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I'm using the MagSafe power adapter from my old multibody Macbook Pro:

http://www.infobarrel.com/media/image/35698.jpg

On my new unibody Macbook Pro:

enter image description here

The MagSafe power adapter has become very hot and emitting a faint burning smell. It's not scalding hot. I can still hold it in my hand. If I were to guess, it's 150 Fahrenheit. The smell is similar to what you would smell when you turn on a cheap blender for too long. It is properly charging though. I see the percentage increase on my screen. I'm not in a foreign country, so voltage is not the issue. So I'm wondering, is the unibody Mac not compatible with the multibody Mac's power brick?

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Yes they're compatible, however if the wattage of the charger is less than what the MacBook needs, it may not charge while the MacBook is running. That's typically only a consideration when you're using a charger from a smaller MacBook on a larger one. It shouldn't cause a burning smell or other malfunction.

If you're smelling burning, I'd get it checked out. Those things have been known to melt, particularly around the Magsafe connector, or where the cable meets the power brick. Check for frayed wires, etc. But I doubt it's related to using it on a different MacBook.

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  • The power cord / brick has no visible damage. At the moment, I am running Handbrake (video transcoding), which is maxing out the CPU (it's expected). If I'm pushing the Mac to its limits, is it expected that the power brick run hotter? I've never ran intense software on my multibody Mac because the processor is crap. So this is more likely a problem with power need VS power supply rather than power cord incompatibility?
    – JoJo
    Sep 3, 2011 at 20:35
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    They can definitely run hot, and if you're taxing your computer, it's drawing more power, so it's more likely to run hot. I wouldn't worry about the heat too much, but the burning smell is definitely a cause for concern, even if everything looks okay. I'd take it in to an Apple Store and tell them you smell burning, see what they say.
    – robmathers
    Sep 3, 2011 at 20:40
  • The smell is faint. I'm not suffocating or anything. A blender will emit a more potent smell.
    – JoJo
    Sep 3, 2011 at 20:44
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    The wattage of all older MacBook pro like the one pictured is 85 w - plenty for any unibody MacBook Pro. Something else is causing the heat other than a wattage mismatch.
    – bmike ♦
    Sep 4, 2011 at 3:25
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Yes - an 85 W magsafe adapter is an 85 W magsafe adapter no matter what the end cord arrangement. The newer adapters have a thin barrel more like the 45 W macbook air barrel style adapters first required due to the limited space where it connected.

The heat and burning smell could be a safety issue (especially if your sniffer isn't very sentitive) - have it looked at by a professional that sees a lot of adapters or just replace it if your sense it it's not working properly.

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I had the exact same issue, old 85w brick as a back up for a new mbp. I kept the new brick at work in order to travel. I also had occasional smells until it ultimately failed and shorted. The plastic around the wiring at the brick melted away. No damage to the mbp.

I spoke with a fella at the Mac store who said the point where the wire meets the brick is a common failure point. Seems many users, myself included, would wrap the wiring too tight. Over time the wires fail. He suggested leaving and inch of leeway before wrapping tightly.

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At work, we have various MacBook Pros ranging from 2008 to 2011 models. In meetings, we share the power without any problem at all.

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I agree with the others that the power adapters should be interchangeable, but that the heat + burning smell is cause for concern. I had a brick that was doing that and then one day, it gave off a "pop" sound and sparks, and melted a section of the cord, near the point where the cord enters the block. Scared the crap out of me! If that had happened when I wasn't nearby, depending on the materials nearby, it certainly could be a significant safety risk.

I've seen the recommendation to pub a spring from an old ball point pen around the cord at the inflection point, to prevent the wear and tear that comes from repeated bending there. Haven't tried it myself. But if you are already getting a smell I'd use that on the replacement power adapter, and retire this one.

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