Solar surge: iPhone fully loaded

Rob Scott is based in Seattle and recently made a design that caught our eye here at Ponoko: a solar USB charger for an iPhone. We completely agree with Rob when he says: “It actually turned out prettier that I thought it would – the crystalline structure of the solar cells is nice to see in the sun.”

Why did you choose to use to ‘make with’ Ponoko?

I saw the contest announcement on Sparkfun‘s website, and that lead me to Ponoko. I’d previously used TAP Plastics, but wanted to see what other companies offered. After looking at Ponoko, I thought that the capabilities offered by Ponko could make my design more robust.

What type of product(s) did you make with Ponoko, and what was it for?

A solar USB charger, for use with my son’s iPhone and other devices. He, (and my wife),  joined me for Cascade Bike Club’s Ride Around Washington, which is a week-long bike trip, and it was important for him to have his phone charged so that he could stay in contact with us. I’d built a similar device for myself last year, which is what my wife and I used to keep our phones charged.

The solar array generates approximately 13 volts at 220 milliamps, for a total of 2.86 watts. This is stepped down by a Dimension Engineering switching regulator to 5 volts for use by the USB device, and should deliver about 500 milliamps to the USB device.  A resistor network, based on the schematic from Lady Ada’s Minty Boost, is connected to the USB data +/- pins to tell the USB device that a charger is sending current. (At least for iPhones running iOS earlier than version 4).

How would you describe your creative process?

I used the Inkscape tutorial and templates from Ponoko’s website, and threw away my first three tries. Trying to be too clever really doesn’t pay off on your first project!  I spent way too much time trying to optimize the use of the non-project part of the panel for other uses.

What material/s do you use/ have you used and why?

I used acrylic, mostly because I’ve used it before and am familiar with it.  It’s easy to drill and glue.

Have you been surprised by anything in the Ponoko process: positives/negatives?

One of my attempts to be clever backfired. The height of the regulator used to step down the solar panel’s output was too tall to be accommodated by the width of the acrylic sheet, so I decided to use heavy engraving to route out a cavity in the top and bottom panels. Unfortunately, I forgot to change the cavity outline from cut to engrave color, so imagine my surprise when I opened the Ponoko box and two neatly engraved rectangles dropped out from the panels!  Fortunately, I had a couple of pieces of scrap acrylic that I was able to use to fix the problem, but it did compromise the water resistance of the design.

I was very pleased that my order was able to be delivered just in time for the project to be completed. It arrived at about 4:00 pm, and I was able to finish the project and still pack before the trip started the next day. I was pleased the first time my son plugged in his phone and it actually began charging! (Though a friend’s iPhone, who’d upgraded to iOS 4, complained that it was an “unsupported” charger, and refused to charge).

The overall accuracy of the cutting process lead to a well made project when it was completed.

Also impressive was the attention paid by Ponoko to my design. Apparently Inkscape can introduce a 25% scaling factor, which was caught and fixed by Ponoko.

I was also unclear about the orange safety zone in the template. I attempted to use what I thought was the edge of the panel to reduce cutting, but the safety zone edge is actually not the edge of the panel.

Do you have any tips for other users?

Work in millimeters, and always snap lines to grids. I like a 1 x 1 mm grid, personally.

Check and double check measurements and calculations. I almost made an enclosure that was too small!

Use the tutorials and blog entries. Finding out how to eliminate overlapping lines in Inkscape was much easier than trying to use constructive geometry to accomplish the same goal.

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Rob Scott

BTW, Lady Ada’s website has been updated to show how to charge iOS 4 devices:

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