Bloody outrageous isn’t it!!
Hello,
Can someone please explain me what hyst setting does?
I can’t find it and everyone uses different values of this.
ps, I am new with raspberry and home assistant.
Sure. It is only required if you have added the POE+ hat onto your RaspberryPi.
It is a small board that allows the RaspberryPi to be powered from a POE (Power Over Ethernet) switch. Regular switches can’t PoE. That way you don’t have to power it by USB.
The setting above controls the fan speed on that board, according to temperature. So it is only used if you have the PoE hat.
Thanks for your response,
I have a PoE+ hat, and set your values in the Config.txt
They do work, the fan is much quiter 
But I do not understand what the “poe_fan_temp1_hyst=3000” does or why its 2000 3000 4000 5000 etc.
It says its Delta Temperature? But i have still no idea on why to set them on what value?
I haven’t thought much about the values themselves 
I just tried the once I found, and they worked
'Params: poe_fan_temp0 Temperature (in millicelcius) at which the fan turns on (default 50000)
poe_fan_temp0_hyst Temperature delta (in millicelcius) at which the fan turns off (default 5000)’
This was what I found, but doesn’t say much
Ah oke haha,
I set dtparam=poe_fan_temp2=62000 to =65000. Hoped that the temp would not reach 65 and staid in temp1. But when setting 62000 to 65000 the temp also went from 60000-62000 to 63000-65000 
so did not matter, was trying to find a way to keep it in temp1 speed.
Don’t know if its okey for the Fan to go on/off continuous at the temp border from temp1 to temp2…
Hyst stands for hysteresis. The 5000 value means that 5°C temperature change is needed after the previous state change (fan off / speed change) before the next change will happen. This prevent the fan from switching states very rapidly.
The explanation for what the four temperatures actually are can be found in my earlier post: Pi PoE HAT fan control - #12 by SarumaN
I included part of that post below.
If fan noise is not an issue for you temp0 should be lower that room (ambient) temperature (fan always on) and temp4 should be lower than your target temperature of 65°C. For example
T1:15°C
T2:22°C
T3:30°C
T4:45°C this means that starting at 45°C the fan is at full speed.
The hyst parameter should always be smaller than the T1, T2, T3, T4 differences. Hyst=5°C.
Thank you very much for the explaination!
For fan noise is fine at temp0 and temp1, afther that its to loud.
I have set:
# PoE+ FAN TEMPERATURE CONTROL
dtoverlay=rpi-poe-plus
dtparam=poe_fan_temp0=45000,dtparam=poe_fan_temp0_hyst=3000
dtparam=poe_fan_temp1=50000,dtparam=poe_fan_temp1_hyst=3000
dtparam=poe_fan_temp2=62000,dtparam=poe_fan_temp2_hyst=4000
dtparam=poe_fan_temp3=70000,dtparam=poe_fan_temp3_hyst=5000
But the problem at this is that the fan keeps going from Temp1 > Temp2 > Temp 1 > Temp 2 and so on.
It keeps going faster for les than a minute and then back to Temp1 for maybe a bit more than a minute.
To prevent this, i should increase temp1_hyst, or temp2_hyst?
So an option to change this can be
From your example, to my temp values, is this correct?
Params:
poe_fan_temp0 Temperature (in millicelcius) at which the fan
turns on (45000)
poe_fan_temp0_hyst Temperature delta (in millicelcius) at which
the fan turns off (42000)
poe_fan_temp1 Temperature (in millicelcius) at which the fan
speeds up (50000)
poe_fan_temp1_hyst Temperature delta (in millicelcius) at which
the fan slows down (47000)
poe_fan_temp2 Temperature (in millicelcius) at which the fan
speeds up (62000)
poe_fan_temp2_hyst Temperature delta (in millicelcius) at which
the fan slows down (58000)
poe_fan_temp3 Temperature (in millicelcius) at which the fan
speeds up (70000)
poe_fan_temp3_hyst Temperature delta (in millicelcius) at which
the fan slows down (65000)
So for my problem, the hyst of temp 2 is to low?