PWM fan controller for external hard drive

[Alan] noticed that his external hard drive was getting quite hot to the touch after a few hours. He says that it was probably designed to handle the heat sufficiently, he thought it would be fun to beef it up. He’s using a pic 12f675 microcontroller as the brain and an LM35 temperature sensor. The Fan speed is varried in 8 steps from 35 degrees C to 45 degrees C.


  1. Andreas says:

    …”The Fan speed is varried in 8 steps from 35 degrees C to 45 degrees C.”…

    Oops, since when do we measure speed in degrees centigrade?? ;-)


  2. john says:

    Since the scientific community and the rest of the entire world ratified it a handspread ago. GOSH. Grow up.

  3. Imroy says:

    @Andreas: It’s been called Celsius since 1948. Get with the times.

  4. davo1111 says:

    *high fives john*


  5. sanchoooo says:

    HDD temps(I work in storage for a big 3 letter company) are always in degC for all the drive types I work with.

  6. Vince says:

    Great idea, wish I had thought of that before my old external drive died of heat :(

    Oh and Kudos @ John

  7. Abbott says:

    I love how none of the comments have been moderately relevant to the discussion. That aside, did anyone else notice that he has one fan as an exhaust and one as an intake? I would imagine that in this setup, both being intake would be a bit more efficient.

  8. James says:

    He’s circulating air through the case, if both were intake, or exhaust, he’d presumably end up with a bottleneck with regards air entering or leaving the case. In this case he blows air in, heat exchanges, and sucks that out. Valid route unless there’s a lot of ventillation on the case, in which case I’d probably blow-through.

  9. bobdole says:

    You guys SERIOUSLY need to hire an editor, or at least proofread your posts. Almost every single post for the last few months has been full of errors.

    First of all, the word is varied, not “varried”. Second of all, this sentence makes no sense and is awkward: “He says that it was probably designed to handle the heat sufficiently, he thought it would be fun to beef it up.” That comma should be a dead stop or at least a semicolon. The first half of the sentence makes no sense, I think you meant to say “**While** (or although) it was probably designed to… he decided to beef it up **anyway**”

    Seriously guys. I’m not usually a grammar nazi, but every single post lately is rife with spelling and grammatical errors. Youtube commenters can make more legible and coherent posts than you. I often wonder if you guys are 12. If you can’t at least write at a grade 8 level you have no place blogging.

  10. Andreas says:

    Oh man, I will never again make a joke like that…
    I’m was not mocking about the celsius scale (I know it’s Celsius – I’m german…) – but about the measuring of SPEED in TEMPERATURE units. Btw., didn’t you notice my “;-)” after it?


  11. Andreas says:

    Sorry for the typo in line 2: “I was not…”

  12. PocketBrain says:

    You gotta admit, the $5 Masscool HDD coolers are a great value.

  13. B1rdm4n says:

    Hard rives actually last longer when they run hot. I never cool my HD’s, because it would actually subtract from their useful life.

    If it’s too hot to touch – that’s a different story.

  14. ris8_allo_zen0 says:

    I wonder if PWM is the right way to control these fans. If they are brushless, their internal control electronics may dislike discontinuous power supply. Or am I wrong?

  15. Devlin is a pussy says:

    WOW what a hack! He put FANS on a HARD DRIVE. Holy shit stop the presses.

  16. JD says:


    PWM is fine for these fans. Most 4 wire fans take PWM inputs to control their speed.


    You’re wrong. I work for one of the biggest military contractors in the world and the ONLY time you’d want to add heat (or not take it away) is in cold temperatures. Extreme cold temps are actually more detrimental to the operation of harddrives, but hot temps will kill them quickly.

    @Devlin is a pussy

    Have you ever used an external HDD case without any cooling methods. You’d be lucky to have a drive last more than a few hours (3.5″ @ 7200rpm). They literally cook themselves. This is a nice cheap hack. The interesting portion of it, is PWM control of the fan speeds.

  17. Devlin is a pussy says:

    JD you’re telling me that a company puts out a hard drive enclosure that will kill a hard drive in a matter of hours? You are an idiot. I bet you love duct tape and arduinos.

  18. Hirudinea says:

    Just from an astethic viewpoint big copper heat sinks would have been nicer/

  19. Benny M says:

    @Devlin is a pussy
    This IS a hack. It’s making use of old bits (the fans) to fix a problem (the overheating HDD). If this isn’t a hack, what is?

    Nah bro, gotta go all the way on that one. I’m talking heat sinks the size of a beer mug with a fan that sounds like a helicopter.

  20. Dan says:

    i ran a WD1200 for a good 7-8 years with little to no cooling – i see no need for cooling if it’s not in a closed case…

  21. davo1111 says:

    To be fair, it is a little overfill. If he had just opened the case, drilled some holes and closed it up – it would be interesting to see what the temperature change was

  22. chips says:

    why does everyone feel the need to waste money on programmable controllers when you could do a proper old circuit. I’m thinking a 555 to clock the PWM, obviously some transistors to beef up its output, and then on the input simply a potential divider with one half thermistor and the other half potentiometer so you could tune it to behave in the temperature range you wanted.
    It takes 30 seconds more thinking about but no time spent programming and no wasting money on fancy programmable chips.

  23. magetoo says:

    It’s not “wasting money” when you’re building it from parts you already have lying around.

    Using a 555 sounds clever/simple, but how many are doing that sort of thing now? I bet that for most readers it’d just be going out of your way to learn to do things differently, when you’d rather just hack something together that works _now_.

  24. chips says:

    I’d hazard a guess as anyone with more brains than bucks :)
    The real difference of course is a fully analogue PWM as opposed to 8 digitised steps.
    Its almost guaranteed to use less power too though that really is nit picking, hey I can’t help it I just feel trollish today
    for a little more trollism how’s about, it is wasting money even if the parts are laying around as then you can’t use them for a suitably complex project at a later date.

  25. David says:

    i guess that hard drive when heavy holds about 5 pounds of data…

  26. Tomasito says:

    Why use a simple transistor, or an 555 when you can go and use a micro?

    It would been 5 times more interesting if he used a transistor or an 555.

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