4 pin PWM (CPU) to 2 pin?

[lemings]

I bought a fan controller recently in hopes to quiet down my CPU fan when using linux (lm-sensors,fan control, and bios have all failed me). The controller only has a 2 pin connector however, where the cpu has a 4 pin pwm connector to it. Is there an adapter or a way to mod the 4 pin down to a 2 pin?

The fancontroller is the NZXT Sentry Mesh and my CPU HS is a Zalman CNPS9900ALED

 

[NiHaoMike]

That fan controller will not work properly with most PWM fans.

 

[Bobnova]

It'll work fine with with most pwm fans. It won't pwm them, but voltage speed control will work just fine.
That controller will have three pin connectors. If you look at your fans they likely have guide tabs for plugging into three pin ports.

 

[NiHaoMike]

That might be the case for fans actually designed for either mode of control. Which, after looking at the description, is probably the case here.

However, you won't get as good of a control range as using PWM and the fan would probably run noisier than using PWM for the same RPM since the inverter would be overmodulating instead of putting out a clean sine wave.

 

[Bobnova]

Lol you're funny.
Guess what: Most computer fan inverters put out a square wave. I'd say all, but I haven't looked at every fan in the world.
Not a whole hell of a lot of modulation involved in a binary output.

Few fans are "designed" for voltage control. They do exist, they have a fourth pin just like a PWM pin, but it takes a voltage signal instead of a PWM duty cycle signal.
Maybe your magical (and, I think, pretend) Lacy Wu Tang Clan Fans of God and Seven Saints don't appreciate voltage control, but you've stepped over an interesting line on this one.
What line? Why interesting?
The line of things that I can test directly, and interesting because I have a nice pile of fans here and a 5 amp power supply that is happy from 12v down to 2.6v. I'll be testing a variety of fans here, ranging from Nidec and JouJye screamers down to silly little AMD heatsink fans, I'll let you know what the results are.

Let's see how well your buzzword bingo stands up to real world testing, shall we?

 

[Bobnova]

Tested!

Non-PWM fans with soft-start features (found only in high amp server fans) don't like trying to start at low (<~7v) voltages. Once running, you get a nice range of speeds. Slightly smaller range than with PWM control, largely due to all of my server PWM fans going to full stop at 0% and re-starting at ~1000rpm at ~5% PWM. Voltage control bottomed out at around 1000-1200 before going to full stop, but did not restart until ~1500 for hard start fans and ~2000 for soft-start fans.
No noise difference was noticeable at all on any fan tested. None.

Consumer fans (stuff rated <3a) had a nice full range of speeds (same as or larger than the same fan under PWM control) and also did not make any more noise than under PWM control.

 

[NiHaoMike]

Sine wave inverters are very common with PWM fans since once the circuit for PWM is in place, it takes very little extra to make it sine wave. Most likely not a particularly clean sine wave (several % THD typical) but way better than a square wave or "modified sine".

 

[Bobnova]

The crackup continues! Got anything more than the usual for me, or are we heading even further into the land of vaguery?

"very common" and "most likely" don't match real well.
Give me a part number for this sine wave PWM inverter, and maybe, just maybe, I'll believe you. Until then, rofl.

 

[NiHaoMike]

http://ww1.microchip.com/downloads/en/DeviceDoc/20005257A.pdf
That's a single chip motor drive inverter from Microchip. For more current, Microchip and a few other manufacturers (most notably TI and ST micro, used in Delta and Nidec fans) have multi chip solutions.

 

[Bobnova]

OMG it's an actual part number! Finally! Thank you!

Clearly that inverter (or a related part) isn't used in any of the PWM fans I've tested, as that inverter doesn't pass any of the input PWM frequency on to the motor (so it says in the datasheet anyway) and all the fans I've tested have passed it on, but it's interesting to see that it exists somewhere.