I am not sure I fully understand the issue, but let me make a couple comments.
- The curve controller you show appears to be working as you have it set
it starts at 45C and the source is at 38C, so the controller is not active
but you are seeing the 2.1V minimum set to the fan
- The minimum you are applying to the fan IS a minimum
meaning the fan will not drop below that value
but can run above it
Is the system water cooled or air cooled?
My system is air cooled.
About your first comment: you are right in everything except "controller is not active". Controller at temperature below minimum is setting voltage value corresponding to the minimum temperature point in curve line. In my case, voltage at temperature 38C is corresponding to 45C and voltage must be 17,5% = 2.1V. And it is 2.1V as must be.
About your second comment: you are right.
All work fine when minimum power is zero, and fan is "Power controlled"
At
38C, the voltage is 2.1V (RPM=330), and when I set minimum power to
2.1V, the voltage grows to
3.8V as shown in second picture. After setting "minimum power" to zero, the voltage decreasing to its normal
2.1V.
Also, when I set fan to "speed controlled" where the MINIMUM RPM is set to
300, the RPM grows to
570. After setting fan to "power controlled", the RPM decreasing to its normal
330.