Making PoE work by replacing Magjacks

Hi everyone,

I want to power my circuit using PoE (12V, 400-500mA) with ethernet support.

I am using Ardiono Nano and ENC28J60 Ethernet LAN Network SPI Port Module.

I see the HR911105A Magjack wont support PoE. If I replace the HR911105A with PoE compatible magjack like

Should this replacement provide me with isolated ethernet for arduino and power for my circuit?

how much important is it to use isolated buck converter (to convert 48V to 12V) instead of using a non-isolated one?

One quick question, if PoE cable is connected to ENC28J60 Ethernet LAN Network SPI Port Module, will it burn the module or will it isolate the 48VDC?

I believe that it is a function of the ethernet circuit board that allows PoE, not the magjack. Normally, passive PoE uses two of the four ground lines to supply power to the ethernet device. Unless the circuit board isolates and regulates those lines, the ethernet circuit board will probably short circuit the power supply on the PoE supply end.

edit: I forgot to mention that there are devices that allow PoE without changing anything on the ethernet circuit board. Do a Google search for "ethernet PoE splitter".

Thanks Surfer, what I wanted to ask is that if Pin 1,2,3,6 are carrying 48VDC alongwith ethernet data, and if I plug this cable to ENC28J60 Ethernet LAN Network SPI Port Module, the MagJack should only pass through ethernet data and not damage the unit by applyinf 48V to Enc28j60 chip?

Sometimes. Use a passive PoE power supply and a PoE splitter. Those use only two of the four ground lines, not the data lines. I recommend using a 7.5 to 9 volt supply, not 48 volts.

Active PoE does use the data lines. Bad news for your ethernet card, KaBoom!! And the magic smoke comes out. It won't work once the magic smoke gets out.

I dont understand why it will smoke the ethernet card? The transformer will only pass AC (or ethernet signals), DC will not pass through.

911105A Magjack doesnt let me use DC component (Schematic on left)

However, bel and other PoE magjacks bring out the 48VDC on other pins.

What I am proposing is to desolder Harun 911105A magjack and solder PoE magjack (right schematic).

Using bel magjack, I can pass ethernet signals to the enc chip as well as use 48Volts for custom electronics I am trying to design.


Go for it! I was only suggesting a simpler alternative.

That transformer in the magjack will only pass AC, not DC, while it is functioning correctly. But when you put 48 volts across it, the chances of it continuing to function correctly diminish greatly.

edit: You can use a 48 volt supply on the PoE power end if you use a DC-DC converter on the splitter end to reduce the voltage to 9 volts to input into the Arduino Vin jack. Use the 48 volts for your other devices.

Just a thought...

WARNING! You can't put 48 volts into the Arduino Vin jack. KaBoom!!