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Sun Inspired: How To Build A Solar Backpack

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Weekend Edition Sunday, April 19, 2009 · Even before the economy tanked, interest was growing in the do-it-yourself movement.

The DIY ethic embraces the notion of recycling and repurposing objects, snatching things from the jaws of the landfill and making them useful again.

Here, a look at how to make something that anyone with an iPod could use: a solar-powered charging backpack.

Inspiration From An Dead Battery

Walking to the subway stop near my loft in Manhattan the other day, I was listening to my favorite podcast when all of a sudden the battery in my iPod conked out.

This was annoying, so I detoured to an electronics store in Brooklyn called Dijitalfix, which sells a knapsack equipped with a solar-charging system that would have kept my iPod playing.

When I got there, owner David Auerbach showed me the backpack, which has three solar panels and can charge iPods or cell phones. It's nice, but a bit pricey.

"This one is $200 and it doesn't sell well," he said. He said he's sold fewer than 10, even though he's had it in the store for two years.

I asked Auerbach if I could make one of these myself.

"You definitely could," he said. "You can make anything, you know."

He got that right. I've done quite a bit of do-it-yourself furniture making, much to the consternation of my wife. But when it comes to electricity and electronic circuits, I'm in over my head.

Tackling A Solar Backpack

So, to make a DIY version of the solar backpack, I went to see a couple of old friends who know how to wire and solder.

I headed over to Tekserve, a store in Manhattan that repairs Apple computers. Mike Edl and Dick Demenus, who work there, are the Click and Clack of DIY.

"We're very methodical," said Demenus. "We're going to engineer this, not just throw it together."

Demenus and Edl decided that for the sake of simplicity — and to keep costs down — a single solar panel would go on our backpack. It would be attached to a USB cable, which is how you connect iPods and many cell phones to computers.

"The first thing I did was to measure what an iPod typically requires to get charged," Demenus said. "So I measured the current. That gave me one parameter. And I know the voltage is 5 volts. So, now I'm looking for a solar cell that will meet those requirements."

Ordering The Parts

You can order this type of solar cell from Jameco, an electronics supplier popular with do-it-yourselfers.

One of my key objectives was to make sure that I didn't spend more than the $200 the solar backpack cost at the store.

I called Jameco and told the saleswoman which solar cell I needed. It's about the size of a 4-by-6 photo print.

I was in luck: It was in stock, priced at just over $26. This was the most expensive part of the project. For 35 cents, I also ordered a voltage regulator, which looks like a peppercorn with three short wires coming out of it.

I already had an old backpack so the only other part I needed was a capacitor, which cost less than a dollar.

Running The Wire

At this point Demenus and Edl needed to find a way to run the wire from the solar panel inside the backpack, where my iPod, or cell phone would be carried while charging. They poked a tiny hole in the backpack with an Exacto knife. It's a serious business, revealing the creative tension that has made these two do-it-yourselfers professional tinkerers.

Wire As Thin As Pasta

"The good thing about using this very thin wire is that you can poke a very small hole through your backpack and get this wire through," Demenus said. "The wire's like angel hair pasta."

Edl said: "It's more like linguini."

But Demenus defended his choice of words: "Definitely not! The wires together are more like linguini but each one is like angel hair."

"No, no," Edl countered. "Either spaghettini or spaghetti."

Demenus stood firm and said it looked just like the angel hair pasta he had bought yesterday.

Once the wire was inside the backpack, it was soldered onto a capacitor and a cable with a female USB plug on the end that will be connected to my iPod.

Demenus encased the solar cell in plastic laminate and surrounded the perimeter with duct tape. He was going to sew through the tape to attach it to the backpack, but that proved to be an arduous task.

Edl suggested gluing it to the backpack.

My ears perked up when he made this suggestion because I seize every opportunity to use Gorilla Glue. I asked Demenus if some form of super glue would be right for the job.

No way, he said.

It turns out that super glue hardens to the consistency of glass and would be inappropriate for the soft backpack. Demenus considered using rivets or bolts, but eventually decided to simply staple the solar panel to the backpack.

A Huge Savings

The total cost of the solar backpack was about $40. So, in this case we saved money. But Demenus pointed out that do-it-yourself projects also provide something that money can't buy.

"When you do something yourself, there's a joy of accomplishment," he said. "And the little things you learn along the way — the little challenges you have — that's building a knowledge base that you can use for other things."

A case in point is the need to solder for this project.

"That's a skill that, if you master it, you've got it for the rest of your life," he said. "And solving these little mechanical problems makes you think about the properties of materials. It gives you confidence in the future. If something breaks — 'Hey! Maybe I can fix it.'"

During my future forays around Manhattan, I'll be charging my iPod off the grid — at least when the sun is shining.

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