Is speedfan able to run pwm fans at very low RPMs (less than 100)

[Cunning linguist]

I dont have a PC to test this out but its very important because i have RGB fans that i want to run at 60 RPM to show off by displaying the large static pressure optimized RGB blades passing slowly. The question is, does speedfan have true pwm and does it run very slowly? Given PWM means constant voltage so it should run and 25hz signal means it should be smooth too.

 

[photonboy]

Speedfan is limited by the motherboard fan control capability, and physical characteristics of the fans (though I'd suggest the motherboard fan control software anyway unless there's some problem with it).

In general from my experience it's usually:
a) 20% max RPM for CPU_FAN header, and
b) 40% max RPM for case fan headers

It's not common to see a radiator fan that starts below 800RPM so 160RPM (ish) is probably about the minimum. About 200RPM for fans that start at 1000RPM. (so 20% duty cycle with 12V PWM controller)

OTHER:
PWM does not mean constant voltage exactly. Yes, it's the SAME 12Volts but it's done in pulses. It's constant within a pulse though.

Not sure what you are referring by 25Hz etc.

*Long story short, is that fans need to overcome resistance to turn on. It's theoretically possible to design them to spin really low but it doesn't make much sense to design things that way.

So...
I still don't quite understand what you are trying to do. Since you don't have a PC either that means you're likely stuck with a constant 12Volts. Not sure exactly what that does to a fan, but it's essentially a 100% duty cycle I guess so that may mean spinning at 100% fan RPM thus not slow at all.

(and if you don't have a PC what's Speedfan got to do with this?)

 

[photonboy]

https://en.wikipedia.org/wiki/Computer_fan_control#Pulse-width_modulation

That's 25KHz (25,000 x per second). So the voltage is fluctuating between 0V and 12V (square wave means changing voltage is very fast). The duty cycle means how long the square wave is happening as a percentage. If it's 50% then half the time the voltage is a flat ZERO volts. The rest of the time it's the cycling square wave.

Now, again, if you apply a simple 12 Volts, DC, with no pulsing I'm pretty sure it would just spin at 100%.

 

[Cunning linguist]

I'm building a PC now so I'm using a laptop ATM. What I mean by constant voltage is that pwm sends pulses of 12v and full amperage. So my theory was that no matter how low the duty cycle it should start( except when the magnets overcome distance traveled at very low duty cycle). The purpose is to spin the blades at an rpm that is visible. Now the question is, does software permit it and in practice does it work?

 

[Karadjgne]

Depends on the fan. I have a Noctua NF-F12 pwm. it's a 1000 rpm fan. Lowest I can get is right around 20% ± fan speed, actually 210-215rpm, if the register is correct. That's about as good as a pwm fan gets, so a 2200rpm fan is looking at 450-500rpm range etc. Analog fans are damned lucky to see less than 60% startup as they need at least 5v for the good fans, but 7v is more common.
There isn't a pwm fan that I know of that'll even closely approach 60rpm. Anything less that what's needed to keep the motor turning and the fan basically shuts off as it doesn't have the current necessary to overcome the inertia. With a pwm fan that's still receiving voltage, but pulses to slow to turn the motor, all you do is cook the contacts, it's not recommended at all, burns up the fan.

Sorry, but what you need, and what's possible are 2 different things.

 

[Cunning linguist]

TBH I don't think current is the problem because the reason voltage control fans stall is because the voltage is controlled with a resistor. Pwm is supposed to not have that issue.

 

[Karadjgne]

A PWM signal contains 2 things, amplitude and time. A motor needs both. A pwm fan is in a constant state of trying to turn on. If you cut the signal time down too far, the motor literally doesn't see enough current to actually kick it over to the next cycle, resultant cycles end up similar, the fan motor loosing enough force to overcome the inertial barrier created by the resistance inherent in any motor.

Think of it this way. if you weighed 240lbs, and you punched a door as hard as you could, would you expect the door to open. No. Now take that 240lbs and get a running start, then hit the door. Door gonna open. Same theory. Cur the pwm signal down too much, the motor literally cant get enough of a running start to hit the door hard enough to make it open, just stands there breaking its knuckles, basically burning out the motor.