Can I Connect a PWM Fan Using a 3-Pin Connector?

[Haravikk]

Okay, so I have a particular fan in mind for my case, namely the Noctua NF-A15, however it's only available with PWM (4-pin) connectors.

Now, I've seen plenty of topics covering whether you can connect 3-pin fans onto PWM power supplies (e.g - from a motherboard) which seems to work just fine. However, what I want to do is the opposite; I'd like to connect a PWM fan using a 3-pin power supply from my fan-controller.

Will this work?

If not, can anyone recommend any similar fans? I like that the Noctua one is actually quite a bit bigger than its 120mm fan mounts, and I have space for it around the 120mm fan mount I want to use on my case. It also seems to offer great airflow for low noise, and I'm hoping I can get away with it as the only fan, since my case is only being used for storage (drives plus RAID controllers) so it shouldn't be running too hot to begin with, and the fan will be top-mounted to just help suck the hot air upward. Silence is a big factor for me; I've seen a couple of other options with high airflow, but that seem like they'd be far too loud.

 

[OlittoTV]

http://www.noctua.at/main.php?show=productview&products_id=12&lng=en

these are good fans and the 4 pin will only fit if the 3 pin connector is not restricted for only 3 pin connectors. the ones in the link are 3 pin and will still keep your system cool

 

[Haravikk]

Thanks for the reply, but unfortunately I've found that neither of these fans will fit as my case doesn't have quite enough room for a 25mm deep fan where I want to put it. Fortunately I found the Prolimatech Ultra Sleek Vortex 14, which is a 140mm x 15mm fan that will fit perfectly, but it's also a PWM only fan.

I recently found this thread which asked the same question I did but four years ago (not sure why I didn't see it in a search). In that thread a user mentions that the PWM connector should be compatible but will run at full speed. But is that really the case?

As I understand it in a normal 3-pin fan, one pin carries the main voltage, which a fan controller will adjust to various levels to control the fan's speed. However, with a PWM fan this pin will always carry the maximum voltage (12v?) with the fourth pin acting as a control signal to tell the PWM fan's controller chip which speed to run at. So if a PWM fan is connected to a 3-pin cable, it won't get that control signal, however it'll presumably still receive an adjusted voltage, but will that work correctly, or will it just cause the fan to do nothing until the voltage is at the highest setting?

Essentially for a 3-pin fan the separate fan-controller will set the voltage going to the fan, and thus the speed of its motor, while for a PWM fan the voltage is always full, leaving the fan itself to decide how much to pass on to the motor. What I don't know is what a PWM fan's on-board controller does if the voltage is less than normal, does it cause it to run slower, or just stop?

 

[OlittoTV]

Thanks for the reply, but unfortunately I've found that neither of these fans will fit as my case doesn't have quite enough room for a 25mm deep fan where I want to put it. Fortunately I found the Prolimatech Ultra Sleek Vortex 14, which is a 140mm x 15mm fan that will fit perfectly, but it's also a PWM only fan.

I recently found this thread which asked the same question I did but four years ago (not sure why I didn't see it in a search). In that thread a user mentions that the PWM connector should be compatible but will run at full speed. But is that really the case?

As I understand it in a normal 3-pin fan, one pin carries the main voltage, which a fan controller will adjust to various levels to control the fan's speed. However, with a PWM fan this pin will always carry the maximum voltage (12v?) with the fourth pin acting as a control signal to tell the PWM fan's controller chip which speed to run at. So if a PWM fan is connected to a 3-pin cable, it won't get that control signal, however it'll presumably still receive an adjusted voltage, but will that work correctly, or will it just cause the fan to do nothing until the voltage is at the highest setting?

Essentially for a 3-pin fan the separate fan-controller will set the voltage going to the fan, and thus the speed of its motor, while for a PWM fan the voltage is always full, leaving the fan itself to decide how much to pass on to the motor. What I don't know is what a PWM fan's on-board controller does if the voltage is less than normal, does it cause it to run slower, or just stop?

it should work because the 4th pin just controls the speed depending on the cpu/motherboard temp