PoE (Power over Ethernet)

By Artie DuncansonArtie Duncanson, on 16 Apr 2013 10:11

RJ-45 Cables come with four pairs of wires. Two of these pairs transmit and receive data, the other two are not generally used. These unused wires can be utilized to provide power to devices ready to accept it if the Power Source Equipment (PSE) has a Power Over Ethernet (POE) connection. A POE device can be advantageous should you wish to provide power for your device where no power supply can be found or in locations where installation of a power supply is difficult.

The Powered Device (PD) you wish to have powered by POE must be manufactured specifically to be compatible with POE devices. A PSE will deliver 48 volts, which will easily damage the many devices not suited to handle that voltage. Therefore, PSE's have a safeguard built into them that will prevent them from supplying power unless it recognizes that the PD is designed to accept POE. The PSE needs to recognize*:

  1. Characteristic Resistance= Between 19K-26K
  2. Typical Resistance= 25K
  3. A maximum Characteristic Capacitance of 150nF

Our goal in the Arduino lab is to bypass the safeguards of the PSE to provide power to our devices not manufactured to accept PoE (of course we will have a voltage regulator installed).

Project Status

Trying to find a viable means of bypassing the safeguards built into the POE switch. We may need to take apart a POE injector and recreate one of those to supply power.
Once we are able to harness the power from the Ethernet cable, we will need to fabricate a voltage regulator to decrease the voltage output from 48v to 12-5v; 5/6/13

Bypass Attempt 1


We tried using the POE port from a TP-Link PoE Switch to power a Cisco Ethernet hub. The two pairs of data wires on the RJ-45 cable were connected from the TP-Link to the Cisco Ethernet hub's Ethernet port. The pairs of power wires on the RJ-45 cable were hacked onto an H03VVH2-F power connector, which was plugged into the Cisco Ethernet hub. The TP-Link did not provide power to the PD.
The Arduino POE board was connected simply to make sure the TP-Link PoE Switch was working during the test, which it was.
This attempt was based on an article in Tech2.

*PSE safeguard criteria based on this pdf.

(name files with proper versioning and note stable/unstable release)
File nameFile typeSize
Bypass Attempt 1.JPGJPEG image data232.04 kBInfo
POE_Basics.pdfPDF document298.79 kBInfo