making a permanent magnet generator for a vawt

[malofito]

Hello don't mind the miniature generator prototype... I'm testing coils... First of all, I want to know if any of you know if the inner size of the coil in respect of the size of the magnets is fine or do I need to leave the whole magnet free of  wire in both sides for better output?
The next thing is, I found out something interesting, coil a is 250 turns of 22 gauge wire and 1/2 inch thick and interestingly it's barely produces 0.5 volts; while coil b is 150 turns of 22 gauge wire and is 1/4 inch thick and it produces 0.4 volts... Seems coil shape affects the output preferably having a less thick coil will require less turns for the same voltage.

Im a newbie in generator making and I want to know your opinions.

[Adriaan Kragten]

You should read chapter 9: "Voltage generation in a coil" of my public report KD 341 which can be copied for free from my website: www.kdwindturbines.nl at the menu KD-reports. In this chapter, I give two wayes to understand how the voltage in generated. The second way can best be used for axial flux generators with no iron in the coils. Figure 5 and 6 show the coil pattern for a 3-phase winding of an 8-pole PM-generator. In this figure you can see that the number of coils is 3/4 of the number of poles if you use a 1-layer, 3-phase winding. If you would use a 1-layer, 1-phase winding, the number of coils is only half the number of poles. So for a 3-phase winding you get 50 % more copper in the coils and a rectified 3-phase winding has only a little fluctuation of the DC current (see report KD 340 for rectification). That is why a 3-phase winding is prefered. I would not use only four poles. Eight poles is the miniumum for which you get coils with an acceptable shape. The number of poles must be a factor of four, so 8, 12, 16, 20 or 24 for a 1-layer, 3-phase winding.

Only the radial part of the coil is effective for the generation of the voltage. The tangential inner and outer part must be outside the path of the magnetic flow. The shape of your coil is completely wrong for a 4-pole armature. The pitch in between the heart of the magnets is 90° for a 4-pole armature. So the optimum pitch in between the left and the right radial leg of a coil is also 90° to get the maximum voltage. So for a 4-pole armature you need three very wide coils for a 3-phase winding.

[MattM]

The generation occurs over the sides of the coil.  Each side of the coil, looking from center-out, I'll call a leg.  Your shape of coil has the magnets passing while tilted in relationship to each leg, culling its efficiency.  Ideally the magnet should have the pole facing the coil, and both coil and magnet should be aligned to fit their shapes together to impart maximum flux across your coil.  Poles should ideally be alternated north/south, to get maximum alternating current.  The strength of the magnet and velocity of the magnet also factors in to generation of current.  Improve those things and you will have the results you seek.

[MagnetJuice]

Welcome to Fieldlines malofito.

The reason that the thicker coil with more turns doesn't produce more voltage could be that the magnetic flux from your magnet doesn’t reach all the way across the full thickness of the coil.

The following image will guide you as to the ideal proportion between the magnet and the hole inside the coil.


Maximum voltage is generated when the magnet is passing over the area between the two blue triangles on either leg of the coil.

There will be some voltage generated when the magnet is passing over the blue triangles.

No voltage is generated by a magnet passing over the yellow areas.

If the magnet passes over the red areas at the same time, there will be some voltage cancellation, but not enough to be concerned about. Most builders do it that way because they end up with a smaller diameter alternator that is lighter and uses less material.

The image bellow shows a magnet passing over two different coil legs at the same time. For a 3-phase alternator, one coil will be generating a positive sine wave and the other coil a negative sine wave. That is ideal.


Can you tell us how you measured the voltage of the coils? If you used a magnet, what kind of magnet and how strong.

Good luck hombre.

Ed

[joestue]

Without a pair of magnets, or without a pole piece on the other side to preferentially cause the flux lines to flow vertically out of the magnet... the thinner coil is more effective because half the flux from the magnet is traveling sideways though the thicker coil as it makes its way back through the air to the other side of the magnet.

[malofito]

Welcome to Fieldlines malofito.

The reason that the thicker coil with more turns doesn't produce more voltage could be that the magnetic flux from your magnet doesn’t reach all the way across the full thickness of the coil.

