Which router to pick when Power Over Ethernet is required?

Discussion in 'Tomato Firmware' started by Eddie55, Dec 29, 2013.

  1. Eddie55

    Eddie55 Serious Server Member

    Need to setup an AP in a place with no electrity

    2 possible options

    Option #1
    Buy a poe switch and a poe router (thats supported by toastman or another tomato variant)
    Option #2
    Use a nonpoe router (supported by toastman or another tomato variant) and use a POE adapter

    Thanks in Advance
  2. Malitiacurt

    Malitiacurt Networkin' Nut Member

    Consider this, are there any features you need from Tomato when in AP mode?
  3. Eddie55

    Eddie55 Serious Server Member

    You make a great point and it definitely is an option I have thought of and may use... but just because I like to entertain all options the question still stands..
  4. mvsgeek

    mvsgeek LI Guru Member

    A couple of my WDS AP's are WRT54GL's running Tomato Firmware v1.28.7633 .3-Toastman-IPT-ND ND Std.
    I have them mounted externally in weatherproof combo box/antennas from L-Com, in conjunction with these Passive PoE Injector/Splitters.
  5. kage_

    kage_ Reformed Router Member

    I'd go with option two. You'd have a larger selection of routers to choose from and then you can purchase a dedicated POE switch with the proper number ports and POE power requirements. If it's a small install you could use the router, and then use an external poe injector.
  6. PetervdM

    PetervdM Network Guru Member

    beware that these items are NOT a real PoE solution! with the current generation of routers drawing 1.5~2.0A the voltage drop over a significant length of utp cable will be to high to leave a reliable voltage level at the router side. also the RJ-45 connectors are not suitable for this much current.
    real PoE use a higher voltage, upto 57V which is reduced at the router side by means of a DC-DC buck converter and hence uses much lower current.
    more info pls see: https://en.wikipedia.org/wiki/Power_over_Ethernet
    mvsgeek likes this.
  7. mvsgeek

    mvsgeek LI Guru Member

    Thanks for that info, this thread already had me wondering if those PoE components were contributing to a weaker than expected RSSI from one of the AP's (as measured at the 'main' router, about 1000 feet away). The router/antenna box is mounted on an external wall of a residence, and is connected through the wall to the power supply in the attic by a 10' cat-5 cable. I had read the Wikipedia entry you referenced, but not until after I'd already installed the router. Therefore, a couple of questions...

    1. Is a 10' cable going to cause a significant voltage drop?
    2. Can I upgrade the 12V 1A wall wart to a 1.5A without frying the router?

    Disclaimer : I'm a mainframe software dinosaur, not an electrical engineer - I never progressed much further than Ohm's Law.
  8. PetervdM

    PetervdM Network Guru Member

    1. we are talking about ohm's law here. quality grade 24AWG wire is rated at about 30 ohms per 1000 feet, so your 10 feet utp cable is about ( 10/1000 ) * 30 = 0.3 ohm per strand. power drop at 1.5A for 2 strands ( forth and back ) is 2 * 0.3 ohm * 1.5 ampere = 0.9 volts. add the unknown voltage drop at the 2 RJ-45 connectors and you will end up below 11 volts. it depends on the router whether it will work reliable at such a low voltage. parts inside will work at voltages as low as 3.3 or 5 volts, but chances are the wifi transmitters work at a higher voltage.

    2 you can upgrade your power supply with another one when the output voltage and ac or dc indication is the same. the new one has to have a higher amperage as the old one. and mind the connector, especially the polarity.
    but even if you plug in a 20A power supply, it won't help you with the voltage drop over the cable.

    "real", or "active" PoE converters have electronic circuitry to deal with this voltage drop.
  9. Eddie55

    Eddie55 Serious Server Member

  10. PetervdM

    PetervdM Network Guru Member

    hard to say. it certainly should, but it does NOT conform to the PoE spec 802.11at or even to 802.11af according to http://downloads.linksys.com/downloads/userguide/1224638675637/WAPPOE12_V10_UG_C-WEB.pdf . these units only converts the 12 volts to 48v, reducing the current by a factor of 4 and so reducing the loss, and also have the electronic circuitry to compensate the voltage for the loss. the manual has no spec for the maximum current, only states rather old and less power demanding compatible equipment, so i'm not sure it will handle 1.5A+. however, the voltage drop has to be compensated as it also leads to power loss. also the electronics in the units do not have a 100% efficiency, that's an other 10~25% loss, this loss has to be compensated too. so in order to use these devices you need a more powerful adapter. add approx. 0.5A.
    the maximum power within the 802.11af spec is 15.4W, approx 1.3A @ 12V. 802.11at spec is 25.5W, approx 2A @12V, needing a 34.2W power source, 2.85A @12V
    to be better safe than sorry you should use a real 802.11af or 802.11at device, depending on the power needed.
    Last edited: Dec 30, 2013
  11. Eddie55

    Eddie55 Serious Server Member

    Ty for the thorough explanation...
    After much deliberation I ended up getting a ubiquiti AP...
    Partly because it looks nice... partly because its going to mounted on a ceiling and dont know where I would put the adapters... partly because the price is great... partly because it has great reviews...
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