Can I have my case fans thermally controlled?

[CamaroGuy]

Is it possible to hook up my case fans to a thermal switch of some sort?

I want to be able to have the fans turn on only when the temperature reaches a certain degree and then turn off after operating for a set amount of time or until the temperature drops down. Kinda like the way a thermostat controls a home a/c system.

In case you're wondering, the reason behind this question is simply that I don't want my 2 x 108 cfm fans running all the time since they're so loud. I only want them on when they are needed due to excessive heat. I have 2 x 30 cfm fans for normal case cooling.

-CamaroGuy

 

[SubzeroPC]

I'm sure that can be done, but it would be somewhat complicated to design a system to do that for a computer fan.

As an alternative you could run the fans at 7volts instead of the stock 12volts. That would give you about 63CFM of air each. To connect a fan to the power supply for 7volts you just move the fans neg. lead wire to the 5volt power supply wire (red). Leave the fans pos. lead connected to the 12volt power supply wire (yellow). The difference between the two charges will give you 7volts.

Another alternative is to just get some quieter fans such as the Panaflo 120mm. more info here >>>http://www.subzeropc.com/store/fan12384a.htm

Subzero,

You will cease spamming these forums for your web site.

Anandtech Moderator

 

[CamaroGuy]

I'm not an electrical engineer...but is connecting the ground to the 5V lead safe? Can that cause any damage to the fans or other components?

 

[Thump553]

I use a thermally controlled 80 cm fan for my exhaust fan (sensor set to speed up as temp rises). It is a JMA Datatech Model 0825-12HBTL (sold direct by RDJD/JMC) and costs about $10. Its quiet. Frankly, it seemed like a great idea in principle but I don't really see any difference. It may be that my case never heats up enough to really have this fan spin up. Its always on when computer powered on.

 

[Fragmeister]

Yes, it is possible. In fact, I am building one in a few days that will control 4 fans. This thermally controled unit will be the replacement for my fan switches which I have had for over a year now. If anyone is interested in how my thermaly controled unit turns out, you can find my email in the contact page at the website I work at http://www.hardware-unlimited.com . Just email me and if I get enough people interested in it then I might write up a how-to that will be posted on the site. If you are interested in just switching your fans, you can check out my old article on making them here --> http://www.3dgameforce.com/articles/fantoggles/ This is the first of my many switch designs, I just haven't written articles on my newer units

 

[etech]

It's not hard to make a controller for a fan.

On/off - use a voltage comparator(LM 139) coupled to a mos-fet(IRF511). One lead of the comparator would be tied to a resistor and thermistor. Simple circuit.

Voltage controlled fan- change the comparator to a op-amp and you can control the voltage of a fan from 7 to 12 volts based on the temperature. It takes to pots to set the low speed and the gain but is also a simple circuit to make.

If anyone is interested I have a schematic of the voltage controlled circuit available.

 

[CamaroGuy]

Etech, could you please elaborate a bit, or at least explain the part about mos-fets and thermistors in layman's terms? I know you said it is a simple circut, as it may be for you, but I'm having a little trouble following.

Also, what are those numbers in parenthesis? Any help you can give me will be greatly appreciated.

-CamaroGuy

 

[Mikewarrior2]

I was wondering when SubZero was gonna be forced to stop advertising his website on his posts...




Mike

 

[Mday]

YES, it has been done. of course i don't know enough to tell you or do it myself

 

[vss1980]

Etech has said exactly what I wanted, but only that I would have recommended using a transistor rather than an FET. For two reasons, 1) as its running off of a PSU you dont have to worry about a little current loss, 2) Transistor circuits require little calibration whereas an FET circuit always needs a little tweak now and then and the average computer user may not be able to do this.

 

[CamaroGuy]

Cool! Can someone now please explain to me how to hook up a thermistor, resitor, transitor, and everything else. Like I said before, I can follow a schematic diagram pretty well, but all this talk of mos-fets, voltage comparator, etc., etc. is going straight over my head since I'm a computer science major and not a double-e student. I can do basic soldering and splicing, that's about it.

-CamaroGuy

 

[vss1980]

If you have any test equipment to help calibrate the circuit, the FET circuit suggested by Etech would be the best as you can tailor it perfectly with a little tweaking. The problem with schematics is that the actual circuit varies slightly in performance (not by a lot) and FET circuits vary more than transistor based circuits (in my experience).

But yeah, now all you need to do is wait for Etech to send you the message.

 

[etech]

My posting time has been limited recently, busy at work and home.
These threads from Ars may help a little.

http://forum.arstechnica.com/forum/ubb/Forum9/HTML/000263.html
http://arstechnica.infopop.net/OpenTopic/page?q=Y&a=tpc&s=50009562&f=77909585&m=03109985


vss1980, one of the reasons I used a mos-fet is that the gate drive is easier and uses less components then a transistor. The stability does not matter in this circuit for two reasons, the circuit is controlling a fan a little change will not matter and the mos-fet is inside the control loop of the op-amp, the op-amp will adjust for any change in the mos-fet gate characteristics. The only tweaking is the orginal setup for low and high speed at a specific temp, after that it is as stable as your op-amp characterestics. I calibrated for 7 volts at room temp and 12 volts at ~98.6f. Only used a voltmeter.

 

[vss1980]

Very nice Etech, a clever use of feedback (where would half of the control circuits be without them?)

 

[thermite88]

CamaroGuy,

I think that the Digital Doctor is what you are looking for. It is available from several vendor on the net. CyberGuy probably has the best price.

http://cyberguys.com/cgi-bin/sgin0101.exe?UID=2000071416512298&GEN9=5CG01&FNM=00&T1=148+0500&UREQA=1&UREQB=2&UREQC=3&UREQD=4

 

[spencer]

thermite88,

Are you sure it can be used with large fans? Camaroguy didn't mention the size other than they are 108 cfm which probably means atleast 120mm. I read here http://www.plycon.com/ddoc2.htm that the Digital Doc II can't be used with 120mm fans.

 

[bigjon]

I'm working on a case and putting a 7v/12v switch on the case's front panel so I can control which voltage the fanbus uses. Usually I don't mind the full 12v noise, but my computers are in the "guest room" so visitors appreciate 7v at night! I'm not sure if you meant to word it that way CamaroGuy, but DO NOT connect the power supply's 5v wire to the power supply's ground wire, just replace the ground for the fans with the 5v lead (fan's black wire goes to the 5v red power supply wire, and the red fan wire goes to the 12v yellow power supply wire). It does not hurt the power supply in any way; you're just using the voltage difference between 12v and 5v (12-5=7) instead of between 12v and 0v (ground).

 

[Oldsalt]

An attic fan controler makes a good thermo control for fans.
You can set the temp for on/off. Can control more Amps than ever needed. I have used them to bypass fan dropping resistors and/or turn fans on/off.
os

 

[etech]

CamaroGuy, I was wondering what circuit/method you had picked to control your fans?

 

[Quickfingerz]

I run all of the fans in my case at 7v. Even for my athlon that is running at 900 mhz and using a RDJD k701.

I like quiet cases. I can finally hear my hard drive while it's on.

 

[CamaroGuy]

Etech: I went with Fragmeister's switch setup. I figured that that would be easier for me to do and it gave me the ability to turn the fans completely off when I'm just reading web pages or working on homework. Your thermally controlled setup is awesome, but I don't quite have the electrical knowledge to build it. Thanks for the input, though.

-CamaroGuy