Use a POE switch to power ESP32 wired

Hi folks,

@dynamicdave and @zenofmud have been helping me tremendously to get up and running with EspEasy on Wemo D1 mini devices :pray:

So I have a couple of those running already via WIFI. Works very nice! But now I need to install a couple of sensors in my garden (and in underground vessels) where I don't have wifi. And I also don't have any mains plugs in the neighbourhood.

To solve this, I have installed EspEasy on a wt32-eth01 and now I can read an ultrasonic distance sensor via ethernet :champagne:

Two years ago I have been digging a tube into the ground, containing a waterproof ethernet cable. So now I would like to connect my wt32-eth01 to that cable. But since I have to power both the wt32-etho01 and the ultrasonic sensor, I would like to use power over ethernet (POE) to avoid having to install an extra power cable, and to avoid needing to install row of power adapters in my house. A poe switch is a very compact and neat solution...

I was thinking of this approach (since the wt32-eth01 doesn't support POE):

  1. So first I would like to buy this affordable POE switch. It is only 100Mbit, but that is enough for my use case (i.e. read a sensor periodically). If I understood it correctly, this switch delivers 48Volt, with a total maximum of 120Watt (and maximum 30W on a single port).

  2. A POE splitter cable, to separate the DC voltage apart from the ethernet signal.

  3. A step down converter, to convert 48V to 5V (to power the wt32-eth01 and the jsn-sr04t)

  4. A fuse is added, in case e.g. a shovel breaks the cable (introducing a short circuit).

Does anybody sees things I have overlooked in this solution, or things I should take into acount?

Thanks !!!

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Looking good - I assume it will be in an suitable box (IP rated). Don't want to start another battle but you could include fuse(s) at the the converter :wink:

I see you went over to the dark side (EspEasy ) - not Tasmota :crazy_face:

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Bart, do these use the same logic levels?

[EDIT] The jsn-sr04t is TTL (5v) and the wt32-eth01 can use 5v or 3.3v on the serial inputs.
Looks good!

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A POE ready ESP32 exists: ESP32-POE - Open Source Hardware Board
It may make the installation more robust: avoid the splitter, avoid the converter.
And it is working with ESP-HOME too...
Never tried those, however.

I guess the only other thing to think about would be lightning - a strike near a long cable, even if buried, might cause quite a mess of your switch and the devices. :cloud_with_lightning:

I'm not an expert so I couldn't say what might be needed to protect from that or even whether it is a realistic issue.


Having had a strike on a tree in front of my house in '97 I can tell you that you're probably not safe within 50 yards. I lost a in/outdoor temp unit, a RS232 chip on a board with a cable attached only on one end, a light bulb in the basement, and a circuit breaker tripped but wasn't damaged. A neighbor about 50 yards away lost a microwave oven and in the other direction a guy lost his weather station.

Even with that I'd go ahead, @BartButenaers, as the risk is not that great unless you're in a very frequent lightening area and have had near strikes before.


Hey @smcgann99,
I have added it to my original post now. Although now I re-read your sentence and I see you write 'at the converter' while I have added it at the side of the poe switch...

I have taken that board into consideration last year, but it was quite expensive compared to the wt32-eth01. But indeed then the splitter can be avoided. However I don't think the converter can be avoided, because you need to convert the voltage to 5V.

Hey Julian,
Yes that is true. But I have now arrived at a point that I need to exclude such riscs from my list, otherwise I will never live the day that I have any sensors running :wink:

The main reason why I started with EspEasy is that it supported the wt32-eth01 out of the box. While Tasmota required an unofficial build (if I understood correctly). And I wanted to have the same firmware on all my devices (wifi and ethernet), to keep my setup as simple as possible. But it could have been that Tasmota was even better for my purpose. But currently EspEasy fullfills my needs...



Just one thing (and taking into account other posts of yours) i would not go for a 100MB switch - you have recently raised questions re IP cameras - most of which you would want to do as POE and ethernet - 100MB/s will not then cut it for multiple cameras at high frame rates or with multiple streams.

Moving to a Gigabit switch with POE is not that much more expensive


If you are plugging the ethernet cable directly into the ESP32-POE (which is the reason for using a POE model) then the ESP device is already converting voltage down to whatever the rest of the board requires.

However, be aware there is a physical limit to the amount of 5V current available to the POE-powered ESP32-POE and attached devices. From the FAQ for the ESP32-POE board linked to above:

Q)  What current is available when the board is powered via the Ethernet connector (PoE)?
A)  The PoE circuit can safely provide up to 4W, i.e. 800mA @ 5V. Part of this wattage is used to power the ESP32 module, the battery charger, and other circuits part of the board design; the remaining wattage is available for additional circuits (up to around 600mA).  Make sure the total current consumption does not exceed 800mA @ 5V.
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Same price for the gig version - YuanLey-Gigabit

Hey Craig,
Good that I write down on Discourse all my personal plans, because then people like you can remind me about it afterwards :wink: . Good one! Especially since @smcgann99 found below a Gig version...

Hey @DonBurch,
Welcome to discourse!! You got my attention already immediately on your first visit :+1:
Very stupid of me, but I hadn't thought about the fact that an ESP32-POE can be connected directly to an 48V POE switch.
And the physical limit section is also very good information.
Thanks !!!

While the esp-poe is probably the right answer you can also get prebuilt down convertors to microusb connector style like -


Serendipity! That is just the thing I need for an idea I have. Cheers Dave!

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Hey Dave,
That is indeed better, to make the setup smaller, because one component less.

However a wt32-eth01 does not (unlike e.g. a wemo d1 mini board) have a micro-usb connector unfortunately...

I had to install the firmware on it via a usb-to-serial flasher, because it does not have a micro-usb interface...

If I could find these but with 5V instead of 12V, that would do the job I think...

Well you can get pure passive ones instead - then use whatever voltage supply you like rather than a POE switch...

Or indeed just cut off the micro USB as that module doesn't seem to have any power connector at all - so either you wire up something or go direct to the board anyway.

Sounds like a plan :wink:
Then you can add an inline fuse before the ESP and sensors, given this can output 2.4A


Yes that was my first idea. But then I need POE splitters on one side and POE injectors on the other side. And then I need multiple power supplies, and I also need step-down converters because 5V on a longer cable is not optimal...
So therefore a POE switch is a very neat solution, because it is nicely all within one box and you just need to insert your cat cables.

When you shared your link today of the converters, that popped also in my mind. But to be honest I always feel bad when I need to start cutting in nicely fabricated stuff that I just bought. Then I always think: perhaps this is not my best idea ever :wink:

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Of course you can compensate for a long cable with a higher voltage input to allow for the drop.

But yes cutting new stuff always irks me. But soldering two wires to connect it to the board is easier than wiring up a micro usb socket just so you keep the plug. And the whole thing is only 3 decent coffee or 2 beers.

Found an active POE splitter that got my attention (here on Ali):

I assume these 5.5mm female DC jacks will fit to them, so I don't need to start cutting of my cables:

That way the setup becomes very solid and simple:

Unless somebody sees something nasty that I have forgotten, I am going to put some stuff into my shopping basket :wink:

BTW on the above link (about the splitters), I see also an example image of a Raspberry being powered via POE:

I assume you will need a more expensive POE switch to be able to power a series of those devices. However just wanted to share it here, because it might trigger the creativity of some folks in this community...