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Induced charge in coil from other static coils?

  1. Jul 28, 2007 #1
    Hello ALL,

    I have a question about magnetism and generating electricity in a coil from a group of another coils that are alternately switched on/off (cascade).

    Would a current be generated from a group of coils that are switched on and off in sequence, having another coil parallel to them to "collect" the charge ?

    Ultimately, you would be repeating the same theory in a generator but with no moving parts... replace the magnets with a group of coils to perpetuate a magnetic "wave" past the collector coil.

    Any input or questions welcome!

    Please see attachment for visual explanation (rendered art work)

    Attached Files:

  2. jcsd
  3. Jul 28, 2007 #2


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    It'd depend on what you did to energize the peripheral
    There'd be very little magnetic coupling between the
    central coil and peripheral coils 1,2,6,7.
    There'd be significantly weaker coupling between the
    central one and 3,5.

    Assuming 4 and the central coil are tightly magnetically
    coupled they could share some reasonable mutual

    Anyway the coupled flux from any coil to any other
    coil is a function of the mutual inductance of the coils
    which is dependent on the geometry and materials and
    winding details. If the coils have a geometrically weak
    mutual inductance then the induced current in one from
    a change in current in the other would be weak.

    And there's no such thing as "collecting" charge with
    inductors. Induction is the the flux generated relative to
    the current flowing, that's all. Mutual inductance is the
    flux generated in one circuit as a result of current in the
    other circuit.

    Also you talk about generators and generating -- the
    function of a generator is to convert MECHANICAL energy
    into electrical energy; it's the MECHANICAL work that's
    done against the magnetic field that 'generates'
    electrical power by converting it from mechanical power.

    You can couple electrical energy from one coil to another
    coil all day long (at a loss of energy due to resistance,
    stray flux, eddy currents, et. al.), but you're just moving
    existing electrical energy from one place to another
    about the same as if you'd conected the circuits with
    wires. To 'generate' electricity as in make more electric
    than you already had, you'd need a source of mechanical
    energy to convert into the electrical energy.

    But if you're just asking if the coils would couple energy
    from one to the other? Yes, in amounts depending on
    the geometry / materials / resistance / circuits / currents.
  4. Jul 28, 2007 #3
    Thank you for the detailed explanation!

    There would be a dc source on the coils. Each coil would pulse for a short period then the next would be charged (pulse). but fast, maybe 100 times a second.

    When you say "coupled flux" are you talking about the point at which the coil and magnet (in a generator) go past each other and the flux (form the magnet) moves through the coil and causes a current to flow ?
  5. Jul 29, 2007 #4


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    You're welcome.

    What is the effect you're trying to achieve?
    I don't think that there's anything about such
    a physical arrangement that would be particularly
    useful to construct in and of itself.

    If you're just trying to couple electrical energy from
    one coil to another you don't need to geometrically
    arrange them akin to a rotor/stator type of arrangement.

    That arrangement is just used in generators
    because it's a physically spinning turbine that is being
    pushed hard by a mechanical process that is doing the
    work that is converted into electrical energy.

    In motors it's used because it's the key point of
    converting electrical energy to physical rotation energy.

    If you're just looking for variable coupling of circuit
    energies thatcan be done in a variety of ways without
    a geometrical situation like that.

    When I say coupled flux I do not mean to refer
    in any way to a specific physical arrangement of
    two coils, though geometry certainly does play
    a part in dictating what the coupled flux will be.

    Don't take this analogy TOO far (since it's inaccurate
    in a lot of other ways) but JUST for the purpose
    I am about to describe -- imagine there are two coils,
    one is a shower-head and the other is a drain.

    The geometry and physical materials
    of the shower head and the environment it
    is spraying into dictates the greometric pattern of
    its spray. The amount of spray is dictated by
    the flow rate of the water (current) going to the
    shower head, and the current (flow rate) is driven
    by the pressure/energy difference between the
    pipe feeding the shower head and the space the
    shower head sprays into -- that is the voltage.

    So with a constant water flow rate (current) and a
    fixed set of geometric and environmental circumstances
    the shower head will always produce the same spatial
    pattern of spray and the same flow rate of spray.

    The spray of the showerhead is the magnetic flux,
    and its spatial pattern of field density
    (amount of spray passing through a given square inch
    of space) is the main aspect one can measure it by
    beyond its total quantity over all space.

