Combining data and power on the same cable brings more uses and greater efficiency.
By Daniel P. Dern
May 17, 2012
Plus, or PoE+. PoE+ is backwards-compatible to 802.3af , and has two other modes: one delivering up to 25.5 watts, and another delivering up to 51 watts at the end of 100-meter cable.”
For comparison, a standard desktop USB port typically provides up to 500mA at 5 volts — about 2.5 watts — and only 200mA on most laptops.
802.3af was initially used for lower-powered network access points, fixed network cameras and other some other devices. With PoE+‘s greater power comes the ability to power outdoor network access points and PTZ (Pan/Tilt/Zoom) cameras, zero and thin client devices and their displays, videophones, and more.
The major differences needed to achieve these levels, says Feldman, were changes “in the cabling infrastructure — defining the minimum cabling needed. PoE+ requires ‘CAT5 or better,’ versus ‘CAT3 or better,’ and increasing the current from 350mA to 600mA.”
Products to Provide PoE
To do PoE, you need a way to put power over the Ethernet, and a way take it off — somewhat like needing products to put audio or video signals over radio and television broadcast frequencies. (Similar in that you need them, not in how it’s done.)
You can add power either with devices that are “PoE-enabled,” meaning they include the requisite circuitry, or by adding in devices to “inject” power to, and “extract” power from the Ethernet cabling.
On the “inject” side, network switches increasingly often include PoE capability, meaning they can push power to the cables along with data. For example, D-Link’s DWS-4026 Unified Wireless 26 Port Gigabit L2+ 802.3af PoE Switch.
Companies looking to take advantage of PoE but not ready to replace existing switches can use “injectors” to add power into specific Ethernet cables.
Injectors can be multiport, such as Microsemi’s PowerDsine PD-5524G, fitting into the same rack as the switch — or smaller, such as D-Link’s DWL-P50 Power over Ethernet (PoE) Adapter.
At the other end of the cable, the power has to get out, of course.
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