The following image will guide you as to the ideal proportion between the magnet and the hole inside the coil.
(Attachment Link)

Maximum voltage is generated when the magnet is passing over the area between the two blue triangles on either leg of the coil.

There will be some voltage generated when the magnet is passing over the blue triangles.

No voltage is generated by a magnet passing over the yellow areas.

If the magnet passes over the red areas at the same time, there will be some voltage cancellation, but not enough to be concerned about. Most builders do it that way because they end up with a smaller diameter alternator that is lighter and uses less material.

The image bellow shows a magnet passing over two different coil legs at the same time. For a 3-phase alternator, one coil will be generating a positive sine wave and the other coil a negative sine wave. That is ideal.
(Attachment Link)

Can you tell us how you measured the voltage of the coils? If you used a magnet, what kind of magnet and how strong.

Good luck hombre.

Ed

Hi thanks for your answer, I'm using 76lb pull force magnets 1.5x0.75x0.125 with 1509 surface gauss. which you can see in my previous image where the coil is.

[malofito]

You should read chapter 9: "Voltage generation in a coil" of my public report KD 341 which can be copied for free from my website: wwwkdwindturbinesnl at the menu KD-reports. In this chapter, I give two wayes to understand how the voltage in generated. The second way can best be used for axial flux generators with no iron in the coils. Figure 5 and 6 show the coil pattern for a 3-phase winding of an 8-pole PM-generator. In this figure you can see that the number of coils is 3/4 of the number of poles if you use a 1-layer, 3-phase winding. If you would use a 1-layer, 1-phase winding, the number of coils is only half the number of poles. So for a 3-phase winding you get 50 % more copper in the coils and a rectified 3-phase winding has only a little fluctuation of the DC current (see report KD 340 for rectification). That is why a 3-phase winding is prefered. I would not use only four poles. Eight poles is the miniumum for which you get coils with an acceptable shape. The number of poles must be a factor of four, so 8, 12, 16, 20 or 24 for a 1-layer, 3-phase winding.

Only the radial part of the coil is effective for the generation of the voltage. The tangential inner and outer part must be outside the path of the magnetic flow. The shape of your coil is completely wrong for a 4-pole armature. The pitch in between the heart of the magnets is 90° for a 4-pole armature. So the optimum pitch in between the left and the right radial leg of a coil is also 90° to get the maximum voltage. So for a 4-pole armature you need three very wide coils for a 3-phase winding.

thanks for the advice I will check it out, and come back if I dont understand something.

[MattM]

Rule of thumb with generation is that electrons move perpindicular to magnetic lines.  In 3 dimensions, that leaves two planes to flow.  The movement of the magnet is across one of those planes, meaning your electricity will flow along the remaining plane.  Fleming's righthand rule will describe the direction of your electricity.

[brandnewb]

as far as I understood the most basic interpretation of Lenz's law
https://en.wikipedia.org/wiki/Lenz%27s_law

which goes something along the lines of

e (voltage)= B(magnetic field strength) x I(length of the conductor) x v(velocity at which the 2 (conductor and field) are passing each other)

If this is indeed relevant then you can also consider this in addition to the suggestions you have already had.

My 2 cents is that, if you are looking to maximize the voltage out of your coils, is to have one side of the coil under the influence of the south/north pole of a magnet
and the other under the influence of the opposite pole.

This suggestion might sparke a debate about cogging, but that might be beneficial as not all my information sources seem to worry about that as much as some do.

[Adriaan Kragten]

as far as I understood the most basic interpretation of Lenz's law
https://en.wikipedia.org/wiki/Lenz%27s_law

This suggestion might sparke a debate about cogging, but that might be beneficial as not all my information sources seem to worry about that as much as some do.

