receiver to be mounted near to the item to be powered:

    LinITX.com - Passive PoE Injector/Splitter Set
    The details on that page are mis-representative. They are not power-over-ethernet splitters, they are just a cheap way of piggy-backing the power from your normal supply over the same cable to the access points. Do not mix and match supplies and APs with these devices, you will blow things up.

  6. #21

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    Quote Originally Posted by powdarrmonkey View Post
    The details on that page are mis-representative. They are not power-over-ethernet splitters, they are just a cheap way of piggy-backing the power from your normal supply over the same cable to the access points. Do not mix and match supplies and APs with these devices, you will blow things up.
    To amalgamate some responses to my posting and add a bit more:

    Agreed, thery are a cheap way of piggybacking DC over Cat 5.

    I must go watch my kit to see whether after several months of using these devices they are about to blow up - maybe their time has come.

    RJ jacks are typically rated at 125V AC/DC at 1.5A Max,. having grabbed some kit - I note the following:

    IP Camera: 5V@1.5A
    Netgear AP: 7.5V@1A

    Yes, voltage drop over a significant amount of Cat5 could be an issue, but our maximum run from cabinet to camera is around 20m and we have not had any problems.

    I also run around 20 PoE VoIP phones on the LAN from a 3Com 4500 PoE switch and UPS and would agree that in this case there's no other sensible way to do it unless you want power bricks and mini UPSs at every desk.

    You pays your money etc..

  7. #22

    matt40k's Avatar
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    Could you even plug such things into UPS, just thinking AC\DC issues?

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    Quote Originally Posted by matt40k View Post
    Could you even plug such things into UPS, just thinking AC\DC issues?
    The whole rack is UPS protected - switches, servers, DSL kit, routers, APs etc. No problems.

  9. #24

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    More thinking if you plug in, say a wireless access point, directing into a UPS, will it be ok? Not via POE switch.

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    If you plug the mains adaptor for an Access Point into a UPS's power outlet there should be no issues with most decent kit.

    The only caveat I'd put on that is the 5V switch mode 'wall warts' that DLink were using a 3+ years ago tended to die if the power source wasn't clean (eg: a cheap and awful UPS) - heck, they even blew sometimes if you unplugged them and plugged them back in again.

  11. #26
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    or if you have to much time on your hands build your own..
    NYCwireless | PoE — Power over Ethernet

    Buy'em it's easyer..

  12. #27
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    There is loads of info about 802.11af out there.

    Have a look for..

    POE Injectors
    POE Splitters
    Midspan Injectors

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