How can I tell what fans on any given mobo support speedfan?

coopers · Post by **coopers** » Mon Nov 05, 2007 9:15 pm

Hi folks,

apologies if this is a n00b question - but how do you tell?

Some more questions:
I understand PWM, that's fine, does this necessarily directly translate into being able to use speedfan?
Typically when you set PWM in a bios, does it allow you to dynamically increase fan speed as temp goes up? Or do you just set the fan to a fixed speed?
What about controlling case fans dynamically? how can one do that?

thanks!

cmthomson · Post by **cmthomson** » Tue Nov 06, 2007 5:44 pm

Go to Newegg, look up the motherboard, then click on Manufacturer's Site, then download the manual for the board. Look in the manual for the headers (anywhere from two to five), then look at the BIOS screens section of the manual for fan controls. These are typically in the power monitor screen.

If you find that multiple headers share a name (eg, CHA1 and CHA2), this usually means they also share a controller, so two fans can be plugged in but they will both receive the same effective voltage.

If the BIOS screen includes the option to set DC vs PWM on a fan header, then you can control a 3-pin fan with SpeedFan (in the DC setting; note this is still PWM, it's just that the 12V pin is modulated instead of the controller pin).

In general, more expensive motherboards have more controllable headers (eg, P5W and DQ6 have lots of them), while "mainstream" (ie, inexpensive) boards often can control only the CPU fan header.

As for dynamically adjusting fan speed based on temperatures, that's what SpeedFan is all about. You configure a target temperature, link it to a fan header name, and set the fan's minimum and maximum percentage. Done.

coopers · Post by **coopers** » Sat Nov 10, 2007 4:26 pm

Thanks cmthomson, that's very helpful.

I can definitely see that a lot of the mid-range boards seem to only control one fan - the cpu fan. That's annoying. It means more money is required.

When I read about fans, I see that some fans are called "PWM" fans - what does that actually mean? I thought the fans were fairly dumb, and were just driven by the voltage from the fan controller - so what is a PWM fan as opposed to a non PWM fan?

You can drive any fan with PWM/Voltage control...?

bonestonne · Post by **bonestonne** » Sat Nov 10, 2007 4:32 pm

well, while many motherboards only have one PWM fan controller, you can also use Speedfan to control fan speeds on other headers. While there are motherboards that don't support that [seemingly every board i've ever owned] there are plenty of boards that do support it, you just need to do a little poking around.

PWM = Pulse Width Modulation. in english: more heat causes the fan to spin faster, less heat will cause the fan to slow down.

PWM is a 4 pin fan header, the 4th pin is extra, and is for moderating the speed of the fan. Similar to how a fan can have a temperature sensor, only PWM is all on the motherboard. You can use a non-PWM fan on a PWM header without any problems, however it wont be controlled the same way.

jessekopelman · Post by **jessekopelman** » Sat Nov 10, 2007 9:40 pm

coopers wrote: When I read about fans, I see that some fans are called "PWM" fans - what does that actually mean? I thought the fans were fairly dumb, and were just driven by the voltage from the fan controller - so what is a PWM fan as opposed to a non PWM fan?

"PWM" fans are designed to be controlled using the Intel spec for PWM. They have a 4-pin connector. If you plug a 3-pin fan into the 4-pin PWM header on most boards the fan will run at full speed regardless of what you have set the PWM rate to in BIOS or SpeedFan (or other software). Unless you know that your specific board can control 3-pin fans from its 4-pin headers, the only way to get software/BIOS control out of those headers is to use them with 4-pin "PWM" fans. Right now, the best PWM fans that can be bought as separates (many CPU heatsinks come coupled with such fans) are the Arctic-Cooling line.

cmthomson · Post by **cmthomson** » Tue Nov 20, 2007 3:48 pm

coopers wrote:When I read about fans, I see that some fans are called "PWM" fans - what does that actually mean? I thought the fans were fairly dumb, and were just driven by the voltage from the fan controller - so what is a PWM fan as opposed to a non PWM fan?

PWM stands for pulse width modulation. It's a scheme where the main voltage is output as a variable-width square wave (ie, all on/all off for varying ratios) rather than as a constant reduced voltage. This is more energy efficient.

Intel CPU fans are a special case of PWM. They use a 4-pin header, where one of the pins is constant 12V, and another is a low-power PWM control signal (the other two are ground and sense). The fan itself modulates the 12V line, rather than the motherboard. This has several advantages, but the most important one is that the tachometer sensor always receives 12V and is thus more accurate.

Some high-end motherboards include support for software control of 3-pin fans as well as 4-pin fans. These boards also use PWM (even though it's called "DC" in the BIOS), but in a more traditional way: they modulate the 12V pin. But there's a twist. The tachometer in most fans requires that 12V be present for at least 1/4 turn (sometimes 1/2 turn), and if you just used PWM, this wouldn't be true and the sensor wouldn't work. So the motherboard fan controller puts out periodic "long" (100ms or so) full-voltage pulses. This makes the sensor reliable, but has the side effect of making the fan "click" due to the periodic acceleration in its motor.

BTW, I misspoke above about the DQ6; it actually has only minimal fan control. The P5W and some ABit boards have lots of controllable headers.