PoE (Power Over Ethernet) enabled switches costs a lot of money, so I decided to make my own. After some research i found out how PoE works, and it’s fairly easy to modify an existing Fast Ethernet 10/100 Mbit/s switch.
Here is how Ethernet cable / UTP cable is wired:
PoE is based on the 2 wire pairs who are not used in 10/100 Mbit/s networks, 1 pair + 48V DC and 1 pair Ground. ( 1 pair = 2 wires)
My modification to the switch is similar to “Passive PoE” injectors. it’s based on “PoE 802.3 af” and it injects 48V DC but without the auto sense protocol to check if the connected device is PoE capable. This can cause permanent damage if you plug in other devices in the modified switch who are not PoE capable. In other words, it’s a dumb PoE switch.
Note: Do not try this with Gigabit switches because these use all 4 data pairs instead of only 2 pairs for 10/100 networks!
Note: Use only straight cables, no cross over cables. These can damage the connected device.
All components i needed for this mod:
– 10/100 Mbit/s switch (5 port switch i had laying around)
– electronics wire 0,2 mm²
– External 48V DC power supply
– Fuse holder with fuse (20 mm glas fuse, 0.75 A)
– 5.5mm/2.1mm DC plug
– LED with resistor (power ON indicator)
– Diode 1N4007 (polarity safety)
– Glue gun & glue sticks
Here is the result of the switch:
On the back the 48V DC input with green power ON led:
The connections to the Ethernet cables:
The + 48 VDC is connected to pins 4 & 5 and ground (-) to pins 7 & 8 of the 4 outgoing PoE ports, the incoming LAN port is unmodified. The 20 mm glass fuse is a regular blow 0.75 A. Just in case something goes wrong.
All switches have resistors connected to ground on unused wires to avoid interference, in my case each unused wire was connected with a 75Ω resistor to ground. If these resistors are not removed, the 48V input would flow through the resistor to ground. And there are 8 resistors in total for 4 ethernet ports.
Not a good idea to leave those resistors there, 1 resistor will have a current of 48V/75Ω = 0,64 A !
This is how to prevent this: just break the PCB traces!
I use this switch to power PoE capable IP camera’s (CCTV) with solid 100% bare copper UTP cable.
Note: Do not use CCA (Copper Clad Aluminum) UTP cables, these are not suitable for conducting currents (too high resistance) and can cause high power loss in the cables. Remember why they removed all aluminium conductors from residents?? Because the cables were overheating and causing fire.