I'm trying to invent viable hand-crank energy generator for charging phones and similar low-power appliances. I want to avoid gears altogether in the design, because they are hard to manufacture at home and because I don't want to lose any of the already small power generated by hand to friction between gears. With a single axis device, there is almost no friction or wear.

The concept looks like this:

enter image description here

This is what it would look tiled. The idea here is that you can tile it indefinitely, the only limit is your own strength (and patience when putting it together).

enter image description here

The magnets will be neodymium magnets. There's intentionally six of them but only five coils - this aims to reduce the "zero point" strength - the most stable point of attraction between coil cores and magnets.

The coils would have ferrite cores and each would have its own rectifier.

The magnets will be altered in polarity so that two opposing magnets will always be attracted to each other and therefore exert maximum possible field over the coil.


  • Is this a good design for low RPM (40-100 RMP)?
  • What would be the ideal number of turns if the target voltage is 5V, given the aforementioned RPM?
  • Are ferrite cores good idea? Or should I use iron or air cored coils instead?
  • \$\begingroup\$ Do you intentionally avoid employing gears? Most similar devices use a reduction gearing to turn the slow hand cranking action into a much faster rotation on the generator \$\endgroup\$ – anrieff Apr 14 '18 at 21:36
  • \$\begingroup\$ Yeah, I should have mentioned that. Gears mean power loss to friction and durability loss due to wear. Single axis device is pretty eternal compared to geared one. \$\endgroup\$ – Tomáš Zato - Reinstate Monica Apr 14 '18 at 21:39
  • 1
    \$\begingroup\$ A normal gear is incredibly efficient, and it would bring more than it takes, and also you can buy them off the shelf, no need to manufacture. Otherwise seems like trying to reinvent the wheel. In your design the % of rotation that a magnet is in front of a coil is like 50%, which will also limit a lot efficiency. As you iterate with your design you'll converge to a modern motor \$\endgroup\$ – Andrés Apr 14 '18 at 22:04
  • \$\begingroup\$ Hand crank generator to charge a phone battery-not bad, if you can do it - I mean the charging. A smallish battery has 2000mAh at 4V. It's about 29kJ energy. That's equivalent with lifting 100kg mass to 29,5 meter altitude or 60 times a 0,5m lift. Or only 10kg 600 times 0,5m, with a hand. Congratulations! BTW have you done any calculations how wide magnetic flux variation you can achieve in one coil? \$\endgroup\$ – user287001 Apr 14 '18 at 22:38
  • \$\begingroup\$ Looking at the above figures another way: 29 kJ if delivered in 1 hour would require 8 W continuous without friction, resistive and conversion losses. That's probably difficult to sustain by hand especially if the unit is hand-held. For reference a normal adult should be capable of sustaining 150 W when cycling. That works out close to 1 kWh over 8 hours. \$\endgroup\$ – Transistor Apr 14 '18 at 23:11

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