How are Mac Chargers compatible when they are different voltages?
This is not a question specific to this Macbook, but I am just trying to understand how this works all works. I recently had my Mac charger die on me, so I just cut the end off and soldered it on to an old Lenovo charger I had laying around. It works fine, but I am trying to understand how the chargers actually work.
Looking online, the different Macbook Magsafe chargers actually all have different max voltage outputs:
- 14.5 V DC for the 45 W units supplied with MacBook Air
- 16.5 V DC for the 60 W units supplied with MacBook and 13" MacBook Pro
- 18.5 V DC for the 85 W units supplied with 15" and 17" MacBook Pro
- 20 V DC for the 85 W units supplied with 15" MacBook Pro Retina
Why is it done like this? Why not just have all of the chargers work at the same voltage and simply limit the current on each charger based on the wattage?
Even more important, how does the computer manage to accept higher voltages? I can use an 85W charger on a Macbook Air without problem and it will work just fine, but the chargers are just a simple 2 wire connection between the Magsafe Adapter and the brick so I don't understand how the laptops "tell" the chargers to supply a lower voltage.
I can hook the Magsafe charger end up a fixed bench power supply and it will happily take a tightly regulated 20V.
Is the voltage regulation done inside the laptop? It still seems strange to me that the voltages are different.
If anyone could explain how this works it would be very helpful!