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I have a lightning connector to USB-C I use for programming and development.

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What would happen if I plugged the USB-C end into my late 2016 Mac Book Pro power supply (87 W)?

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*Disclaimer, I already did it, and it works. It charges quickly, but not sure if it's safe to do going forward.

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It will charge. It's not dangerous. That power adapter is designed to supply UP TO 87W. If you plug a 15" tbMBP into it, it will draw all 87W provided. If you plug a 13" tbMBP into it, the MBP will only draw 61W, even though the adapter can provide 87W. Same for you iPhone. It will draw the amount of power it needs (~10W, IIRC), and the adapter has no problem providing only that amount of power.

However, it is interesting to note that the USB plug adapters that come with iPhones provide only 5W, iPhones are capable of pulling more power, and will charge faster when plugged into an iPad (10W) or tbMBP USB plug adapter.

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It will work just fine and won't damage it.

It will charge your iPhone just fine with 2.1 Ampere until it reaches 80 % battery charge. After that point it will charge at a lower rate (also called "trickle charge").

Your iPhone controls how much energy will be drawn, not the charger.


You'd get same behavior if you charge it

  • Do you know why it doesn't charge with 2.1 Amps all the way to 100% ? – random65537 May 11 '17 at 16:42
  • Yes, it does so with every energy source. This is to prevent the battery from being damaged by injecting more energy than the battery can handle. You will see the same slowdown after 80 % with batteries of MacBooks, iPads, Apple Watches and even electric cars like Teslas Models S/Model X. This is also called "trickle charge". – oa- May 11 '17 at 16:45

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