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costabunny

macrumors 68020
Original poster
May 15, 2008
2,466
71
Weymouth, UK
Well I am feeling a lot of love for my new 13" MBP, but I have a question:

I still have a spare 85w Mains adapter and I'd like to be able to use it - my understanding (correct me if I am wrong) is that the MBP will pull the wattage from the mains so a larger one will do no damage. The Apple guy says he wouldn't recommend it (and hence tried to sell me a new 65w one).

Is it safe for me to use the 85w one as my second mains unit? (I like to keep one upstairs and one in the lounge)?

Little advice from someone who understands this wattage thing would be nice....
 
The watt rating indicates the maximum amount of power the adapter can provide. Both the 65w and 85w adapters provide the same voltage, which is what you need to worry about. So, it is safe to use either adapter with your MBP.
 
The watt rating indicates the maximum amount of power the adapter can provide. Both the 65w and 85w adapters provide the same voltage, which is what you need to worry about. So, it is safe to use either adapter with your MBP.

What he said.

I wouldn't do it on my own laptop, but then again I have a 17" so using a 65w or 45w isn't an option. Just seems like it might have *some* unforeseen consequences.
 
Assuming the 65 & 85W units are of the same voltage and MBP connector, you're golden. :D

Only the deliverable current is different, and the computer will only draw what it needs. The higher rated unit should actually run cooler (presuming adequate heat sinking on the Voltage Reg's), and not be as stressed to provide the necessary load, as it's lower than it's rating. Not "force" a higher current through the computer, causing damage. The Apple guy apparently doesn't understand basic electricity as well as s/he thinks. ;) :p
 
Unless something is actually wrong with either the lines in your house, the adapter or the machine, it's going to get the ~65W it needs, and not one...picowatt more.
If something IS wrong with one of those three places, it would be wrong no matter what the specified wattage of the adapter was.

In other words: Use a "larger" adapter if you want, but don't use a "lower", since it will either charge slowly or not at all.
 
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