Possible uses for Power over Ethernet

jsailor writes "Power over Ethernet allows devices to draw power from the Ethernet cable they use for networking. Power is provided by the LAN switch (end-span) or an intermediary device (mid-span). The current spec. is 802.3af and was covered on slashdot before. It provides approximately 13W at the end of a 100 m cable and is commonly used for IP phones, wireless access points, and increasingly security cameras. The technology saves costs associated with running power to the odd locations access points find themselves in and allows IP phones to be moved around with out carrying a power brick. The industry is considering a new standard that would provide up to 39W to a network device. Bizarre uses include electric razors. "

Gigabit ethernet?

[mgs1000]

I guess it won't be compatible with gigabit over cat5e, since that uses all eight wires.

Short circuit

[totallygeek]

I went to a company that cabled about 100 drops. When certain network items did not work properly, they tried everything to figure out what the problem was. Finally, one device was plugged in and did not work at all. It turns out that the cabling was wired with "just the same colors on one end as the other". The installers actually created an elaborate mapping on paper saying, wire 1: red, red/white, blue, blue/white, brown, brown/white, green/white, green. They would look up each cable on this run sheet before punching down the other end. The device that did not work evidently was not "looked up" correctly, and so there were no valid pairings. If this had been POE, something would have been fried.

Another company I worked with found out that their cable guys simply wired everything with 2 pairs only. They would punch down 1,2,3,6 and then cut the remaining wires completely. POE wouldn't work there either.

It is amazing how some companies attempt to save money by getting monkeys to install cables.

Re:Easy enough,

[Ignignot]

This is rated funny, but Nikola Tesla was working on something like this for much of his life. The Wyadcliffe (sp?) tower is just the biggest example. Go check it out on wikipedia [wikipedia.org] like you do for everything else.

Great for wifi access points

[Technonotice_Dom]

I've seen this implemented in a local school (in the UK) that issues all staff with laptops. The laptops then have a student register application running on them, and the staff can wander across the building using it. They've put up lots of D-Link access points scattered all over their buildings, just mounted to the wall on wooden boards - an ethernet cable appears out of the wall, or from a socket, into a little box (size of PCMCIA card, but thicker) which then has two cables (power + ethernet) going into the access point.

Appears to work very well for them.

Wireless Power

[EqualSlash]

Don't send it in the form of electricty..send it in the form of radiation energy just like how the Sun provides us energy wirelessly. Even NASA tested a Laser-Powered Aircraft [nasa.gov] last year.

Possible Uses?

[pete-classic]

Possible uses for Power over Ethernet

Finally convincing the fucking cat to not chew on the cables?

-Peter

Do you need a license now?

[Anonymous Coward]

I know that currently an electrical license is not required to run cat 5 cable in my state (NC) because it is low voltage. I wonder if this will change that law.

Some uses

[owlstead]

Just to fuel your imagination, I've put in some nice uses:
- Networked camera's (more zooming, tilting and maybe even lighting with 39 W)
- Networked printers
- Home server appliances (my VIA EPIA runs great with DVD player and 3.5" HDD on 53W, it would run just great on 39W without the DVD player)
- Media players (MPEG4 & MPEG 2 layer 3)
- Downlink switches

And I do not have a clue why they never use this for PDA's. Use a common network plug to synchronize your PDA, and give the customer a nice powered switch or network adapter instead of those stupid cradles.

Currently the standard is mostly found in Remote Access Points. I would have put my access point (which is at the best place for RF, but not for cables) on power over ethernet, but these components are hard to find. Just putting 5 V and splitting it at the end does not seem to work, probably because of the distance.

I don't know about you, but..

[Myself]

... lots of smaller devices (PDAs, older laptops) draw under 20 watts. The wall-wart for the Vadem Clio (sitting right here) only puts out 11 watts, and that's enough to apply a mild charge to the batteries while running the device.

Around the time HPNA powerline ethernet came out, I waited eagerly for a laptop maker to announce an AC adapter which would also bridge the machine to the network. No such device ever emerged. I'd love to be able to curl up on the couch with a network-connected device and not worry about the battery. I'd be happy to drop an RJ45 outlet in the corner. Will someone make a device that'll use both signals from the same cable?