Clogging or having a certain number of preference positions per revolution is only a problem when there is iron in the stator coils. If there is iron in coil, the armature will take that position for which the magnetic flux flows easiest from a magnet of the armature to the iron of the stator and this position is a preference position. Axial flux generators with no iron in the coils therefore have no preference positions. But for radial flux generators made from asynchronous motors, clogging can be a big problem, especially if there is a ratio with small numbers in between the number of armature poles and the number of stator coils or the number of stator coil bundels. There are several ways to solve this problem. One is to incline the armature poles. Another is to make only a small difference in between the number of armature poles and the number of stator poles. In several public reports like KD 341 and KD 580, different options are described.

[MattM]

Cogging is from induction, Fleming's lefthand rule.  Unfortunately its also impossible to avoid.  The byproduct is heat generation and kinetic resistance.

[MagnetJuice]

Yes malofito, I can see why there was not much voltage with the thicker coil. That magnet is very thin.

Usually, the magnet thickness and coil thickness should be about the same. Adding more turns of wire can increase the voltage, but also increases the thickness and the resistance, and that is counterproductive. There are always compromises; it depends on the particular alternator that you are designing.

In addition, as joestue already stated, the highest voltage from the coil is generated when there are magnets attracting each other on both sides of the coil, or at least a blank (without magnets) ferromagnetic disc on one side.

Concerning AmazingMagnets, the way that they measure magnetic pull strength is different from everybody else. Others would rate those thin magnets that you have at around 15 Lbs. instead of 76 Lbs. as they do.

I buy my magnets from these two places:
magnet4sale.com and magnet4less.com

I have purchased many hundreds of magnets from them, the magnets are of good quality and customer service is very good.

To learn about magnets, I go to kjmagnetics.com. They have an enormous amount of good information on their website.

Any questions just ask.

Ed

[Adriaan Kragten]

Cogging is from induction, Fleming's lefthand rule.  Unfortunately its also impossible to avoid.  The byproduct is heat generation and kinetic resistance.

I thought it was clogging, coming from cloggy, sticky, but cogging is coming from a teeth of a wheel as I found in the dictionary, so this might be better. The Dutch word is kleefkoppel. If I translate that into Englisch, I get sticking torque and I have used that word in my KD-reports about this subject.

I think we don't talk about the same phenomenon. What I mean is the pulsation of the torque from stand still position of the armature. This effect can be felt very well for a old fashioned bike dynamo as for this dynamo, the number of armature poles is equal to the number of stator poles. The armature wants to take that position for which all armature poles are opposed to all stator poles as then the magnetic flux flows easiest from armature to stator. If there would be no iron in the stator coils, you would feel no peak on the cogging torque from stand still position.

The torque will fluctuate once the armature is rotating if you have a 1-phase generator. This is because the power of one phase fluctuates strongly. But for a 3-phase generator, the torque fluctuations of the three phases will flatten each other. The torque peak from stand still position for a generator with iron in the coils can be flattened alsmost completely if the number of armature poles is taken two less or two more than the number of stator poles (see KD 580 for a 34-pole or a 38-pole generator using a stator stamping with 36 poles). However, this type of generator requires a special 3-phase winding with coils around only one stator spoke.

If a little fluctuation of the cogging torque is acceptable, one can also use a generator with 16 mechanical poles in a stator with 36 poles and if a magnetic north pole is formed by four rows of magnets. In this case it is possible to use the original 4-pole, 3-phase motor winding. So the ratio in between the number of mechanical armature poles and the number of stator poles is 4 : 9. This option is described in public report KD 718.

Another option is to use a 60-pole armature in a stator stamping with 72 slots (see chapter 9 report KD 727). The same coil configuration will be found for a 30-pole armature and a stator with 36 poles or for a 40-pole armature and a stator with 48 poles. So the ratio in between the number of armature poles and the number of stator poles is 5 : 6.

[joestue]

A theoretical zero losses magnetic core would still cog, but it would do so with no losses (except for the Eddy current losses induced in the magnets).

Anyhow, OP's magnet and coil will also be influenced by the different shape of the emf produced. (It's not a clean sine wave)

Thermally measuring the heat produced by the two coils when connected to a resistor and the magnets spun at the same rpm would be more accurate. This test can be done at the same time given that only one coil was wound for each rather than the 6 or so you would need to produce a 3 phase alternator with 4 magnets.


