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Homework Help: Power generated from magnet and coil

  1. Feb 10, 2014 #1
    Hey guys,
    I'm an engineering student and for my project i am planning to use a power generator based on magnet and coil like those hand power shake flashlights.

    I am using gauge 45 AWG copper wires (0.051816mm) and coiled to have 200 coils. The coil size will be 2.5cm. The magnet i am using will be N40 Neodymium cylindrical magnet sized 0.5'' x0.5'' with rated residual flux density of 1.25T.

    I am hoping you guys can give me some advice in calculating the power generated from this setup.

    Things i tried: I used Faraday's law to find voltage. After that, i used resistivity of copper and found the resistance of the wire then used P=V^2/R to try finding power but it seem to be too high to be real.


    PS: this is not a homework problem. Its a design project and we decide to use this system. We are mechanical engineering students that's why we couldn't find any professors to help us.
  2. jcsd
  3. Feb 10, 2014 #2

    Simon Bridge

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    Science Advisor
    Homework Helper

    Welcome to PF;
    So you have a permanent magnet that can slide through a coil - the idea being that you shake it or tip it.
    Please note: a "design project" is homework. You have to do the designing yourself.

    The sort of calculations you need to do will depend on the parameters of the design. What is it you need to design exactly? i.e. do you need to design the device to produce a specific output for a specific input - to specific tolerances?

    Maybe it has to charge a battery to some level (i.e. so it runs an LED for a few hours) in some reasonable amount of time (i.e. before your arm gets too tired)?

    When you know the design parameters, the rest will get a lot clearer.

    I suspect you are best served by some sort of approximation.
  4. Feb 10, 2014 #3


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    Staff: Mentor

    Welcome to the PF.

    One keyword that you can use to look for references is "Dynamo". Here's the link to the wikipedia page, which has a number of references at the end of the article to help you find design equations:


  5. Feb 10, 2014 #4
    I actually have to design a energy harvesting floors. Magnetism is just one of my ideas. I just need to find out how to calculate the power it can produce from the coil. how it works is the person walks on the tile and the magnet goes through the coil generating electricity. We might be using a battery or a capacitor to hold the charge to power LED lights. Just need to find out how to calculate the power it produces.
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