Power Over Ethernet (PoE) Injector Modifying
Today I will discuss about a PoE injector device which I got in the basket when I had to install some IP CCTV cameras, but the PoE injector didn’t meet the requirement for me and I had no solution to get another valid PoE injector. So, I decide to take a look inside the PoE injector and see if I can modify the unit so it will meet my requirements. For first, let’s talk about a bit what is a PoE injector.
A PoE ( Power Over Ethernet ) injector is actually a unit which can transfer power through a standard CAT5-CAT6 LAN cable from the power source on one end of the cable to the other end of the LAN cable to the device which is connected to it. Let’s say you have a router on the attic of your house but you have no wall socket there, how could you power your router? Simply, just make or buy a PoE injector.
Connect one side of the injector to the LAN cable which will be connected to your let’s say PC in the living room and the power adapter connect to the same PoE injector. Connect the other PoE injector to the other side of the LAN cable which is on the attic. Then connect the DC jack from the PoE to the router and the LAN RJ45 jack to the router. The same think on the PC side.
There are two type of PoE injector’s, active and passive injectors. The active injectors could be and are in most of case with regulated output voltage. The passive injectors are just injectors which will not regulate or won’t do any modification to the voltage or current which is flowing through them.
I would say, all this devices are in some dimensions just a simply splitters. They split and transfer the data signals and the power rail through the same cable. The major disadvantages of this devices are does you have a limitation in the cable length because of the transfer limitation of DC voltage through long distance. So, take in mind if you are constructing something with this type of devices.
But it is great if you wish to install only one cable from your living room to your router on the attic the cable max. length is around 50-60m. I never used that long cable, often when I use this trick to deliver power to a device is a distance around 10-20 meters. In my case I got an active and regulated PoE injector kit. There are no labels about the manufacturer.
The input voltage is DC 24V – 48V and the output is a regulated DC 12V. The main adapters what I got for the CCTV system are DC 12V. So what could I do?
– Switch to a DC 24V or 48V adapter.
– Modifying this PoE kit to meet my requirements.
I decide not to buy a new adapter but mod this PoE kit.
If you have this type of PoE kit then you have to open the injector with the label “ T ”. I assume this T means “transmit/transfer”, I don’t know reading China language.
There is a small electronic in there, which are actually a simply adjustable DC regulator from 24-48V to 12V DC. But I have a 12V adapter. If I connect into this device the 12V adapter on the other end of the LAN cable I will get an incorrect voltage. My mission is to push over this electronic the input voltage so does on the other end I got the same voltage as on the input.
Let’s take a closer look to this device.
The major think is an ic DJA004 which is the regulator.
There are a coil which I assume is for limiting some starting current, and a small protection is also on this circuit integrated, the D6 which is actually a reverse polarity security diode. If in some case a reverse connection will appear in the DC line then the diode won’t conduct and the device which should be powered is protected from reverse polarity.
What I did is simple desoldered all the parts. I don’t need any regulation stuff in there but I need the injector case and possibility to simply connect my DC 12V adapter and power on through the LAN cable my IP CCTV camera.
If I would put the D6 diode back or used it as a protection in my case, I have to calculate with a voltage drop which would cause the diode which is around 0.7V and I’m also current limited. I_max would be the I_max of the diode. So, If you ever have to deal with a unit where you have to do the same think as I’m, take care on other electrical characteristics too before you make think worse…
Here is the almost naked PCB.
Here is my connection what I did.
I just jumped the positive line of the DC jack on the PoE injector so it will deliver the +12V from the DC jack to the LAN connector.
Here is a LAN connector pin out and what actually I done.
As you can see, the pins 4, 5, 7 and 8 are not used in a standard LAN cable.
I put the jumper wire so on the PC does it will deliver the +12V through the pins 4 and 5. The GND was automatically connected on the PoE injector to the pins 7 and 8.
Actually the pin numbers 1 and 2 are for transmitting data’s and the pin numbers 3 and 6 are for receiving the data’s.
Here is the result when I finished my modification:
This is also possible to build this PoE kit with a simple RJ45 connector and a proper DC connector what you have to use for your unit. Connect the pins 4 and 5 together and use it for +12V or whatever voltage you need (3.3V, 4.5V, 6V, 9V… ) and connect the pins 7 and 8 together and use it for GND.
I hope you enjoy this tutorial and will save lot of repair time.
This article was prepared for you by Christian Robert Adzic from Novi Knezevac-Serbia.
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