Slashdot Mirror
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!"
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.
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.