Chosen Solution
Hi there, I replaced my MacBook Air adapter’s wire following this guide, only I installed a replacement wire instead of keeping the old one. I had already done it once and hadn’t had a problem. Since I did, adapter won’t charge for more than about 24 seconds. After that time, it goes completely down, LED is off, computer doesn’t see it at all. Consistently. I have to unplug it from the wall and plug it back in to make it charge again. It consistently works. I don’t need to wait, unplugging it and plugging it back in instantly is enough. Conversely, unplugging it from the Mac and replugging it doesn’t change anything. However, if I unplug the adapter from both the Mac and the wall, then plug it to the wall only, wait 30 seconds, and then plug it to the Mac, it works (for 30 seconds though). I can’t detect any heat during these 24 seconds. No sound either. As a corner case, if I leave the computer charging while closed, then it works fine. Also, in some cases it works fine too, mostly when it has been charging while off for a while. It seems that after about 40 minutes charging while off, if I turn it on then it continues charging without problem. I have tried both the “duck head” as well as the extension chord. I also tried on several power outlets, including through an inverter with its own battery. One potential noteworthy thing is that I am using this 45 W MacBook Air charger on a 60 W MacBook Pro. I had no problem before though. Additional information: I couldn’t find the wattage in System Information, however based on information on Apple’s website, my Macbook requires a 60 W power supply.Based on the information about the replacement wire, it seems to be compatible with both 45 W, 60W and 85 W adapters.
What you describe seems, some overload protection is tripping. Removing and reconnecting power supply to its load (MacBook) is needless, because power supply remains in tripped / shutdown state. Substituting AC connection (“duck head” or cord) is needless, because form of AC connection is not important. ‘I installed a replacement wire instead of keeping the old one.’ Do you know, what kind of replacement? What specific type of MagSafe tip/plug? If your plug identifies as 60W or 85W, then it is no wonder that your 45W supply is overloaded. You can use ‘System Information.app’ (or ‘System Profiler.app’) to find your plug’s identity. Open ‘System Information.app’, view ‘Power’ (subpage of ‘Hardware’), look under heading ‘AC Charger Information:’. What ‘Wattage (W)’ is reported? Addition 2018-03-03: For an idea of what ‘AC Charger Information:’ looks like, a clue as to what to look for, you can look at this screenshot hosted on Apple Support Communities. Pictured is a full ‘Power’ report section; near bottom is ‘AC Charger Information:’. Whoever snapped this image had a 85W plug.
