With power over ethernet, one cable is all you need for power and data! As part of my Layer-N design challenge project, I wanted to experiment with the POE capabilities of the Omega GW-001-03 Layer-N wireless gateway. Just like POE IP cameras, WIFI accesses points, and VOIP phones, only needing a single cable for power and data greatly simplifies the installation process. By only needing one cable the layer-n gateway can be mounted in a location that can improve layer-n coverage on site. In my project, I have chosen a location in the attic for its a high elevation above ground level, as to hopefully achieve the advertised 3 km range of Layer-n wireless links.
Many commercial network switches already include POE on their ports. You can also purchase POE injectors for a fairly economical price.
For my project, I wanted to make some power consumption measurements of the gateway in different operating scenarios. So, I decided to put together a little POE test injector with an old network switch. For 10/100 Mbit ethernet links, power is distributed over the spare pairs on an ethernet cable. So, all I need to do is to add to banana jacks to an old network switch as follows:
Taking a look at the PCB of my old network switch, we can see there are no traces routed to pins 4,5,7,8 of each RJ45 jack:
I drilled 2 holes with 19 mm spacing in the enclosure:
Installed 2 banana jack binding posts:
I was hoping to include a ferrite bead inside the switch, the one shown in the photo above doesn’t fit:( . Until I source a smaller one, I can clamp it onto the power leads externally. I also soldered the 2 power wires onto one of the RJ45 jacks:
I now have my own DIY POE test injector:
First Test
I connected my POE injector to the POE port of the GW-001-03 gateway with a CAT5 patch cable:
I programmatically ramped my bench power supply from 0 V to 50 V and recorded the resulting POE load current:
One can observe that for POE voltages of approximately 3V to 10V the gateway presents 23.5 kOhm resistance, to signal that a POE Powered Device is connected. For voltages of approximately 15 V to 20 V, the gateway sinks 28 mA to signal that it would like up to 13 W of power (based on the Wikipedia page https://en.wikipedia.org/wiki/Power_over_Ethernet):
At least in this first test, the GW-001-03 appears to be pretty power efficient only requiring 2 W of active power.
All for now, thanks for reading!
