Would like to quickly ask please: what things do I need to calculate or consider if I’m looking at running an RPi and a length or 2 of LED strip lights over PoE? How would I go about working out if there’s enough power etc.? I have it all currently (successfully) running from a 5V power adapter for the LEDs and the standard RPi power adapter for the RPi, but hoping to get rid of both of these and run it all over PoE if possible.
Excellent question, you should be able to do that. How long are the strips, and how much current do they draw per metre?
As seen above, you’ll want to check the standard for which type and cable should do the job after this is determined. As for the actual setup itself, active PoE injection with splitters is probably the easiest way to go. Core Electronics has a few parts that you may be able to get away with using for this such as that which I’ve linked below. Although, the current ratings tend to be a little low, particularly given how power hungry strips tend to be. If you’re running a Pi 4 they can draw a fair bit too.
If you determine all of the ratings for the Pi and your strips when operating at full brightness with that resource I linked earlier, you should be able to work out the most appropriate standard to use in your setup, and what parts would be most appropriate. I hope that helps!
Just a further question on this please: if I have BOTH an RPi and separate LED strip light length to power over PoE, is there sort of a ‘double adaptor’ that would split the power from the PoE Splitter to both the RPi and lights?
FWIW there are quite high standards for the amount of power you can send through an Ethernet cable, right up to 71w available at your device at the moment, so assuming you had a supporting Device you could power quite a few devices from an Ethernet cable…
So it would be fair to say then, that the power won’t be an issue to power both an RPi 3 B+ and some LED strip lights via PoE, but I’d need a PoE splitter and a 2-way DC Barrel Jack Splitter to then split out the power for each device. Connected to the Barrel Jack Splitter then would be what - some form of transformer for the RPi and lights?
to get the full power out the other end of the cable you’d need the right Switch, the right cable and the right PoE extractor/converter (to correctly communicate with the switch and enable the switch to send the 70w down the cable)
from there you’d need to figure out your Pi max power draw and LED’s cumulative max power draw
in theory the LED’s can do around 60ma each (0.03w), the Pi up to 7w… so in theory you have a good 60w left over with the right equipment… so something like 2000 LED’s in a perfect world (feel free to check my maths
now keep in mind that the right switch will also have a power budget, so if you were to try and get 71w out of each port in a 48 port switch from every port at the same time you’d need something with an appropreate budget.
All PoE switches I’ve seen talk about output in W - either maximum per port or total output. So if I do the math, to power a RPi 3 B+ I assume I need about 12.75W (2.5 x 5.1)? If I add say 2 lengths of some programmable strip lights, then I assume based on the suggested power adapter, that they will draw around 20W (4 x 5)?
Assuming the above is correct, I’m guessing I’ll need about 32.75W per port? If I need 6 ports, then I’d need something that could support up to around 200W right?
Many ‘affordable’ 8 port switches I’ve seen only do around 120W. If I rethink my IoT device programming a bit, then I guess I could light the LEDs in sequence rather than all 6 at the same time. This would imply I need around 76.5W to run all 6 RPis + about 20W for just one lot of LEDs = 96.5W. That’s correct right?
Then at my ‘IoT end’ I’d need a splitter capable of this sort of Wattage right?
I believe I spoke on the phone with you on this one. I’ll summarise what we found below:
A Pi 3B+ can draw about 1.8A from the board with no peripherals at full tilt. with a PoE+ Hat that leaves you 5 - 1.8 = ~3.2 amps to play with for strips. Since the strip you listed can draw up to 7.2A at full tilt, you’d either need to chop it in half, or pick a strip with a lower density.
Even then, I’d look into the schematics and traces on a PoE+ hat to see where you’d be able to extract your power from, as running it all through the Pis small traces might be a bad idea.