chassis fan speed control (case fan)
I have two desktop machines running pclos 2007 (2.6.18.8). Both have a chassis fan and it is running full speed making a lot of noise.
How can I configure the system to control the speed of the fan (i.e. slow it down so it's not noisy) Machine 1: white box w/ MB Asus P5GC-MX, Celeron D, Intel 945 chipset Machine 2: emachines T3302, AMD 3300+ , VIA chipset Both machines are pretty basic, use on-board sound, video, 1GB ram, 1 HD, 1 DVD-CD/RW Thanks |
easiest way is to replace the fans with fans that have built in controls. Antec makes a series of such fans.
Harder way is to obtain 3rd party fan speed controllers and wire them in. Hardest way is to make your own fan speed controller. You need a square-wave oscillator with frequency of a couple hundred hertz (best if tunable; you should match it to the fan motor), a mosfet (or power darlington, but mosfet'd be better), and associated components. Actually, as I looked into this a bit it would appear that most commercial speed controllers for computer fans are not using pulse width modulation controllers. That kind of surprises me because PWM gives full torque while modulating RPM. The commercial devices I see are varying voltage to the motor. The best choice I see is one that uses a variable voltage regulator to control the voltage to the fan. The simplest I see connects the fan between the power supply 12V line and the 5V line (rather than between 12V and ground), giving a net voltage of 7V to the fan. This would work just fine, but isn't adjustable. Wrong way is to use a potentiometer. At least one controller I saw takes this route. |
A lot of motherboard have places on them to plug in fans. You usually can adjust the fan speed via the bios. A lot of times you can tie it to the temperature of something on the motherboard. Just make sure you are not drawing more power than the motherboard can provide.
Good Luck Lazlow |
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Most of the devices that you will find are using the technique because of cost. And are not engineered properly. Sure PWM would be the way to go but not the simplest for the lay person. You have to remember that most of these are just 'hacks'. I've gotten several deals from shops that put fans in their junkbox because of the 'pot' technique. Just redesign the interface and use it in one of my many personal systems. Heck the fan is worth more that the buck/two that is charged. Sure my time is worth more but I don't have to pay the premium price for a well designed system. My charges are mine! Plus all the fun. |
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Google shows that the 'Asus P5GC-MX' supports a chassis fan. You can look further since I don't know the fan specs. For the emachine, you need the motherboard manufacture not just the chipset. I personally would prefer a separate fan controller for the chassis fans instead of the MB controller. Sure you won't know the fan speed via a system monitor but you won't load the MB controller with a potential error or damage if the match is not correct. There are some good engineered fan speed controllers with active monitors but expect to pay some $$. The cheap 'hacks are not the way to go if you value your systems and time. |
I found the spec for P5GC-MX here
http://dlsvr03.asus.com/pub/ASUS/mb/...mx_content.zip on page 2-30 it says: CPU Fan Speed [xxxxRPM] or [N/A] or [Ignored] The onboard hardware monitor automatically detects and displays the CPU fan speed in rotations per minute (RPM). If the fan is not connected to the motherboard, the field shows N/A. Configuration options: [Ignored] [xxxRPM] The fan has 3-pin connector that matches the MB 3-pin connector and is connected to the MB Yet, the bios shows [N/A] ? |
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I prefer off board fan controllers for that very reason. I don't need feedback for a chassis fan. Just strobe blade and measure the current to set the speed. |
Some of the three pin connectors only have two wires going to the fan. If this is the case, the fan is not reporting back it's rpm.
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A potentiometer is not the wrong way. It is just another way. A a two or five watt potentiometer cost a lot and the customer have to read the manual to know the maximum limits. The best way to create very minimal noise with a lot of efficiency it is to use stepper motors. Another way is to use a servo motor. |
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As for the potentiometer use; power loss/waste which is not going to be the way I would suggest? Quote:
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I checked the fan connector - now the bios shows the chassis fan rpm
I think that means the P5MX-GC has the hardware, bios code to monitor and control the fan's speed It just does not do that. Perhaps I do need drivers to for the OS to do that. |
I don't want to get into a debate over controller technology here, but a PWM controller is quiet if it is properly matched to the load. Also helps to low pass filter it to round the leading edge of the pulse (gentler turn-on).
All other techniques are less efficient; the potentiometer technique is grossly inefficient. |
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