How does a hand crank generate electiricity?

Question

It seems like flashlights that are powered by cranks take some effort to turn and don't generate enough power to illuminate anything but lame LED lights. Is there a formula to determine the tension vs. power generation in a crank. Or is electrical output determined by revolutions... So tension is created with a big gear spinning a small gear?

I'd like to know how the power becomes electricity. There is power & force everywhere, but turning a pulley doesn't spontaneously create electricity... What reaction takes place that generates an arch or charge of electricity.

Answer 1

The typical generator works because a conductor has been passed through a magnetic field.
The generator is made up of a lot of conductive wires being passed through the magnetic field.
The more power being generated, the harder it is to turn the generator. Regardless of the efficiency of the drive mechanism you can't generate power without inputing the work.
That power out-put form the generator IS NOT FREE.It takes energy and since it is not 100% efficient, the power in is greater than the power out..
Easy proof.
If you have a portable auxiliary generator handy, find a large load to apply to it. (Possibly a high powered drill).
Have the engine powered generator operating at a constant speed, then start the electric motor of the drill.
Notice how the generator responds.
The engine driving the generator suddenly has to work very hard to carry the additional load and you are sucking more gasoline into the engine to keep the generator turning.
If that weren't true, the power companies wouldn't have to charge you more for the extra power you use, and they wouldn't need to build more generating capacity.

Answer 2

I agree with Phillip H on the no such way to create "free energy" bit.
The best way to describe a dynamo is that it's pretty much like an electric motor. The only difference is that instead of power flowing into the motor and turning the crank, you turn the crank and it's action on the motor creates power. In the example you mention, the crank tightens up a spring (like that in a wind-up clock). Ratchets and gears prevent the spring releasing suddenly, so as the spring slowly unwinds it turns an axle that operates a small dynamo, until all the torsion in the spring is used.
Using a gearing system, theoretically it is possible to reduce the amount of time needed to "wind up". Like shifting gears on your bike can make it easier to pedal uphill but means you have to pedal faster. However, this uses space, creates weight, and friction.

Answer 3

Many variables. Those radios you refer to use gear multiplication to spin what is nothing more than a small motor similar to what Mabuchi markets in hobby shops. It is not that much power. Many of those radios use an efficient circuit so they do not draw large amounts of current in operation, and the batteries you are usually charging are a bundle of three nicads that are half the size of an "AAA" cell. If you swap those for some regular AAA cells, the charger will not charge them. The same if you tried NiMH types. They have been making hand powered flashlights, like the "Shake lite" and a flashlight you continually squeeze to keep the small generator spinning for over a decade. When the Soviet Union collapsed, many items from their military became available on the open market, and they had piezo powered night vision scopes, monoculars and binoculars that remain energized as long as you held even pressure on the lever, and those go back over 20 years. This makes calculators childs play to power because their whole history was about making them more energy efficient from the first TI Datamaths in 1972..

Answer 4

Power equals force times speed. So how much power you put into that crank depends on how fast you turn it and with how much force you do it.

The electrical output is the power put in, times the efficiency. So if the efficiency is e.g. 30%, only 30% of the power you put in will come out as electricity.

Answer 5

Remember u can not get more out than u put into it. The electricity is generated by the magnetically field cutting by wires that is part of the generator.

Answer 6

Well, I'm not going to give you some huge lecture about energy cannot be craeted or destroyed, it can only change form, but the energy from the cranking is turning all sorts of gears inside the flashlight, which, obviously, created friction, which, therefore, can run the flashlight with that heat energy.