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Controling cpu fan with pot, need advice...

Discussion in 'General Electronics Discussion' started by Vortez, Oct 26, 2011.

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  1. Vortez

    Vortez

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    Oct 26, 2011
    Hi, i just replaced the fan on my computer cpu heatsink, and it make a lot of noise compared to the original one, so i'd like to do something to reduce the fan rpm, but i can't decide which method sould i use. Here's what i've though so far:

    1-Use a 100 ohms pot and control rpm by plugging the resistance in series with the fan.
    2-Use any pot and control rpm by plugging the fan in parallel with the resistance, giving variable voltage instead.

    3-use a simple switch and toggle between 12v and 5v

    4-use some kind of knob with 10 positions, adding a diode between each connection, dropping voltage by 0.7v increment.

    Now each of the method avobe should work, but all have their advantages and inconveniants.

    I think #1 is the best solution since i could adjust the fan within a range that dosen't stall the fan, and i could do it very precisely. The downside is the extra heat generated and the fact that i need the resistance to handle at least 1w.

    #2 is good too, but it would stall the fan if i turn it too much(between 0-5v). But i could use any resistance i want with it and i wouldn't generate heat at all with high resistance value.

    #3 is simple really, it's probably the easiest way to do it, but then you can't adjust anything.

    #4 Seem nice too, no heat(i think) generated by resistance, but is a bit less precise than a pot and would be the most complex to build.

    What do you think?
     
    Last edited: Oct 26, 2011
  2. davelectronic

    davelectronic

    1,087
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    Dec 13, 2010
    CPU heating changes all the time, in peak high demand use your CPU will generate a lot of heat, does your MB support fan control ? i would not slow the fan by adding resistance, heat damage = dead CPU, find a quieter fan, they do exist, or if you really need to try temp fan control, then there is a small program i used once, not bad, but if you set it up wrong you could damage your CPU, link below, but only use if you understand the risks.
    Dave. :)

    http://www.filehippo.com/download_speedfan/
     
  3. davenn

    davenn Moderator

    13,429
    1,806
    Sep 5, 2009
    Hi vortez
    welcome to the forums :)

    I have to agree with davelectronic, slowing down the fan on a cpu is a really bad idea.
    most of these modern cpu's are already running very hot and you are seriously likely to cause it to overheat and let the smoke out.

    find a quieter fan :)

    cheers
    Dave
     
  4. Vortez

    Vortez

    2
    0
    Oct 26, 2011
    Thx for your answers, but...

    I know i sound like a noob, being new on the forum and all, but im electrician, so i know what im doing, i know all the basics of electronics and been doing simple circuits stuffs when i was younger. Im also able to repair my pc without problem if something break. As for the extra heat on the cpu, im not worried at all, let me explain.

    Since almost 6-8 months, my old original heatsink fan was running very slower than usual, but i didn't noticed it till this summer. Instead of running at 1800 rpm, it was turning at 5-600 rpm, and sometime, before i noticed the problem, the fan just didn't started at all, it even ran an entire day without the fan turning without problem(that's when i discovered the fan was dying...). The only problem i had was that when playing a game, the computer turned off itself, but if the fan was turning, even at 600 rpm, it was fine. I have a black edition amd processor, so it can run a little hotter than normal processor without trouble. In other words, i was getting around 50-60c idle and 65-75c full load, even seen 80 once, and my cpu is still working prefectly fine. Now with the new fan, things got back to normal, idle temp of 40c and 50-55 on load.

    So i know my cpu can take the extra heat, i dont intent to turn it too slow either, just like to be able to slow it down a bit when im not playing since the noise is very anoying. For example, this one turn at 3000rpm, id like to turn it down around half of this when not playing game. That's why i think either the potentiometer or the diodes would be great for this. Diodes seem nicer since they don't change the circuit resistance and current, but as i said it would be more soldering to do, and i hate soldering. Im also tempted to use a simple 3 pin switch as i said, switching between 12v and 5v from a molex connector.

    I don't want to buy another fan since that exactly what i've just did, didn't know it was going to be so loud through. And all my fans have 3 pins so software like fanspeed and the like wont work, it need a fan with a 4th pin in order to work.
     
    Last edited: Oct 26, 2011
  5. davelectronic

    davelectronic

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    Dec 13, 2010
    Pc cpu fan

    Your CPU if your happy with the heat, i do know CPU's cut back on data processor power when the heats to much, thermal safe area control, so in a word less air more heat = less CPU power for computing tasks.
    Dave.
     
