Homemade three-phase AC generator with a

[Michel37]

Hello everybody

I am new to this forum and my project (already somewhat advanced) to manufacture a three-phase AC generator.

My knowledge of magnetic induction is very recent and sometimes quite limited but I am very well documented on the internet to know a minimum.

I am also inspired by the project of MatEA57 and exchanges he had with Dedelco among others.

I just received my 40 Iron Neodymium Bore magnets for 350 €, phew!
This is to say that my project is serious and that I wish to succeed without giving too much room to improvisation.

It is not a question of making a wind turbine (alas I am classified site therefore the Buildings of France ...) but to manufacture a generator like wind turbine to produce current with low rotation of the rotor.

Specifications :
- enamelled copper wire AWG 14 gauges diameter 1.6 mm
- rare earth magnets diameter 35 mm thickness 15 mm, force N45, remanence of 1.32 T or 13200 Gauss, adhesion strength announced of 32 kg
- 2 rotated and perfectly balanced steel rotor discs, diameter 300 mm, thickness 10 mm, bore 25 mm to be mounted on a 25 mm steel guide shaft and placed on 2 ball bearing housings
Each disk receiving the magnets will be mounted opposite the other with the poles NS, SN, NS-, SN alternate.

I specify that the frequency in Hertz is of little importance since it is a question of straightening and smoothing the voltage by diode bridges and a capacitor as long as the generator delivers at least 24V up to 72 V in relation with the number of RPM and if possible with a high current.

Finally my questions:

Question 1
Knowing that the B field is on the axis of symmetry of the axially magnetized cylinder, to which diameter should the mandrel of the coil correspond to obtain the maximum of the induction flux?
I mean, is it important that the inner diameter of the coil be equal to that of the magnet to get the maximum voltage induced by mean coil?

Your answers involve thinking about the dimensions of the coil => int and ext diameters, thickness to determine:

A - the number of turns and the average diameter of this one to calculate the tension under a certain frequency in Hz and a value of B conceivable and all that according to your formula:

2xPix50Hz x B x (Pi xr ^ 2) I took here 50Hz as for your example with MatEA57

B - the number of transposable coils to respect the balance of 4 magnets per series of 3 coils for a three-phase current, keeping in mind that I use a rotor of 300 mm in diameter!

Important precision: I estimate that I can make the stator with the magnets at a distance of 2 mm from the coils => 1 mm provided between the stator and the magnets and under 1 mm of epoxy resin, hence a certain value of B which can be calculated according to the formula:

https://www.econologie.info/share/partag ... crjBbN.doc



I found 3849.37 gauss is about .385 Teslas !! very low as value, I am disappointed given the power of magnets!

Question 2
Will B be increased with a soft iron core inside the coil?
I think I know the answer with a difficult training problem related to the attraction where certainly a high torque to turn the rotor, is not it?

Will B be different with a coil sandwiched between a North Pole and a South Pole?

Question 3
It is estimated a magnetic flux density according to the characteristics of the magnet and its distance from the average diameter in m2 of the 1ère turn, all this is theoretical!
But how can one have a realistic idea of ​​the voltage and the current knowing that n turns is n times farther, at each longitudinal winding, of the North or South pole of the magnet?


Well I stop with all my questions, I have others dormant but will be asked when I finally have been able to determine the format and the number of reels to use.
(ie, calculation of the value of the current induced in A ...)

Can you enlighten me on this specific project?
I hope I have not been too exhaustive, the worst is yet to come (lol!)

Thank you, Michel37

[dedeleco]

I prepared an answer to these varied questions first in MP, but useful for others.

Will B be increased with a soft iron core inside the coil?
I think I know the answer with a difficult training problem related to the attraction where certainly a high torque to turn the rotor, is not it?

yes, clearly, especially useful with weak fields on old alternators and motors, which otherwise do not have enough induction and do not work.
We are very careful to have very small gaps.

With these new magnets (15 20 years) we arrive close to the saturation value of the iron and therefore the gain is much lower, and therefore the soft iron is not crucial to operate.
Without iron we would not have electricity !!

but it is necessary to take finely divided cores, lamellae or isolated wires, one of the others, well disposed, against the induced eddy currents that lose all energy in heat., true brake.

Question 1
Knowing that the B field is on the axis of symmetry of the axially magnetized cylinder, to which diameter should the mandrel of the coil correspond to obtain the maximum of the induction flux?
I mean, is it important that the inner diameter of the coil be equal to that of the magnet to get the maximum voltage induced by mean coil?

The optimum is complex exactly, different for the max voltage or the max power, because it is necessary to compute the field in any point (visible with the lines of flux that deviate and the field which decreases, and those which leave the magnet returns without having arrived at the coil), to calculate the flux (integral of the normal field to the coil) for each turn and to summon on all the turns.
.
If the coil is against the magnet, its optimum diameter is that of the magnet. further away from the magnet, the max flux is a little larger.
But as your coil has a lot of turns, the optimum for the voltage without current is to put a max of turns to have the maximum flow, even that small to small or large diameter.
For the power it is different because the internal resistance of the coil increases as the number of turns and therefore it is necessary to avoid having too many resistive losses with too low voltage.

In a simplistic way it is advantageous to put the copper max with turns giving significant voltages to a factor 2 (roughly) therefore wound on a smaller mandrel of 30% than the diameter of the magnet and 30 50% at beyond and the thick splus possible without losing the flow too much.
We can do lots of calculations. (field as we see the poles of magnets in steradians and integral elliptic out of the axis).

or measure with turns of different sizes the voltage induced by the magnets (in pairs) with oscilloscope, measure their resistance and make simple optimum calculations with these measurements, adding the properties of the different turns.
In addition you measure the properties of magnets that may have lost part of their residual field, if lack of luck or mishandling for free energy engine.

will it be different with a coil taken in "sandwich" between a North pole and a South pole?

it will be the double half way of the two magnets facing each other for the same distance of the value for one for a single magnet.
If the very long magnets are very close, the value is Br remanent, the double of Br / 2 of the formula with z = 0 and D infinite (very long magnet).
Otherwise you have the effects of demagnetizing fields.

This formula set in steradians is valid in any point out of the magnet even out of the axis. (steradian surface of the sphere resting on the poles of the magnet centered on the point where the field is calculated and divided by the square of its radius)

The steel chucks can disturb your magnets well or badly and therefore to think carefully, to measure in field, and also eddy current in this steel dice that you pull a good power of your coils.
With too much power you can demagnetize your magnets (stay below the coercive field for the field created by the current in your coils, especially with iron core).

Since you are straightening the current, the three-phase is not crucial, the hexaphase (6 instead of 3, if you have enough voltage) is better.
If you turn slowly, you may run out of tension.
It all depends on the desired power.
With thinner wires and more turns you can have more voltage and less current at equal power, especially related to the weight of copper put in the significant flux of magnets.