Solar power is big these days, from power plants to rooftop arrays! This guide shows how to build your very own solar charger for small electronics. This charger will charge most small USB devices such as cell phones, mp3 players, iPods, and iPhones. These directions are designed to use parts from our Solar USB Charger 2.0 Kit though you can also find many of these parts elsewhere online. We have also included a circuit diagram and files for the laser cut enclosure (Step 1).
This project was designed for beginner Makers and students. It requires a base knowledge of soldering. While you can charge small gadgets, this project is not appropriate for camping or to be relied on for survival situations.
Time: 30 - 60 minutes
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Step 1: What You Need
1x 1N914 Diode
18 inches Stranded Wire
3 inches Shrink Tubing
Wooden Enclosure Parts
1/8th Inch Plywood
16 x 6-32 Screws
16 x 6-32 Hex Nuts
Double Sided Foam Tape
Hot Glue Gun
Access to a Laser Cutter
Sourcing Your Own Parts
This section will be most useful for those sourcing their own parts, if you are building from a kit, feel free to skip ahead.
USB Charging Circuit
USB charging requires 5V at around 500mA of power to charge most gadgets. In order to meet these criteria in a small package we use a USB Charging Circuit, which boosts low voltage (2V) DC up to 5V DC. Nothing comes free though; we trade our increased volts for fewer amps. To avoid this tradeoff, we could use larger solar panels and larger batteries, but this would result in a larger, heavier, and more expensive charger. Take a look at our Lithium Heavy Duty Solar USB Charger 2.0 if you want something with some extra power!
If you're using an older Apple product, make sure your USB Charging Circuit is compatible. Typically a USB gadget requires just power from a USB port to charge. Most iPhone models, however, require a tweak to USB to work. iPhones will check the USB data ports in order to identify what kind of device it's plugged into and change charging speeds if it thinks the port can support it. Unfortunately if it doesn't see anything on the data tabs it will refuse to charge. This is a problem that plagues many generic USB chargers, especially older ones.
If you don't have an iPhone or iPod, then any old USB Charging Circuit will work. If you do have an iPhone or iPod you may wish to grab one of these charging circuits, as they're the only ones we have found that seem to work.
Our USB Charging Circuit needs a minimum of 2V to operate, so we need to choose power sources with this in mind.
We always advise the use of power storage when doing a solar project. Solar is inconsistent due to the inconsistent nature of the sun. Using batteries helps stabilize the flow of power, and also lets us hold onto that energy for later use.
In this project we use three rechargeable AA batteries. Rechargeable batteries put out 1.2V of power and using three in series gives us 3.6V. Using two batteries will cause our voltage to drop below 2V too quickly, and our USB Charging Circuit won’t be able to operate. Four batteries would require a much larger solar cell to charge.
Batteries require a minimum voltage in order to charge, but raising the voltage will not cause the batteries to charge faster. The general rule is to provide 1.5 times as much voltage as your battery needs (for us 3.6V x 1.5V = 5.4V), but with solar we want some wiggle room. We want our solar panel to meet the minimum voltage, even on days with a few clouds, so a 6V panel does well.
When charging AAs using a wall adaptor, we're able to charge them at high speed due to smart chips that constantly monitor the battery. Since our circuit is "dumb," with nothing to monitor the batteries, we trickle charge the batteries using the 10% rule. AAs can be safely charged as long as they don't have more than 10% of their capacity thrown at them at any one time. This means our 2,000mAh batteries should only get 200mA of current.
Our solar cell is rated for only 80mA, so we're completely safe! Different panels and batteries vary, so make sure yours work well together. One good aspect of the trickle charge method is that it will never over-charge the batteries. Once they're full they just stay topped off.
Above is a circuit diagram for this project. It's designed so that the solar cell is always charging the batteries and the toggle switch turns the USB circuit on/off. A diode has been put in place to prevent power from flowing the wrong direction into the solar cell. This is a very common design for solar chargers.
Our kit comes with a wooden enclosure made from 1/8-inch laser cut Baltic Birch plywood, with holes cut for wires, switches, and ports. Wood works well because it is non-conductive and easy to paint or decorate. We have included the files here for anyone who has access to a laser cutter.
If this isn't an option for you there are more simple ways of making an enclosure. Inexpensive and easy to find, plastic food containers or bins work well. If possible find one with a rubber o-ring, which helps keep moisture out. These makeshift enclosures are also are easy to modify with a box cutter or exacto knife, just watch your fingers!
It s also possible to find "Project Boxes" at many online stores. These also work quite well for enclosures, but tend to be more expensive. However, we advise against metal enclosures. Altoids tins and metal project boxes may look nice, but they are difficult to modify and can easily short out projects if left uninsulated.
Step 2: Solder the Solar Cell
- Cut three six inch lengths of wire.
- Using a wire stripper, expose about ¼ inch of wire on each end of all three wires. If you have our kit, this may already be done. You can also strip the battery pack wires at this time.
- Solder one wire to the positive (+) tab on the solar cell and another wire to the negative (-) tab on the solar cell. You should have two wires attached with two loose ends when you are done.
