If you have a Mac laptop (or any other laptop come to that), it can be frustrating trying to charge it from a 12V plug, like that in a car or boat. The draw on a Mac power source can be high, as much as 85 watts for a MacBook Pro.
The initial solution is to buy a small “converter” that will change the voltage and power to something usable. This works well enough, but it’s horribly inefficient. The voltage has to be converted twice before it gets to the laptop, and the converter will often get pretty hot.
Fortunately, there is an easy solution, get a 12V GPK Car Charger from GPK Systems.
The problem with the converter approach is that basically is a transformer. The “brick” part of the power cord for a laptop is also a transformer. So the voltage is being changed twice, with efficiency loss both times. On a boat this can drain your batteries pretty quickly. The answer is to get a SINGLE transformer that will juggle to power conversions in one step. I purchased a charger from GPX systems that does just this and tested it out.
The test was pretty simple, on my electrical panel I am able to read the current being used at any point in time. So, after turning off everything else on the boat, I plugged in my MacBook Air using a transformer.
Here you can see a draw of 4 amps while charging the laptop. After a few seconds, the transformer starts getting hot and its own built in fan kicks in.
Next we use the GPK Car Charger that goes directly from a cigarette type 12V connection to the MacBook Air power plug.
You can see the load drops to 2 amps and the transformer is much cooler.
A difference of just 2 amps does not seem like much. But it can take half an hour to charge a laptop. If you have a couple of laptops in your family, you are quickly looking at 3-6 Ah (amp hours) a day. Every little bit can make a difference. On top of that, charging devices inefficiently basically means that you are turning on a 50 watt heater for a hour. Not such a great idea if you a sailing in the summer!
I used the GPK Car Charger for a whole week of sailing with no shore power. It charged quickly and efficiently, took up less room and ran cooler. This bit of gear is a keeper on our boat.