As I get more 12v devices setup in my home office/ham shack I have started venturing into more and more electronics projects.
I started researching alternatives to the Apple MagSafe power adapters and did not come up with much. There seemed to be few willing to experiment with powering their expensive laptops from alternate sources.
In looking at my power adapters and Apple laptops I determined that a power source of 16.5v into a MagSafe cord would work. With none of my available power sources supplying 16.5v, I had to purchase a voltage step-up converter that would support the 3.65A load of my 13″ Retina MacBook Pro is rated for. I found one on Amazon that would support a 6A continuous load. I tested it on my bench and verified the output voltage on the built in display with a multimeter and found that it was off by about a tenth of a volt, not a show stopper.
While holding my breath, I connected it to my laptop and… the green light indicating charger was connected lit, and the charger was recognized in OSX. I drained the battery a few percent, and it charged up. I then drained the battery down to about 50% and successfully charged it up. Recharge times were roughly the same as using the AC Adapter. The only apparent difference I have found is that the Apple adapters only put out 6v until a load is present. This no doubt saves power on an adapter that is always plugged in, but I turn my 12v power supplies on and off as I use them.
I mounted everything up in a project box with some hot glue, a PowerPole lead, and a switch. I drilled a few vent holes around where the heatsinks of the voltage step-up converter are to allow for heat dissipation. I rarely feel the housing get more than just warm to the touch, but plan to drill more for a margin of safety.
I used the adapter for several days in my home office with no issues to report. I believe I will be switching back to the AC adapter for day-to-day operations, and will use this adapter for portable operations.
Word of warning – fuses are your friend
One time while checking the voltage at the MagSafe connector I shorted it against the magnetic collar. No permanent damage occurred to the power supply, voltage step-up adapter, or the MagSafe connector, but I have since decided to add a fuse to the output to prevent this from being an issue. With the MagSafe pins exposed, using a traditional quick-blow fuse may become an issue because the likelihood of shorting is high. I am going to try out a self-resetting poly fuse and see if the response times are adequate to prevent damage to the electronics.
Voltage step-up converter: http://www.amazon.com/gp/product/B00HVD1XU0
MagSafe2 Cord: http://www.amazon.com/gp/product/B00B0U5F2W
Project Box: http://www.amazon.com/gp/product/B00CSRW6UU
Power Switch: http://www.amazon.com/gp/product/B0087YAHOK
3 Replies to “DIY 12v MacBook MagSafe Charger”
Does the step up up converter have any current limiting or can you just apply 16.5v direct to the magsafe cable and to the mac. Is there a schematic please.
I have not applied any current limiting. The charging circuitry is located in the laptop. The only thing the power adapter does is provide voltage, the Apple-branded adapters have a low voltage/power mode to lower power consumption when a computer is not connected to the adapter, but since I only use this adapter when needed I do not worry about this kind of circuitry.
Nice project – I’ve been considering something similar myself.
In my 12V off grid set up charging my MacBook Air is a real energy hog because I have to fire up the inverter. Annoying!
Thanks for sharing.