Harvesting power from ethernet?

rmeldo

Senior Member
Hello,

I have a project where I use NodeMCU boards to transmit temperature data in my flat to a web server through WiFi.

It all works fine but, due to the high power consumption of the NodeMCU (about 150mA at 5V) I need to connect it to a power supply plugged into the mains.

I am thinking about enhancements, specifically how I can get rid of the power supply and talk to my phone as well.

I would like to use Picaxe+Bluetooth+battery for the temperature measurement and transmission. This way I could make a low power device and house it in a nice 3D printed box with no external wires.

For the receiving end I thought it would be cool to take data from the BLuetooth receiver and send them to the internet by connecting to the router via its ethernet port.

Now comes the question:

Because the temperature sampling is every 10-20 minutes, would it be possible to find a way to CONTINUOUSLY harvest (and store) power from the router ethernet port and then use it in bursts to power the ethernet transmission?

It would be something nice to have a go at.

Thanks
Riccardo
 

lbenson

Senior Member
I can't answer your specific question (although Power over Ethernet (PoE) is done with additional hardware--https://en.wikipedia.org/wiki/Power_over_Ethernet), but if you're using an ESP-01 for your wifi, the most recent version of the AT firmware from the SDK (July 19, 2016 was the latest I could find) appears to reduce power consumption when idle, and fixes a high-current race condition that I encountered.

If you're using lua (as I guess NodeMCU would imply), I don't know whether the lua firmware ever had the high idle current problem.
 

hippy

Technical Support
Staff member
It is possible to have power passed along an RJ45 cable so that can be supplied from the router end rather than at the device end. That can be easily 'kludged' rather than needing a full PoE solution.

Harvesting power is possible; the link below is to a paper discussing doing exactly that and a search engine may turn up more. How practical it is beyond proof of concept I haven't really analysed -

https://www.diva-portal.org/smash/get/diva2:524347/FULLTEXT01.pdf
 

Jeremy Harris

Senior Member
I have a crude but effective PoE set up, just to get rid of a couple of wall wart power supplies. It works fine, I power a VDSL modem via 12V DC run down the spare pairs in an Ethernet cable, and also power a router and network switch the same way. I now have one 12V power supply running all three devices, which as the VDSL Modem is located right next to the incoming phone connector means I have a much neater set up.

 

rmeldo

Senior Member
Thanks for the advice.

I will read the link provided by Dippy. It seems to be exactly what I was thinking about.

A straightforward solution which I hadn't thought awould be to make an extension cable for the router power supply and tap off that to power my device. I will probably need to use a voltage regulator to go down to 3v3 or 5v.

Riccardo
 
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