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I have a 2011 Macbook Air.

The original Magsafe cord was getting flimsy, so I cut the old cord, got a spare one from eBay and soldered it to the power adapter.

However, I realised the wattage rating information built into the connector's chip is 60W in the new cord (which was probably obtained from a dead 60W adapter), as reported by "System information" and CocoaBattery, while my adapter's actual rating is 45W.

So far the Air seems happy with this new cord, but I wonder what risks this might incur, especially since 60W adapters are supposed to deliver 16.5v, instead of the 14.5v the Air needs.

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If I'm reading your description correctly, then the replacement cord has a higher rating (60W) than the 45W that is drawn by the 2011 Macbook Air. This is fine because all it means is that the cord has a thicker gauge to handle a higher wattage (than what you are are actually using).

The replacement cord would not affect the voltage, so your adapter would still be delivering what it is specified for, namely the 14.5 V.

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    And the other way around? – CousinCocaine Apr 28 '15 at 13:42
  • MagSafe chargers are queried by the laptop and the laptop will only draw as much power as it's rated for. Here is a description of the query but I haven't found a description of the current draw process yet. – Alan Shutko Apr 28 '15 at 13:46
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    The other way around? You mean if you use a 45W cord instead of a 60W? That would officially be what is called "a fire hazard." The cord would be subject to excessive heat, which would likely cause the insulation to wear at an advanced rate. – Vzzdak Apr 28 '15 at 13:47
  • Thanks. I wonder, however, how the Air handles the higher voltage from the adapter. As far as I know, the adapter doesn't care what model it is connected to and supplies its default voltage (e.g. 20 volts for the 85w adapter). How can the Air cope with a higher voltage? Does it reduce the voltage somehow? – eternal404 Apr 28 '15 at 19:40
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    If I read your description correctly, then all you did was swap out the cord, but kept the adapter. The cord is merely a conductor; it wouldn't cause any change in wattage or voltages. It is the adapter that determines the wattage that it can supply. – Vzzdak Apr 28 '15 at 20:25

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