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ReLik writes "The BBC has an article regarding power supply via networks. 'Instead of needing adapters, computer networks could soon be supplying the devices they interconnect with both data and power. Some makers of network equipment are already putting the power via data cable system into their products. The basic plugs for computer networks are the same all over the world, raising the possibility that powered data cables could become a universal back-up power supply.'" We've talked a little about specific 802.3 spec advances previously.
states that if you rub two sticks together you get fire.
Seriously, how long have did it take people to release there is a current in their ethernet cable? I known of products (home made and retail) that have been around for years that utilise this power supply.
Here is some info by POE from NYCWireless...
Now just give me wireless repeater base stations powered by tesla coils and I'll be in heaven.
Wouldn't supplying substantial amounts of power through network cable (lets say cat5) make enough EMI to scramble the data going through the other pairs?
Not if done properly.
Also, would this work in situations using coax cable, where there is no other pair?
Yes.
Lastly, can you put 120VAC along wires that thin without causing lots of power loss and making a lovely fire hazard?
You can't, but the problem is worse. Your notebook doesn't run on 120VAC. It runs on DC power that is much lower voltage. The power supply steps down the voltage before the power gets to your system.
The problem is that when you lower the voltage, you raise the current, and current increases heat as it gets higher. So, low voltage, high current power transmitted over CAT5 would be a big problem.
Actualy it works VERY well for there voIP phones and a few other devices like intel AP's and mini managed switches. It' DC and nut much current enough the run a laptop and probably not enough for a full desktop replacement. Last I check it supplied 18 watts.
No sir I dont like it.
umm...
I'm no EE, but as far as I know PoE is DC, which won't cause interference in UTP or anything else...
--
Phil
This does not look like it will be used for anything larger then small hand helds and other similary sized devices. Cat 5 is normally 24 AWG which has very high resistance per foot making long runs useless. at around 50ft you might have about 4 or 5 ohms. Unless you have 2 or 4 pair cat 5 with a pair of 18awg or larger in the same jacket it doesent have much use for anything drawing more than 10 watts or less. although making such a cable wouldent be such a bad idea.
Would be cool to have some type of hybrid connector that carries 12V @ 10 or 20A (or maybe more volts to carry more power) with ethernet and switches can become both ethernet and power supplies. Small server farms or disk arrays etc. could be attached using just one cable for all functions.
This is a little DC power for IP Phones and WAPs not 120VAC for your computer.
48V at 350mA max DC.
There have been quite a few posts so far about how running power over data lines is a bad idea and would cause all sorts of bad EMI, killing the data signal. But it actually doesn't. The power going through these is low-voltage DC (I think 12v), *not* high-voltage AC like wall power. AC produces changing magnetic fields which cause EMI, while DC produces a static magnetic field, so the data could care less. This is the same way that USB works (at 5v) and even POTS (plain old telephone systems...those have a full 48V DC...not always very nice when you forget that fact doing wiring). I haven't actually played with any of the equiptment myself, but from what I've read everything is low-voltage and low-power enough not to cause any sorts of problems at all.
Check out the prelimary specs for 802.1u - power over wireless ethernet. They are planning on using microwaves to send the data and power to wireless devices around the home and office.
When information is power, privacy is freedom.
Wouldn't supplying substantial amounts of power through network cable (lets say cat5) make enough EMI to scramble the data going through the other pairs?
If it's DC only and well filtered/buffered, no. If it's RF, or DC that's not well filtered(noise is generated from any kind of switching, even in low power ICs). Buffering it isn't that tough- you can sorta think of it like a bucket under a faucet. As long as your average water needs over time don't exceed the flow out the faucet, you can take whatever you want, even large amounts suddenly, without causing pressure changes in the rest of the house. Now, imagine drawing a cup of water every once in a while from a faucet directly and shutting the water off really hard- helloooo water hammer!(similar things happen when you switch on/off power down a long line, or to/from an inductive component.)
Also, would this work in situations using coax cable, where there is no other pair?
Actually, Dallas Semiconductor(now part of Maxim) came up with what they call the One Wire protocol; it only needs one line for power+data(hence the name, even though you still need some sort of ground.) It's a pretty well set up system, works nicely- plenty of info on the web and their site, and there's even guides on designing a proper network- and shows the effects of cable length on things like pulse smoothing, noise, etc caused by communications and device power draw. It's VERY thorough.
Lastly, can you put 120VAC along wires that thin without causing lots of power loss and making a lovely fire hazard?
Actually, power loss is less with higher voltages- that's why high tension wires are tens of thousands of volts. P = I * V; 100W at 120V is .83 amps, but at 12v, it's 8.3A.
This is important, because the higher the current, the higher the voltage drop; V = I * R. All wire(except superconducting) has some resistance, and the lower the current, the lower the voltage drop end-to-end, and the lower the amount of power(heat) the wire absorbs. Wire(or perhaps more accurately, cable) is rated in terms of maximum voltage mostly from the insulation type(its dielectric strength) and current- its gauge, or thickness of the solid or stranded bundle(larger #'s = smaller thickness).
This is one reason automotive manufacturers want to go to 48V systems; the wiring between the battery and main bus/alternator can be much thinner, for example. Take a look at your battery cables some time- they're VERY heavy gauge. Also, as previously mentioned, stuff like dirt on contacts and corrosion between clamps+terminals or in splices are much less bothersome at lower currents.
Please help metamoderate.
That's why you run fibre between buildings. A copper->fibre 10 or 100 bridge is quite cheap these days. The fibre is also not so expensive anymore.
Light has no ground.