resister for fan

Discussion in 'General Hardware' started by Gus K, May 25, 2003.

  1. Gus K

    Gus K NTFS abuser

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    Anyone know what size/type resister I'd need to drop the voltage from 12v to 6v for a Thermaltake 80 fan?

    Thanks
     
  2. Zedric

    Zedric NTFS Guru Folding Team

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    Normally a resistor would be a bad choice for this. I suggest you use one of two other ways:
    1. Get a voltage regulator for 6V. I know there are 5V and changable regulators so I guess you can find 6V somehow.
    2. Connect the fan between 5V and 12V giving it 7V. Close enough?
     
  3. XP Abuser

    XP Abuser Guest

    wire up an adjustable resister to it or get a step down transformer... id go with the former
     
  4. LeeJend

    LeeJend Moderator

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    Gus

    Ignore both of the previous answers.

    A decent voltage regulator with heatsinking will cost as much as a new fan with a built in speed adjuster. Any reasonably sized variable resistor will burn up under the current (0.5-0.7 Adc) a fan draws.

    The resistor idea works fine. I've been using it on a noisy fan for the past 6 months. I put 2, 10 ohm 10 watt resistots in parallel and it drops the 12 Vdc down to ~9.5 Vdc which turns the 6800 rpm shrieker into a nice quiet 5200 rpm fan and it still does a good job cooling. Radio shlock has 2 pack power resistors for $1-2. You could get 5 ohm and use a single one but I used the 2 in parallel to spread the heat.

    NOTE: A 10 watt rating on a resistor means that it can handle 10 watts when attached to an infinite heatsink with a 72 deg F temperature. I taped my fan slowing resistor to a metal channel running across the PC to help keep it cool.

    Or just go buy one of the new fan control modules for $20 bucks or a volcano 9 with its own speed control for $20.
     
  5. Gus K

    Gus K NTFS abuser

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    Makes sense, thanks to all.
     
  6. Taurus

    Taurus hardware monkey

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    i know i'm late. but this is my favorite method. :)
     
  7. Maveric169

    Maveric169 The Voices Talk to Me

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    RatShack should have 12V variable resistors, I have used them before.
     
  8. Zedric

    Zedric NTFS Guru Folding Team

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    Really? That's got to be some really cheap fans!
    A very decent voltage regulator (witout heatsink, none needed) costs about 50 cents here.
     
  9. XP Abuser

    XP Abuser Guest

    lol

    im just trying to think how does that 12v and 5v make 7v **** work
     
  10. Taurus

    Taurus hardware monkey

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    the positive lead for the fan goes to the 12v... and the negative lead goes to the 5v... 12 - 5 = 7 volts. :)
     
  11. XP Abuser

    XP Abuser Guest

    ahhh i see
     
  12. Zedric

    Zedric NTFS Guru Folding Team

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    Yep, I thinks it must be the most common "mod" ever. :)
     
  13. XP Abuser

    XP Abuser Guest

    rub it in then zedric :(
     
  14. Zedric

    Zedric NTFS Guru Folding Team

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    No offence intened! :)
     
  15. XP Abuser

    XP Abuser Guest

  16. LeeJend

    LeeJend Moderator

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    Doesn't dropping the voltage to 7 Vdc make the fan turn too slow to get enough airflow? My 6800 @ 12Vdc is at 5200 @ 9.5 Vdc.

    Anybody got any speed numbers for the 5-12Vdc conenction?
     
  17. Taurus

    Taurus hardware monkey

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    sure, it still moves air. you can feel it. a fan at 7v runs roughly 60% the speed of 12v. if you want something between 12v and 7v, then i think you're only choice is a regulator or resistor (not sure what the difference is).
     
  18. Zedric

    Zedric NTFS Guru Folding Team

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    A regulator is guaranteed to give you a certain voltage, regardless of load (ut to a limit of course), but a resistor gives different voltage on different loads.

    Thus a regulator is better. :) You can add more fans to it if you wish.
     
  19. Taurus

    Taurus hardware monkey

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    thanks, zedric... i'll be looking around for a couple to play around with.

    since they aren't resisting current, they don't create heat, do they? i mean, they aren't drawing more current from the mobo/psu than the fan needs, correct?
     
  20. XP Abuser

    XP Abuser Guest

    no zedric is right resisters limit electricity by changing the energy from the electricity into heat. thus reducing the voltage but they do not have a constant voltage...



    but its not a case of wiring it up you have to build a circuit with a few resisters and capacitors to actually tell the VR what voltage to regulate