The power is out, and you need to order a pizza, and your phone is dead! Thank goodness you already built a hand crank phone charger as part of the summer 2024 Clean Energy Deep Dive. This apparatus turns a cheap plastic gear motor and a simple regulator circuit into a slow but effective phone charging appliance, and even includes measurement points so you can calculate how much power your cranking efforts produce!

Safety

The electronics part of this build involves a bit of thru-hole soldering with an iron. We don’t have certifications in place as of yet for this process, so students should be closely supervised throughout. There are two main concerns here:

• high temperatures: soldering irons run at 750 F or higher, which can cause instant burns and may contribute to starting fires in the right conditions. When not in use for a brief period, they must be returned to their stands; when not in use for an extended period, they must be shut off. While soldering, students must be seated and paying close attention to the task at hand, and must wear safety glasses in case of splatter. Soldering should only be performed on a suitable surface with sufficient work-holding, such as a Stick Vise on an anti-static mat.
• fumes: while not sufficiently hazardous to necessitate the use of extensive PPE (such as a respirator), the fumes given off by vaporizing flux can irritate lungs and cause health issues with long-term exposure. Students must always use a fume extractor which is placed close enough to the work area to actively extract fumes. Note that activated carbon filters mostly knock out heavy particles and dilute remaining fumes into room air, so the back end of the extractor should be aimed away from students.

Beyond these two concerns, students should also be careful trimming leads as the ends can fly off; keep the safety glasses on and use hand tools with care. At this point all of the leaded solder should be purged from the work area, but instructors should double-check before soldering starts. Wash hands when finished.

Build It!

Classroom assembly involves soldering on a few thru-hole parts and fitting together the generator apparatus. This should take pairs of students a half hour, give or take.

Tools and Materials

• Tools, which can be shared between groups
• soldering iron
• tweezers
• flux
• lead-free solder
• safety glasses
• soldering surface
• work-holding device (such as a stick vise)
• multimeters and probes (optional, for quantifying device performance)
• wire flush cutters
• small flat-head screwdriver (for terminal blocks and mounting PCB)
• Materials, needed for each hand crank phone charger
• partially assembled regulator board
• thru-hole electronic parts
• USB receptacle
• terminal block
• header
• shorting jumper
• 6-32 x 5/16” pan head slotted machine screw
• 3” C-clamp
• laser cut wood parts
• base piece, 1/4” plywood, with 6-32 T-nut preinstalled on the back
• small gear, 1/8” plywood
• large gear, 1/8” plywood, glued to shaft and handle dowels
• bushing, 1/8” plywood
• handle pivot sleeve
• yellow right-angle gear motor from amazon
• small zip-tie
• an inch or so of 1/8” aluminum craft wire
• USB-C or Lightning cable for phone

Construction

Electronics - We already did this for you :)

1. Insert the terminal block into the circuit board with the wire openings facing away from the regulator. Use a bit of blue masking tape to temporarily hold it in place.
2. Flip the printed circuit board upside-down and secure it in the stick vise.
3. Add a drop of flux to each pin. A tiny bit is sufficient.
4. Tin, wipe clean, and re-tin the soldering iron tip.
5. Solder the exposed pins one at a time by holding the iron to the board so it touches both the pin and the pad, and then feeding solder into the joint until the fillet is shiny and slightly concave. Remove the iron after feeding in the solder.
6. Carefully snip the leads flush using flush cutters.
7. Remove the blue tape.
8. Repeat for the USB receptacle, using caution as the metal housing will get hot during soldering. Start with the two outer structural pads and then solder the four pins.
9. Carefully trim the header using flush cutters into three two-pin units. Repeat the soldering process for the three measurement headers.
10. Install the shorting jumper on the current measurement header marked Iout. Note! Do not short out the two voltage measurement headers (marked Vin and Vout)! Those two headers should be left free.
11. Ask an instructor to inspect your work before moving on. Good job!

Apparatus (Students start here 🙂)

1. Line the circuit board up with the marked outline. The thru-hole soldered connections should fit into the holes in the base board.
2. Screw the 6-32 x 5/16” pan head slotted machine screw into the mounting hole with the pre-installed T-nut on the back and tighten to secure the board.

