Can 4 pin fans be controlled by 3 pin voltage?

Rockbox · 7 Feb 2022 at 14:49

I have 2 4-pin fan headers. One goes to a 3 pin case fan, the other through a y splitter to 2 fans on my heatsink. Recently, I found one of the fans rattling. Thought it was because it wasn't getting enough power, but at full blast, which helped me isolate it, the rattling speeds up, while the other doesn't. I have a 4 pin pwm fan. Can those be controlled on the same y splitter? Thinking of whether to tolerate it, or put one heatsink fan and case fan on the splitter, while the 4 pin goes straight to the motherboard.

Rockbox · 8 Feb 2022 at 09:00

doyll said:
Your fan rattle is most likely not the result of PWM control. As already said, it's most likely either bad bearings or loose mount.

Just because motherboard has 4-pin header does not mean it's PWM.

It's not at all uncommon to have a 4-pin header that is variable voltage with pin-4 connected to nothing.
It's also not uncommon to have 4-pin headers that can be set in bios to be PWM or to be variable voltage.

There is not problem running 4-pin PWM fans on 3-pin variable voltage fan headers.

Pin-2 is variable voltage on variable voltage controlled 3-pin and 4-pin fan headers when using variable voltage control.

PWM fans default to variable voltage control when there is no signal on pin-4. This means a 4-pin fan on variable voltage control header becomes s variable voltage fan.
Pin-2 is 12v on PWM controlled 4-pin headers and pin-4 is PWM control to pulse pin-2 power to fan for speed control.

Shortening / lengthening 12v pulse slows /speeds up fan speed. The slower / shorter the 12v pulse the slower the fan spins.

Hi. We talked earlier about me replacing my stock NH-D14 fans with DeepCool ones. I switched them back and got better performance, but the F14 has a faint but noticeable rattling sound. Let's hope it's a bad mount, but like I said in my other thread, I have a Noctua F12P(WM) ready to go if it isn't. My question was whether I could run both a F12 4 pin and P12 3 pin off a splitter, while the mobo controls fan speeds, and you seem to imply that I can.

Rockbox · 8 Feb 2022 at 10:14

Took the 140mm fan out. It rattles on its own. Tried the pwm fan on the splitter. While it works, it isn't quiet, so it can't accurately control voltage and pwm fans, which is what I wanted to know. What I'll probably do is hook my 3 pin case fan to the y splitter, and have the f12p on a board of its own. It's quiet IMO, and I heard 140mm fans spill over heatsinks designed for 120mm.

Rockbox · 8 Feb 2022 at 11:18

I see, good to know. Unfortunately there's a new problem. The F12P is indeed louder than the P12. It's not accoustically tuned to the D14, and the out-of-sync sound is worse than the whirring from thr P14 when under load.

Is it a good idea to oil the fans? I have sewing machine oil, which I was told works great on fans. But I don't want to ruin the P14. I feel like a monitor enthusiast with a sub-par panel, that has to decide risking a return and getting a worse panel.

Good thing I didn't take the clips off the P14 yet, and I assume I have to replace both the P14 and P12 to get harmony? Replacing just the P14 with something like an A15 will presumably give me the same sound issue.

Rockbox · 8 Feb 2022 at 11:35

With regards to oiling, I saw someone break their fan trying to take it apart here.

Then I saw that you had to use grease instead of oil here. So seems I can't just drip oil into the fan gaps. It might even be sealed off. So any ideas, besides sound dampening?

Rockbox · 8 Feb 2022 at 12:24

Noctua P14. But now there's another dilemma. It's quieter under load, but there would be other noises going on during that time. When web browsing, both are quiet, minus the clicking from the P14. So the F12P might be drowned out by other noises when needed. I'll probably give it a day to see how I adjust.

Rockbox · 8 Feb 2022 at 15:19

doyll said:
I'm assuming your "Noctua P14" is NF-P14 Flex and "F12P" NF-P12 as original fans on NH-D14?

Sorry, yes. P14 is NF-P14. P12 is NF-P12. F12 is the successor to the P12 and F12P uses PWM instead of voltage.

I take it that the hunk of metal they chopped off the NH-D15 to allow more RAM clearance allowed the D14 to cool better, although it's within error. So long as I'm using low-profile RAM, clearance should never be an issue. However, after replacing those Deepcool fans, I've now seen the importance of fan quality. My Bitfenix, Cougar and Coolermaster fans might not cut it anymore.