- If you are using a laser cut case, apply foam tape to the bottom of the solar cell. Leave the protective film on the tape. We won't secure it until the end. Now thread the wires through the holes in the lid of the case.
Step 3: Attach the Battery and Diode
Please read all steps before continuing.
- Strip the ends of the battery pack. It may be necessary to snip off their exposed ends first.
- Take the negative (black) wire from the battery pack and twist it together with the negative wire coming off the solar cell. Do not solder this yet.
- Grab the diode. One side of the diode has a black line (negative) and the other side does not (positive). You'll want to take the positive (+) wire coming off your solar cell and twist it together with the positive side of your diode. Push the wrapped wire all the way up next to the head of the diode. Solder it in place and snip off the extra wire from that side only.
- Wrap the positive (red) wire from battery pack and wrap it around the negative side of the diode. Push it up into place and solder. DO NOT cut that end of the diode.
Optional: It is helpful to use shrink tubing or electrical tape on this setup for protection. Align all the wires together, then slip the shrink tubing up past the diode. At the end of the project we'll use a heat source to shrink it into place.
Step 4: Connect the Toggle Switch
- Grab the twisted together negative (-) wires from the battery pack/ solar cell. Solder this to the middle pin on your toggle switch.
- Take the last 6 inch piece of wire and solder it to either one of the remaining outside pins. It doesn't matter which one.
Tip: If you can't thread the wire through the little holes on the Toggle Pins don't worry. Using a Helping Hand you can easily solder to the side of the pins.
Keep in mind that the toggle switch is made of metal and plastic. It is possible to melt it if you hold your soldering iron in place too long.
Step 5: Connect the USB Charging Circuit
The circuit in our kit has metal tabs coming off of the board which you will solder wires on to. If you found your own USB Charging Circuit it may have through hole connectors.
- On the under side of the board locate the positive (+) and negative (-) symbols.
- Wrap the left over side of the diode around the positive (+) tab from the circuit board. Solder into place.
- Wrap the wire coming off the toggle switch around the negative (-) tab coming off the circuit board. Solder into place.
- When you finish soldering, clean up by clipping off any bits of wire that stick out.
- Our USB Circuit has a small three-position switch on the side. Move the switch so that its positioned back towards the soldering tabs. (If you have batteries in place the Red LED will be on.)
The white LED is not used in this project. You can cut it off, or position it straight up and out of the way.
Step 6: Testing & Trouble Shooting
At this point your project should work. Grab a small USB gadget and plug it in. We like to test ours with a USB LED Light, but a phone or MP3 player will work as well.
If everything works, use a lighter, hair dryer, or heat gun to close up your shrink tubing over the diode.
If it isn't working try these steps.
- Are your batteries dead? Try some different AAs, even regular ones, to see if that does the trick.
- Is your toggle switch in the right position? Toggle back and forth just to be sure.
- Is it your gadget? Some large phones and most all tablets won't charge off either circuit. Grab a small mp3 player or different phone to try it out. I use a simple USB LED light to test mine.
- Does your iPhone to say "Charging Accessory Not Supported"? This probably means your AAs are low or the switch on your Apple Circuit Board is in the wrong spot.
If none of these fixes work for you, check your wiring to make sure you have good solder connections, and that everything is connected correctly.
Step 7: Putting the Case Together
The wood enclosure requires a screwdriver to assemble. While the box is strong you should still take care. Over-tightening the screws will break the joints.
- Make sure you have 16 nuts and screws. It helps to start a nut onto each screw before continuing.
- Start with the bottom piece and attach the sides to it. The screws will require a small amount of pressure to get into place. DO NOT screw them in all the way. Tighten them just enough to hold together; we'll tighten them up at the end.
- Once the bottom and four sides are in place you'll want to attach the electronics. Screw the toggle switch into place on the side of the enclosure. Make sure it’s oriented the right way!
- Put a generous amount of foam tape on the battery pack, and a small piece on the USB Charging Circuit. When putting the battery pack in, pick up the box and apply pressure from both sides. Press firmly until it holds. The USB Circuit may need some extra help to keep from moving around, hot glue works well to keep it stuck down.
- Now attach the top, still loosely tightening screws. Remove the foam tape from the solar cell and press it into place, hopefully centered.
- Lastly, tighten everything up. Please keep in mind that you can crush the little screw tabs. Take care when screwing into place.
If for some reason you destroy your case, or part of your case, just use some wood glue to hold it together.
Step 8: The End
Your Solar USB Charger is now complete!
Once again, please keep in mind that this charger will not charge larger gadgets such a big phones and tablets. It's also not suitable for camping or emergencies due to the fact that it takes several days to charge up.
If you're looking for a solar solution for camping check out our more powerful Lithium Heavy Duty Solar USB Charger 2.0 instructable. It features a high amperage USB output, a lithium ion battery, and a 5W Solar Cell.
If you're looking for something premade check out the Solar Gear over at BrownDogGadgets.com.
I hope you learned a thing or two about solar power from this guide. It's easy to scale up this project to do bigger and better things.
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