I have some questions about different sizes of a magnet passing over a coil.

[rukiddingme]

Suppose I have a circular coil 3" across with a 1" hole in the center.


I am wondering what the difference is between passing 
different sized magnets over the coil.


In the 1st case,
I pass a 1" magnet over the coil centered on the coil's hole.


In the 2nd case,
I pass a 2" magnet with the same gauss over the coil.


In the 3rd case, 
I pass a 3" magnet with the same gauss over the coil.

In the 4th case,
I pass a 4" magnet with the same gauss over the coil.

In the 5th case,
I pass a 6" magnet with the same gauss over the coil.


My question is, when a magnet passing over a cicular coil,
at what point does the width of the magnet relative to the
center hole make it so the energy produced by the coil
does not increase?


And . . .


When a magnet passes over a coil and the magnet is the
same size or bigger than the coil, is the energy produced
less than when a magnet the same size as the center hole
passes over the coil?


And . . .


At what size in relation to the size of the center hole of a
coil is the optimum size of a magnet passing over the coil
to produces the maximum amount of energy?


And . . .


Does a magnet that is bigger than the size of the center
hole of a coil decrease the energy output of the coil?


And . . .


Does a magnet that is bigger than the size of the coil
decrease the energy output of the coil?


Thanks in advance.

[Magluvin]

Ive found that its best to have one magnet passing one half of the coil and another magnet of opposite polarity passing the other side of the coil.

If the coil OD height is 3 in then each magnet should be also 3 in. I would use bar magnets 3in in length, as high as the coil height, and the width would be the width of each half of the winding. If the coils winding radius is 1in from the inner side of the winding to the outer side of the winding, the the mag should be 1 in wide, or even 1 1/2in wide so the mags can be butted against each other on the rotor, etc.

Another mod would be winding square or rectangular coils where the windings that are passed over by the magnets are all perpendicular to the magnet face movement. With a round coil, the upper and lower parts of the windings angle off to being in line with the magnet direction of movement, so only the portions of the windings that are perpendicular to the magnet motion get induced the most. If we look at most all motors or gens today, the portions of the windings that are interactive with the magnets or stator windings are straight and the windings are basically rectangular or even oval ended, depending on the designer in having one way or the other.

The only time we see round magnetic windings is for solenoids, relays and such where the armatures move in line with the field applied by the coil.

I prefer the 2 mags passing each side much better than just one side at a time for one basic reason. If one mag passes just one half of the coil at one time, I believe that the inductance of the coil as a whole may be a bit of an impedance by the self inductance of the side of the coil that is not being directly induced by the mag at the time.

Also, with 2 mags, we are inducing more of the winding and generating more available current in the winding as a whole, instead of just inducing a small portion of the coil as a whole.

Mags

[rukiddingme]

Thanks.

[sm0ky2]

Assuming the gauss of each magnet to be constant
As well as the coil remaining constant
And further assuming that the magnets are passed
   perpendicular over one end of the coil


In the extreme example of the 6" magnet
   Energy will be produced slower at the same RPM
For two reasons -
1) the field of the magnet is larger than the coil
    A portion of the field is not affecting the coil.
2) the field is spread rather uniformly through the material.
    Meaning per volumetric area there is less flux from the moving magnet.
   
In the case of the 3" magnet: the entirety of the field is
  Condensed to within the 3" area.
The 3" magnets (solid disk type with no hole) should be the most efficient for a 3" coil.


Generally speaking the size affects the generated signal in the following manner:
-- smaller magnet = greater amplitude, shorter pulse width
-- larger magnet = lesser amplitude, extended pulse width




In all cases, the 'effective field' as observed by the coil
  Extends slightly beyond the physical dimensions of the magnet
   So even the 1" magnet will produce "some" electricity.

[Magluvin]

Assuming the gauss of each magnet to be constant
As well as the coil remaining constant
And further assuming that the magnets are passed
   perpendicular over one end of the coil


In the extreme example of the 6" magnet
   Energy will be produced slower at the same RPM
For two reasons -
1) the field of the magnet is larger than the coil
    A portion of the field is not affecting the coil.
2) the field is spread rather uniformly through the material.
    Meaning per volumetric area there is less flux from the moving magnet.
   
In the case of the 3" magnet: the entirety of the field is
  Condensed to within the 3" area.
The 3" magnets (solid disk type with no hole) should be the most efficient for a 3" coil.


Generally speaking the size affects the generated signal in the following manner:
-- smaller magnet = greater amplitude, shorter pulse width
-- larger magnet = lesser amplitude, extended pulse width




In all cases, the 'effective field' as observed by the coil
  Extends slightly beyond the physical dimensions of the magnet
   So even the 1" magnet will produce "some" electricity.

"In all cases, the 'effective field' as observed by the coil
  Extends slightly beyond the physical dimensions of the magnet"

I totally agree.  If it were air core, the windings should be flat and as close to the mag surface as possible.  Core base windings, the mags tend to drag the fields across the windings a bit different. As the field of the mag is dragged from core pole to core pole, the field is dragged through the windings between poles. If you visualize it, the field kinda has to travel the surface of the poles between other poles so its kinda like it traverses that inner surface faster and possibly cutting the windings a bit faster.

I have pics somewhere of a car cooling fan pancake motor. The armature is flat, less than 1/8in thick about 3.5in dia. The magnet is a doughnut with sections NSNSNSNS  Brushed motor. The surface of the rotor is very close to the magnet and the metal casing on the other side of the rotor is basically the core where the field of the mag meets back at the other side of the magnet. Very torquy motor. Works as a gen too. But in the end it is called a coreless motor. Coreless in that the armature windings are encased in what seems to be a hard bakalite plastic. So the windings are like a homopolar motor broken up into individual windings all in series. I believe it circled the rotor 3 times before meeting the opposite end of the series winding. The brushes are not 180 deg. More like 30 deg. neat motor to play with. I want to build a new casing out of plexi and put neo disk mags on both sides of the rotor. The bearings on the rotor are fixed to the axle. Would be a nice little demo piece.

Here is a guy building his own...

http://build-its-inprogress.blogspot.com/2015/02/coreless-axial-flux-motors.html

Mags