PWM or DC mode

[Winter_German]

I was fiddling around with some BIOS settings and set my case fans to the PWM mode.  When I went into Windows and checked my speeds, my rear fan was running lower than it usually does at 50%.  I set the mode back to the default DC mode, and everything went back to normal.  Im now wondering, while DC mode is giving me the correct speeds for my fans, is it possible my motherboard is using voltage control instead of PWM control?  I would think that using DC mode on a PWM fan would damage it, but I'm not sure.  Any info or opinions would be appreciated.

 

My motherboard is an MSI Z370 A-PRO and my case fans are Corsair ML120 Pro White LED (rear) and Corsair ML140 Pro White LED (front).

[ShadySocks]

PWM means that it turns the power on and off super fast, where it spends a larger percentage of time on for the percentage speed you want. I'm guessing DC mode turns down the voltage or current to decrease the fan speed. DC mode on a PWM fan won't damage it.

[Bartholomew]

30 minutes ago, Winter_German said:

I was fiddling around with some BIOS settings and set my case fans to the PWM mode.  When I went into Windows and checked my speeds, my rear fan was running lower than it usually does at 50%.  I set the mode back to the default DC mode, and everything went back to normal.  Im now wondering, while DC mode is giving me the correct speeds for my fans, is it possible my motherboard is using voltage control instead of PWM control?  I would think that using DC mode on a PWM fan would damage it, but I'm not sure.  Any info or opinions would be appreciated.

 

My motherboard is an MSI Z370 A-PRO and my case fans are Corsair ML120 Pro White LED (rear) and Corsair ML140 Pro White LED (front).

No it wont damage it.

 

A DC fan set to pwm mode will run at 100%, regardless of curve or settings. PWM uses a seperate pulse line on the cable to control the speed (which is ignored by a DC fan which doesnt have that signal wire). A pwm fan controlled in dc mode usually also runs (either full speed or goes into a dc mode).

 

Check the cables for your fans, 3 wires is DC mode, 4 wires is pwm. Specs for the 2 you mention say 4 pin so are pwm.

 

So likely youd be better off using pwm mode for these, allower longer range of rpm control. If the fans now to 100% continously, likely your system will become a lot less noisy  (likely this is why when you tried pwm you noticed reduced rpm)  just make sure your fan curves etc are proper so that under load the provide enough flow.

 

 

[Winter_German]

43 minutes ago, Bartholomew said:

likely this is why when you tried pwm you noticed reduced rpm

 

 

It was just weird that only the rear one changed, and it wasn't running at its true 50% when I set it there.

[WoodenMarker]

9 hours ago, ShadySocks said:

DC mode on a PWM fan won't damage it.

Except on ML's which require 12V for the magnetic levitation to work properly. 

7 hours ago, Winter_German said:

It was just weird that only the rear one changed, and it wasn't running at its true 50% when I set it there.

The signal to rpm curve varies between different fans and different methods of delivering power. For ML's you shouldn't be using DC in the first place.

[Winter_German]

5 hours ago, WoodenMarker said:

The signal to rpm curve varies between different fans and different methods of delivering power. For ML's you shouldn't be using DC in the first place.

It's just strange that the fans wouldn't run at the proper rpm.

[LogicalDrm]

16 minutes ago, Winter_German said:

It's just strange that the fans wouldn't run at the proper rpm.

How do you know that? What was the rpm for 50%? As PWM uses different method, the point in curve which would match DC's 50% might be actually at 35-40%. If you monitor rpm, this is simple math to verify. Also remember that most fans report speed with 10% marginal.

[Winter_German]

13 minutes ago, LoGiCalDrm said:

How do you know that? What was the rpm for 50%? As PWM uses different method, the point in curve which would match DC's 50% might be actually at 35-40%. If you monitor rpm, this is simple math to verify. Also remember that most fans report speed with 10% marginal.

If it might actually be closer to 35 or 40%, that would make a lot of sense as it was running at 1250 rpm while the 50% is supposed to be about 1400 rpm.