Circuit design help - variable voltage fan controller

Cardinal-FangCardinal-Fang
edited May 2009 in Hardware
My ancient MB has half-assed fan speed controls on the CPU and SYS fan headers that work fine, except for one major thing: the voltages only vary from 8v to 12v. The minimum of 8v is just way too much, and especially on the SYS fans, the case temps only range from around 32c min to 36c max. A wider voltage range would let me use a wider spread between the low/high temps and make the speed changes much less noticeable. The board does not use the RPM signal from the fans, it only varies the voltage according to the low/high temp settings.

What I'd like to build is a circuit that takes the variable 8v-12v input and outputs 4v-15/18v to the fans. I have looked at lots of lists of circuit projects, but haven't found anything like this. Any suggestions on where to start?

Comments

  • trolltroll Windsor, Nova Scotia Icrontian
    edited May 2009
    You could drop them all a few volts just by using resistors no.... I don't think you'll find any variable dc-dc conversion circuitry that will automatically convert 8-12 to 4-18... The controller would be more than board...

    http://www.analog.com/library/analogdialogue/archives/38-02/fan_speed.html

    Or I just use a fan controller... :)
    13-999-251-02.JPG
  • Cardinal-FangCardinal-Fang
    edited May 2009
    A resistor would make it even more useless than it is now. Cutting it down from 8v to 5v with a resistor would mean 12v = 9v at full speed, and at only 9v the case and drive temps go to +40c. Having to turn a knob on the front panel is about as appealing to me as herpes. Same goes for all the fancy 'programmable' bay fan controllers - I tend to look at my monitor most of the time, not the front of the case under the desk.

    I have seen the Sunbeam Theta which is software controlled (you know, through the part of the computer you actually look at, the monitor...), but those are extinct. And there's the really neat mCubed stuff that's software controlled, but just cost way too much. I guess I could try going without food for a few months...
  • SoundySoundy Pitt Meadows, BC
    edited May 2009
    Cardinal Fang wrote:
    My ancient MB has half-assed fan speed controls ...

    Sounds like time for a new mobo ;)

    I'm just sayin...
  • Cardinal-FangCardinal-Fang
    edited May 2009
    Soundy wrote:
    Sounds like time for a new mobo ;)

    I'm just sayin...

    Since it's a S939/DDR setup that means board + CPU + memory + (probably) PSU so unless you want to loan money to somebody with no way to repay it...
  • SoundySoundy Pitt Meadows, BC
    edited May 2009
    I might have a spare S939 board kicking around... Asus A8V Deluxe :)
  • Cardinal-FangCardinal-Fang
    edited May 2009
    I would follow up on that if it wasn't K8T800/AGP vs my AX8's K8T890/PCIx :mouldy:

    I would have even considered it given my lifelong loathing of everything ASUS, thanks to this lovely A7A-266:
  • trolltroll Windsor, Nova Scotia Icrontian
    edited May 2009
    I'm sorry I misunderstood...

    http://jos.vaneijndhoven.net/fancntl/index.html

    Excellent fan control circuit...
  • Cardinal-FangCardinal-Fang
    edited May 2009
    As usual, China can do it cheaper. Hooray for slave labor!
    http://cgi.ebay.com/_W0QQitemZ160327517221

    It isn't perfect, but it should be simple enough to either replace a resistor with a pot or use a different thermistor to get it right.

    But first, I'm going to hack the fan controller in the PSU (Neo 480). Like the ebay thing, it too needs some 'adjustment' to get it in the right temp range.
  • ThraxThrax 🐌 Austin, TX Icrontian
    edited May 2009
    +1 for Asus hate.
  • Cardinal-FangCardinal-Fang
    edited May 2009
    Thrax wrote:
    +1 for Asus hate.

    The majority of Asus users seem to think the more something costs the better it is. R.I.P. Abit :shakehead
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