Case fan % seems off

[trawetSluaP]

Hi all.

I control my case fans using a fan controller all works well, however, the fans seem to behave strangely based on the % they are running at.

So for example if the fan is a 2000rpm fan will run at around 600rpm 50%, 1200rpm at 90% then the curve ramps up in the last 10% where it reachs 2000 rpm at 100%.

I have the min and max % set at 0 and 100 respectively.

I guess it's possible this behaviour is normal but just seems strange to me!

I use Silent Wings 3 fans, a mix of 120s and 140s.

Any info would be appreciated.

 

[AlienALX]

That sounds like PWM behaviour to me. Are they 4 pin?

 

[trawetSluaP]

That sounds like PWM behaviour to me. Are they 4 pin?

Yeah, controlled through PWM. Would it be better to set control differently?

 

[AlienALX]

I don't know if you can. Basically pulse width will send pulses to the fan. So it's not like a 3 pin. With a 3 pin you control the speed with the voltage, but a PWM is a signal basically telling the fan to go on, then off. Well, not off, but just not on....

So for low speed the pulses are slow. On.......on.......on etc. As the speed increases so do the speeds of the pulses but IMO it's nowhere near as accurate. That may be why you are seeing the RPM change in the last 10%.

With any water cooled rig I basically set the fans once (I use 3 pin) and usually around the 7v mark. If they are not capable of cooling the rig sufficiently I up the voltage (depends on the RPM of the fans) until they are either barely or still not audible, then I leave it there.

If I had to have them spinning any more than they do always it would be too noisy. If it's too hot? you don't have enough surface area (or rads, basically).

 

[trawetSluaP]

It's not too hot and I'm sure I have plenty of surface area with a 360mm and 2 x 420mm rads, however, I live in a very stuffy house and it gets very hot in the room where my PC is so I have a fan curve set-up depending on the water temps.

 

[AlienALX]

Hmm. All I can advise in that case is to find your "almost worse case scenario" and just leave them there.

 

[grec]

It doesn't sound particularly typical imo, that's somewhat inverse to what you'd usually expect, where because of the effects of inertia and resistance, particularly air resistance, which can be an x^2 relationship with speed, usually you need notably more power to gain RPM towards the top end.

A worst case scenario for a motor is like this:

But because PC fans are quite light(And usually have an IC within them to regulate the form of the pulses) it's usually closer to an ideal linear relationship like this:

So I'd assume something isn't spot on, whether that's the tach(You should be able to ear test that one), the PWM output not being linear with the %age input you set (Maybe it's pre-biased to try and cancel out the above effect), maybe the input voltage dropping from 12V (Possibly because too much current is being drawn through the fan controller) or something else limiting the current.

Of course, maybe the PWM IC within these fans are just a bit weird, so may be worth checking one on its own or something if you can.

 

[Warchild]

Yeah, controlled through PWM. Would it be better to set control differently?

Well with controllers you can do several things with PWM.

not only can you set a range for 0-100% PWM which in turn means 0-100% RPM to an extent,

but you can also set a range for the power going to the fan.

e.g. I set a max power for the fan of 9v so when its at 100% PWM its only supplied with 9V, that means your true max fan speed isnt achieved, even though your settings say max PWM.

In addition to that, some controllers can behave like this by default, for example to keep low noise, they might not supply 9v to your fan when its at 80% PWM, but if you set PWM to 100% the controller realises you want full juice so sends 12V through.

 

[trawetSluaP]

I'm sure I've set the fans up to use the whole PWM range being PWM controlled.

Here are how I have them set up:

These are 2000rpm fans and as you can see, at 49% they are only at around 500rpm.

 

[grec]

Should you set the minimum power to 12V? Is it not reducing both duty cycle and voltage if not? Not too familiar with that software.

Also does that "speed control" setting offer closed-loop loop functionality using the tach?

 

[trawetSluaP]

Should you set the minimum power to 12V? Is it not reducing both duty cycle and voltage if not? Not too familiar with that software.

Also does that "speed control" setting offer closed-loop loop functionality using the tach?

I tried that and it put the fans at 100%, think that's just to set a ratio between fan and controller.

Not sure what you meant by the speed control, however, if I set it anything other than PWM the fans go to 100%. Would imagine this is because they are PWM fans.

 

[Warchild]

Two places to configure this.

1. As you have done

2. In Controllers (make sure controller is also 100%)

Here is mine. So if your contrller is not at full power. It doesnt matter how much you set it too in the fan setup, it would be the full 100% PWM

 

[trawetSluaP]

Two places to configure this.

1. As you have done

2. In Controllers (make sure controller is also 100%)

Here is mine. So if your contrller is not at full power. It doesnt matter how much you set it too in the fan setup, it would be the full 100% PWM

I actually have these fans set-up on a curve using the controller.

But even if I use a single point controller the % I set the fan at doesn't seem to correlate with the RPM.

So at 85% my 2000rpm fans are only running at 1300rpm.

If I change the power to 100% as you suggest the fan runs at 100% regardless of PWM setting.

 

[Warchild]

Try using same controller parameters I do and check your RPMs then.

I have a tolerance of about 10% which is a little on the high side, but not as bad as yours. e.g. 100% = 2400 for me

50% im reading 1150 +/- 10%

 

[trawetSluaP]

Try using same controller parameters I do and check your RPMs then.

I have a tolerance of about 10% which is a little on the high side, but not as bad as yours. e.g. 100% = 2400 for me

50% im reading 1150 +/- 10%

Where do you mean? If I enter 100% under the controller menu it runs the fans at 100%.

 

[Warchild]

Add a new preset value controller with power at 100%, then map your fans to that one instead of your curve controller

 

[trawetSluaP]

Add a new preset value controller with power at 100%, then map your fans to that one instead of your curve controller

That just runs the fan at 100%. Or whatever the max value of the fan I set to under the "Fans" section. It doesn't correct the % discrepancy unfortunately.

 

[Warchild]

That just runs the fan at 100%. Or whatever the max value of the fan I set to under the "Fans" section. It doesn't correct the % discrepancy unfortunately.

What fans are they? I am not having your issue.