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!"

Comments

Cisco already does this...

[ZorinLynx]

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.

Great for powering wireless APs

[kriegsman]

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

Problems with older installations

[JKR]

Is this going to work with cheap installations which are already using the extra pairs in Cat5? RS sell a splitter / combiner which (as a last resort) lets you use the "spare" pairs in an existing 10/100 base-T run to run a parallel 10/100 base-T connection.

I can smell burning...

Jon

Power on bus generally a Bad Idea

[Chriscypher]

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.