Raspberry Pi often used in 24/7 projects. In this mode, the issue of cooling becomes critical. One of the most common options is PoE HAT with built-in fan. At first glance, it may seem that it is enough to connect the HAT and everything will work automatically. But in practice, nuances sometimes arise, as it happened to me.

I bought Waveshare PoE M.2 HAT+. I connected it according to the instructions, but I noticed that the fan worked constantly at maximum speed. Of course, this behavior is unexpected and I started looking for a reason to eliminate it.

Kernel parameters

The PoE HAT fan does not run “directly” from voltage. He is guided kernel parameters and a special driver that reacts to the temperature of the processor and changes the revolutions. These parameters are configured in the Raspberry Pi configuration file /boot/firmware/config.txt

The following block of settings must be added to this file:

# Fan settings
dtparam=cooling_fan=on
dtparam=fan_temp0=55000,fan_temp0_hyst=2000,fan_temp0_speed=80
dtparam=fan_temp1=60000,fan_temp1_hyst=2000,fan_temp1_speed=140
dtparam=fan_temp2=65000,fan_temp2_hyst=2000,fan_temp2_speed=200
dtparam=fan_temp3=70000,fan_temp3_hyst=2000,fan_temp3_speed=255

I will describe this block in more detail using the example of the first line:

• dtparam=cooling_fan=on – enables the hardware fan driver on the Raspberry Pi 5.
• from_temp0=55000 – threshold in milli-degrees °C (55,000 = 55 °C). When this temperature is reached, the fan will turn on.
• from_temp0_hyst=2000 – hysteresis (2 °C). This means that the fan will only turn off when the temperature drops below 53 °C.
• fan_temp0_speed=80 – speed of rotation at this threshold. Values ​​range 0–255 (where 255 = maximum revolutions). 80 ≈ low speed, effectively “quiet cooling”.

After applying these changes, I rebooted Raspberry Pi, but no changes occurred, the fan continued to run at maximum speed. I was forced to look for other reasons to solve the problem – constant maximum fan speed.

Fault diagnosis

Since the entered parameters did not affect the behavior of the fan, I decided to look at all possible parameters that could theoretically be responsible for the temperature and fan speed. To do this, I ran three commands in sequence.

cat /sys/class/hwmon/*/fan1_input
13863

Shows the number of pulses per secondfan.fan1_input – standard sensor in Linux hardware monitoring (humon). Usually, the values ​​here fluctuate depending on the PWM signal (that is, what speed is set via fan_tempX_speed or target_pwm).

/vcgencmd measure_temp
temp=27.9'C

Utility vcgencmd reads CPU temperature (via GPU firmware). Means the ARM core is currently at 27.9 °C. This is the “official” way to see the temperature of the Raspberry Pi, and it is this data that the cooling system uses.

cat /sys/class/hwmon/hwmon0/temp1_input
27050

The same CPU sensor, but accessible through an interface Linux humon. temp1_input gives the temperature in millidegrees Celsius. 27050 = 27,050 m°C = 27.05 °C. This is a more “raw” way of accessing temperature that type utilities use sensors or monitoring systems (Zabbix, Prometheus, lm-sensors).

Since every parameter gave me data, it means that the sensors are active and working. I started looking for a hardware problem. First I turned off and unplugged the Raspberry Pi, unplugged the PCI Express cable, and completely unplugged the PoE HAT board. I saw that one of the pins on the Raspberry Pi fan connector was bent, and this became a big problem, because the connector itself is very small, and even the needle size scale seems quite large. So that you understand the scale of the thumbnail, I took this photo with a macro lens.

As you can see in the photo, the contact was pressed to the bottom and slightly deformed. I was able to lift it with a needle only to a vertical position, but the contact itself remained bent. In order for it to enter the connector correctly, I had to use a needle to widen the hole for it. After connecting, the Raspberry Pi started, and the fan began to receive signals about the number of revolutions depending on the temperature.

By now executing the command to check the number of fan pulses cat /sys/class/hwmon/*/fan1_input i got the value 3447 which is three times less than the previous value. This way I overcame the problem and now my fan is controlled correctly depending on the CPU temperature.

The main conclusion is as follows: for stable and quiet operation of PoE HAT on Raspberry Pi it is necessary not only to correctly adjust the parameters in config.txt, but also make sure the integrity of the connector and pins. My example clearly shows that this should not be neglected, and if a problem has already occurred, it is not easy to solve it, because the connector elements are so small that it will be either impossible or very difficult to physically align them, and for this a needle or tweezers will be quite large tools.

Raspberry Pi 5 has become a real breakthrough in the world of single-board computers. Updated hardware, a more powerful processor, PCIe support via FPC cable – all this opens up new horizons for enthusiasts. However, one key detail is still missing, namely the official POE HAT from the Raspberry Pi Foundation for the fifth generation.

