Faraday electricity generator.To increase the amount of elec. gen. should u use more wire or stonger magnet?

Question

I want to try an experiment for electrical generation with a mocked up faraday flashlight type setup using different shaped magnets and wire coil configurations. In the interest of not spending too much on magnets I would like to know if stronger magnets will increase the amount of electricity generated or increasing the amount of wire in the coil or does it really not make a difference?

Answer 1

Faraday's law for a coil is:

V = - N * d(phi)/dt

phi represents magnetic flux in Webers, N turns of wire, and V voltage.

phi can be replaced by the magnetic flux density B, by substituting phi = B * A where B is measured in Teslas and A is the coil cross sectional area in square meters.

The formula becomes:

V = - N * A * dB/dt, assuming A is a constant.

This formula states that an emf is generated when magnetic lines of flux change with respect to a conductive loop (N = 1) or loops (N turns). It doesn't matter whether the magnetic field changes or the magnetic is moved relative to the coil or the coil is moved relative to the magnet, the effect is the same.

With a permanent magnet the magnetic field (H) is constant, but the magnetic flux density observed by the coil will vary when the magnet is in motion. If the magnet is going to be "shaken" back and forth through the coil, then the flux density will vary with time sinusoidally. Assuming a sine variation of the magnetic field, this would give:

B(t) = B * sin(wt),
dB/dt = w * B * cos(wt)
V = w* B * N * A * sin(wt)
w = 2 * pi * f
V = 6.28 * f * B * N * A * sin(wt)

You will obtain the largest peak voltage from the generator by using a strong magnet, increasing the number of turns, increasing the area (diameter) of the coil, and increasing the motion of the magnet through the coil (or vice versa). However, the cross sectional area really should be kept just larger than the magnet to maximize the number of flux lines cut by the coil...if it was made too large none would cut through the coil and no voltage would result. Also, doubling the magnetic field strength by buying a slightly more expensive magnetic is much easier than doubling the number of turns (say from 500 turns to 1000 turns).

I have listed some web sites that may interest you. The first two give Faraday's law along with other electromagnetic formula, the third looks like it describes a similar project, and the fourth is a company that I have used to buy strong magnets for reasonable prices.

There is also a generator known as a "Homopolar Generator" which Faraday discovered. This uses no coils but a conductive disc. It is pretty interesting as well.

Hope this helps!

Answer 2

Generators create electricity when a wire cuts through a line of magnetic flux. Therefore, the more wire you have, the more often you cut a line of flux, and the stronger the magnet, the more lines of flux you have to cut.

Since arranging the wire will probably be more difficult than arranging the magnets, I think the extra money on magnets would probably be worth it.

Answer 3

Either way will work. Try looking up the formula for generator theory.

You can use more windings or stronger magnets or you may want to just "bump up" the RPMs a little.