3. Position the motor under the board with one of the shafts sticking up through the hole, and the wires on the underside.
4. Secure the motor with a small zip tie through the two mounting holes and trim the zip tie flush. Make sure to pull it good and tight!

5. Press the small gear onto the motor shaft. It should be a tight friction fit. Don’t bottom the gear out against the back plate; there should be a slight gap so it can rotate freely.

6. Drop the large gear into its mounting hole and rotate until it meshes with the small gear. Push the bushing onto the rear shaft, leaving a slight gap so the gear can rotate freely.
7. Secure the bushing by inserting the aluminum craft wire and bending the ends into an S-shape. Be careful, the craft wire may be a bit sharp from cutting.

8. Connect the red and black wires from the motor to the terminal block on the circuit board. Red should go to “+”, black should go to “-”. To do this, insert the metal pin into the open gate on the side of the terminal block and tighten the screw until it grips the pin. Test the connection by gently pulling the wire; if it comes free, loosen the screw and try again, tightening a bit more this time.

9. Clamp the apparatus to the side of a table using a C-clamp as shown. To keep the assembly from rotating, gently push the side of the motor against the edge of the table top. Tighten the clamp securely.
10. Drop a handle pivot sleeve onto the handle; this will make long generator sessions immensely more comfortable!
11. Give the generator a test run! Turn the handle clockwise; the green LED on the circuit board should light up. Note that turning the handle counter-clockwise won’t light the LED, but won’t damage the circuit either.

Use

Charging Phones

Plug a USB charging cable into the onboard receptacle, and then into a phone. Turn the crank. The phone should start (slowly) charging! Huzzah! How long does it take to gain one percentage point? Can you feel the phone switch charging modes?

Measurements

The PCB has three onboard headers: one for measuring the input voltage directly from the motor/generator, one for measuring the output voltage at the USB receptacle, and one for measuring the current consumed by the thing plugged into the USB receptacle.

1. Measure input voltage

Connect a multimeter to a cable that ends in a pair of header sockets, noting which connects to the positive terminal. Slide the positive header socket onto the Vin pin marked “+”, and the negative header socket onto the Vin pin marked “-”. Set the multimeter to 20 V DC and make sure the multimeter positive lead is connected to the voltage measurement terminal. Turn the crank clockwise: you should see up to ~9 V DC depending on RPM, and the LED should turn on at ~3 V DC. What happens to the reading if you turn the crank counter-clockwise?

2. Measure output voltage

Follow the instructions for measuring input voltage, but connect the multimeter to the Vout header instead. What voltage do you see when you turn the crank clockwise and the LED lights up? What about counter-clockwise?

3. Measure current

Remove the shorting jumper from the Iout header and connect the measurement leads as described above. Make sure the multimeter positive lead is connected to the current measurement (mA) terminal. Set the multimeter to 200 mA DC and connect a load like a phone to the USB receptacle. Turn the crank clockwise to charge the phone: what happens to the current reading? Does it change when you turn the crank faster? What about when the phone changes charging modes, or when you disconnect the phone?

4. Calculate output power

Connect the output voltage and current measurements simultaneously, as described above. Attach a phone to the USB receptacle and turn the crank clockwise. Write down the voltage and current readings, then multiply them by each other. Since the current is displayed in milliamps, multiply the result by 1000 to see output power in watts (since P = I * V). How many watts are you producing while the phone is charging? What about when the phone changes modes?

5. Estimate phone battery capacity

Connect the meters as described for calculating output power. Turn the crank steadily until the phone charge percentage increases by 1%, then start a stopwatch. Write down the output voltage and current when they are at steady-state. Stop the timer and crank when the phone charge increases by another 1%. Multiply the calculated power in watts by the number of hours (minutes / 60): this is how much energy you sent to the battery in watt-hours. Since this accounts for 1% of the phone battery capacity, multiply the energy value by 100 to estimate the phone battery capacity in watt-hours. How does this compare with your phone’s published specification? Why would it be different? How could you improve the estimate?