Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Can someone explain a DC electromagnetic generator in lamen terms for me?

  1. Jun 9, 2010 #1
    I have been researching generators lately, whilst contemplating building my own wind powered generator. I think I understand the general layout: a central magnetic core that rotates with an outside ring of conductive coils spun in specific alternating turns with their own magnetic cores. If I am wrong please correct me, the best general description I could find for building one was:


    I still have a few questions and appreciate any help that can be given.

    I understand that the number of turns of the coil effects the voltage output. I was wondering if there is a simple way to calculate the number of turns of the wire without sitting down and manually trial/error testing turns. I found a few sites, but they gave me different explanations yielding different answers.

    As far as the magnetic cores of the coils go, does it matter how the poles of these cores are arranged? Or does it just matter that it they be magnetic?

    What is the best material to hold the actual rotating magnet with. In the website above they use wood, but this is just a simple homemade solution. Wouldn't some sort of light metallic core be better?

    Would it take a relatively large generator to create ~20 amps at 12V? I know that engineers hate this kind of question, but as far as generators go am I looking at a smaller one that can be powered by wind, or am I looking at something that has to use a gas motor?

    Obviously I am no engineer, but just a guy that likes to tinker with things. If something that I say sounds ridiculous please correct my ignorance. All help is greatly appreciated.
  2. jcsd
  3. Jun 9, 2010 #2


    User Avatar
    Science Advisor

    My advice - don't try to replicate a century of learning in building these devices - go find one already built. You can probably find a 12V automobile alternator at a junkyard for free that will do about what you are trying to do.
  4. Jun 9, 2010 #3
    Well what's the fun in that silly :) I appreciate the thought and have considered it, but would rather enjoy building one. Think it would be fun. And I like learning how things work. I have my hands on one, but having one doesn't really answer my questions so I figured I would ask. Thank you
  5. Jun 17, 2010 #4
    Induced voltage depends on speed of rotor, flux in machine, and number of current paths, length and number of conductors.

    eind=(v x B) dot l ,(speed, flux density, length) vector quantities.

    Make a sketch and do the math. A visit to the library wouldn't hurt either, many good books on the subject. As phyzguy pointed out, don't re-invent the wheel.

    Without much study i belive the generator inn the link is a AC synchronous generator. Like the car alternator. Principle is the same, but you need a rectifier.
  6. Jun 17, 2010 #5


    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    Wave a coil in front of a magnet and prove to yourself that magnetic induction works by looking at a meter. Take a cycle alternator apart, look at how it works and onserve the effect of speed changes and load changes. Then go out and find a cheap / free 12V car alternator. You probably don't have the knowledge or facilities to make anything that will do anything as well at that. That's if you actually want to use it for a serious application. You wouldn't want to waste all that effort in building the turbine bit and then produce just a few measly watts, would you? Even the commercial small wind turbines don't do much!
  7. Jun 17, 2010 #6


    User Avatar
    Gold Member

    Correct me if I'm wrong, but wouldn't you need a constant 12v field to operate a regular car alternator, and doesn't this defeat the purpose of building a homemade neo-magnet alternator?
  8. Jun 18, 2010 #7


    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    Yes. That's a point. You only need a small battery in the system, though. It also would mean you could regulate the output voltage.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook