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I just got a MacBook Air and noticed the charger has 5 (i.e., an odd number) pins. Shouldn't there be a pair number, one for positive, one for negative charge?

I thought about it being ground, but the charger does not have a ground plug. (Note: the cord does, nevermind)

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up vote 10 down vote accepted

From MagSafe Wikipedia page

Pin 1 - Ground
Pin 2 - V+ @ 16.5 V DC
Pin 3 - Charge control pin
Pin 4 - V+ @ 16.5 V DC
Pin 5 - Ground

  • The inner large pins are V+ (16.5 VDC). Measuring with no load will give 6.86 V DC; the full 16.5 V is provided to the proper load.
  • The outer large pins are ground.
  • The tiny center pin is a charge control pin that assists with changing the LED color, as well as reporting the connected adapter type and serial number to the connected Mac.
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The center pin does nothing with regard to switching the adapter off. It's only used for controlling the LED on the plug, and reporting to the laptop which kind of adapter it is connected to. The actual cable between the magjack, and the adapter has only two conductors (power and ground). –  Fake Name Apr 24 '13 at 6:49
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