build me a temperature controlled fan

Discussion in 'The Projects Forum' started by popup, Feb 10, 2012.

  1. popup

    Thread Starter New Member

    Feb 10, 2012
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    Hi can anyone on here build me this if (yes) let me no how much you would build me it :) you must be in the uk like me. and i will pay with paypal

    i have a 5v dc laptop fan .. i want to control the speed of the fan

    i want the fan to run at 3v but when the temperature reaches or goes over 50c it will then run the fan at 5v till the temperature goes below 50c

    so below 50c fan runs at 3v

    50c and over 5v

    the input voltage for this device will be 5v

    maybe add a potentiometr (VR1) so i can set what temperature the fan runs at 5v

    here is a very quick pic of what i mean :)

    [​IMG]

    http://www.freeimagehosting.net/vf29o
     
  2. luvv

    Member

    May 26, 2011
    186
    31
    Hello popup,

    Couple questions, why 3-5v ?

    Not much power for a standard muffin fan, is it a teeny tiny fan or battery powered?

    And question number two, why not use a linear solution?

    Linear is power waster, but makes a nice thermal controller as it ramps up voltage as the temp goes up and decelerates as it cools.

    I have used both the stupid simple single n channel mosfet w/ thermistor schematic .

    And the op amp based thermal controller, both work well the op amp needs hysteresis to keep from constantly kicking on and off but is fairly accurate .
    Where the single mosfet schematic is very smooth but also very linear and waste power constantly..

    op amp :http://www.rason.org/Projects/fancont/fancont.htm

    Mosfet:http://www.heatsink-guide.com/tempcontrol.htm

    -luvv-
     
  3. bountyhunter

    Well-Known Member

    Sep 7, 2009
    2,498
    507
    That's a REALLY bad idea to try to use voltage control for a DC fan. Just cycle the fan on and off using the rated voltage when the temperature rises to the preset limit. DC fans don't run "linearly" as you change the voltage and most have internal controller ICs that monitor motor current and they don't like being starved for voltage. As you reduce the voltage the fan stalls at a certain point.
     
    Last edited: Feb 11, 2012
  4. luvv

    Member

    May 26, 2011
    186
    31
    Yes i should have mentioned the "linear" Mosfet controller will indeed make the fan "growl" if adjusted to low.
    As far as it being a bad idea because of internal IC's inside of the fan, all i have ever seen inside of the fan is hall effect sensors and only those on three wire fans.(don't use the third wire)

    Both of these controllers are fast and dirty, they do work as i have made and used a few of them w/ no ill effect.

    If you want precision control,you are gonna need a PIC and some programming skills.
    You could use a PWM controllerhttp://www.bit-tech.net/modding/2001/12/03/pwm_fan_controller/1 it's pretty simple but will also make fans stall and growl if not adjusted correctly.

    Al in all, if you want precision you are going to need a temp sensor not a thermistor.
    And a PIC to to interpret the feed back and adjust duty cycle accordingly.

    But then if you have the skill and money to make one of those chances are you can afford a retail unit built by fan experts like coolermaster etc.

    This one is pretty neat http://www.newegg.com/Product/Product.aspx?Item=N82E16811999218

    Anyhow,i'm sure one of the experts here will come up w/ a perfect controller for the OP.

    -luvv-
     
  5. popup

    Thread Starter New Member

    Feb 10, 2012
    6
    0
    i should of explained why i need to do this.. i have a laptop it automatically controls the speed of the fan.. but buy the time it turns the fan on full speed the temps are too high and its too late. i have forced the fan to run at 3v which is quiet speed and keeps temperatures at 41c (watching films-web surfing) but if i rip dvd or do something very process hungry the temps go up to 68c this is the reason i need a very small and simple device to run the fan at 3v then when temps reach 50c it runs the fan at 5v

    this is a known problem of this type of laptop and there is no bios updates. so i have to fix the problem myself and this is the only way i can do this.. laptop has been cleaned of dust mx-2 thermal paste on. even copper chims added. the fan does not stall at 3v i have the fan on constantly at 3v ( i soldered wire from a 3v source on the motherboard direct to the (+) on the fan.

    would this work with a 5v power source ?
    http://www.radiolocman.com/shem/schematics.html?di=47949
     
  6. luvv

    Member

    May 26, 2011
    186
    31
    Sorry popup I've never used either of those circuits for a 5v fan:(

    And i have very little experience w/ laptop repair/mods,(meat hooks for hands).

