Raspberry Pi PoE+ HAT
Les Pounder thought the PoE+ HAT was new headwear inspired by the dashing Star Wars hero Poe Dameron. Unfortunately, it is not.
Les Pounder thought the PoE+ HAT was new head wear inspired by Star Wars hero Poe Dameron. It is not.
March 2018 saw the release of the Raspberry Pi 3B+, which featured new PoE header pins. It wasn’t until August of that year that we saw the PoE HAT go on general sale. PoE is Power over Ethernet and it provides a one-cable solution for powering your Pi and connecting to a network.
The original PoE HAT worked, but the first batch of units had an annoying “buzzing sound” hardware fault that led to Raspberry Pi offering a replacement scheme. Fast forward to 2021 and Raspberry Pi has released an update to the original model designed with the Raspberry Pi 4 in mind. Yet while it fixes some issues, it creates some new ones, too.
The Raspberry Pi PoE+ HAT is designed for the Raspberry Pi 3B+ and 4, with an emphasis on the Raspberry Pi 4 thanks to an improved power output. The PoE+ HAT works with PoE injectors and PoE-enabled switches that provide between 37 and 57V DC, which is then reduced by the onboard switch mode power supply to the 5V necessary to power a Pi. The amount of available current at 5V has been increased: 4A versus the original model’s 2.5A. This gives the PoE+ HAT ample power for a Pi 4, and the possibility of USB-based storage.
Staying cool under pressure
Dominating the centre of the board is a 25x25mm brushless fan, necessary for keeping our Pi 4 cool. Fan control is automatic, triggered by a sensor reading the CPU temperature, but we do have to add a few lines to our config.txt file for the fan to know when to react. We set our config to react when the CPU temperature reached 50°C and the fan kicked into life, keeping our Pi 4 at around 54°C and surprisingly there was no noise from the fan!
As you may have already guessed the PoE+ HAT is a HAT and that means it connects to all 40 pins of the GPIO, and an additional four PoE pins only found on the 3B+ and 4. The GPIO is completely covered: there’s no access to any of the GPIO pins unless we use an expansion header. It’s a hack, but it works. The online instructions tell us to install all four of the M2.5 standoffs to prevent the PoE+ HAT from touching the Pi. But this does introduce an error. The bottom-right machine screw of the CPU fan blocks the Raspberry Pi camera slot. We can replace the screw with a shorter screw, but you would’ve thought that this would’ve been picked up in the design/QA process! If you don’t use the camera this isn’t a problem, but when we consider that the PoE HAT was a popular choice for makers looking to add Pis to remote locations, such as sheds and outdoor projects, this is an irritation at best.
So who is the PoE+ HAT aimed at? The first customers are going to be the networking enthusiasts who want to minimise their wiring and power their Pi-based home server projects from PoE. For those customers, the PoE+ HAT is perfect. It’s quiet, easy to install and provides more than enough power for the Raspberry Pi 4. For the makers, the PoE+ HAT GPIO and fan screw issues can be easily mitigated, but these problems should’ve been solved at the source. For just a little money we can get the screw and GPIO extension ourselves and fix the issue, so don’t let it put you off the PoE+ HAT.