Being low-voltage, you don't need to call an electrician to move network cable around. Thank goodness. There are murmurs within the electrical industry of trying to legislate a change to this, be watchful and let your representatives know that low-voltage wiring is not hazardous and should remain unregulated.

One problem with PoE is deciding which device gives and which receives. Right now, the cable modem, the router/firewall, and the 8-port switch all have wall warts. With PoE this could be reduced to one, but which one? For a simple star layout, it's simple. I fear the mess of adapters isn't going to get much cleaner, however.

Cameras and APs are the obvious early beneficiaries of this. Another poster mentioned doorstrikes and cardreaders. How about motion detectors, thermostats, and other environmental sensors?

If the HVAC system is plugged into the ethernet anyway (Or just running back to the same wiring closet, even if it's on separate hardware) then let's toss the duct dampers and other controls onto the same system. Wire the whole building with one type of wire, run it all back to one place, and have flexibility later.

And since we're replacing all the building's auxilliary systems with PoE connections, how about overhead music / paging systems? Individually addressible bidirectional speakers would enable all sorts of talk-and-listen applications, as well as point control of which programs go where.

13 watts is also enough for things like cash register scales, receipt printers, barcode scanners, and the like. A lot of that stuff runs on USB now, which is great. I can see applications where remote scales might take advantage of ethernet's distance capability. Also consider that powering down the USB host takes all the devices with it, but with ethernet-attached devices, the network can still "see" the RFID scanner if the register takes a crap for some reason.

Things like JetDirect print servers would also benefit from wallwartlessness. Yes, decent printers have a slot they sit in and receive power from, but there seems to be no shortage of standalone ethernet print servers.

How about postage scales that print "electronic postage" from a company's central account? They're great, they never need recharging, but they still need a network connection /and/ a wall-wart.

And, dare I say it, credit card terminals? We'll just make the manufacturers promise not to transmit the card stripe data in cleartext. (ATMs use some serious encryption, why can't Lowe's?)

Re:13W could be dangerous...

[lars_stefan_axelsson]

Your professor is a bit confused about the electric chair business: it was Thomas Edison who claimed publicly that Westinghouse's 60 Hz. system was much more dangerous than Edison's own direct current power system. This was strictly a marketing ploy: he and Westinghouse were going head-to-head in an all out corporate war and Edison wanted to win, badly. He had no scientific basis for his claims. In other words, he lied, publicly and repeatedly.

No that's not true. Edison had plenty of data from animal research. He even had a traveling road show that demonstrated (on sheep mostly) that they died when a comparatively much lover AC voltage was applied than when a DC voltage was applied. "You could turn the dial much higher." And it wasn't all sheep, they even electrocuted an elephant in New York (that had been condemed to death for killing its keeper). He even had billboards that said: "Don't use the executioners electricity in your homes!" (or words to that effect).

AC was indeed used for the first electrocution, suggested by Edison who build the apparatus. Westinghouse wisely refused to sell any equipment but then Edison arranged a purchase in secret and shipped it in unmarked crates to the place of execution. The first electrocution itself was a horrible botched affair, where many of the witnesses fainted from the stench of burning flesh. And the condemed man was first thought to be dead and the steam let out of the engine, only for the officials realising that he was still alive and everyone having to wait for the steam engine to be fire up again.

Also, your statement that DC is more dangerous than AC is not quite as straightforward as you make it to be. While at higher currents DC does tend to lock the skelettal muscular system more readily than AC; that doesn't in fact kill you as easily as electricity induced teatanus of the heart tends to resolve once the current is removed (hence defibrilation units use of DC), i.e. the heart starts again. AC otoh tends to cause fibrilation of the heart, which won't resolve itself and kill the patient (unless defibliration is available). We're speaking here of 50/60 Hz AC of course, as AC in the ten-kilohertz range or so is practically safe due to skin effects (your skin is a pretty decent conductor as other's have pointed out). Also, AC will also induce tetanus, though I'm not sure about 120V in the common case (Europe being on a 400/230V system. 230V can be enough to 'stick you on the circuit'.)

The best links I could find was this [allaboutcircuits.com] and this [allaboutcircuits.com]. Note the table half way down on the second page that lists the amperage needed for various effects on the body. I've had a better link before, but I can't find it now.