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Magnets and coils configuration for electricity generation

  1. Jun 20, 2016 #1
    My dad is working on a project where he intends to convert mechanical into electrical energy, and he was wondering if a particular magnet and coil configuration works for electricity generation. And if it does, how are the voltage and current calculated.

    Lets say:
    • The coils have a diameter of 10 cm
    • There are 100 coils in that solenoid
    • The magnets moved with a speed of 5 m/s
    • The magnet has a value of 0.334 T on its North face
    • There is a 1cm wide gap between the magnet and the coil

    I created a little gif and attached it to this thread to illustrate the configuration that he was achieving. The coil is stationary, while the magnet moves across its surface.

  2. jcsd
  3. Jun 20, 2016 #2


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    Staff: Mentor

    Welcome to the PF.

    You need to minimize the gap width to maximize the power transfer... :smile:
  4. Jun 21, 2016 #3

    jim hardy

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    First, i have no idea what you're describing.
    You'll learn a lot studying how it's done in real products.
    Take apart a lawnmower engine and study the charging coils

    voltage is in proportion to rate of change of magnetic flux.
    Magnitude of flux is proportional to magnet strength and inversely proportional to air gap
    observe that practical small generators have an air gap much smaller than 1 cm,
    without an iron core in the coil to maximize magnetic flux you won't get much voltage

    old jim
  5. Jun 21, 2016 #4
    Thank you for you reply Jim,

    Sorry for being vague, I was just giving any related information that my dad's giving me.

    I see that most configurations in motors and generators have the coils in the middle and the magnets on the outer side (as shown in the lawnmower engine above). May I ask your opinion on this particular configuration (GIF below) if it was being use with the intention to convert mechanical to electrical energy? From what I've read, wind turbines uses a similar configuration?

    If the GIF is too vague, the orange are the solenoids. The red/blue represents the N/S of the magnets (attached to a rotor).

    Also, thank you for your info on the iron core.
  6. Jun 21, 2016 #5

    jim hardy

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    Yes, there are many "youtubes" showing homebuilt alternators with that arrangement.

    You will learn that magnetic flux travels in a closed loop just as does electric current
    and it much prefers to travel in iron
    that's why you minimize the fraction of the magnetic path that is air.
    You'll want to get your head around magnetic basics, start with what are the units, look them up
    Flux = Weber, you might also look up the old cgs unit "Line" or "Maxwell"
    Flux Density = Tesla, look up also old cgs unit Gauss

    then it's a lor easier to grasp the formulas


  7. Jun 24, 2016 #6
    Hi Jim,

    I've been reading up on my physics, and watching the DIY wind turbines. My physics is just first year university level, and even then, I've forgotten a lot of my physics.

    I'm able to make calculations for simple situations (e.g. where magnetic fields are assumed constant everywhere, where resistance is assumed to be zero, where there is no iron core) but I think it's much more complicated in this situation? Flux density is not constant everywhere, so I think different part of the coils will have different induced emf?

    Do you know how energy production can be estimated? Or do you know an article/journal that can help in this situation?

    Thanks Jim,
  8. Jun 24, 2016 #7

    jim hardy

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    not really, i don't.
    I never looked very hard at making a homebuilt-from-scratch axial flux machine because i'd use parts from an automobile or outboard motor instead.

    Hobbyists are finding the new washing machine motors handy

    some modify automotive alternators

    Voltage per turn is rate of change of flux inside the area encircled .
    If you're alternating between ±0.334T , how many Webers (Teslas X square meters) is that and how many times per second does it happen?
    Load current will make a mmf that opposes your permanent magnet, so #turns is a tradeoff between magnitude of voltage and 'stoutness' of voltage under load.
    You'll have to know how much air is in the magnetic path to calculate much of anything.

    Train your search engine... Keep searching on keywords in the articles you find and it will adjust itself to your interests..
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