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Power-over-Ethernet: IEEE 802.3af Draft
SkewlD00d writes "Want power (~10W) and your fat 10/100Mbps pipe (1Gbps maybe) on the SAME jack. Surf the web and recharge your handheld w/o finding its clunky base/transformer, home automation, and control systems are just some of the possibilities. Using suitable hubs/switches or dongle, power can be provided over unused pairs, or possibly raise the signal offset above DC, X10-style (no link, u know why). See IEEE 802.3af DTE Power via MDI Task Force. Maxim (not that one :o) already has some goodies. They have schematics for 8.25W/12.5W single-output and 14.2W triple-output 802.3af PSU. Try FindChips if you're looking for them; they're in production and are NOT vapor-ware!"
Not sure how standard it is, but many Cisco switches support Inline Power, which is used by their Voice-Over-IP Phones. We deal with this constantly where I work.
It can be annoying because if you want to run several phones on one drop, they need power supplies if you don't want to use an expensive inline power capable switch.
Here's a useful how-to on powering wireless base stations using Power-Over-Ethernet (POE). Several wireless vendors already sell POE kits for wireless APs. Here's a POE kit for the AirPort.
Power+Ethernet over one wire is a great combination for settting up APs, because many of the interesting places to put a wireless access point (e.g., in the attic, by the pool, in the middle of the ceiling) may not have a power outlet nearby, or you may simply not want to run two sets of wires (AC power + ethernet) to the location.
-Mark
The latest firewire standard can do 800Mb and provide up to 45W of power
I use this extensively with my Lucent/Orinoco wireless APs. Been doing it for about 2 years now. It's also part of 3Com's Ethernet switch/jack technology, and has been implemented for VoIP.
I've found it to be a godsend for my wireless APs, as I can mount my APs near the ceiling (away from students), and not have to worry about finding an outlet, or having them unplugged by the cleaning crew!
- why no links on X10 ?
Because they are misinformed. They are thinking of X10-the-company, which is notorious for pop-under ads. But what they really mean is X10-the-protocol [scroll down a bit for a good introduction], which is used by many companies.
- which maxim is obvious ?
Maxim is a "gentleman's magazine" that has been pushing the limits of how much semi-porn you can include without getting banned from shelves. Recently this and competing magazines went too far for Walmart.
bp
While overstated, I wonder what the power safety capabilities are in some of the already-available implementations of this.
I'm not as worried about shock, but about unintentional shorts burning out switch ports or misplugged equipment. It'd be awesome if there were software-resettable breakers on the switches so that you wouldn't lose line cards. I had the misfortune of accidentally shorting a couple of Merlin phone system ports and those ports are dead, dead, dead forever.
I also wonder what it does to existing wiring codes and cable plants if any significant power starts to become present on data cabling. It'd suck to become dependent on this power only to have data cabling drops become more costly due to tighter code restrictions on where they can be placed.
Number one cause of device failure for SCSI devices: power shorts on SCSI chain.
Number one cause of device and motherboard failure for Firewire devices: power shorts on Firewire chain.
Notice a pattern?
There's good reason to have two cables running to each device: when a cable inevitably goes bad or the user mis-mates a hot connection, the chance for device damage is minimal.
"You have liberated me from thought."
The hot-swap chip is required by the standard and handles unitentional shorts. From the data sheet: "Provides Safe Hot Swap for +10V to +65V Power Supplies". This also 1) limits maximum inrush and 2) limits steady-stage current to 1) avoid "drooping" the supply voltage and 2) handle faults on the secondary (e.g. 6 V) side. I haven't looked at the standard recently, but there are supposed to be limits on the supply (-48 V) end to handle faults there. The reasons -48 V is used are it is very standard in telecom so low cost parts available for DC/DC converters and it is less than +/- 60 V which is the limit for "low voltage" in existing wiring codes.
The Linear typical app seems to be much smaller, with fewer external components because it's actually optimized for the application.
The Maxim chips appear to be generic hot-swap IC's not optimized for power-over-ethernet. Using slashdot is an interesting way to publish an app-note and get some publicity.