Hand Crank Generator

The Playing with the Sun Hand Crank Generator, revision 3.

The hand crank generator makes power when you crank it vigorously. Just plug it into a motor, hold the crank body with your left hand and crank clockwise with your right, and the motor on the output wire will turn. You can also use it anywhere else that a power source is needed -- like to charge up a powerpack.

Sourcing Parts

Everything you need to build a crank generator.

The Hand Crank Generator is composed of two inexpensive and commonly available components wired together: A generator (a driven DC gear motor) and a 5V power converter module. The generator makes the power, but it does it wildly in a range between 12 - 24 Volts depending on how hard its cranked. The power converter takes that dirty power and conditions it so it always comes out at a relatively clean 5 Volts. You'll find links below, but don't think you need these exact parts: anything electrically equivalent will work.

Hand crank dynamo

A robust hand crank that spits out power in the roughly 12 Volt / 20 Watt range so the step down converter can condition and reduce it to 5V. Something like the link below. These appear to be widely available at low cost on Ebay and many other vendors. Make sure to buy one with a crank, as there doesn't appear to be an easy way to make and attach one short of doing difficult metalwork.

Vendors: - Aliexpress - EBay Buying a hand crank dynamo online.

DC-DC step down 5v power converter

Something that takes 9-35 Volts of DC input current (with a diode to prevent reverse current flow) and spits out 5 Volts DC relatively regulated. It's nice if it has an indicator light.

Vendors: Aliexpress Buying a step-down converter online.


  • XT30 female connector (which looks like a "plug" and not a "socket") with wires soldered on to make the output cable, or an XT30 patch cable with the male (which looks like a socket) end cut off.
  • 2 x 10 cm pieces of stranded wire (14-22 gauge will do), ideally in red and black.
  • heat-shrink tubing for generator terminals
  • 1.5 inch PVC or silicon tubing cut to 11 cm length that just fits around the round motor body on the back of the crank generator, and optional hose clamp if it doesn't already fit tightly enough.
  • 8 hole length of plumber's strap, to crimp end of tube.
  • small bolt that fits into the holes in the plumber's strap (approx. 4mm), nut, and a lock washer. These will keep the tube crimped at one end.


Tools you will need:

  • Soldering iron
  • wire strippers
  • small screwdriver (for power converter terminals)
  • heat gun (for heat shrink tubing on generator terminals)
  • voltmeter (for testing output of generator)

Assembly Instructions:

  1. Attach the crank to the body of the generator gear motor. If it didn't come with a bolt that fits the driveshaft hole tightly, a large cotter pin makes a good substitute. Bolts that are too skinny tend to get sheared off.
  2. Cut one each of the black and red wires at about 10 cm length. Strip the insulation off of the ends, as well as off of the ends of your XT30 output cable.
  3. Check the polarity of the output terminals on the generator with a volt meter and mark them. You want to know which is positive when the crank body is held in the left hand and the crank is cranked clockwise with the right. (Polarity of the output depends on crank rotation direction). Normally the generator terminal with a red paint spot next to it is the negative (black) terminal when cranked this way, but check to make sure.
  4. Solder your wire leads onto terminals of hand crank generator, with red on the positive and black on the negative. Heat shrink the connection to the terminals to make sure that they don't short against the electronics you will embed in the pipe right next to them. Back of motor with wires soldered to terminals and heatshrink applied.

  5. Join the black wire from the crank generator with the black wire of the output wire with the XT30 plug on the end. You might need to cut off some excess strands of wire to make them both fit together and be small enough that they can fit into the middle "common" or "ground" screw terminal of the power converter. The two black wires placed in the ground terminal of the power converter.

  6. On the power converter, insert positive lead from crank into the input terminal, two joined negative wires into single middle ground terminal, and the wire corresponding to the + of the output wire w/ XT30 into the output side. The input / output terminals should be marked on the silkscreen of the converter board.Power converter terminals wired and oriented towards the back.

  7. Position things so that the terminal block of the converter (and the output wire) is facing away from the generator. Slide the 1.5 inch pipe over the output wire and converter onto the generator motor, with the voltage converter screw terminal block facing outward. Wiggle it on until the voltage converter terminal block is about 2cm from the end of the pipe.

  8. Use plumber's strap (8 hole length folded in half) to crimp the end of the large tube on both sides, and drill through one of the middle holes so you can put the bolt through between or close to the XT30 output wires. Tighten the bolt so that it compresses the tube end tightly around the XT30 output wires. This will provide strain relief in case someone pulls the output wire, so it doesn't pull out of the terminals. Completed crank generator.

  9. Test it by holding it with your left hand and crank it clockwise with your right. Now draw a big arrow with a sharpie on the pipe so that users can see which way to crank the crank.

Crank away!

Desired improvements

For future revisions, here are a some desired improvements.

  1. The ideal handcrank generator will give the desired 5V 20 Watt output no matter which way the crank is turned. So some sort of basic rectifier circuit to do that without adding too much complexity to the build, or possibly a different power conditioner that takes any polarity of input, would improve things. We don't see a pedagogical value to knowing which way to turn the crank, so this would simplify things and lower the floor.
  2. It would be nice if the time to crank up a 5F powerpack was a bit shorter. I'm not sure why this one takes longer than the rev. 1 blue box cranks. Possibly they have better power conditioning circuitry.
  3. The rev. 1 cranks also gave a kind of clearer feedback when the powerpack was full, in that the crank would suddenly get easy to turn. You can sometimes feel it in this one, but it's not as clear for some reason. That intuitive felt feedback is nice though.

Past revisions

Rev. 2a and 2b. A Little too Cheap

2a. Was a clear handheld one with a lightbulb that lit when you spun it. It strips the gears when you crank too fast, feels flimsy, and takes too long to charge a powerpack. And we had to add a diode in to keep the powerpack from back driving it like a motor. It was nice that it was clear though. You can kind of see it in action on this link to a Toot on Amos' Fediverse.

2b. Is a cheap little USB one. About 1/2 of 5 I ordered didn't work, they charge very slowly and broke very quickly. Junk, unfortunately. Failed, defective, poorly made power generator.

Rev. 1. The Blue Box

  • Charges quickly and can be set to 5V and many other voltages, which works well but adds risk and complexity. If the kids set it to any higher voltage, it will blow up the component it is plugged into. We put duct tape over the controls and made an XT30 charge wire, and this worked fairly well. But it's much more expensive than later revisions, and also larger, heavier, and seems less robust.
  • Note of risk: Using the USB output doesn't confine it to 5 volts, which means if you plug anything USB into it and set the voltage higher than 5, it will probably blow that up too. :(

The Blue Box hand crank generator