12v Charging Electronics on the Water or Road

In the past and in general on the boat, we’ve always relied on inverters to convert the D/C battery current to the A/C necessary for all the important things like charging my camera batteries, powering the laptop and, most importantly, making coffee.  However converting from the batteries 12v current to A/C wastes amps.

MacBook Air powered by my 12V power cord in the travel trailer.

MacBook Air powered by my 12V power cord in the travel trailer.

Although the wasted energy varies depending on how much is needed and the inverter used, it’s my understanding that a good average is 15% wasted.  Doesn’t sound like a lot, but every amp counts when you’re operating with limited power resources such as on my boat… or now in my travel trailer.

So I’ve been trying to figure out how to power stuff directly from D/C (i.e. batteries), i.e. 12v – like your car cigarette lighter.   It’s relatively easy to charge a phone from a 12v outlet, and I’ve figured out how to power my IPad via 12V, but the laptop was a challenge.  Luckily John K, a CC reader, posted a comment introducing an Apple 12V power charger (be careful to make sure you get the adapter if your MacBook Air is post 2012!).

In my research, I found that since laptops are all over the map when it comes to power requirements, it’s necessary to find a 12v power cord that matches your specific laptop.  For example, my MacBook Air requires 45 watts, but my recently deceased MacBook Pro required 60 watts — both are 13″ displays.  Must be something to do with the solid state design of the Air, but regardless, you cannot just find a 12v plug and assume it will power your laptop or computer.  And that’s before you even start to think about the connection on the laptop end!

The MagSafe adapter required for post 2012 MacBook Air - and the green light showing the laptop is topped off with juice.

The MagSafe adapter required for post 2012 MacBook Air – and the green light showing the laptop is topped off with juice.

I finally found a 12V power connection that works with the MacBook Air — with an adapter for the post-2012 models.  It’s not cheap, but it’s less expensive than Dell’s version of a 12v power connection for David’s Dell Inspiron (at 90 watts, btw).  Here’s the info:

The rest of the story - the 12v plug showing a light indicating power and the power strip also lit indicating power.  Nice.

The rest of the story – the 12v plug showing a light indicating power and the power strip also lit indicating power. Nice.

1.  12V 14.5v 45 watt power connector for my MacBook Air (also available for pre-2012 MacBook Air).   This looks much like the regular Mac power cord for A/C, but so far it works well in the trailer, and I’m sure it will work equally well on sv Winterlude.  Here’s the link to MarineBeam.com.

Dell12VCharger2.  12V 90 watt power connector for David’s Dell Inspiron (that also runs our Nobeltec Odyssey navigation software underway) … directly from Dell — the more questions I asked, the more confused I got, so I figure it’s best to buy it directly from Dell.  They asked for the Serial Number and model number of his computer to match us up with the right 12v power source.  I supposed it’s possible to fry sensitive electronics with the wrong 12v power cord?  Here’s the link:  Dell 90 watt Auto-Air Converter for Select Laptops

Unfortunately, I’m still stuck with either a small inverter or our main boat inverter to power things like the coffee pot and my camera battery charger.  We’re in the process of buying a new one for the trailer, but haven’t decided which one yet, here are some possibilities.

Anyone have a recommendation on a small inverter?  Are the USB ports necessary or even useful?  How much power – our small one on the boat is 300 watts, but I notice you can get alot more watts these days for not much money.  The two small inverters we have aboard the boat are both very noisy and tend to overheat quickly – plus they’re 10+ years old.  Anyone have a recommendation for a small inverter that would allow me to charge my camera battery?  I figure the coffee pot is going to require either a manual approach during quiet hours (see Java Dilemma) or our Honda 2000 generator.  So I’m not concerned with big items, just little stuff.

Please leave comments and let us know your solutions and how you like them.  THANKS! Cheers!  Jan



  1. Jill B G says:

    Very interested, will be following for use on our sailboat. Have been checking out portable solar charging options for phone, tablet, and laptop, but no purchase yet. P.S. Your recommendations have helped us greatly; we have our kayak mounted on Garhauer racks, and our 20-yr-old Lighthouse windlass just came back from Calif after being refurbished ! Thanks for.all the info & ideas!

    • Hi Jill! I was looking at a portable solar solution for charging the laptop too, but decided to try the 12v option first — it’s a chunk less expensive. May still add solar to the trailer, love the solar on the boat, although we could use 450 watts and only have 225. Glad someone could use the info on refurbishing their Lighthouse windlass — ours is just like new again, so glad we did it! Cheers! J

  2. Keith Davie says:

    Jan, one thought on “over-sizing” an inverter: the larger an inverter’s potential output, the greater its need for cooling. I would expect a higher capacity inverter to have a more powerful internal fan, and chances are the fan will have only one speed – “on”. This larger fan will draw a suprising amount of power, even if your using only a small part of the inverter’s capacity.
    So, check to see what the unit’s idleing current draw is, but you may be better off with the “right sized” inverter, rather than sizing for the exceptional use if amps used is important.

    • Hi Keith! It’s always something, isn’t it! THANKS for the insight into oversizing the small inverter. I didn’t think of the fan consuming energy too — so not only are we losing the approx. 15% in the conversion, but we’re also losing whatever the fan is consuming. I think we’ll just get a little inverter – charging my camera batteries & such doesn’t take much and nothing we get will power the Keurig coffee pot – except the Honda 2000, but it’s so noisy early in the AM in a totally quiet anchorage or campsite – it ruins MY mood, let alone disturbing anyone else. 🙂 Thanks again! Cheers — J

  3. Hi,

    We use a Prosine passively cooled inverter for the small jobs.
    Inverters are most efficient around 2/3 capacity Thus, our main inverter is too large (3Kw) for our needs but, it came with the 3Kw we need for charging the batteries when the sun has failed us.

  4. Great post. I like the 12 volt charger you found. Here is a great article from the guy I consider my electric guru on why it’s better to charge from 12 volt instead of an inverter. http://www.pbase.com/mainecruising/ipad_charge_

    Fair winds,


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