In my opinion the best way to prove an air core motor or generator is to short circuit the windings and apply a known constant torque to the shaft.

The coil configuration that provides the lowest rpm is the best. You have 3 variables: number of coils, inner diameter of the coils, and thickness.

For an overlapping coil system of 2 layers, you have the width of the coil as a variable as well. Too big and you have more end turn losses, too small and the voltage produced is lower.

You also have the width of the magnet as a variable, usually it's at least 80% of the space available. So for a 12 pole rotor, the gap between the magnets is 5 degrees, the magnet takes up 25 degrees. 12x30 is 360.

[Adriaan Kragten]

If the voltage would vary according to a pure sine wave, the current will also vary according to a pure sine wave if the load is a resistance. So the power, which is the product of voltage times current, will vary according to a sin^2 function. If you have only one phase, the torque will therefore also vary according to a sin^2 function. However, if you have a 3-phase winding and you add the torque curves of three sin^2 functions wth a phase difference of 120° you will see that this results in a constant torque. If you rectify a 3-phase current in star, the current will flow only during 2/3 of the time in one phase. This results in a small fluctuation of the DC voltage and the DC current and therefore also in a certain fluctuation of the torque. If the fluctuation of the voltage in one phase isn't a pure sine wave you will get an even stronger fluctuation of the torque.

[brandnewb]

Cogging is from induction, Fleming's lefthand rule.  Unfortunately its also impossible to avoid.  The byproduct is heat generation and kinetic resistance.

I have heard something similar before indeed. Although what Adriaan said earlier regarding iron core in coils also just feels intuitive.

Anyway, did you mean that when a coil is under load and then a magnet spinning over it gets the coil and magnet attracted to each other and thus cogging? This is how far I have understood it thus far.

[MattM]

Electrical flows create magnetic fields, and vice versa.  Cogging, as a term used in this forum, generally comes from eddy currents forming counter productive flows and fields.  Resistance from generating, which is not what people refer to as cogging, is a byproduct.  Cogging is eddy currents creating unintended magnet fields that add unintended resistance.  Some people utilize the electrical resistance as a brake.  Short the circuit and your generator will come to a stop.  Open the circuit and you lose the resistance.  Braking is not cogging.

[Adriaan Kragten]

Cogging is from induction, Fleming's lefthand rule.  Unfortunately its also impossible to avoid.  The byproduct is heat generation and kinetic resistance.

I have heard something similar before indeed. Although what Adriaan said earlier regarding iron core in coils also just feels intuitive.

Anyway, did you mean that when a coil is under load and then a magnet spinning over it gets the coil and magnet attracted to each other and thus cogging? This is how far I have understood it thus far.

In my KD-reports, I don't use the word cogging. I use number preference positions per revolution. So it means that a non rotating armature wants to stand in that position for which the magnetic flux flows easiest from the magnetic poles in the armature to the iron coil cores in the stator. This is the position for which the overlapping area is largest. If you turn the armature very slowly left or right hand from this preference position, the torque increases strongly untill it reaches a certain peak value. So you have a certain peak torque even if the armature isn't rotating. From that peak point, the torque is decreasing and the armature jumps to the next preference position if you continue the rotation. So you can have a peak torque without rotation of the armature and without the generation of any voltage and current in the coils. Therefore this torque has nothing to do with the torque which is caused by rotation of the armature if a current is flowing through the coils. This rotational torque may also fluctuate and this can be called cogging.

If the stator coils contain no iron, there is no armature position for which the magnetic flux flows easiest and therefore there are no preference positions. The peak torque for a stator with iron in the coils can be decreased strongly if the number of preference positions per revolution is increased to a very high value like it is obtained if a 34-pole or a 38-pole armature rotates in a stator with 36 stator poles (612 or 684 preference positions per revolution).

[JW]

I'm reminded of Flux in one of his postings...

Just because its turning doesn't mean there is power there...

Flux has 6000 posts I was able to keep them all working, yes this user made all those posts and Flavio kept the second generate etc. We are way along further with the modern/comprise  database.   

