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Brushless cooling fan

Discussion in 'Home Brew' started by Cpt shakes, May 3, 2018.

  1. Cpt shakes

    Cpt shakes Active Member

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    Not sure where to post this question. Does anyone know what the third wire is for on a brushless fan?


     

  2. sp5it

    sp5it Master of puppets

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    Speed control
     
  3. Cpt shakes

    Cpt shakes Active Member

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  4. Cpt shakes

    Cpt shakes Active Member

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    Is it based upon how much ground is apply to the third wire?
     
  5. sp5it

    sp5it Master of puppets

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    Speed control is done by 7V variable applied to 3rd pin.
    MIke
     
    rabbiporkchop likes this.
  6. 543_Dallas

    543_Dallas Sr. Member

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    The 3rd wire on the fans I've dealt with is the speed sensor for a fan controller. All it does is let the controller know how fast the fan is spinning. The fan controller varies or pulses the voltage to control fan speed.

    Do you have a model number for the fan? Since you've gotten conflicting info we can probably dig up a manual for it.
     
  7. nomadradio

    nomadradio Analog Retentive

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    Sometimes the third wire will be for a stall sensor. Stays inactive until the fan blade gets stuck and won't spin.

    Finding a data sheet with the full technical description would clear this up.

    Unless it's printed in chinese.

    73
     
    Tallman likes this.
  8. Tallman

    Tallman W9WDX Amateur Radio Member, KW4YJ EXTRA class

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    Nomad has the right answer. It is used as a protection circuit for heat critical circuits.
    Some devices have to have air moving to protect devices that generate lots of heat.
    I used them in systems I designed for "Ruggedized" uses.(Military adaptation of civilian products.) If no signal was present the power settings were dialed back to lower levels and alarm circuits were activated. But it can be used as a tachometer input for a speed control.
     
  9. Tallman

    Tallman W9WDX Amateur Radio Member, KW4YJ EXTRA class

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    If you don't need fancy fan control just cover the bare end with heat shrink tubing and leave it alone.
     
    unit_399 likes this.
  10. Cpt shakes

    Cpt shakes Active Member

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    I use them a lot and was just curious about the third wire because I never use it.
     
  11. unit_399

    unit_399 EL CAPO

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    BEST answer!!

    - 399
     
    psycho and Tallman like this.
  12. Onelasttime

    Onelasttime Well-Known Member

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    Some fans send timing data to processors/controllers. If the fan speed falls below a predetermined limit the cpu will shut the unit down to prevent damage depending on what we are talking about. This means that in some situations you either have to supply a timing signal if you want to use a different fan or turn it slower or you have to use a similar fan to keep the cpu happy.

    So all of the above answers can be correct depending on the application.

    I have to say I like systems with lots of nanies to protect the system. It is only a problem when it works against you! Right? LOL.....

    Since I value durability and reliability over almost all else I would rather have my system go down than have it suffer damage I could not help to fix in a timely manner or at great expense.

    When you have systems without nannies then the have to have a lot of gauges and watch them like a hawk and be able to spot issues and react quickly. Having learned to fly in ancient aircraft I am used to watching a ton of instruments scanning the sky talking on the radio watching the radio navigation systems reading charts and flying the plane all at once! If you do not want to train people though to a high standard you end up with nannies and idiot lights and systems that you cannot easily override. Just depends on the market!

    Vechiles today mostly have idiot lights for two reasons. 1) Most customers are idiots and think about as much as a hamster while driving or operating machinery. 2) Not sending real-time data to a gauge reduces warranty issues with random customers thinking something might be wrong when it is completely normal or OEM has really low standards.

    On something like a server farm, you can not expect people to keep a close eye on things real time not practical. For a CB or ham operator, it is possible to expect smart operation but it is easier to plan for an idiot and build accordingly.

    The important bit here is that you do not have to use the third wire if your system is not that smart and not looking for a signal on a third wire!Some systems with 3 wire fan are not that picky and will still work with out the signal but most if they have a 3 wire fan they want the data on that wire!
     
    #12 Onelasttime, May 10, 2018
    Last edited: May 10, 2018
  13. Tallman

    Tallman W9WDX Amateur Radio Member, KW4YJ EXTRA class

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    You cannot beat the idiots. I had what I thought a "Fool Proof" system. Idiots 1 Me 0.
    I designed a cabinet refrigeration device for industrial applications and they worked great. There were problems with standard Freon system because Hydrogen Sulfide is extremely corrosive and loved the silver in silver solder.
    One new customer bought one 2500 Btu units and I tested it extensively to be sure it worked properly. It was perfect.
    The customer receives the unit plus the DC power supply with printed instructions for installation. They hand it off to a junior maintenance technician. He uses all of the templates for panel holes. Done, Looked nice. Wired directly to 220vac. Unit died a horrible death. I replaced it at no cost and wired it up for them. It has been working ever since.
     

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