The Idea Dude

CONNECTING THE DOTS ONE AT A TIME

Friday, July 16, 2010

My MacBook is now even cooler!

I finally decided to buy a laptop cooling fan. After upgrading my MacBook to 4GB, adding a higher capacity hard drive and driving a 24 inch external display, things starting to heat up. When I first bought my MacBook, the temperatures were in the 50's and now consistently it is in the 70's and sometimes 80's. (all figures in centigrade)

So I sprung some well-earned dollars and got a Zalman cooling fan. It's not ideal, the two fans are smaller than others and the airflow is towards the bottom 2/3's of the cooling platform. The MacBook gets the hottest at the top where the exhaust vents are and on the top left where the graphics card is.

Your notebook will heat up if:

  • You add more hardware like more memory, bigger / faster harddrive or connect external devices like an external monitor. More hardware means more current. More current means more heat.
  • Running screensavers will keep your CPU's and GPU's hot because there is very little or no disk access. Your CPU's will end up running 30% or more capacity and more importantly (all the time, not just sporadic bursts). This translates to more heat and less battery life.
  • If you leave your browsers open, be aware what is running in the windows. Rotating ads, flash advertisements, animations will drive your CPU and GPU nuts just like screensavers. Your CPU could reach 50-80% depending the page. And all this is happen while you step out to lunch or throughout the night.
  • Keep an eye what what is running in the background and what their CPU consumption is. If it is occasional like a printer manager waking up for a brief period, you're ok. But it all adds up. I've noticed that Google Docs have some bug that occasionally, it gets into a loop and my CPU max's out until I close the browser window. And I wasn't even editing the doc!


There are so many threads about notebooks mysteriously draining power overnight or overheating when not in use. Because you're not using it doesn't mean the notebook is being used!

So on to cooling pads, here are some tips:

  • If noise is important to you. Get the cooler with the larger fans. They range from 70mm to 230mm. Large fans don't have to run as fast to generate the same airflow. Fan speed is the biggest source of noise. Small fans have to run faster and generate more noise. I would have love to get the ones with 230mm fans, unfortunately, their design means the whole notebook is raised by an inch which is not acceptable to me. I type pretty much 8-12 hours a day.
  • Most of the cheap products don't tell you what the airflow is (usually this is measure in cubic feet per minute (CFM). You can usually guess by looking at fan size and fan speed when comparing different products.
  • Before buying a fan, look at where the hotspots really are on you notebook. Sometimes it is on the side furthest from you (MacBooks) or on the side (ThinkPads). Remember, the fan is there to move hot air away from the hotspot.
  • Running a cooling pad will not necessarily reduce your normal operating temperature of the CPU as much as you think. Here's why. The CPU gets hot, the heatsink draws the heat away from the CPU, the fan blows the air away through the vents or towards the body of the notebook. Under normal conditions if you can remove the hot air from the notebook body and the vents, the internal fan detects the internal temperatures are down and slows down or stops. The CPU stays relatively hot. So extra cooling on the outside at some point doesn't translate to lower CPU temperatures. You're reached steady state and the temperature gradient from inside to outside doesn't change. To reduce the CPU temperature, you have to make the internal fan run even if it thinks it doesn't have to so the air from the CPU can be moved away.
  • External cooling fans do their best work in the extreme cases. That's when the CPU's hot, the internal fan is blowing and you need to move hot air fast. Since getting the notebook cooling pad, the temperature seems to be fairly constant between 66-75 deg C while running the internal fan at around 3000rpm. This is true even when watching a YouTube video or the SlingBox TV channel. Before the cooling pad I would see temperatures rise over 80 deg C and the fan blowing over 4000-5000rpm.
  • Don't forget that your ambient temperature impacts your steady state. My office is good 5-6 degrees cooler than my loft at home. My MacBook sensors show the notebook body is correspondingly 3-4 deg lower at work than at home. Ambient affects what your steady state temperature flow.


So my conclusion, notepad coolers are great. Don't expect them to do much at normal loads (but then you would be buying one anyway). But they help keep heavy load conditions close to normal operating temperatures. High temperatures shorten the life of your components and increase the risk of failure.

Right now, my MacBook is even cooler in every sense of the word.

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