Fan Control Questions

ScruffyDogg · Post by **ScruffyDogg** » Tue Jul 15, 2008 9:30 pm

Background: I am in the middle of building a system that is to be a nice compromise between power and silence. I have a question when it comes to fans and fan controllers. My motherboard will only control one fan (the cpu fan). I am trying to control 2 other fans so that occassionally I can crank it up on rpm speed, but typically will have it very low. I understand computers and most parts well, but it is the first time I have turned my attention this way towards fans and fan control...

Question: What fans can be controlled? Must they specifically state "PWM" or do they have to have a specific "connector". What is the difference between a 4 pin and 3 pin connector in regards to control if any?

Don't ask about system specs as that is irrelevant as I am asking the above question and not a question on my specific system. (I get annoyed when so many, in so many forums try to be an expert and state regurgitated info on a system,... so understand, if you can answer the question then system specs are meaningless)

frenchie · Post by **frenchie** » Tue Jul 15, 2008 11:31 pm

Hi,
from my experience you can control any 3/4 pins fans connected to your motherboard provided your motherboard lets you (so it does depend on your specs

).

I suggest you read this post for more info : viewtopic.php?t=46812

ScruffyDogg · Post by **ScruffyDogg** » Wed Jul 16, 2008 12:09 am

Well put this way,...(which does make specs irrelevant),... if I am not connecting these to the motherboard, but rather to a fan controller, or similar type of controllable resistive device, do fans have to have anything other than just a regular 3 pin connector (the power, ground and sensor -yellow)?

frenchie · Post by **frenchie** » Wed Jul 16, 2008 12:32 am

I would say that any normal 3 wire fan will work (no reason why they shouldn't and since most fans are 3 wire fans.....).

But I've never used a manual fan controler myself...

random example from Zalman (according to the specs, it works with 3 connectors) :
http://www.zalman.co.kr/eng/product/Pro ... sp?Idx=209

merlyn · Post by **merlyn** » Wed Jul 16, 2008 3:18 am

My experience = two different types of fan: 4 pin PWM and 3 pin DC. The 3 pin DC can be controlled by PWM device but 4 pin PWM cannot be reliably controlled by DC device. All fans can be controlled however. How control is achieved is a personal preference.

So far I've only seen 4 pin controllers as CPU fan headers on motherboards but again, from what I've seen, these can be set to DC to control a 3 pin fan.

PWM controllers start the fan more reliably due to the fact that they tend to use short pulses of 12v rather than, say, 5v from a DC controller. Again here it depends on preference, would you like your fan to be always turning at a low speed or do you want it to only come on at certain times? I find that a fan spinning up can be distracting so I leave them running at very low speed until needed (usually

).

ScruffyDogg · Post by **ScruffyDogg** » Wed Jul 16, 2008 5:40 pm

So in essence (I hope I got this), if I wanted the fan to be motherboard controlled, it should be a 4 pin "PWM". If I wanted it controlled by a commercial controller it shouldn't matter if the controller uses "PWM" chips on the controller. If I wanted to create my own,... it would probably be best to go with a 3 pin or use an adapter going from a 4 pin on fan to 3 pin.

I am also assuming "DC" is just Direct Current and you can create a controller be having something that adjusts (some resistor type of setup) the amount of current/voltage to the fan, however some fans don't play well with lower voltages,...

Is my thinking correct on this?

frenchie · Post by **frenchie** » Wed Jul 16, 2008 11:39 pm

summary from what I understand :

on your motherboard provided the hardware supports fan control :

- 3 wire fan on a 3 pin connector : control works
- 3 wire fan on a 4 pin conenctor : control doesn't work (fan at full speed) UNLESS you can manually change the type of conenctor (from 4 to 3 pin) on the motherboard, usually via a setting in the BIOS.
- 4 wire fan on a 4 pin connector works
- 4 wire fan on a 3 pin connector should work

If you use an external fan controler it doesn't matter what you plug in as long as the controler supports both 3 and 4 wire fans.

If someone could confirm this, it would be great.

tehcrazybob · Post by **tehcrazybob** » Thu Jul 17, 2008 2:26 pm

4-wire PWM fans can be controlled using a timing signal sent along the fourth wire. This control is usually accomplished by connecting to the motherboard and using software or BIOS settings.

3-wire fans are controlled by varying the voltage running to them. This is how most fan controllers function, and the method should also work on 4-wire fans if you don't have access to a 4-pin control system.

3-wire fans could theoretically be controlled through PWM, if the controller supported it. This approach would be more efficient but might cause more motor noise than voltage control. Ignore this method, because to the best of my knowledge, no motherboards and only a tiny fraction of the manual controllers on the market support it.

Summary:
4-wire fans can be controlled through PWM on the motherboard.
Both 3-wire and 4-wire fans can be controlled by varying the supply voltage, which is the most common approach in manual controllers.