    Now position another coil (our 'drain hole')
    somewhere in space. The drain hole will have a
    certain size, a certain distance from the shower head,
    a certain orientation angle relative to the shower head.

    Depending on the factors of the drain's size/placement
    and the shower head's spatial field density of 'spray'
    (flux), some fraction of the flux from the shower head
    may pass through the 'drain hole' that represents
    another coil.

    As is intuitively obvious, anywhere from as close to zero
    as you could imagine to nearly the full amount of the
    shower head's flux (spray) will pass through the
    'drain hole' depending on the physical/geometric
    factors I mentioned.

    As is also intuitively obvious, if the shower's flux is
    spread out at a very wide angle, it'll be very difficult
    for much of its flux to pass through a drain hole if
    the shower head isn't either right NEXT to the drain hole
    in a face to face orientation, or even better, the shower
    head could be stuck INTO the drain hole.

    When the shower head is NEXT TO and FACE TO FACE
    with the drain hole that's like two coils being face to
    face and oriented in the best possible way to couple
    given their separate positions.

    When the shower head is stuck all the way into the
    drain hole, that'd be more like winding one coil directly
    on top of the other.

    So the 'coupled flux' is just the total amoung of flux
    that makes it down the drain hole given the setup
    that exists.

    The total flux is the total amount of flux emitted by
    the shower head wherever it may go in space and
    however much of it is coupled or NOT to the drain hole.

    Any circuit in the universe has SOME mutual inductance
    with any other circuit in the universe, but usually
    unless they're RIGHT NEXT to each other or ON TOP
    of each other, the coupling is very weak, as in a few
    percent at best in many cases.

    Even when they're literally on top of one another or
    right next to each other, special design circumstances are
    generally necessary to get the coupling factor to exceed
    about 25%.

    Now the inductance of a coil is how much
    magnetic flux it produces for a given current flowing in it. This is an area where the shower head analogy breaks
    down badly -- a shower head will emit the same flux
    of water out as there's a flux (current) of water in the
    pipe going into the head. In magnetics there's
    a ratio known as 'the inductance' that determines how
    much magnetic flux is generated by how much current
    flowing in an inductor.

    When I speak of mutual inductance, that refers to
    the mutuality or coupling of current to flux between
    two circuits. The 'mutual inductance' of the
    shower head / drain is defined as the ratio of water
    captured by the drain (the flux that goes THROUGH the
    drain) to the total water current flowing in the shower
    head. The current generates a certain amount of
    total flux, but the MUTUAL flux is only that fraction of
    the total flux that goes through the drain as opposed
    to elsewhere.

    So the coupling factor is coupled flux / total flux,
    and the mutual inductance is
    flux in the drain / current in shower head.

    There's an important theorem in physics that says
    that if you switched the roles of the drain and the
    shower head, the MUTUAL inductance remains the same,
    it's a mutual quantity, not one that's unique to going
    from one direction to another -- that's another difference
    in the shower head analogy to real magnetics.

  6. Jul 29, 2007 #5


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    BTW in a generator or motor any pole pieces that
    aren't pretty close to DIRECTLY being next to each other
    have essentially insignificant mutual coupling.

    The motor/generator doesn't benefit from or use the
    effect of there being an arc sequence of progressive
    coils / fields that have some kind of elusive cumulative

    The only relevant effect is between the two poles that
    are in very close proximity, and the rest of them are
    just there 'waiting' because at some LATER point they
    WILL be in close proximity. Until then, the mutual
    coupling is minor compared to that between the ones
    that are very nearly aligned.

    So the arrangement and sequence of your coils
    is irrelevant, there will just be some minor amount of
    mutual coupling between any given one and any given

    That mutual inductance from any given one to any
    given other is the only thing that determines the effect
    of a current in one to the flux in the other. The position
    or presence of the others is entirely independent of that.
  7. Jul 30, 2007 #6
    My main goal was to create a field that travels from 1 to 7 inducing a charge in the main coil. I was thinking that, like in a generator, the coil moves past the magnet and creates a charge in the coil.

    To replace the magnet with a series of coils which do not move but create a magnetic field that travels across the head of the main coil.

    My goal is to induce a moving magnetic field over a coil with no moving parts, there by inducing a charge in said coil
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