Chassis fan vs CPU fan?

[rayden54]

My motherboard, Asrock z87m Extreme4, has two "chassis fan" connectors (1 4-pin and 1 3-pin) plus a 3-pin "CPU fan" connector?

What's the difference? Is there one?

Edit: Sorry I asked the wrong question. In addition to the CPU fan and "chassis fans" I've got something called a "Power fan." That's the one I'm not sure about.

 

[CaedenV]

Well... the CPU fan is for the fan on the CPU, while the chassis fan is for fans on the case (aka chassis).

All right, enough with being a smartass.
The CPU fan has a speed regulator which is controlled by the temperature profile in BIOS based on the temperature of the CPU. CPU gets hot, the fan speeds up to compensate. CPU cools down and the fan slows down, and in some cases can turn off entirely. These are typically 4 pin fans, but are compatable with 3 pin fans (for example I have 2 3pin fans on my CPU cooler as my motherboard has 2 4pin CPU headers)

Chassis fans are typically 'dumb' fans which spin at a specific speed. If you want your fan to spin slower/quieter then you add a fan line resistor. If you need more airflow then you buy faster rated (and typically noisier) fans, or you can put more fans in the system.
Mid-level motherboards will have a little bit of logic onboard so that you can set your case fans to an arbitrary speed, or set them to a predetermined 'low, medium, or high' setting within BIOS to select your best compromise between noise and airflow.
High end motherboards have a full fan controller onboard. This lets you link your fan speed to a temperature sensor, allowing you to speed up all of your fans if your case, CPU, or GPU reach a specified temperature. This is very nice as it allows you to never have to think about your case temperatures when OCing or gaming, where on a cheaper motherboard you would have to manually set your fans to high beforehand.

Another neat tool is speedfan. This is a software based fan controller which works with most motherboards and allows you to set your individual fan speeds from within Windows. The issues of course is that it is at the software level, not hardware, which means that if the software environment crashes, then it does not control your fan speeds properly which can potentially cause damage. Also, it is a really old program, and has 0 support, so if you run into any bugs or issues then you are SOL.

 

[Sakkura]

It has two CPU fan connectors, one is 4-pin and the other is 3-pin. Same setup for chassis fans. The 4-pin connectors support PWM fans, the 3-pins don't (well, the fans will work, just without PWM). The motherboard will probably refuse to boot if neither of the CPU fan connectors are used - safety feature to make sure there's cooling for the CPU.

There may or may not be differences in how the fan speed of each set of fan connectors is controlled.

 

[CaedenV]

*correction, my motherboard is the older version of your motherboard. Like yours, mine has 1 4pin and 1 3pin CPU fan headers.
For my CPU cooler I am using the mighty but cheap Hyper212 EVO cooler. I was unhappy with the noise it was producing (I am super picky about noise), so I swapped out the stock 120mm fan with a much better (quieter and prettier) Corsair fan. I was so happy with it that I eventually got a 2nd corsair fan to attach to the other side of the cooler for a push-pull effect. The 2nd fan allows me to run both at their absolute minimum fan speed (~700rpm) and even at that slow speed my system tops out at ~72*c when under a full benchmark load, and the highest I have ever seen it get under a real world load is 64*c

 

[punahou1]

Most mobo manufacturers provide a utility that allows you to control fan speeds and this is why they differentiate between chassis and cpu fan plugs. If you are not going to use the utility then it really doesn't matter where you plug in your fans. Some fans have 4 pin connectors while others only have 3 pin connectors so this is why your mobo offers two types of plugs. The 4th pin is typically a command link to control fan speed. I assume you are using some type of cpu cooler that has a fan - if so, just plug that fan into the cpu fan socket as your mobo will regulate that one by monitoring cpu temperature.

 

[Sakkura]

Most mobo manufacturers provide a utility that allows you to control fan speeds and this is why they differentiate between chassis and cpu fan plugs. If you are not going to use the utility then it really doesn't matter where you plug in your fans. Some fans have 4 pin connectors while others only have 3 pin connectors so this is why your mobo offers two types of plugs. The 4th pin is typically a command link to control fan speed. I assume you are using some type of cpu cooler that has a fan - if so, just plug that fan into the cpu fan socket.

No. The 4th pin is for a PWM signal. The fan speed can be controlled without PWM, but PWM is better in various ways.

 

[rayden54]

Sorry guys, I asked the wrong question. I need to know what the "power fan" is.

 

[Sakkura]

The power fan header can sometimes be used to connect the power supply to the motherboard to allow it to monitor the fan speed of the power supply. That's a rare feature though, so the power fan header is really just a fan header that can run a fan at full speed - there usually isn't any way to control the fan speed.

 

[rayden54]

Thanks. Sorry about that.

 

[punahou1]

Most mobo manufacturers provide a utility that allows you to control fan speeds and this is why they differentiate between chassis and cpu fan plugs. If you are not going to use the utility then it really doesn't matter where you plug in your fans. Some fans have 4 pin connectors while others only have 3 pin connectors so this is why your mobo offers two types of plugs. The 4th pin is typically a command link to control fan speed. I assume you are using some type of cpu cooler that has a fan - if so, just plug that fan into the cpu fan socket.

No. The 4th pin is for a PWM signal. The fan speed can be controlled without PWM, but PWM is better in various ways.

Yes you are correct that speed can be controlled without the 4th pin. The 4th pin does, however, act as a command link so that you don't have to mess with voltages on the other pins to control the speed.