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I have a project from my subject which that project was to create a manual generator that can produce up to 9 volts of electricity. I've been searching some samples that is homemade manual generators, but I've found they are powered only by batteries, and using a dc motor..

Is there any other samples of manual generator which is not powered by batteries or with the help of dc motor or should I say manually operated? And it can produce electricity up to 9 volts? and also can you give me the materials to be used in creating the generator?

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  • \$\begingroup\$ You can make a generator out of a brushed DC motor that has a permanent magnet field. You just need to arrange to turn the shaft. The voltage you get out will be proportional to how fast you can turn the shaft and the construction of the motor itself. To get a high enough voltage you may need to provide a gearing between the hand crank and the shaft so the shaft turns many times faster than you turn the crank. \$\endgroup\$ – Michael Karas Jul 1 '16 at 4:12
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    \$\begingroup\$ I don't really get the "examples of homemade generators I've found are powered by batteries" sentence. How does it make sense? If you have to power the power generator, it somehow defeats the purpose, no? \$\endgroup\$ – dim lost faith in SE Jul 1 '16 at 8:00
  • \$\begingroup\$ @dim I think he means something like, generator: something which outputs a voltage. A battery in a box will do that. At least that's the only way for the sentence to make sense. :) \$\endgroup\$ – pipe Jul 1 '16 at 8:48
  • \$\begingroup\$ How do you want ti drive the generator? Hand powered or ....? \$\endgroup\$ – Russell McMahon Jul 2 '16 at 8:28
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Any generator may be driven by any mechanism - electric motor, gasoline or diesel engine, steam engine, water wheel, or hand crank.

The voltage produces by a generator will depend on its construction, and RPM.

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Any motor with permanent magnets inside will produce a voltage when the shaft is turned.

A brushed DC motor will produce DC. Stepper motors, and those nice powerful brushless multiphase BLDC motors produce AC, which would need rectifying.

The problem is that you have to turn the motor at its rated speed to get (almost) the rated voltage.

If you used a 12v brushed motor, then turning at its rated speed should give you at least 9v. Unfortunately small motors run quite fast, and it might be difficult mechanically to gear up from a manual handle to get high speed on a motor.

The solution with a brushed motor is to get one with a higher voltage. For instance a 48v motor would only have to be turned at 25% of its rated speed to give you something approaching 12v.

Both stepper and BLDC motors tend to have lower rated speeds than brushed motors. Either of these are ideal candidates for producing DC after a rectifier, as they are both multi-phase. Using a multi-phase rectifier will produce DC that doesn't drop to zero (like rectifying a single phase AC waveform would).

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