    Since you obviously have some solder skills, why not just mod a micro switch on the oustide of the case so yo can manually switch the voltage supplied to the fan when running heavy loads?
     
  7. popup

    Thread Starter New Member

    Feb 10, 2012
    6
    0
    i was going to do that but would like it to do it automatically ...think im going to just attempt to build one myself i think.. anyone now a good online website i can buy resisters and so on off cheap ?
     
  8. popup

    Thread Starter New Member

    Feb 10, 2012
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  9. luvv

    Member

    May 26, 2011
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    This is equal to the op amp and thermistor link i gave you.

    it will turn a fan on or off based on the temp, it won't speed up or slow down the fan.
    to control speed based on temp you need either a PIC that interprets a digital signal from a temp sensor and adjust duty cycle to a fan

    OR a PWM circuit that relies on a thermistor to change resistance and alter the duty cycle of a 555 timer like the one in the link from my last post.


    OR and this one is the one that isn't um..good practice
    single Mosfet one i gave you a link to in the first post..it works because the thermistor and potentiometer act as a potential divider to the gate of the mosfet.
    The mosfet never gets fully on or fully off aka linear mode,when in linear mode the mosfet don't conduct as well hence limiting fan speed.
    The downside is all that energy being restricted..gets burned off as heat.
    It's not particularity good for the health of the mosfet but...i have used them w/ next to nill heat released.
    Just be sure to get one rated 10x the voltage/current you plan to drive w/ it..you wont have issues.
     
  10. bountyhunter

    Well-Known Member

    Sep 7, 2009
    2,498
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    They have speed control ICs (or they did when I used to use them) which is why you can block the blade when it's running and the motor doesn't fry itself. The IC controls the stall current to a safe value.
     
  11. hwy101

    Active Member

    May 23, 2009
    91
    28
    I have one of those Acer laptops from hell that had the same problem, AMD cpu's run hot, by the time the fan kicked in it was too late. the CPU fan is 5V so I just wired it to a constant 5V source, no need for any controllers.
    It's been running great for 2 yrs, zero problems.
     
  12. luvv

    Member

    May 26, 2011
    186
    31
    Interesting,i have never seen anything other then a hall effect sensor used as a tachometer in a 3 wire standard "muffin" pc fan.

    But then i've only tore apart few of them,and now i will have to kill a few more in the name of discovery:D
     
  13. popup

    Thread Starter New Member

    Feb 10, 2012
    6
    0
    i have a old pc fan controller that has about 5 mosfets in it.. could i use one of them ? the fan controller is rated at 12v.. if not can u recommend me a mosfet ? i will buy some and attempt to build this > http://www.radiolocman.com/shem/schematics.html?di=47949
     
  14. luvv

    Member

    May 26, 2011
    186
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    the ones i built i used these from this sellerhttp://www.ebay.com/itm/5-x-IRF540N...277?pt=LH_DefaultDomain_0&hash=item4aae8fdb4d

    But i have to say i only used them because i had them for another project you could use much smaller mosfet and get away w/ it.

    I use that seller not because they have the cheapest price,but because they can get the parts to my door in 3-4 days max.

    If you have mosfets laying around perhaps you should experiment w/ those first.

    If they get hot fast..the are not big enough but w/ 5v and what 500ma max, i cant see any TO-220 mosfet even getting remotely warm.

    Also make sure you are using the NTC thermistor not the PTC thermistors
    http://stores.ebay.com/Thai-Shine/T...11322018&_sid=916346548&_trksid=p4634.c0.m322

    -luvv-
     
  15. popup

    Thread Starter New Member

    Feb 10, 2012
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    thanks for the links ! i use ebay all the time so thats perfect! can i use the pc temperature probes ? as there small so i can put them really close to the gpu graphics chip. i will try some mosfits ivgot here and if they dont get warm or really hot im good to go with them then.. dont suppose you no were the cheapest place is online to buy a 500g reel of solder do you ?
     
  16. Ctenom

    Member

    Nov 1, 2010
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  17. Geoffr67

    Member

    Dec 5, 2011
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    What about a PNP and pwm modulation with a PIC 16f88. or somthing to that effect. Even a mosfet.
     
  18. bountyhunter

    Well-Known Member

    Sep 7, 2009
    2,498
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  19. bountyhunter

    Well-Known Member

    Sep 7, 2009
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