On 24th May 2021, Eben Upton announced the Raspberry Pi PoE+HAT on the Raspberrypi.org Blog. Given the challenges experienced and discussed with the original PoE HAT which I covered here and then here, I was keen to get my hands on this latest edition so quickly placed an order for a couple of units from the ThePiHut.
The key difference between the original and the new Raspberry Pi PoE+ HAT is the support for the 802.3at PoE+ standard which increases the available power 25.5W, a significant increase compared to 15.4W limit of 802.3af PoE of the original HAT. The ability to use all the extra power may still be a challenge depending on your needs, more on that soon.
Looking at the new Raspberry Pi PoE+ HAT both sides of the PCB are now heavily populated with components doubling the weight of the HAT to ~40g. The component density is a stark change from the original HAT, where the top side only contained the fan. The PCB on the new HAT also appears to be slightly thicker, 1.46mm vs 1.36mm, though according to the published information both HATs used 2oz Copper on a 4 layer board. Many of these changes are no doubt to enable the HAT to deliver nearly double the maximum power output compared to the original PoE HAT.
The 4-pin PoE interconnect also looks like it may have been improved. The 4-pin surface mount socket on the original HAT could be accidentally ripped from the PCB if the HAT wasn’t removed carefully, at the connector was only attached via 4 small pads. The new design shows that the connector is attached to larger traces on the bottom of the PCB, I’m not willing to try and break off the connector, but hope that this change does provide the mechanical strengthening needed.
The original 2 wire 5V Sunon MagLev fan has been replaced by a variant similar to that use in the Pi Case Fan accessory though using a higher speed version, AD0205MX-K59. These ADDA fans appear to be Raspberry Pi specific variants with a K59 designator on models which appear to be normally 2 wire 5V K50 version. The K59 versions are 3 wire versions, which should enable the speed of the fan to be measured, however I’ve yet to determine if this can be read by the user or if the data is purely used by the control circuitry.
The ADDA fan also has a smaller central hub, fewer but longer fan blades than the Sunon version. This smaller hub design provides more of an opening in the PCB to push air through, which may help reduce noise. As the fans adapt to the temperature of the Pi, noise is only a significant issue when the Pi temperatures reach ~50°C.
|Raspberry Pi PoE HAT||Raspberry Pi PoE+ HAT|
|Model||MF25060V2-1000U-A99||AD0205MX-K59 (data based on K50 version)|
|Voltage||5 V||5 V|
|Current||75 mA||110 mA|
|Power||0.38 W||0.55 W|
|Max speed||10,000 rpm||12,000 rpm|
|Air flow rate||2.2 cfm||2.4 cfm|
|Pressure||0.16 inch H²O||0.185 inch H²O|
|Noise||18 dbA||30.5 dbA|
Fan Not Working
On initial testing, the fan on the PoE+ HAT didn’t work at all. Fortunately, this appears to have been a timing issue between suppliers sending out the new PoE+ HATs and the OS being updated to add the necessary support. This was added on 28th May, so users will need to ensure their system is fully up to date, using:
sudo apt update && sudo apt upgrade
What can I do with the extra power?
The launch blog post stated:
The original PoE HAT implements the 802.3af standard, and can deliver a guaranteed minimum of 13W to the Raspberry Pi. This is enough to power a Raspberry Pi 4 at maximum load, but not quite enough to power the hungriest USB peripherals at the same time.Eben Upton – 24th May 2021 – https://www.raspberrypi.org/blog/announcing-the-raspberry-pi-poe-hat/
The PoE+ HAT implements the 802.3at standard. When used with a compatible switch or injector this means it can deliver up to 25W.
This 25W capability represents up to 5 Amps at 5 Volts (the standard Raspberry Pi voltage). However, this doesn’t mean you can now connect multiple heavy load USB devices to your Pi. The Raspberry Pi 4 still has a 1.2 Amp current limit shared across all 4 USB ports and that doesn’t look to be changing, perhaps in the next Pi incarnation, this will be increased.
So this extra power is there to allow users to use the maximum USB current loads, whilst also running heavy workloads on the Pi, driving other accessories connected to the Display, Camera or GPIO headers and potentially overclocking. It also brings the available power above the minimum 15W requirements of the Raspberry Pi 4 specifications.
If you need to drive higher current USB loads, you will need to continue to use Powered USB Hubs. Please ensure the USB Hub doesn’t backfeed power to the Raspberry Pi (aka backpowering), as this can result in damage to the Pi.
The new Raspberry Pi PoE+ HAT does offer a higher voltage output compared to the original Raspberry Pi PoE+ HAT. This was tested using a Raspberry Pi 8GB along with a constant current variable USB Load device.
Using the same Ubiquiti UniFi USW-24-PoE switch each configuration was tested increasing load using the constant current USB load, the voltage is measured and displayed on the USB Load device. PoE Power measured is as reported in the UniFi Dashboard.
As can be seen the voltage output of the original PoE HAT is ~ 0.1V lower than than the PoE+ HAT, and this different is maintained throughout the test until 1100mA. Above this load the Raspberry Pi tripped the USB current limit, though the original HAT did briefly reach 1200mA.
The power usage reported by the switch shows that at low load the new PoE+ HAT is consuming nearly 1.9W more than the original HAT. As load increases these difference diminishes to 0.35W. It will be interesting to see if this extra power consumption results in any thermal issues.
Coming up in Part 2 – Potential problems!
In the second part of the review of the Raspberry Pi PoE+ HAT, I’ll take a closer look at power, thermals and some other potential problems with the design. For the time being, I’d be cautious about recommending this new HAT.
- Raspberry Pi 4 (Amazon) (Pimoroni) (ThePiHut)
- Raspberry Pi PoE+ HAT (Pimoroni) (ThePiHut)
- Raspberry Pi PoE HAT (Amazon)
- Ubiquiti UniFi USW-23-PoE (Ubiquiti EU | USA)
- USB Load (35W) (Amazon .co.uk|.com)
Amazon links, are affiliate links that help support the site, where possible I’ve used links that should take you to the product in the Amazon store in your region. Links to other suppliers are included for your convenience.