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Thread: Electronics Expert Needed - How to slow a Case Fan?

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    Electronics Expert Needed - How to slow a Case Fan?

    I bought a couple sharkoon fans for my new quiet PC, a 1000RPM 120mm and a 2000RPM 80mm. the 2000RPM 80mm fan is the noisiest thing in my case, I don't overclock, so I wish I bought the 1000RPM...

    Some electronics expert here must know a cheap/free way I can slow it down? like putting a resistor in the middle of the wire?

    Or my other thought is... what voltage do case fans run on? 12v? Could I connect it to the 5v to half it's speed?

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    Does he need a reason? Funkstar's Avatar
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    Re: Electronics Expert Needed - How to slow a Case Fan?

    The little lable on the center of the fan should say what voltage it runs at, but yes they are usually 12V. Swaping them to use 5V is an easy way of slowing them down. Easiest if they have a moliex connector, you can just move the wire to another pin hole.

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    Re: Electronics Expert Needed - How to slow a Case Fan?

    can also make them 7v iirc

    but not looked in to how google will show you the way im sure

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    Re: Electronics Expert Needed - How to slow a Case Fan?

    To make them 7V, connect live to 12V and ground to 5V giving you a potential difference of 7V

    I'm sure it works without a problem, but i wouldn't be comfortable in doing it.

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    Senior Member Andaho's Avatar
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    Re: Electronics Expert Needed - How to slow a Case Fan?

    Quote Originally Posted by Funkstar View Post
    The little lable on the center of the fan should say what voltage it runs at, but yes they are usually 12V. Swaping them to use 5V is an easy way of slowing them down.
    Hmm, thinking about it on the molex connector... they're actually 5v aren't they... the red wire is 5v and yellow is 12v.

    so not so simple to change it to 3v.

    --- EDIT ---

    hang on... just had a closer look at a molex adapter thing I got here, it had a red and black wire going to the fan, but when plugged in, it actually goes to the yellow and black on the molex plug!

    so...

    if it's a 2000RPM fan, how fast do you think it would run at 7v?
    Last edited by Andaho; 26-09-2007 at 03:53 PM.

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    Re: Electronics Expert Needed - How to slow a Case Fan?

    Yeah, thats pretty normal

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    Re: Electronics Expert Needed - How to slow a Case Fan?

    The usual mod is 7V, I doubt the fan will even start on 3V.

    There are resistors you can get, but they are quite chunky ones as they will be dissipating a few watts of heat. I have one that came with a Zalman 80mm fan.

    Does your motherboard not had a fan control? You can often set fan speed reduction in the BIOS if it has the 3 pin connector.

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    Re: Electronics Expert Needed - How to slow a Case Fan?

    Quote Originally Posted by Andaho View Post

    if it's a 2000RPM fan, how fast do you think it would run at 7v?
    usually pretty linear so 11-1200rpm

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    Re: Electronics Expert Needed - How to slow a Case Fan?

    Quote Originally Posted by DanceswithUnix View Post
    Does your motherboard not had a fan control? You can often set fan speed reduction in the BIOS if it has the 3 pin connector.
    Thanks for that suggestion, don't know why I didn't think to look.... I have the new Gigabyte P35-Express mobo... I'll restart and have a look

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    Re: Electronics Expert Needed - How to slow a Case Fan?

    Nah, no settings to slow the fan in the bios... only a couple settings about how to control fan speed for the CPU, which has nothing to do with it.

    I'll have a google about wiring it up to be 7v

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    Senior Member Andaho's Avatar
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    Re: Electronics Expert Needed - How to slow a Case Fan?

    Ok, so to get 7v... I connect the fan positive to +12V and the fan negative to +5v? I've never heard of using a +line as a negative before... sounds dodgy... can someone confirm that's what to do?

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    Re: Electronics Expert Needed - How to slow a Case Fan?

    It's DC there is no negative really. you have 0v, +5v and +12v.

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    Re: Electronics Expert Needed - How to slow a Case Fan?

    that was nice and easy.... Used the molex converter cable that came with the fan, and swapped the pins in the molex socket. Now it's the quietest thing in the case.... but when plugging in the white cable to the mobo, it doesn't show the RPM.... my PCis so quiet now... I can hear the quiet power buzz of my sub-woofer louder than the PC!

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    Re: Electronics Expert Needed - How to slow a Case Fan?

    A quike way to half the voltage would be to fit a resistor the same resistance as the fan coil in to the +v wire

    But to be honest, they are only cheap, couldn't you but the 1000 and fob the other one off to someone else?

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    Re: Electronics Expert Needed - How to slow a Case Fan?

    get some scrap electronics and measure a bunch of resistors or find a volume control or a knob/slider of some sort and put it on the positive signal of the fan...I have about five scrap fans round here which are ultra quiet shame shame

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    Re: Electronics Expert Needed - How to slow a Case Fan?

    If half the voltage is dropped in the resistor, then half the power is dropped in the resistor, so it will get *very* hot. The resistor that Zalman use in their resistive lead is about the thickness of a BIC biro, and it needs to be.

    A better way is to get a second fan and wire it in series, as a fan motor is not a pure resistive load and you will get some air movement for your power used.

    The 7V thing is elegant and safe, and uses the high efficiency regulation of the PSU to do the job.

    Zalman also do a variable speed controller for fans, and it is very cheap and small.

    Andaho, I would ignore the RPM meter, that could get tricky to make it work and it isn't that necessary.

    Hey, occasionally a degree in electronic engineering is useful

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