SMCFanControl did not kill your MacBook Pro's perfectly good fans

Discussion in 'MacBook Pro' started by J the Ninja, Sep 30, 2008.

  1. J the Ninja macrumors 68000

    Jul 14, 2008
    Let me elaborate. First though, let's read a wikipedia article on computer fans, shall we?

    OK, so now you know about some types of fans. Now, onto your MBP's cooler. Inside, there are a set of heatpipes the draw heat off the GPU, CPU, and Northbridge, and carry them to two heatsinks just below the screen. A pair of centrifugal fans are rigged up to suck air in through the keyboard and under the logic board and blow it over the heatsinks to actively cool them. The heatpipes rest against the floor of the case too, making the base of the laptop a passive secondary heatsink (or an active heatsink if you aim a fan at your machine)

    Now, these little fans have a rated speed of roughly 6,000RPM. Like most fans, they run at as long as they are fed power. Always. These types of fans can run until their bearings fail, which can takes many years, even if run continuously (see the wikipedia chart on bearing lifespans, remember those ratings are always done at full speed, since the manufacturer can't guaruntee the client will be using it in a device with a PWM controller).

    They run off of 5v DC power, I believe, which is what many components in your machine use as well. They receive it through a 4 pin header like the one described in the wiki article (or that's what it looks like, anyways). Well, 6,000RPM is fast. Really fast, even for a small fan like these. Meaning it's NOISY! What to do about that?

    Well, if you switch the power on and off REALLY FAST, the result is the same as if you had only half the power. If you vary how many times you turn it off and how many times you turn it on each second, you can vary it's speed from within the program controlling the switch. This is called pulse-width modulation, or PWM for short.

    Combine this with the fact that 6,000RPM is an excessive amount of airflow most of the time, well, PWM is employed to slow the fans down to so they are lessy noisy and irritating. Sometimes though, the end user doesn't always agree with the settings chosen for this program, they'd rather punch the fan speeds up a bit. Mac users often use SMCFanControl for this, which is a pretty simple app the raises the base fan speed.

    This leads to a paranoia, however: "ZOMG, I BE OVERCLOCKIN MEH FANS!", no, you aren't. You are removing Apple's "underclock", the was put in place to reduce noise and battery drain (no other reason, just that).

    Look at it another way: Remember when we didn't have this technology, and our computer fans worked for years anyway? Many desktop case fans still do not use a controller, they simply are connected to the PSU. Yet they last years. Do you think fans suddenly stopped getting less durable now that we have PWM all over the place? No, of course not. Cheap fans just don't die that easily.

    So go change your fan speed to what you feel is a good balance or cooling and noise. Have fun.

    And since I can hear the "But it broke my fan!!!!" comments already....let's play pretend: Let's imagine that MBP fans are the lowest quality sleeve bearing fans negotiable (which they aren't, they are made by Delta, who is a major manufacturer of these sorts of things) - they would have a lifespan of 30,000-40,000 hours at full speed and the temps you get in an MBP case. Now, let's imagine you bought the original MBP the first day it came out. Now, let's imagine your fans never left that 6,000RPM/high-heat state (maybe you edit video and fold at the same time, and have it fold some more while you sleep). Well, your fans wouldn't have died yet, because the MacBook Pro was only released about 22,000 hours ago.

    And considering how over-the-top this a realistic the world, the fan lifespan is probably somewhere around 50,000-60,000 hours, and you probably would sleep the machine at night while you get the picture
  2. Aznhiga13 macrumors member

    Sep 16, 2008
    good post and information. I always wondered about this. I heard the fans were underclocked but i never knew if it was a good idea to speed them up. Well now i have my fans up to about 5500 rpm while running windows because it gets pretty hot while playing games and such. I also wondered that by doing this, will it prolong the GPU failures because of the reduced heat on the GPU?
  3. Big-TDI-Guy macrumors 68030


    Jan 11, 2007
    To rain on your parade a little. :D

    A fan running at a higher speed has much greater centrifugal force, and a greater moment of inertia. Meaning a laptop that is rotated around the center of rotation in a perpendicular manner, this WILL cause excess flex/stress, and may lead to premature failure. Whereas, when the fan is moving at a lower speed, there is a lower moment of inertia, allowing it to move with less stress.

    Granted, your HD platters / heads have already likely gotten killed from this same movement -- but faster fans CAN, theoretically, cause failure.
  4. killerwhack macrumors regular


    Aug 5, 2004
    Los Angeles, California
    Core Duo - 2nd fan just replaced

    Thank you for the post. It was informative and well written.

    I have a 2.0 ghz core duo. It is my home office machine that is on almost all the time but sleeping for a large percentage of that time.

    The right fan failed about 10 months ago and the left fan failed 4 weeks ago. By failed, I mean, that it first started making horrible noises and would not run at a high speed. Eventually it slowed to a mere slow twirl.

    I can tell you I was surprised the fans failed while knowing how much use the machine received.

    The first fan was replaced by the Apple store in Pasadena, California. The list price of the fan at the Apple store is about $80 Plus labor (the machine was 13 months old at the time). The second fan was replaced by myself through a purchase at for about $49.

    So I have looked carefully at the fans. I would be surprised if they lasted for 30,000 hours at full speed. They appear to be made with cost in mind.
  5. alphaod macrumors Core


    Feb 9, 2008
    Well I used to run FanControl, but after uninstalling it, my boot times decreased, so I'm good. I didn't use it much before anyways, so I don't miss it.
  6. kolax macrumors G3

    Mar 20, 2007
    Wait - you want to stop the fans coming on because of noise?

    While I completely agree the noise is embarrassingly loud, I want them to come on at 6000rpm when doing things like encoding video.

    Right now, I'm encoding a TV recording using HandBrake, and my CPU and GPU temperatures are 85'C. If I cut off the fans, I'm sure it would creep into the mid-high 90's

    MacBook Pro is too slim for all the power it packs, and fans running 6000prm making a racket is a huge price to pay for something that doesn't need to be 1 inch thick. I'd rather it was what, 1.5 inches thick (like the PowerBook G4) to control the air flow better.

    For a laptop like the MacBook Pro, a "desktop replacement", being so thin isn't necessary. Yes, it makes it more compact, but I'd rather it was slightly thicker and designed better to allow better air flow/temperature control.
  7. Aznhiga13 macrumors member

    Sep 16, 2008
    So do you guys recommend running the fans at a higher rpm with smc? I think sometimes that apple forgets about the function of their designs and focuses on the form more than anything else. If the macbook pro gets any thinner i think that more problems will come with it.
  8. Beric macrumors 68020


    Jan 22, 2008
    Bay Area
  9. mathcolo macrumors 6502a

    Sep 14, 2008
    Very good information... Thanks for sharing this.:)
  10. Big-TDI-Guy macrumors 68030


    Jan 11, 2007

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