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Discussion Starter · #1 ·
I have seen some power supplies that vary the fan speed based on temperature. Anyone know what electronic components would be needed to build a little bread board circuit to do the same thing for a chassis fan?
 

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Discussion Starter · #4 ·
Thanks Teeps, that is a nice circuit, but it appears to only turn the fan on and off. I would like to build a circuit that varies the speed according to temperature. I would think a variable circuit would use a thermistor for a sensor?


The fan posted by gooki might work as is, but the temp curve may need to be different. Since the sensor is built into the fan, there is no way to monitor a specific location.


The ideal circuit should allow me to fine tune the temp at high speed and low speed. It should have a fixed resistor value at low speed so that the fan does not stop. Then any temp over the minimum would gradually increase the fan speed.
 

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Discussion Starter · #5 ·
any ideas for a variable fan speed circuit?
 

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If what you want is a variable speed fan that you can use speed monitoring software with as well, Papst http://www.papst.de/english/home.html make such a beast in different RPM ranges. What you need is a pulse sense variable speed model. You'll more than likely have to have it specially ordered in. They don't have fully adjustable performance curves but if you're supplier is knowledgable, they should be able to advise you on using a resistor in series with the thermister to lower the full performance curve.


In terms of a little circuit to do what you want, I previously scouted around for just such a thing some time ago with no luck. I ended up buying a ready-made unit from an electronic shop while I was on holiday in the Netherlands - it was very hard to find. Good luck!

PS forgot to add, the 80 x 80 x 25 mm fans have seperate thermistors so you can put that whereever you want ;)
 

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I chased down some designs for a crt projector heatsink that I would like to cool down using a variable speed fan.


Here's a thermistor design using a TC642 PWM Fan Speed Controller:

http://www.rpi.edu/~hicksm/fan/fan_detail.html


Here's a data sheet for the TC642:

http://www.onsemi.com/pub/Collateral/MC642-D.PDF


Here's another thermistor design using the Micrel MIC502 Fan Controller (the datasheet has some good theory of operation notes):

http://www.chipcenter.com/analog/pro...es/prod257.htm


Ray
 

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Discussion Starter · #9 ·
Thanks for the great suggestions!


I want to avoid using a special fan since there are so many different fans to choose from based on requirements. A circuit that works with any fan would be a better solution.


The ADM1030 chip has some very impressive features. This would be a ideal solution for very critical temperature sensitive electronics. I don't know how to go about controlling it very easily. It would be cool to integrate this with a VFD to display separate temperature readings for your CPU/GPU/MB as well as the fan speeds. Then with software you could fine tune the RPM to balance the temp levels.


I like the MIC502 chip circuit the best. It seems to be very similar to the MC642, so I will take a closer look as to which will work best for me.


PWM looks to be the best way to control the speed without worrying that the fan may stall. My only concern would be if the cicuit or motor makes any noise while switching. You can change the switching frequency, but I wonder if that will just make it growl at a different RPM? I use a PWM controller in my electric RC car. It switches at a very high frequency and makes a high pitched squeal at low RPM.
 

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Also, I gathered some approaches to the problem in the Silent PC meta FAQ in the HTPC Meta FAQ (link below). I'll add the info here to the FAQ.
 

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I don't know how to go about controlling it very easily.


Many motherboards have an smbus connector (I know at least the Asus do). You still, of course, need the relevant driver.


The stand alone solution is certainly easier
 

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Discussion Starter · #12 ·
I have a ASUS MB and I did just notice that my hardware list shows a SMBus taking up a IRQ, also two more IRQ's are taken by the UBS ports. I always thought that the SMBus was just for adding another USB device. I would like to know more about what the SMBus can be used for?
 
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