I got two Apple Magsafe charges, one for which I needed to cut and rejoint the cables. The fix went well and now when I plug in the charger it works and charges my Macbook Pro.
Though when I measured the voltage with a multimeter on I get some strange values, and they are also differing from the fixed and untouched charger (do not know if they differed before the repare). When measuring I plugin the charger to the AC output and measure with the multimeter pins on the corresponding pins on the plug. There is o load and I can not reach the pins to measure when the plug is connected, thus I cannot make any Ampere-tests.
The voltage should be 16.5 V but I could understand if the charger has some functionality that basically turns it off when there is no load at all, thus the values on the untouched charger. But how come the values on the fixed one?
Untouched:
Fluctuating voltage of 0-0.5 V
Fixed:
Fluctuating voltage of 0-7 V
What does this mean and should I not continue to use the fixed charger even if it works?
Best Answer
MagSafe chargers can output variable voltage. When disconnected from a computer, they output a very low voltage. When connected, the computer requests the voltage it needs, using the center data pin. Your voltmeter is acting as a resistor in this circuit, which may be fooling the charger into thinking a computer is attached.
According to this link, the original MagSafe uses 6V when disconnected, and MagSafe2 uses 3V. So I can't explain your 0-0.5V fluctuation, except that maybe you're not making a good connection with the test leads.
http://www.righto.com/2013/06/teardown-and-exploration-of-magsafe.html?m=1