  6. davenn

    davenn Moderator

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    1,806
    Sep 5, 2009
    you will only find 2 and 3 wire fans for computers
    there are a + wire a - wire and a rotation sense wire. Older fans just had 2 wires + and -

    The rotation sense wire lets the BIOS know if the fan has failed

    Dave
     
  7. jackorocko

    jackorocko

    1,284
    1
    Apr 4, 2010
    this is really quite simple, larger fans move more volume with less disturbance == quieter. So you kill two birds with one stone. Beat the heat and the noise.
     
  8. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    A resistor is not good for reducing the speed of these fans. A zener diode in series does a much better job, try some in the 3-5V range. Fixed speed is not the best though.
    You may want to build one of these super simple temperature regulated fan speed controllers so you won't need to fiddle with knobs & switches.
    The TL431 version has a sharper characteristic but both will crank up around 40 deg.C. Put the NTC in the exhaust air from the fan/heatsink.
     

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    Last edited: Oct 27, 2011
  9. davelectronic

    davelectronic

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    Dec 13, 2010
    Good luck with that, unless its CPU temp feed back, those schematics are not, ok maybe i am sticking my neck out a bit, but dont wreck your pc on an experiment, CPU / MB feed back to cooling is there for a reason.

    If the above two circuits where ok for pc cooling, AMD and INTEL would be using them, NTC control is not precise enough as an ( add on ), IE delay.

    Those circuits are fine for other cooling app's . Cut your pc some slack, run your fan, if its noisy get a better make fan, i had a thermal-take it lasted 3 months before it started getting noisy, or as offered as a solution already bigger 120mm axial's are very quiet.

    Its not a case of experience in electronics, or an electrician, its common sense.
    Look after your hard ware.
    Dave. :)
    PS, If you know what your doing, and your gear will support it, fan speed program is good on fan control, you can set up the parameters how you want, IE, RPM for a given temp, but be sensible.
     
  10. Resqueline

    Resqueline

    2,848
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    Jul 31, 2009
    I think the issue needs to be seen in a perspective. It's not about life-support gear, and it's not the end of the economy & world for the owner. CPU's are quite cheap.
    Besides, after a couple of years the CPU & MB are outdated and are tossed out anyway. That being said there are indeed a few things to consider.
    The AMD black edition CPU seems to have the lowest temperature tolerance of them all, namely 61 deg. C (55-69). Still, reaching 80 won't crack it instantly, it takes time.
    As NTC's have thermal mass and delay, so does the CPU & heatsink themselves.
    I don't believe an NTC in the airstream and a slopey regulator adds a substantial criticality to a system with normal reserve capacities (temperature headrooms).
    I once used a computer with a directly load controlled CPU fan. It was a very tiring computer to work with, as every second the fan would jump up & down in speed.
    You don't want a fan that reponds instantly, and it's not that long ago that factory fan control was a whole lot more primitive & inefficient than those schematics.
     
  11. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,270
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    Jan 21, 2010
    Resqueline is absolutely correct.

    If you've seen how much dust clogs up some heatsinks of still perfectly working PC CPU's, you'll realise that critical is not a word that describes the normal situation.

    In addition, many motherboards are equipped with circuitry to shut down on overtemp, and are most modern CPUs.

    The only caveat is that maybe you would be advised to open up your computer annually and get rid of accumulated dust (in fact I advise that to anyone who keeps a computer longer than 12 months (gay-mers need not apply)
     
  12. davelectronic

    davelectronic

    1,087
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    Dec 13, 2010
    PC fan control

    So top advice, if your pc is older then 12 months bung it out. Older machines run happily if looked after, not evey one is minted to buy a new pc evey year. Good service on your machine and upgrades can save you a lot of money. There is nothing wrong with MB cooling support. Trying to improve your system is great, EXTRA cooling circuits are fine, but to dump MB fan support for your diy cooling circuit is madness. Seems some know more than intel and amd. Yes ok sure.
    Dave.
     
  13. davelectronic

    davelectronic

    1,087
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    Dec 13, 2010
    PC fan control

    So older machines are fine so long as current hardware supports upto date software whats the problem ? Ive come across similar single minded shallow nonsense loads over the years. So in a word the OP can make his own mind up. and us mear mortals will continue with are current pc technology thats still supported. re engineering your MB is fine if your an intel / amd top research designer for the company. Any member with over inflated egos should not apply, future technology needs experts. LOL.
    Dave.
     
  14. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    I think you misinterpret what I meant.

    I meant everyone who keeps their machines for more than 12 months (i.e. everyone other than hard core gamers) should take the time once every 12 months to clean out the accumulated dust from their machine.
     
  15. davelectronic

    davelectronic

    1,087
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    Dec 13, 2010
    PC fan cooling control

    Ok if i got the wrong end of the stick i apologise. My misunderstanding of the meaning of ( gay murs )
    So on my part, sorry.
    Dave.
     
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