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Making a fan controller to use in my PC’s ductwork

post #1 of 9
Thread Starter 
When I’m running computer intensive tasks, I want the fans to cool my processor. When I’m not, I want the fans to be quiet. While I could use a manual rheostat to control the fans, I want to learn more about HVAC and control systems. So, I want to make a fan controller that senses the temperature and adjusts the fan speeds accordingly. I would like to get your input for my plan.

I’m starting from a project I did a while ago where I used ductwork to route air through my PC. 5” diameter dryer duct hose connects the front and back fans (Silverstone FM121 - http://www.silverstonetek.com/produc...d=118&area=usa) to the heat-sink (CoolerMaster Hyper 212+ http://www.coolermaster.com/product.php?product_id=3096) that is mounted on the processor.



What I’m planning to do is to install a temperature transducer to measure the temperature of the processor. A PLC (I was going to use an Arduino Uno http://arduino.cc/en/Main/ArduinoBoardUno, because it is cheap and easy to program) would read the transduced temperature. Based on a set-point that I enter and the temperature it reads, the PLC would vary the fan speed.

Below are some puzzles that arise with this approach that I haven’t figured out how to solve. I would appreciate your input on any or all of them.
Edited by JamesWatt - 11/6/11 at 6:52am
post #2 of 9
Thread Starter 
Which temperature transducer should I use?
I’ve seen a variety of temperature sensors out there:

There are various sensing technologies (http://www.maxim-ic.com/app-notes/index.mvp/id/3229)
•RTD (e.g., http://www.mamacsys.com/TE-701-702or...nformation.htm)
•Thermistors (e.g., http://www.mamacsys.com/TE-701-702or...nformation.htm)
•Thermocouple + transducer e.g., (http://www.pc-s.com/multi/MultitekTRtherm.htm)
•Integrated circuit (e.g., LM35 http://www.ladyada.net/learn/sensors/tmp36.html). I can’t think of a good way to mount an IC.

There are various mounting styles (http://www.mamacsys.com/TE-701-702or...nformation.htm)
•Flange
•Bulkhead

There are various resistances (http://www.mamacsys.com/TE-701-702or...nformation.htm) from 100 ohm to 100 kohm. The PLC I’m planning to use takes 0-5V on its analog inputs.

Which of these varieties do you recommend for my project and why?


Where should I put the temperature probe?
At the end of the day, the temperature I care about is the temperature on the surface of the processor.

The most accurate way to measure this I’ve seen is to mill a channel in the processor and put a thermocouple in it (for example, http://www.hardocp.com/image.html?im...lfMV8zX2wuanBn). However, I milling the surface of a $225 processor a bigger risk than I’m willing to take.

So, my best idea right now is to measure the exhaust heat by putting the probe right after the heat-sink.



One of my concerns with this is that it will inhibit the airflow too much. Another concern is that I don’t want air to be escaping from the hole the probe pokes through. Do you have ideas for solving these issues?

What algorithm will take in the set-point and current temperature and calculate the fan power?
Another puzzle that I need to figure out is which control algorithm I want to use in the PLC. I’ve heard about the following (http://en.wikipedia.org/wiki/Control_systems):

•Binary control: if the temperature is above the set-point, turn the fans on. One problem with this is the fans need to be running at a low level all of the time to prevent the processor from overheating. One way around this would be to run the fans at a low level (e.g., 50%) as a default state; when the temperature pierces a certain threshold, I would run them at 100%. I could see the fans cycling on and off at a high frequency with this approach and wasting a lot of electricity.
•Proportional control: the PLC would vary the fan speed in proportion to the difference between the current temperature and the set-point. So, for example, if it is way hotter than it should be, the fans will run at 100%, while if it is barely hotter, they will run at 40% (their minimum speed). Wikipedia talks about downsides to this, but I don’t understand them.
•PID control. The PLC would also consider the rate the temperature is changing and historical temperatures when deciding how much power to apply to the fan. One challenge with this is how to implement the algorithm. I would have to spend some time programming the thing. The lazy (and expensive) solution would be for me to pick up a PLC with the algorithm already built in (e.g., http://www.mcmaster.com/#38615k73/).

