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My wife ordered a new adapter for her 2013 Mac Air Model A1466, Amazon sent the wrong one and we did not notice because the mag fit perfectly and it appeared to charge. This seemed to charge fine for a couple weeks, but last night it went totally dead. When I press the power button, there is absolutely no reaction--it does not matter whether it is plugged in or not.

When first connecting the charger, it appears green for a few seconds and then orange and never goes back to green no matter how long it's plugged in (13 hours charging overnight and no response when pressing the ON button).

When examining things this morning, I discovered that the Mac Air is rated for "14.85V 3.05A Max" and the Charger's output is rated at 20V 4.25A. I understand that an overpowered amperage is fine--no problem--the device will take what it needs: But overpowered voltage is critical and will fry your device!

My question is . . . what protective mechanism or circuit does Apple use to prevent the motherboard from being fried? Do you have a diagram or name of the replacement part? Any description where it is located would be helpful as I looked and could not readily recognize the circuit inside. Thanks in advance.

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  • Have you tried SMC reset?
    – lhf
    Sep 30, 2021 at 17:08
  • Before assuming something has been fried you should perform the more basic trouble shooting steps like an SMC Reset and checking to see if it charges with a different Power Adapter. Sep 30, 2021 at 17:15
  • Do you have access to a known-good power adapter that you can test with?
    – pion
    Sep 30, 2021 at 17:55
  • I have tried the SMC reset, no reaction. But I will not have a new Power Adapter until tomorrow. I have also ordered a new battery, which should be here tomorrow. I will try to charge the old battery first with the new charger to eliminate the charger being the problem. Sep 30, 2021 at 19:16

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It does not to me seem evident that that any "overvoltage burnout" occurred at all.

The MagSafe 2 connector is a 5 pin connector, where the center pin is used to establish a data connection between the computer and the charger. Through this connection, the computer tells the charger what kind of wattage it needs. Your MacBook Air would request 45W. The charger then applies the voltage suitable for a MacBook Air (14.5V).

The MagSafe 2 chargers comes in various variants that include the voltages 14.5V, 16.5V, 18.5V and 20V. As described, the computer and power supply negotiate the correct voltage before applying a load.

As described in Apple's support pages, you can connect a higher wattage (and thus voltage) charger to a smaller Mac model without any issues (i.e. for example a 85W 20V charger for a 15" Retina MacBook Pro connected to a 45W-rated MacBook Air).

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  • I did have to replace the battery. Checked the voltage and it was .25v where the new one was 7.5v. So I think is was the battery. I found the Apple Support pages you linked to -- very helpful and comforting that the Magsafe charger communicates and has overvoltage protection. Many devices don't have overvoltage protection (burned out two drills before I realised the charger had the wrong voltage). I did return the previous charger and replaced with 14.85v 45w charger. It took a full day before the light turned green and allowed the Mac to start. Oct 4, 2021 at 1:52
  • No, higher wattage does not necessarily mean higher voltage. The wattage of the power adapter specifies the max current (speed of charge) it can supply at the required voltage. Excessive voltages place components under stress and can destroy them.
    – Benice
    Mar 12, 2023 at 15:23

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