Although the official release is already “on the way”, according to rumors, many users do not want to wait. They want compactness, convenience and powering the Raspberry Pi without unnecessary cables and a separate 220 V outlet. This is where the Waveshare POE M.2 HAT+ comes into play. It is an unofficial, but extremely practical solution for PoE power supply and simultaneous expansion using M.2 drives.

Waveshare POE M.2 HAT+ is a solution for those who do not want to wait for the official release of POE for Raspberry Pi 5

Raspberry Pi 5 Power Supply

Raspberry Pi 5 is sold as a separate board without a power supply included. Users are offered the original 27W USB-C PowerSupply EU power supply. At the first stage, I bought this power supply, because other manufacturers offered devices that were almost the same in price and power, so there was no point in looking for something else.

27W USB-C PowerSupply EU device – box

27W USB-C PowerSupply EU – logo

27W USB-C PowerSupply EU – specification

This power supply supports the following modes:

• 5.1V, 5A;
• 9V, 3A;
• 12V, 2.25A;
• 15V, 1.8A

If we consider the option of connecting Raspberry Pi 5 via Waveshare POE M.2 HAT+ using as a source my UniFi USW-Lite-8-PoE switch which supports the 802.3at standard and supplies an input voltage of 48 volts, then the power characteristics will be as follows.

• Input voltage = ~48V DC
• Power = up to 25.5 W
• Current approximately = 0.5 – 0.6 A

Package

I made an order in an online store in Ukraine, so the seller’s sticker was already stuck on the box. However, the original Waveshare inscription was visible through this sticker. The model code was also indicated: SKU: 28411. Since the Waveshare brand is Chinese, it is logical that this board was also made in China.

All elements are packed in individual bags, namely:

• PoE M.2 HAT+ x1
• Metal heatsink x1
• 16P-Cable-40mm x1
• Thermal tape (3PCS) x1
• Screws pack x1

I suggest considering each component separately, for this I took a photo

Waveshare POE M.2 HAT back

Waveshare POE M.2 HAT face

Waveshare POE M.2 HAT Metal heatsink

Waveshare POE M.2 HAT 16P-Cable-40mm

Waveshare POE M.2 HAT Thermal tape

Waveshare POE M.2 HAT Screws pack

Connecting POE M.2 HAT+

The connection process has its own sequence, and consists of several simple steps:

Applying thermal tape

The kit includes three square thermal tapes, they are in a protective film that must be removed before sticking. Stick the largest square on the processor, and the other two on the Wi-Fi / Bluetooth chip and the memory chip.

• Processor
• Wi-Fi / Bluetooth
• Memory

Fixing the metal heatsink

The heatsink has two diagonal fasteners, it is easily fixed on the Raspberry Pi board. The springs will cushion this radiator. After fixing on the back of the board we will see two harpoon-like fasteners. This will indicate the successful installation of the radiator

POE M.2 HAT+ Mounting

This board is attached to the Raspberry Pi using 4 racks, which are screwed in from the bottom and top with screws.

Interesting fact: the kit includes 5 racks and 10 screws, perhaps the extra ones are considered as spare.

Connecting the cooler power cable

We tighten the 4 racks from below with screws.

We connect the board via the GPO contacts. We need to be careful with the wire to the cooler so that it is placed compactly and does not interfere with the components.

We twist the racks from the top

Thus, our board is installed and connected, the only thing left is to connect the PCI cable.

Connecting the PCI cable

The cable has two sides, so it is important not to confuse the direction and position of the connection

16P-Cable-40mm socket

16P-Cable-40mm socket rpi

16P-Cable-40mm plugged

Testing

As a power source, I will use the Ubiquiti UniFi Switch Lite 8 PoE (USW-Lite-8-PoE) switch. This switch has 4 PoE+ ports with a total power of no more than 60 watts, and no more than 30 watts per port. I connected the Raspberry Pi 5 to the first port. Literally a second later, the boot began, and the cooler started spinning, which indicates that both the cooler and the PCI cable are connected correctly.

The two network port LEDs are lit, indicating PoE+ power and data transmission.

Of course, I was curious to know what the real consumption of the Raspberry Pi 5 was? To do this, I looked at these values ​​in the Ubiquiti – UniFi Network controller, in the Ports section and by selecting the Stats tab.

Ok, 5 watts compared to the 6 watts of the previous model seems a bit low, but there are a few features, namely, here’s what reduced consumption:

• SSD not connected via PCI
• USB flash drive not connected
• Raspberry Pi almost idle

When the load increases or additional devices are connected, consumption will certainly increase.

Conclusions

Waveshare POE M.2 HAT+ is not just a replacement for the official PoE HAT, but a more functional option that combines three features at once:

• PoE power supply without a separate unit.
• M.2 storage for server projects.
• Active cooling is necessary when working with a heavy load.

Until the official solution from the Raspberry Pi Foundation appears, this is the best choice for enthusiasts who want to use the capabilities of the new Pi 5 as efficiently as possible.