Running multiple Fans using PWM (need help with MOSFET Selection)

Discussion in 'The Projects Forum' started by Electro Monkey, Jul 6, 2012.

  1. Electro Monkey

    Thread Starter New Member

    Jul 2, 2012
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    Hi,
    I am trying to build the circuit shown in this link: http://www.dprg.org/tutorials/2005-11a/index.html

    I want to use this cicuit to run several 12-18v fans (in parallel).

    My aim is to be able to control the speeds of all of the fans at the same time. E.g. make all of then run at 50% to 100% speed.

    The main thing I would like to know is, in the circuit an IRFZ46N MOSFET transistor is used. (Here is the data sheet: http://html.alldatasheet.com/html-pdf/441363/VISHAY/IRFZ24/436/2/IRFZ24.html)

    The problem is I cannot get hold of the same MOSFET and I was wondering if I could use this IRF540A MOSFET instead. (Data sheet: http://www.hackerbotlabs.com/wp-content/uploads/2009/02/irf540a.pdf)

    My main concerns are about the delay times of the IRF540A MOSFET, they appear to be a lot greater than the IRFZ46N

    MOSFET transistor. Could this stop the circuit from working correctly?

    Any advice will be greatly appreciated!


    Ps sorry for all the links. :s
     
    Last edited: Jul 6, 2012
  2. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Electro Monkey likes this.
  3. Electro Monkey

    Thread Starter New Member

    Jul 2, 2012
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    Thanks so much for the quick reply.

    I have looked at those data sheets and the delay differences are relatively small.

    I believe the fans are brushless DC; they are similar to CPU or case fans.

    Do you know of a way that I can run these fans at variable speeds?

    I have tried using a variable resistor, but it overheats. :/
     
  4. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    How many wires on the fan?
    Got a part number?
     
  5. Electro Monkey

    Thread Starter New Member

    Jul 2, 2012
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    There are 3 wires on the fan; red, black & yellow. I have looked around and I think the fans are the same as the ones on this heatsink. (http://www.deepcool-us.com/Product/NBRIDGE2/) I hope this helps.
     
  6. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Not gonna work with PWM..
    red/black=power
    yellow is output (TACH) speed signal..not an input

    You can vary the input voltage though to adjust the speed.. Not the best solution but it works.
     
  7. Electro Monkey

    Thread Starter New Member

    Jul 2, 2012
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    Ok, seems like im back to square one using a variable resistor.

    Do you know of anyway that I can vary the voltage to the fans without cooking my variable resistor?

    I was trying to put about 6 of these fans in parrallel.
     
  8. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    You can always buy fans with a PWM control pin.
    Or build a variable LM317 supply.. Thats what I did (2 x 12V fans in parallel) for my LED light I build.. I can go from 5 to 12V and it works just fine.
    You need to know how much current each fan will require though to ensure you aren't overloading the variable voltage circuit with multiple fans..
     
  9. wayneh

    Expert

    Sep 9, 2010
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    I think that would work unless the fans are too big.

    If you need more current, you could make an op-amp controlled, constant current supply with a MOSFET or two on a big heat sink. Or a darlington using a 2N3055 with another smaller transistor if you already have these laying around. The op-amp watches the voltage drop across a shunt resistor and compares it to a reference voltage set by you with an inexpensive variable resistor. Its output controls the power transistors to let more or less current through the bank of fans.

    These linear solutions are functionally the same as your resistor, but can handle much higher currents with ease and precision at a lower cost. A variable resistor to safely handle your load is just too expensive.
     
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