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Can I use an 85W MagSafe power adapter to safely charge my MacBook Air?

Posted by Lakesen Guo on

You may heard of these questions like “Can I use an 85W MagSafe power adapter to safely charge my MacBook Air?” , or “Can I use the high wattage MagSafe to my mac which need the low wattage?“。The answer is following and very clearly. Yes, you can If the ports of the adapter fit .

For all this kind of questions, Apple’s office answer is “You can use a compatible higher wattage adapter without issue, but it won't make your computer charge faster or operate differently.”

Link is Here: http://support.apple.com/kb/HT2346  

We’d like to mention that the only advantage for use a high wattage adapter powering a lower power mac might even run cooler than the smaller wattage adapter.

We will give the details explanations for why Apple’s answer is correct.

Here is the Magsafe specifications from Apple:

Everybody know wattage equals voltage times current (Watts = Volts * Amps), so if wattage is higher, that means maybe the voltage is higher, or maybe the current is bigger, or maybe both of them are higher and bigger.


1). For bigger current: 
The use of bigger current adapters with devices requiring smaller current is okay because the current is pulled from adapter by your laptop, not pushed by your adapter. How many current will pull through is depend on your laptop need. For example, if your original adapter is MagSafe 45W, that means the maximum current your laptop need is 3.05A, in this case if you use MagSafe 85w power adapter, your laptop only pull 3.05A current also , although the 85W Power adapter can supply 4.6A current.


2). For higher voltage:
The use of higher voltage MagSafe with Mac requiring lower voltage is okay, because there is a DC-DC convertors (with their own regulation) in your mac inside, this DC-DC convertors will give it the voltages needed for its components from either the adapter or the battery, and to charge the battery. For example, if your original adapter is MagSafe 45W, that means the maximum voltage power supply is 14.5V, when it enter your Mac, the DC-DC convertors will convert the 14.5V to correct voltage ( for most of laptop it is 5V), in this case if you use MagSafe 85w power adapter alternately, the 85W MagSafe will supply 18.5V power, when it enter you Mac, the DC-DC convertors will convert the 18.5V to same correct voltage also.
The internal convertor have wide input voltage range, I don't know about the range specifically in Mac, but it should from 14.5V to 20V at least depend on Apple’s office answer to this questions.
 
The conclusion: You can use a compatible higher wattage adapter without issue, but it won't make your computer charge faster or operate differently. But Lower wattage adapters don't provide enough power.

 


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  • Great answer. The difference in output voltage between the power supplies was what had me confused and worried but as you pointed out, all mac’s down-regulate the voltage anyway (via internal DC-DC converter) and for Apple to say each power supply can be used on any mac clearly indicates that all macs are compatible with the output voltages from these different power rated magsafe psu’s.

    Martin Cooper on

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