centripetal force to electricity

[casrip1@gmx.com]

hey guys, i was wondering how to calculate the voltage output of an inverse generator (so instead of coils on the shaft surrounded by magnets, its magnets on the shaft, surrounded by coils).

 

i want to calculate at frequency at which a flywheel with a certain mass needs to spin to produce certain voltage. assume mass, magnetic field strength etc is given, what is the procedure to to calculate voltage given mass and diameter of the fly wheel, and the magnetic strength of the magnets mounted on the wheel

[John Cuthber]

The mass of the magnets doesn't (directly) affect the voltage.

The voltage depends on the rate at which the conductors pass through the magnetic field, and the strength of the field.

Generally, a bigger magnet will produce a stronger field and it will have more mass.

But you might also get a stronger field by using a different material for the magnet e.g NIB instead of steel.

[swansont]

The voltage will be [math] N\frac{d\Phi}{dt}[/math]

N is the number of turns of wire and the derivative is the rate at which you are cutting the flux lines, which will be proportional to the speed. Which, of course, will vary radially.

[casrip1@gmx.com]

mass doesn't directly affect voltage, correct, but it will affect power output. as i extract electricity from the system it will slow down the flywheel, so mass of the flywheel has more to do with how much power i can extract. which raises another issue in my eyes, will voltage drop as the flywheel slows down? since the number of passes drop along with the speed.

 

EDIT: and i will need to isolate the flywheel in a vacuumed structure to reduce friction. i am also planning on using electrodynamic bearings if i can buy some for a reasonable price. i originally intended to use magnetic bearings but it seems like for my purposes that would be adding another layer of complications as i'd have to worry about the whole magnetic bearing management... so i'm wondering if anyone knows of a easily available material in which i can house the flywheel in a vacuum without having the housing interact with the magnets (so it can't be a magnetic material). it would have to be a spherical shape to allow maximum vacuum without collapsing the housing on itself.

 

EDIT 2: basically, i want to build a small scale flywheel battery that will be as efficient as an amateur could make it. and i need a lot of help with it because i haven't done anything of the sort before so i need help with both the math of it and the general info of what i could use, where i could find it ect.

 

the goals i have for the finished product are to have a 10cm diameter, a voltage capacity of ~9 volts that could run for a couple of hours per charge (2-4 hours at least), and should be chargeable by solar power

Edited June 18, 2013 by casrip1@gmx.com

[imatfaal]

have you actually calculated how much energy you could store as a theoretical maximum?

 

You would be looking at:

 

[latex]E_{rotational} = 1/2 I \omega^2[/latex]

 

I is the moment of inertia and omega is the angular velocity

 

the moment of inertia for a cylinder is

 

[latex]I_{cylinder} = 1/2 MR^2[/latex]

 

Just using back of envelope calcs - I get a flywheel the size you have described holding about the same energy storage capacity as a D-cell.