Which algorithm do you advise I use?

What is a good online HVAC controls distributor?
I’ve seen a variety of sites that have just a listing of the manufacturers they carry and then a link to CGNA (http://www.cgnacontrols.com/search/), which seems to have a limited selection. One easier to use site I found was controlstop.com. What do you usually use?
Edited by JamesWatt - 11/6/11 at 6:52am
post #3 of 9
Before you go spending lots of money on sensors and controllers, and relying on software, please consider a different approach.

Start with this, available here. I use a three-way PWM splitter to control my two heatsink fans and the top-mounted intake fan that feeds the cpu heatsink cool air. You'll need the five-way harness, and at least four PWM fans, though I'd suggest five: one front intake, one mid-duct, one heatsink push, one heatsink pull, one exhaust.

With a PWM splitter you can control several fans with the signal from the cpu header in your motherboard, automatically settling to low when the computer is idling and running up to high when the computer is on load.

There are more and more pwm fans available and coming to be available, from the Cooling SWiF2 120P to the Akasa Viper to the Cooler Master Blade Master, and lots of others.

That's what I'd do. I'm very happy with my current setup.
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post #4 of 9
I'm totally agree as stated by ehume...
using the PWM splitter will control all your PWM fan according to your cpu temps

and don't forget that SOME mobos, allow us to control the regular 2 or 3 wired fans according to NB or SB temps...
you can always build your own 3 wire fan power splitter (as this will be lot easier and cheaper than building your own MCU), just be sure you don't overload your mobo fan header

post #5 of 9
Thread Starter 
Thanks. That's an elegant solution. Were price, performance, and reliability my top considerations, that's exactly what I would do. However, an additional value I'm trying to get out of this project is experience with hvac control systems. For that reason, I'm more inclined to build a system more from scratch. What I may do is set up the system you describe and use it as a benchmark for my own efforts.

I do like your suggestion of adding more fans though. I will add a second one to the heat sink. My only reservation with adding another one mid duct is the turbulence might get out of hand, though that concern isn't grounded empirically.

I ended picking up 1k rtd probes, both in bulkhead and flange varieties.

I also picked up a stroboscopic tachometer to bench test the plc's ability to vary fan speed with pwm.

I still haven't decided where I want to put the probe or what control algorithm to use.
Edited by JamesWatt - 11/8/11 at 2:03pm
post #6 of 9
Just one thing: don't you think you're leaving some components with no cooling? Ram and northbridge.

I chose not to use a fan duct in order to have those parts cooled to. And besides that, the CPU fan and rear fan made sure the CPU got fresh air, and no hot air was left inside the case.
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post #7 of 9
Quote:
Originally Posted by cloppy007 View Post
Just one thing: don't you think you're leaving some components with no cooling? Ram and northbridge.

I chose not to use a fan duct in order to have those parts cooled to. And besides that, the CPU fan and rear fan made sure the CPU got fresh air, and no hot air was left inside the case.
ONe nice thing about removing your rear grill: you can leave it fanless and put a pull fan on your heatsink. A pull fan on your heatsink will also exhaust your case. See item 2 in my sig for a very silly but firmly compelling example.
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post #8 of 9
I bought this for mine a few weeks back and I like it..

http://www.newegg.com/Product/Produc...82E16811998808

But not sure if that may be what you are interested in.



Chuck D
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post #9 of 9
Quote:
Originally Posted by ehume View Post
ONe nice thing about removing your rear grill: you can leave it fanless and put a pull fan on your heatsink. A pull fan on your heatsink will also exhaust your case. See item 2 in my sig for a very silly but firmly compelling example.
I had better results with rear fan and push heatsink fan, than no rear fan and pull heatsink fan (the hot air was being completely pulled out of the case). I guess it depends on several factors.
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