Raspberry Pi - PoE+ Hat fans

I've been tinkering around with my Raspberry Pi's recently, and since i've know got two, i thought it was time to get as lightly nicer set up! So, i bought a network switch, a multi-pi case, and a bunch of small (20cm) ethernet cables. In order to reduce cable clutter, I thought it could be neat to power the Pi's via Power over Ethernet, so I also bought a couple PoE+ Hats.

They're pretty easy to set up, but the second i booted up the Pi, the fans started spinning, and wouldn't stop... Was it running too hot?

$ vcgencmd measure_temp
temp=49.5'C

hm.... That really shouldn't be causing the fans to spin. After a little digging, i found the settings:

add these to your /boot/config.txt:

dtparam=poe_fan_temp0=65000
dtparam=poe_fan_temp1=70000
dtparam=poe_fan_temp2=75000
dtparam=poe_fan_temp3=80000
dtparam=poe_fan_temp0_hyst=2000
dtparam=poe_fan_temp1_hyst=5000

Save, then reboot, and all should be well. Here's a little more detail on what those settings do (taken from Pi firmeware README)

Params: poe_fan_temp0           Temperature (in millicelcius) at which the fan
                                turns on (default 40000)
        poe_fan_temp0_hyst      Temperature delta (in millicelcius) at which
                                the fan turns off (default 2000)
        poe_fan_temp1           Temperature (in millicelcius) at which the fan
                                speeds up (default 45000)
        poe_fan_temp1_hyst      Temperature delta (in millicelcius) at which
                                the fan slows down (default 2000)
        poe_fan_temp2           Temperature (in millicelcius) at which the fan
                                speeds up (default 50000)
        poe_fan_temp2_hyst      Temperature delta (in millicelcius) at which
                                the fan slows down (default 2000)
        poe_fan_temp3           Temperature (in millicelcius) at which the fan
                                speeds up (default 55000)
        poe_fan_temp3_hyst      Temperature delta (in millicelcius) at which
                                the fan slows down (default 5000)
        i2c                     Control the fan via Linux I2C drivers instead of
                                the firmware.