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One of the problems we would like a solution to is Multi-plexes with no house power. We would like to be able to mount a radio on the Plex and connect it via Ethernet to all the units in the Plex. But Quad-plexes and below generally do not have house power.

We've tried borrowing power from one of the units, but every so often the one critical unit will turn off the breakers when they go on vacation, or fail to pay their power bill, or the power company shuts off their meter when they move out. These situations are never fun to fix.

My idea is to have a PoE Switch with at least 4 PoE inputs and one PoE output. The switch should be able to operate and power the attached radio on the PoE out port when only one PoE input port is supplying power, and yet not do anything crazy when all the PoE input ports are supplying power.

One nice option would be to disallow an Ethernet link on any input port that is not providing power, so tenants can't plug in without getting a power adapter. This ensures no one cheats on supplying power, and then complains that their Internet quit when their neighbors move out

It's possible that this could be done as a modified version of your 6-port switch, giving 5 PoE in and 1 PoE out...

I think that this is enough of a corner case that it wouldn't make sense to add to the switch. Also consider that the PoE switch ports are typically output and only 1 in a wISP situation would be an input. I don't know of a PoE switch that has a port that flips between input or output. Probably better handled with an injector midspan with multiple PoE inputs and a single DC PoE or barrel output to the switch. The circuit isn't too hard to build, to take multiple inputs and isolate them via diodes or mosfets etc for redundant supplies or an IC (often called a PMIC). An EE would calling this ORing or power muxing. That said, the simple way to do this basically would work with 100Mbps, 2 pair injectors. 4 pair injectors would be much more complicated.

While I agree that this is a corner case in the realm of PoE Switches in general, I believe it is a far more common need in the realm of WISPs.

You've mentioned a couple of basic design ideas for for a mid-span PoE extractor that could do this. Have you built any for your own use? Do you think they would meet code? My boss, as a licensed electrical administrator, is of the opinion that if we build it ourselves, it's unlikely to meet code. So I wait and hope for a UL approved device to appear that does this...

Yes... I would buy many. Dave-D would buy them. Everyone I talk to about this says, "I WOULD BUY THOSE... but they are probably too small of a market for anyone to make"....

If someone makes one I think they'll make a killing.

I'm just thinking out loud here... have not confirmed whether or not it will work...

How about using four AGWs, one for each unit powered by a PoE brick. Mount the AGW outside the apartment, backwards so the PoE out is the in and turn off the radio. Use the male PoE in plug to grab the voltage and isolate them from each other with diodes. If the AGW loses power the traffic stops to that unit. You can remote in to the AGW to cut off a sub for non-payment or virus spewing.

Use a http://routerboard.com/RB260GSP and power it through the barrel connector with the power collected from the four AGWs. The RB260GSP can then power the radio on the roof.

lligetfa wrote:I'm just thinking out loud here... have not confirmed whether or not it will work...

How about using four AGWs, one for each unit powered by a PoE brick. Mount the AGW outside the apartment, backwards so the PoE out is the in and turn off the radio. Use the male PoE in plug to grab the voltage and isolate them from each other with diodes. If the AGW loses power the traffic stops to that unit. You can remote in to the AGW to cut off a sub for non-payment or virus spewing.

Use a http://routerboard.com/RB260GSP and power it through the barrel connector with the power collected from the four AGWs. The RB260GSP can then power the radio on the roof.

I like your thinking even if it is convoluted ;) Don't need the AGW, just an injector (unless you want the AGW). Power out up to a box where you blend it.

The poor man's solution to this is to create 'one way' power cables. So the + power coming from each unit is cut and then the leads on the diodes are shoved directly into the blue pair thus reconnecting the leads, and then heat shrinked up. Now power can only flow from injector up. Then just connect all the blue and brown leads to a barrel jack to power the 24v router/switch. Diodes don't tend to be very efficient so you will lose some power, but the 24v .5a supplies from ubnt are easily enough to handle a small router/switch and you will have multiples. If you wanted to get really crazy, put LEDs in the diodes location and a resister on one side. That will drop the power more because of the resistor but you'll know if you have power on the line!

rebelwireless wrote:

lligetfa wrote:Use the male PoE in plug to grab the voltage and isolate them from each other with diodes. If the AGW loses power the traffic stops to that unit...

I like your thinking even if it is convoluted ;) Don't need the AGW, just an injector (unless you want the AGW).

In your OP you had the requirement that tenants that cheat by unplugging their power be cut off. The AGW does that since the diode is after the AGW so the AGW only gets power from the tenant's PoE brick. No power to the AGW, no ethernet.

If you didn't have the requirement, then I would have just proposed PoE pickers which are just injectors in reverse.

n your OP you had the requirement that tenants that cheat by unplugging their power be cut off.

ah, yes. so add a relay to split a conductor out of the orange when there is no power, close that conductor with power. Now the line is automatically 'dead' when there is no power. Ethernet won't negotiate with only 3 conductors. Add a second for the solid green if you want to be thorough.

You'll probably want a 4 pole single throw n/o '4PST' relay for this. It can handle all 4 conductors for 100Mbps ethernet off a single coil and is 'open' when not powered.

Here is an example, S4EB-24V, perfect for 24v injectors:
http://www.mouser.com/ProductDetail/Panasonic/S4EB-24V/?qs=%2fha2pyFaduj5cundUd0yOJhfhHT23dLyPM4ZR90%252b0nE%3d
or on ebay
http://www.ebay.com/itm/1-pc-new-Panasonic-Aromat-S4EB-24V-S-Relays-24vdc-4A-4PST-N-O-/251720990969?pt=LH_DefaultDomain_0&hash=item3a9bbd80f9

How to get a relay into a package that preserves the CAT5 specs and still be affordable? I ain't asking Chris for an economics lesson.

The AGW can be had for $17.50 so X 4 = $70 + the switch for $56 and maybe $30 for keystone jacks, wire, and a NEMA box totals $156.

I probably should have included the PoE injectors but most of us would have lots of them kicking around already.