Hacked Gadgets Forum

April 9, 2010

PWM Fan Controller used to cool an External Hard Drive

at 12:19 pm. Filed under DIY Hacks, Electronic Hacks


I made a PWM Fan Controller to cool my external hard drive that got quite warm when it was running for an extended period of time. There are 4 videos documenting the build below. Have a look at the project page for the schematic, code and additional information.

The heart of the PWM Fan Controller is a PIC 12F675 microcontroller. This microcontroller is reading the analog output of a LM35 temperature sensor using a ADC (analog to digital converter) . The resulting digital value is converted to a temperature and a fan is powered proportionally to how hot the sensor is. The sensor is mounted against the hard drive chassis so it is measuring the actual drive temperature and not just the air temperature inside the housing.


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6 Responses to “PWM Fan Controller used to cool an External Hard Drive”

  1. NatureTM Says:

    Very nice! I’ve been worrying about my disks since I read there was such a strong correlation between temperature and drive failures.
    I’ve got a fancy PC case with an overkill number of fans, and most have speed switches instead of pwm. It can be pretty loud when they’re all on max, but I worry about my components since I’ve pushed my overclock pretty far. I’ve found when I turn them all down I can actually hear whats going on in my apartment, outside, and in my head. I’ve been thinking my next big project is going to be something like this but for all my fans and possibly multiple thermal zones. The videos definitely made me feel this is something I can accomplish.

  2. Hey Alan Says:

    Nicely done, haven’t you thought of lowering the temperature of shutting off these fans a little bit lower than the temperature where they are switched on? avoiding fans from rapidly turning on/off when the temperature happens to be in that switching point?

  3. Lars Says:

    Looks to be working good, the cooling.

    I ‘tested’ some LM35’s yesterday, they work nicely.

    Thanks for the video’s.

  4. Fan Hack – How to Make a Hard Disk PWM-Controlled Fan! Says:

    […] via hackedgadgets Download latest version of Flash to view video!. Click Here to View in Full Screen Mode Did you get an iPad? Don’t forget to check out our Top 10 Best iPad Accessories Review!.’; Tags: fan hack, Hard Disk, hard disk fan, how-to, make, pwm-controlled fan Categories: Circuits, DIY, Featured DIYs, Featured Gadgets, Featured Hacks, HOWTO, Hack, Hard Disk, Projects. […]

  5. askjacob Says:

    Looks like you need some hysteresis to stop the cycling from becoming distracting and driving you nuts!

    Some comments I’d like to make:

    The holes are not really good for air flow – you would have been better off just removing fan-sized circles.

    Because there is no baffle between your push and pull fans, a lot of the air must be getting bypassed from one fan to the other without doing any cooling – a small foam “baffle” between the fans would prevent that.

    Internally there is a large metal plate where your vent are – again that could be perforated, or a baffle added to make sure the air circulates through the drive before exiting (instead of just hitting the plate then exiting).

    Still, this will provide better cooling than the original sealed box.

    I was very impressed with the detail you went through with the build – a great job and I think it will help out many getting started with this kind of project.


  6. Alan Parekh Says:

    Hi Jacob,

    Thanks for the comments. I am thinking of adding a time delay before the unit switches off to stop that oscillation when it initially turns on. For example, if the unit is cool enough to turn off a delay of 30 seconds will be in place before it spins down, if during that time the temperature is such that the drive needs to operate the speed will be set and the timer will be reset.

    My initial concept had the two fans mounted tight to the cover so that all of the air would be forced to flow into the case. The electronics would not quite fit with this arrangement so I mounted it slightly away from the cover. If the air flow was not sufficient to provide good cooling I was going to make a small extension ring to allow the fans to couple to the cover better but it seems to cool good enough as it so I just left it.

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