MagSafe Pinout question

I have a 2012 MacBook Pro whose hard drive has failed. I also have a 2013 MacBook air. The MagSafe connectors are different shapes. One is round & the other is square. I was hoping to keep the MacBook Pro AC adapter & charger & use it as a backup for my MacBook air but the pins are incompatible. Both have 5 pins. According to Wikipedia:

The MagSafe connector pins allow for the adapter to be inserted in either of two orientations. The first and second pins on each side of the tiny central pin have continuity with their mirror pins.

The inner large pins are V+

The outer large pins are ground.

The tiny center pin is a data pin using the 1-Wire protocol. The computer uses this pin to change the LED’s color and retrieve the serial number and wattage of the power supply.

Only two wires – power and ground – go to the charger unit. There is no data communication via the adapter sense pin with the charger unit itself.

Why are there 2 voltage & 2 ground pins? Why not 1 voltage & 1 ground pin for a total of 3 pins?

Mac mini, macOS High Sierra (10.13)

Posted on Aug 27, 2018 5:09 AM

Similar questions

18 replies

macnerd48 Author

Level 1

43 points

Aug 31, 2018 8:21 AM in response to Grant Bennet-Alder

I don't have the tools to open the laptop & replace the hard drive.

Aug 27, 2018 7:30 AM in response to macnerd48

The data pin connects to a truly tiny circuit board in the cable-end, with the LEDs mounted on it.

The reason for doubling the pins is to allow the connector to be installed upside down or right side up, no matter.

Aug 27, 2018 9:58 AM in response to macnerd48

The voltages at the power adapter output are unregulated, and circuitry inside the Mac regulates and conditions it to exactly what it wants for its battery charging.

You can always use a power adapter with more capacity with impunity. The computer only draws what it needs and is not "overpowered".

Using a smaller one can cause some issues with powering and running at the same time, and you may see sudden uncontrolled power-down is certain high-stress situations. This is because the computer freely "borrows" from the battery when the power adapter is connected, especially in high-stress situations.

But using a smaller one for overnight charging while powered off should not be an issue -- it will just charge slower.

This thread has been closed by the system or the community team. You may vote for any posts you find helpful, or search the Community for additional answers.

MagSafe Pinout question