1. Nov 30, 2009

### JoonasN

1. The problem statement, all variables and given/known data
I am trying to build a faraday flashlight and I need to know if this generator would work.

2. Relevant equations

I added a rough diagram to help illustrate this...

3.
The attempt at a solution

I have a DIA20 x L10 cylindrical Neodymium magnet moving up and down inside a plastic tube 30mm long. Both ends of the tube are closed. The ID of the plastic tube lets the magnet move along the tube smoothly. Enameled copper wire is wound around the outside of the tube to form a 10mm long solenoid at the center of the tube, about 16 turns are used. Both ends of the wire are connected to a CRO. Will the CRO record any output? If yes, then would adding 4 Schottky diodes double the voltage?

Thanks,
Joonas

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2. Nov 30, 2009

### vk6kro

You would get a positive going pulse as one pole entered the coil and a negative going pulse as the other end entered the coil. And you would also get pulses as the magnet came out of the coil.

Rectifying this series of pulses would let you charge up a capacitor, because the rectified pulses would all have the same polarity, but all diodes have to have a minimum voltage before they will conduct. So you can lose some of your voltage like that.
As you suggest, Schottky diodes are better at this than most other types as they have a lower threshold voltage.

Neodymium magnets are very brittle and will chip easily if they are allowed to hit anything, so you need to be aware of this. Some of them are nickel plated and these seem more resistant to chipping, but they still chip if you hit them against anything.
Maybe you could put soft foam or something like that at the ends of the tube, to absorb some of the shock.

Welcome to the Forum. Questions like this can go in the Electrical Engineering section if you like as it isn't homework related.

Last edited: Dec 1, 2009