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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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3 Answers 3

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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, 2013 at 6:49
  • I have 4 different MagSafe chargers and not all of them output 16.5 volts. Reading the labels I see listed output voltages as 16.5 (60 W), 20 V (85 W), and 2 rated for both 16.5 and 18.5 V (65 W). As I recall they were all interchangeable. 1 of my 3 MagSafe laptops is in need of some work at the moment so I can't test that theory.
    – MacGuffin
    Feb 22, 2021 at 11:18
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In other laptop chargers the pin is of round shape, so that there is no orientation of direction for the connection i.e. always +pin of charger connected to +ve pin of laptop and -ve to -ve.

In Apple's version out of 5 pins, 1 pin (middle) is for the battery status which provides a signal to LED to change color red/green.

As the connecter is of rectangular type, suppose if there were only two pins (+ and -) then there would be wrong connection possibility depend on the direction of pin connection. So to ensure correct connection in both way 4 pins are needed.

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  • It's possible to get a "flippable" power connector with only 3 pins, such as have a central +V pin and 2 outer ground pins. 3 track model trains used this for a very long time to avoid looped tracks from short circuiting. The center track provided power and the outer rails a ground return path. Using only 2 pins is possible with some circuitry, this adds costs and power losses and so is avoided when possible.
    – MacGuffin
    Feb 22, 2021 at 11:32
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By Ground you mean negative as the charge block itself is two prong implying no grounding. A positive vs ground circuit would break the electrical design principles as grounding is to bleed off excesses int he circuitry that need not flow along to the next device.

Correction:

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

Careful with DC; it's known to give you a more harmful shock than AC.

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    Sep 9, 2021 at 2:51

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