How to Power a Laptop in the Desert?
March 7, 2013 6:47 AM   Subscribe

My friend Paul Salopek is walking across Eastern Africa and needs to stay connected. Power from his solar panel passes through an inefficient AC inverter. He's not getting enough power to stay connected. Can you advise?

I'm an MIT gradstudent, and I'm asking MIT contacts as well as friends at One Laptop per Child, but the answer isn't turning out to be easy.

We're hoping that some capable traveler has already solved these issues. I wrote a post for Paul's site with a detailed overview of his equipment and needs, but here's the basic story:

Paul has a lot of equipment to power (image), including his satellite data terminal and his Macbook Air. His solar panels are going through an automotive power inverter, which is too inefficient to keep the laptop running. So far, people are suggesting:

- eliminate the inverter by getting a DC battery charger to charge all the batteries directly (this is just a theoretical idea so far)
- get a hand crank (maybe like this)
- get a solar panel with a battery (maybe like these)

What are your suggestions?
posted by honest knave to Computers & Internet (11 answers total) 6 users marked this as a favorite
[Please put the link in your profile if you'd like people to look at it.]
posted by jessamyn (staff) at 7:03 AM on March 7, 2013

I would try this kinetic energy power supply in place of solar. It creates energy while you walk, from your movements. I think a bottleneck on solar is that you basically need to stay put all day to really charge up. This would create power from your travels, while you travel. I don't know exactly how much it would create. I never had the chance to try it.

I switched from a netbook to a tablet to rough it. It is smaller, lighter weight, more tent friendly, has a longer battery life, and is generally less fragile than laptops or netbooks. You do have to learn new apps but apps for tablets are getting better all the time. It comes with a built in camera and video recorder. I would try to make a tablet work in place of both the computer and camera.
posted by Michele in California at 7:06 AM on March 7, 2013 [2 favorites]

Can you get a better estimate of the power needs? I think the best solution would be a bigger, better solar panel. I'll see if my friends in that business have specific knowledge, but knowing actual need will help. Storage batteries will make a big difference - doesn't Paul have any at present?

getting a DC battery charger
A DC to DC charger isn't a good solution because it will still have to do conversion and thus be lossy (the solar panel almost certainly gives a different voltage than the batteries need for charging.)
I like Michele's suggestion but I don't think the tech is up to it yet.
A hand crank would work, but someone would need to be cranking all the time power is required or storage batteries will be needed.

I've been following Paul's trip, enviously: What a cool thing to be able to do. Surely Nat Geographic knows about keeping devices powered in remote areas?
posted by anadem at 7:33 AM on March 7, 2013 [1 favorite]

Michele in California: the nPowerPeg looks very cool, and might be a nice think to try for some of the phones and cameras.

anadem: it seems that a lot of the solutions out there are designed for expeditions involving vehicles, or are designed for on-foot needs that require less power, like the nPowerPeg. That's why we're still looking.

jessamyn: Thanks for the tip! By profile, do you mean the top part of the question? Can I edit it, or is this just advice for the future?
posted by honest knave at 7:40 AM on March 7, 2013

By "put the link in your profile", Jessamyn means go to your profile page and click the "edit profile" link (at the top next to "honest knave's profile"). Then add the link in the Homepage URL or "Blurb about you" fields.
posted by EndsOfInvention at 7:56 AM on March 7, 2013 [1 favorite]

Have you seen this on charging a Macbook in the desert?

You absolutely do want to get rid of the DC to AC and back to DC conversion. This is simply not efficient and DC/DC voltage conversion is much more efficient.

It looks like Paul has a lot of different things to keep charged, so it will be a bit of work to get proper adapters and connectors for everything. There are solar/battery systems now that can output 5V via USB, which may be able to charge a number of those devices. Otherwise, it is a matter of arranging DC/DC converters with appropriate connections for everything. It is probably a good idea to have an outside battery system to use as a buffer (so Paul can arrange to have the solar panel charging the battery while moving). It would be best to then run the laptop directly from the outside battery connected to the solar panel, rather than charging the internal battery (more efficiency losses).

The hand crank option you link to only outputs 15-20W. The Macbook Air needs 45W to charge, so that isn't enough power. The solar panel makes more sense.

I wouldn't recommend getting a bunch of different charging options for different pieces. There is lots of sun in the desert, so use solar, and keep things as simple as possible. Step one is to upgrade to efficient DC/DC converters. Step two is to figure out how to use the sun all day. Step three is to upgrade the solar panel if that still isn't enough.

Do bear in mind that the power needs of this whole suite of devices can be fairly high if used frequently. The reason that there aren't good solutions for people on foot requiring this much power is that the equipment to generate and store power is heavy and bulky. There isn't some magic solution out there.
posted by ssg at 7:57 AM on March 7, 2013 [1 favorite]

To power the Mac: if the power source (battery + solar panel or whatever you end up with) has a standard 12V DC auto socket, then you could use the HyperJuice Magic Box kit, which includes a 12V DC to MacBook 16.5 or 18.5V converter. It's not at all obvious from the company's diagram on that web page, because the diagram doesn't actually show the 12V converter that's included with the kit. (So, ignore their diagram for the purposes of this discussion.) The converter looks like this. This should in principle be more efficient than using an AC inverter, because it's only a DC-to-DC boost converter. It's also lighter and smaller than an inverter.

As you probably already know, you cannot use the Apple MagSafe airline adapter directly with a 12V source, even though the Apple airline adapter has an auto plug, because the MacBooks need 16.5 or 18.5 volts. (I think it's 16.5 for MacBook Airs, but I'm not 100% sure.) The HyperJuice kit basically lets you use the MagSafe connector from either a MacBook power brick or the Apple MagSafe airline adapter, and splice it to produce a cable+adapter combo that can then go from a 12V auto socket to the MagSafe connector for the MacBook. This reduces your power supply problem to finding something that has a 12V auto socket.
posted by StrawberryPie at 8:11 AM on March 7, 2013 [1 favorite]

ssg: thanks for linking to the post, I hadn't seen it, and it looks very helpful! I also like the idea of having the laptop charged from an outside battery.

Your suggestion to find a way for the solar panel to be up throughout the day is a good one-- it may be compatible with some parts of Paul's walk.
posted by honest knave at 8:46 AM on March 7, 2013

I'll be teaching EE labs in Building 3 most of the day Friday but I'm free around lunchtime if you have any interest in kicking around options in person -- feel free to mefi-mail or track me down via my profile.
posted by range at 9:57 PM on March 7, 2013 [1 favorite]

Just to clarify, it is best to run the laptop from an external battery (which is itself connected to a solar panel as long as the sun is up), rather than charge it from an external battery (which would not be efficient due to charge/discharge/storage losses in the battery). I'm not sure how you disable charging of the battery in an Air though, since you can't remove it.
posted by ssg at 1:18 PM on March 8, 2013 [1 favorite]

In addition to these great responses, we have received a number of truly excellent answers from elsewhere on the web. I'm going to try to compile them over the next few days and will post them here as well before closing this thread.
posted by honest knave at 10:15 AM on March 17, 2013

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