Teaching a DIY Solar Charger Project, remotely
Along with my math preps, I also taught a venture-project class this quarter. I had planned a very hands-on project and purchased a LOT of supplies for the students to make solar lamps, solar chargers, and solar cars. When we shifted to remote learning, I decided to try and make this project run, if a little scaled down. I split the kids up into groups, and a group of 6 middle-schoolers got assigned to be on the Solar Charger team. I have never built this project with kids before and have spent the past few years trying to get the electrical design nailed down. But I really wanted to do this project. All of our ventures focus on community needs, and we’ve worked with the FoCo Cafe and Homeward Alliance over the years to bring donations to the homeless. They’ve mentioned before how awesome solar chargers would be. At the shelters, people often crowd around outlets so they can charge phones. For people experiencing homelessness, if they have a phone, it’s a crucial communication tool- a connection to the world. But if you don’t have a permanent place to live, having access to electricity can be a challenge.
Over the past year, I settled on a design for a solar charger using 18650 batteries (these can sometimes be found in laptops and vape pens, but I bought them off eBay) and a TP4056 charging circuit. It’s not a perfect solar charger. If you plug the circuit into the wall using the micro-usb port, the batteries hold enough charge to charge your phone more than once. Although the batteries say they’re 3.7v, they can be charged up to 4.2v with a wall charger. However, if you charge the batteries using the solar panels, it seems the current never quite gets high enough to charge the batteries that last little amount. I can get up to 3.95 or 4.05 volts, which is enough to charge a phone about 2/3 of the way. But after experimenting with a bunch of different charging solutions I determined that for a reasonable price, this is as good as we can do for now.
I worked out the electronics with the help of student testers over about 3 school years, but I never had a mechanical case I liked. In the past, I used upcycled food containers, and they were flimsy.
When I met with students this year in our “charger team” meetings, our first task was to design a sturdy case for the solar charger. We discovered you can collaborate in Tinkercad and it turned out to be a great solution! We all logged onto the same Zoom meeting, and then I created a Tinkercad project and clicked the Collaborate button to share it with everyone.
It’s amazing. You can all edit the same project at the same time. And with this group of kids, it turned out ok. We downloaded a couple of charging-port holders from Thingiverse and embedded them into a box, with some walls to hold the battery pack in place. The kids worked with rulers and measured battery packs and solar panels, and we updated the measurements in the file. Our first design had the voltage-in (micro USB) and voltage-out (USB-A) ports on opposite sides, with a flat lid.
This was iteration 1. The box took a really long time to print. I printed one at home, and showed them how it turned out at our next meeting. I asked the kids if we could make it a little smaller to save filament. So we moved both charging ports to the same side, and made the box exactly the same size as two solar panels side by side – and only slightly taller than the battery pack. I printed multiple copies of this version and then had a meetup with the kids to give them cases and electronics to try and build a solar charger. I parked at the school, and the kids pulled up with their parents where I handed off a bag of parts, soldering irons, and other tools.
The students worked with iteration 2, and each one in the team built a charger. I shared video instructions for creating the charger, and we had a zoom session that was a “learn-to-solder” lesson. The next time we met on zoom, they reported back that overall they liked the design, but the slots for the charging circuits needed a little re-designing. They wanted the slots overall wider, with a lip to hold the circuits in place. We made changes together in Tinkercad and then I printed iteration 3 for each student and did another round of supply-swapping. They built another round of chargers and tested them.
I started printing iteration 3 as fast as I could, and I distributed these to the kids so they could make this year’s final version of the solar chargers. I am really pleased with how they’re turning out. I’ve gotten a few back, and they’re sturdy and high quality and work pretty well!
I even had one student that designed his own case that had an angled top, better for collecting sunlight in the winter. He laser-cut it at home, and it’s awesome. I did not take a picture of it yet, but I’ll do that soon. Maybe that’ll be iteration 4 or a separate branch of solar charger cases.
This is an amazing, fulfilling project. We are going to be donating the solar chargers to Homeward Alliance right after Memorial Day, so they can be distributed to people experiencing homelessness who need them. We expect we will have over 20 chargers to donate. We will also put a link to a survey on the chargers so our “clients” can give us feedback on how well they held up. The students really loved feeling like they were making a difference and experiencing what engineering really is.
If you’re interested in making these, I have posted a YouTube video with assembly instructions, and I’ll also share the parts lists and .stl files here.