Why does my MBP power adapter get so hot?

iToaster

macrumors 68000
Original poster
May 3, 2007
1,742
0
In front of my MacBook Pro
So I've been sitting here doing things until this unreasonable hour, but the curiosity has gotten the best of me. I feel it is required to ask the question: why the heck does my MBP's power adapter get so hot?
 

juanster

macrumors 68020
Mar 2, 2007
2,238
0
toronto
i have a MB but mine gets preeettty hot sometimes too. so hot that in class i put it on a girls neck and made her scream int he middle of a lecture....pretty fun...
 

iToaster

macrumors 68000
Original poster
May 3, 2007
1,742
0
In front of my MacBook Pro
i have a MB but mine gets preeettty hot sometimes too. so hot that in class i put it on a girls neck and made her scream int he middle of a lecture....pretty fun...
Happened with the good old MB as well. I'll have to remember your response next time I have the chance to do so :D. Heh, my MBP's so hot even the magsafe is affected :rolleyes:
 

creator2456

macrumors 68000
Jul 10, 2007
1,649
2
Chicago
So I've been sitting here doing things until this unreasonable hour, but the curiosity has gotten the best of me. I feel it is required to ask the question: why the heck does my MBP's power adapter get so hot?
It's a transformer. Transformers get hot.
 

CortexRock

macrumors 6502
Dec 3, 2006
413
0
Canterbury, England
I'm sure I heard somewhere that the heat given off by a transformer (not the giant robot kind) is the energy that's being wasted by the charging process... shame we can't think of something more efficient.
 

anirban

macrumors 6502a
Jan 9, 2007
690
0
Houston, TX
I'm sure I heard somewhere that the heat given off by a transformer (not the giant robot kind) is the energy that's being wasted by the charging process... shame we can't think of something more efficient.
We could always lower the thermostat during cold days...:)
 

kusanagi

macrumors regular
Jun 18, 2007
106
0
The basic idea around a transformer is two coils, wiht a large amount of wire for each coil, parallel to each other, the energy from one is transferred to another, buy the placement and number of windings of each coil you will be able to transfer x amount of energy from one to another, the byproduct being heat.

Now, a macbook pro consumes 85 watts of power, which is by far rather small seing as most pc tower computers need at least a 200w power supply and they are actively cooled by a fan. The mac pro infact, the cpu ONLY will consume up to 250w! http://docs.info.apple.com/article.html?artnum=304387

So the power consumption is fairly reasonable and the heat out put whereas it may feel extremely hot, is within safety guidelines. Unless tehre's a fault you should never have any problems with it running that hot. Just remember for its size (especially the new ones that are the same size as the 45w macbook brick) is pretty remarkable. I have an old Toshiba Portege that I use for a linux server which is almost twice the size of my MBP's adaptor, runs even hotter and only uses 70w!

Another way to look at it, plug an 85w lightbulb into a light socket, turn it on and feel the heat coming off that (for heaven's sake don't actually touch it!) If that is as hot as your MBP power adaptor then you might be in trouble. Otherwise don't fret!
 

Zel

macrumors regular
Jul 7, 2007
172
0
Most power supplies are between 70 and 80 percent efficient, so 85W is about 75% of the energy being taken in, because 85W is how much is output. That's 113W taken in... minus the 85 given to the MBP leaves 28 wasted as heat.

28W is enough to get warm but nothing to be concerned about. The MBP uses 85W si move things and the spin things and switch transistors (lots of that), but in the end all 85 is spilled out as heat (or light).

The charger is therefore much cooler than the laptop itself, but has poorer dissipation so it can feel quite hot.
 

Roguepirate

macrumors member
Jun 11, 2007
57
0
Most power supplies are between 70 and 80 percent efficient, so 85W is about 75% of the energy being taken in, because 85W is how much is output. That's 113W taken in... minus the 85 given to the MBP leaves 28 wasted as heat.

28W is enough to get warm but nothing to be concerned about. The MBP uses 85W si move things and the spin things and switch transistors (lots of that), but in the end all 85 is spilled out as heat (or light).

The charger is therefore much cooler than the laptop itself, but has poorer dissipation so it can feel quite hot.
I dont the 85W rating is how much is actual power dissipation of the power supply, 85W should be the rated max that the it can supply and it'd be pretty bad if the MBP is running the power supply at full load. I'm not sure how much power the MPB consumes but it might be about 70W if it's an 85W supply. All power supplies get hot, packaging it in a small plastic case without any way of cooling doesn't help.