Pi Cluster: E3 PoE

What is PoE?

PoE, or Power over Ethernet, descibes several standards for passing electric power along with data over twisted pair Ethernet. This way power can be delivered to devices such as Acces Point, Camera’s, Phones,…

From the several common techniques for transmitting power over Ethernet cabling, only three are standardized by IEEE in the IEEE 802.3 standard.

Requirements

In this episode we’ll adapt our cluster to use the PoE switch (or injectors). we’ll do this to reduce the required amount of power plugs from 6 to only 1 (or 2 depending on your switch).
You can follow this guide for a single pi to. This can come in handy when you want to place your Pi so a location where you only have access to an Ethernet cable.

• Cluster of Pi’s (at least 1 Pi)
• PoE HAT for each Pi
• Ethernet cable
• PoE capable switch or injector (802.3 af) 48V

Building up

Before we can mount our Hats to the Pi’s we need to disassemble our Pi Tower.

When done we can remove the pi and install the screws and stand-offs in the correct order.
I mounted them with the screw in the pi and the nut on the plexi. This was before i was thinking about adding PoE.
Don’t mount the Nuts yet. Or even better, place them in a secure location as we will no longer require them. mount the stand-offs that came with the HAT.

Don’t forget to add the heat sink to the lan-chip, but don’t align it properly, move it more to the USB connector as the transformer of the PoE hat will be VERY close.

Mount the PoE Hat and screw it in using the provided set of screws. You’ll have 4 spares since we are using a power case, don’t lose these as they might come in handy later.

Put the Pi Tower back together and lets see our handy work.

As you can see I don’t have a PoE hat for every pi. So to prevent mistakes i plugged the Power connector of the PoE Pi’s with a Micro usb dust cover.

Connecting PoE

Connecting your new PoE Pi’s you either need a PoE switch or a Power Injector.
When buying one make sure its compatible with the 802.3af standard.
I got a TL-SG108PE, a managed PoE switch from TP-Link. When you go for power injectors you’ll have to make sure that they are the correct type (eg. the POE-48-24W-G from ubiquiti)

Connect your Pi using a normal Ethernet cable to the PoE switch and power your switch.
If you don’t need to enable the PoE on your switch (like on the TL-SG108PE) you are good to go.
When you use a power injector you’ll need 2 Ethernet cables.

As you can see the Pi is running on no more then a Ethernet cable. I assure you that there are no hidden cables in the back.

Conclusion

PoE is just great.
You can power stuff that is below 15W (for 802.3af) with just 1 cable and having 1000Mbps of network connection to.

Thought there are some negatives about using PoE.
PoE will increase the cost, you’ll have to buy a more expensive switch (or an additional injector), the PoE hat. the PoE hat alone is around 30€ (or around 35US$ for you yanks)

So when possible using a normal switch and some power adapters for the pi is the cheapest solution. But of course, that ain’t fun!

Have fun with your PoE cluster!