Charging A Laptop on 12 Volts
I bought my MacBook Air back in 2013 because it was lightweight and had a long battery life. Yet, no matter how long that battery life may be, it’s never going to be long enough to not require recharging while on the road. Which brings up a dilemma: how do we charge our computers while boondocking?
Boondocking means that we will be away from a conventional power grid and relying on our 12 DC volt batteries instead.
Why Not an Inverter?
A relatively simple answer is to use an inverter to power 110 V AC power sockets that we can hook our computers to, as if we were on a normal grid. However, this is an inefficient solution as we would be converting DC to AC and back to DC again. That involves power loss at each stage. Instead, we want to tap into the 12 volt system and only convert as much power as is absolutely necessary.
Converting 12 Volts
For a long time, the way computers were charged off of 12 V systems (other than the inverter) was to have a cigarette lighter style converter that powered the specific needs of the computer.’
Cigarette Lighter Charger
The primary means of charging a computer off of 12 V systems (other than an inverter) that has been documented is to use a cigarette lighter style converters powered to specific needs of the computer. This is not a one-size-fits-all proposition. Some computers charge at 15 volts, some charge at 19 volts. Some computers require 45 watts, others require 90.
As an example, I’ll compare and contrast the challenges we have between our computers. As developers, we intentionally purchased different laptops for testing our work. I work off of a 13″ MacBook Air from 2013. Cowboy has a Dell Inspiron 7737 from 2014.
Charging a Dell Inspiron 7737
Dell manufactures their own 12 volt converters. The Dell Inspiron 7737 charger converts shore power to 19.5 volt at 3.34 amps—65 watts. requires a 90 Watt DC adapter which can easily be found by browsing the accessories section for that particular computer on the Dell website. You can also simply search the Dell site with a query such as “Dell 90 watt auto-air adapter“.
Charging a MacBook Air On 12 Volts
Apple has not made alternative living easy. Their proprietary approach has severely limited manufacturers options when serving the Apple using audience. I’m leery of a lot of solutions as manufacturers that do make products outside of Apple’s good graces are already operating in a grey area (If you are using one of these on a Mac, I’d love to hear your experience.) Many Apple owners resort to their own hacked together solutions.*
Reading the incredibly fine light-grey print on the charger that came with my Macbook Air, I can see that it takes in 100-240 volts at 1 amp and converts it to charge at 15.85 volts DC at 3.05 amps. Anecdotally, owners have reported that they are able to use 12 volt converters to keep their computers battery levels static, but not to charge the batteries.
Still, at over 4 years old, it is getting to be about time to replace this little guy. And when I do, I know exactly what I’ll be looking for:
Many new laptops are now being released with USB C ports. These ports look just like the conventional USB ports that we use to exchange data between devices or power smaller electronics from the main laptop. Yet, instead of only allowing power to flow from the port to power your cell phone, USB C also allows power to flow through the port to charge the laptop. This now opens up the potential of charging a computer through the 12 volt system. However, I haven’t found much confirming this particular use case.
I’m not to a point where I need to update my computer just for a USB C port, but Cowboy’s laptop is on its last leg and the USB C may very well be a major selling point for its replacement.
Inverters Might Not Be As Inefficient They Seem
Stepping back to a more general overview, I’ve had a few people make the very astute observation that power efficiency is all relative. Sure, converting DC to AC involves loss, but there is also loss between DC and a different voltage of DC.
Between two optimally constructed devices—one a DC to DC converter and the other a DC to AC inverter and then converter back to DC—the more direct conversion from DC to DC would be more efficient. But, a lot of the specialized laptop converters, especially the cheap ones, are likely to be poorly made and, therefore, quite inefficient. A quality inverter paired with the highly specialized charger that came with one’s laptop may very well be more efficient than the grey market converter for sale on eBay.
Moreover, an inverter will be useful for many circumstances. Where as, single use dongles add clutter to an already small space.
Therefore, I’ve circuitously come to the conclusion that, if USB C is an option, take it! Otherwise, invest in a quality inverter.
Laptop Charging Resources
- “12v Charging Electronics on the Water or Road” from Commuter Cruiser
*There are many references to the Magsafe 12vdc Charger, but I haven’t found one for sale.