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Power Over Ethernet (PoE) Injector Modifying

By on May 23, 2016
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.

Power Over Ethernet (PoE) Injector Modifying

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.

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.

dja004 ic regulator

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.

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.

PoE injector

Here is a LAN connector pin out and what actually I done.

lan connector pinout

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:

PoE Kit 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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  1. sudhir

    May 23, 2016 at 4:46 pm

    wow Christian
    thank you for sharing this knowledge, I had known about POE but modifying it is a difficult task which after your post is easy now.

    Once again thank you for your time and post.

  2. Yogesh Panchal

    May 23, 2016 at 5:38 pm


    Good idea if this modification is subject to "CCTV" but Pleas. do not club it with any an other LAN environment i.e. if you are using Internet router or normal LAN Switch or Computer which works on 5V DC. or that unit can be easily get damaged by connecting this equipment.

    • Chris

      May 24, 2016 at 1:50 am

      Thanks for supporting my article.
      With this modified device you can connect all the standard LAN equipment on the world. If you check the pinout picture you can see there are 3 standardized LAN connections. There are 2 of them which was standardized for POE use by IEEE 802.3 standard. Which means the 10BASE-T and the 100BASE-T. In most of case, commercial network equipment are 10 or 100 Mbs equipment which are use only two pairs of wires for data communication. The other 2 pairs you can use free for transmitting power over Ethernet.
      So, assuming if you bought a router and you will use the original DC adapter with this POE method you have nothing to worry. But! if you use another not compatible adapter to power your router then you have the same effect like you connected it directly to the router, with or without the POE switch.
      But! even then your LAN interface would not be burned on the PC or router because the POE pairs are not in the LAN connector. There are only two pairs of wiring in the RJ45 connector.
      The 3. type of connection is the 1000BASE-T which means Gigabit networking standardized under the IEEE 802.3ab standard. That type of equipment is not allowing use of POE.
      But that is another story...
      So, feel free to use my POE method to use with the right adapter on your router, switch or whatever equipment under the IEEE 802.3 standard what is marked on every device.
      My best regards.

  3. suranga bandara, Suranga Electronics

    May 23, 2016 at 6:53 pm

    hello Mr- Christian Robert,

    good work ! and Thanks for sharing.

  4. Albert van Bemmelen

    May 23, 2016 at 9:51 pm

    Thanks Christian for this very interesting POE article. I've never heard about these POE adapters before, nor have I needed one before. But knowing they exist can be very useful!

  5. Parasuraman S

    May 23, 2016 at 10:26 pm

    VOW! VOW! VOW! Sky is the limit for your knowledge in various fields! Thanks for sharing this valuable info!

  6. David

    May 24, 2016 at 5:42 am

    Seriously? Gig-E equipment uses all four pairs. PoE mandates that a device must negotiate that it receives power *before* it applied to the cable. This article is dangerously naive and following these instructions would be a terrible idea.

    • Chris

      May 24, 2016 at 11:02 pm

      Hi David, thanks for reading my post and for the explanation of the 1000BASED-T communication standard.
      Of course does Gigabit equipment can't be powered through this PoE wiring as I described. It's normally. There fore are several labels on a PC motherboard, routers, switches etc.
      Please, check IEEE standards, check user manuals from well known network manufacturers who makes PoE connections to their devices as I did.
      As I wrote in one of my comment, 1000BASED-T is a different story.
      Also, a technicians who look to the picture where are described the pinouts of
      a LAN RJ45 connector, they would never use the 1000BASED-T pinouts colon because there are no N/C wirings. As a technician I would never mix any signals or voltage through a wiring which is used for another signal.
      But, it is possible to mix the data line and the power line, maybe I will write in another article " LAN through 220ACV wall connector "...
      If you have any normal router, switch or whatever 10/100Mbs LAN device you can power it through a passive or active POE which is the same as I wrote in this article.
      David, I not angry, you are well come and any comment are well come.
      My best regards

      • Greasy Willy

        May 28, 2016 at 4:20 am

        I appreciate Chris taking the time to post this article ... if you can improve on it then perhaps you should post an article, too. don't just criticize ... share your knowledge to help others, if you can.

  7. Gerald

    May 25, 2016 at 10:36 am

    Hi Christian,

    Thanks for sharing this modification. Despite some comments it solved your problem and this is the most important.

    I tried to find some datasheet on this DJA004 but Google didn't return any useful result. I guess it is some kind of Buck Converter and this would explain the inductor and the diode:


    • Chris

      May 25, 2016 at 10:24 pm

      Thank's for supporting my article.
      It make sense what you wrote, it could be a BC. I checked too on the inet for some datasheet but with no result.
      My best regars.


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