coil dimensions for 20mm magnets

[oramafanis]

Hi there,

i have tested varius coils for my 12 mag rotor.
the last one i have very good voltage arround 8 vp-p .



The dimension of the coil is 62mm outer dia , 29mm inner dia and 10mm height.



Magnets are 20mm dia and 10mm height.
As you notice the inner hole is larger than the magnets.
This gives me a small step in my final waveform.



do you think this will give me problems?

[electrondady1]

ideally  the center hole of the coil should be the same size as the magnet and the space between magnets should be the same as the width of your coil leg .

[oramafanis]

YEAP!
I understand that.
But lets talk about these results now. is there any problem with this waveform regarding the small step?
if this will cause problems i will make smaller the inner hole.
I am ok with the voltage so if there is no problem with that i will leave it as it is....
I would like to get more speed on the magnets using this rotor...
Assuming that this will be a 3 phase generator the time that the this coil wont produce energy another coil will produce for sure.
So maybe it isnt so big problem assuming that the step is really small....

[Mary B]

YEAP!
I understand that.
But lets talk about these results now. is there any problem with this waveform regarding the small step?
if this will cause problems i will make smaller the inner hole.
I am ok with the voltage so if there is no problem with that i will leave it as it is....
I would like to get more speed on the magnets using this rotor...
Assuming that this will be a 3 phase generator the time that the this coil wont produce energy another coil will produce for sure.
So maybe it isnt so big problem assuming that the step is really small....

I have seen MUCH worse wave forms so go for it! You are giving up a little bit of voltage, hard to say how much but not enough to worry about. When you wind the next batch of coils make the center smaller!

[oramafanis]

I use 0.65mm wire (22awg). 280 turns.
1st option . go to a smaller inner hole that result on wider legs than the magnets. I don't know if this will be a problem. The rotor size will be the same.
2nd option .make smaller rotor to achieve the desire space between the magnets I will loose the speed and the coil size.
3rd option. Leave it as it is .

The coil:

[oramafanis]

the coil:

[MattM]

Your odd sine wave shape is the result of round coils and spacing of the legs being a bit too close, distorting the middle of your wave.  Your material being arranged to form an evenly distributed spoke pattern would create a smoother shaped wave.  You would use less wire for each coil, too.  That is why you normally see more of a trapezoid or pie shape to coils.

[oramafanis]

nope. i have a vey good shine wave with a hole at 20mm as the magnets are... i made it bigger so to test if the result in voltage is the same so to use less wire. I noticed that i have larger voltage output thought with the bigger hole. This little step is when the magnet do nothing to the coil cause is excactly in the center... this has nothing to do with the circular coil....

[Adriaan Kragten]

You should read chapter 9 of my public report KD 341. In this chapter it is explained how a voltage is generated in a coil or in a wire. If you use coils with no iron core, there is no concentration of the magnetic flux flowing through the coil and then the voltage generation can best be explained by a wire moving through a constant magnetic field. For no iron in the coil cores, the pitch in between the left and the right leg of a coil must be the same as the pitch in between a north and a south pole. The optimal coil shape for an 8-pole generator with a 1-layer winding is given in the top picture of figure 5 of KD 341. The bottom picture gives a slight deviation from the optimum coil shape but this deviation allows thicker coil bundles. Figure 6 out of KD 341 gives a deviation for which the coils have a shape of the rotor of a Wankel motor which simplifies manufacture of the coils. If you use circular coils, the deviation from the optimum shape is very large but making circular coils is easy and sometimes the result is acceptable. Circular coils are logic if you use circular magnets. Such a generator is described in public report KD 679. This generator has been measured. All public KD-reports can be copied for free from my website: www.kdwindturbines.nl at the menu KD-reports.

The shape of the voltage fluctuation in the coil of one phase depends on the variation of the magnetic flux. If the variation is sinusoidal, you get a sine wave form of the voltage. For axial flux generators with no iron in the coils, a voltage is only generated as long as the wire is in between the magnets on both armature sheets. Outside the magnets, the flux density suddenly becomes almost zero and so generally you get a block shaped fluctuation of the voltage for axilal flux generators with no iron in the coil cores.

[oramafanis]

thanks for the info. i have holes that can be mount m5 bolts so in the final stage i will be able to use iron or stainless steel bolts as cores...
I understand what you sent. its better to iuse cores than to be openair cores...
But what about the inner hole? do i have problem if i go with bigger than magnets?
If i make the hole the same i will use more wire and the legs of the coil will be wider than the magnet....
In reallity i have a very small pause of generating electricity....