Yup, what Tealc said about mixing the different "max" rpm PWM fans is correct and makes sense . . . . I'm just not sure if I understand this "stalling" or "minimum" rpm business?
Its not so much if the controller allows it, it goes by what the motor in the fan allows, hence why some pwm fans have lower minimums then other pwm fans.
What you are describing above seems to go against my "basic" understanding of how PWM works . . . I know that a PWM fan needs a full/constant blast of 12v to get the motor turning, overcome mavity and build an initial momentum but once the fan is spinning I thought the only thing that would effect the "minimum" rpms would be a combination of
- 12v Pulse Frequency
- mavity
I am no electrical engineer but I am thinking of this "intuitively" . . . here's a graphic I just knocked up in MS Paint!
So the top of the graphic we can see the old style method of controlling the fan rpm’s . . . the voltage would have been controlled by a rheostat? which reduced its strength down from 12v . . . to 10v etc . . . this in turn would cut down the fans rpm's similar to the way a car reduces speed when you don't press down fully on the gas pedal . . . of course after a certain amount of reduction the voltage becomes so weak that the fans-motor doesn't respond and it "stalls" . . .
The lower portion of the graphic shows how the voltage is controlled in a PWM fan . . . there is only 12v or 0v . . . nothing in-between . . . now I understand that to get the fans motor turning (and overcome mavity) it needs a full and uninterrupted 12v's for a few seconds . . . but once the "motor" is turning and there is fan
momentum I thought it was entirely possible to control the rpm's by regulating the "pulse" of 12v up until the slowest point just before where mavity would overcome the momentum and cause the fan to stop?
As I'm seeing it I understand how a PWM fan has a "max" speed but I thought the minimum rpm’s would be extremely low? . . . at least extremely low once the fan has overcome that initial sticking point and is having it's speed reduced . . . . the only time it could stall when coming down in speed would be when "mavity" overcame the momentum . . . what am I missing?
