Suijin, my Magsafe charger (made by Samsung Electronics) is not faulty. It is rated at 16.5 v / 3.65 a, output which is a fraction over 60 watts.
A good quality sine wave inverter of just under 300 w BUT with a lighter plug DC input lead will not charge my 13" MacBook Pro. The overload signal goes off signalling low voltage input to the inverter. That happens on my boat with heavy wiring
to the cig socket. It also happened in a couple of cars even with the motors running. When I returned it for exchange to Jaycar the supplier, we did those and other tests. Jaycar is one of the biggest retail electronic parts
suppliers in Aus / NZ
The 60 w of the charger is only its output. The charger itself consumes power and an inverter is not 100% efficient. So there is more power being consumed and even the best boat DC wiring
has some voltage drop. Then the connection of the lighter plug / socket and the plug's built in glass fuse drops the voltage a bit more with its spring contacts.
I believe the main culprit is the attached lighter type plug. The inside of even the best quality lighter plug is so confined that a decent heavy input cable is impossible.
We have a good range of inverters available but the lowest wattage of sine wave inverter I could find with heavy DC input terminals is over 300w. It may be possible to hack into a smaller sine wave cigarette lighter type and install heavier cables
but if you try and it doesn't work you can't return the inverter.
Some have run their engine
to make it work where they are inputting maybe 14 v but maybe less if the charge is floating. My solar
was providing around 13v / 14 v when I tried in the boat several times during a few weeks away.
There is no problem with my replacement hard wired 350 w inverter even while occasionally using an Elgato / MacBook UHF tuner to watch TV at night when the MacBook naturally heats up a bit. Don't want to run the engine then and don't want to flatten the MacBook battery.
There are 12 v adapters that some people have reported to charge OK but they report RF interference
. That naturally suggests to me oscillation in the circuit.
Now I'm going to speculate that perhaps they work by rapidly charging and discharging a capacitor producing a pulsing DC of 16.5 v.(much like a camera
flash charges a capacitor and discharges a very high voltage flash) A pulsing DC current
, like that could be smoothed with old fashioned chokes but it would still be pulsing. I wonder why Apple don't seem to sell them as far as I'm aware. But lots of people think that manufactures in general don't know very much. It may or may not be that they could void the warranty. But I don't know.