[joestue]

Electrical flows create magnetic fields, and vice versa.  Cogging, as a term used in this forum, generally comes from eddy currents forming counter productive flows and fields.  Resistance from generating, which is not what people refer to as cogging, is a byproduct.  Cogging is eddy currents creating unintended magnet fields that add unintended resistance.  Some people utilize the electrical resistance as a brake.  Short the circuit and your generator will come to a stop.  Open the circuit and you lose the resistance.  Braking is not cogging.

no, cogging is from the total value of the flux flowing from the rotor to the stator, changing, as the rotor rotates, the pattern repeats every multiple of the magnet tooth combinations. some folks on this board have been resistant to this declaring that the total flux flowing from the magnet is the same all the time. it isn't.

take a magnet and the flux density at its surface might be 1.1 T for a strong neodymium magnet. slip that magnet into a slot cut in a solid block of metal and its flux will increase to about 1.4T. it will also be very difficult to remove from said slot!!  as you slide the magnet into the steel, voltage will be induced both in the magnet and the solid steel block. if the steel block has a magnetic permeability of above 10, it will be nearly indistinguishable from a steel block of a permeability of say, 1000 and if it had a resistance of 100000, you could hook that magnet up to an oscillating multi tool and almost no heat would be generated!! in reality, it will be a good eddy current brake! take the same steel slot and electroplate a .01" thick layer of copper in it, and now the magnet softly lands in the bottom when you drop it in! -electrically, adding the copper would be identical to reducing the resistance of the steel.
some stainless steels are so high in resistance, you can laser weld a stainless steel sleeve inside an induction motor stator, to keep the water out of it. nearly every modern well pump is now built this way! the fact that the steel is non magnetic has little to do with its low insertion losses.. its resistance is so high that the half volt per 4 inches just doesn't generate enough current to appreciably affect the motor performance.

there is a separate issue of torque ripple. bad combinations of cogging plus bad rectifiers feeding a stiff battery load can accentuate each other and get a lot of vibration under load where as a resistor wouldn't. usually this won't be noticed until you reach a mechanical resonance.

every time an electric car goes by and you can hear the pwm.. thats not cogging (they work very hard to find topologies of rotor-stator slot combinations that get rid of it). its torque ripple. or both, combined with the 4-10khz pwm frequency. (so like, you can "hear" the pwm frequency modulated by a lower frequency)

cogging mechanically resonates each stator tooth.. and that wears out motors. so does torque ripple, but to a lesser extent.

[Adriaan Kragten]

Nice explanation Joestue which is in accordance with my explanation of the preference positions due to the easiest path of the magnetic flux flowing from armature to stator.

I agree that vibrations can also be caused by an inverter. Once I visited a man which had a rather large 7 m diameter rotor coupled to a big Chinese axial flux PM-generator. The generator was grid connected by a Danish 3-phase inverter. The generator made a ratling noice when it was grid connected. The man thought that this was caused by the generator. But I said that the generator could not be the cause because it had no iron in the coils and therefore it had no preference positions. If a generator has strong preference positions, it will be noisy at higher rotational speeds. The inverter was changed by a resistance load and the ratling noise was gone.

The inverter separates the DC current coming out of the rectifier in three about sine waves with a phase angle of 120°. But it does this by chopping the current in small blocks with a different amplitude and this causes shocks in the current and so shocks in the torque. The problem may also be caused by the fact that there is some pulsation of the DC current coming out of the 3-phase rectifier and interference in between this pulsation and the pulsation caused by the inverter.

[electrondady1]

the coils you have produced are not a bad size compared to the size of your magnet. Perhaps the bottom of the inside opening could be a bit bigger. but the size of the magnet circle is all wrong. with one magnet positioned in the center of the coil as you have show, the next magnet ( opposite polarity ) should be just touching the outside of the right leg of the coil. As the mag rotor rotates the legs of the coil will be over opposite polarity magnets. it is that change in polarity in the coil legs that creates the electron movement. the faster the change in polarity(crossing speed) the higher the voltage. 
 

[JW]

 
 

but the size of the magnet circle is all wrong. with one magnet positioned in the center of the coil as you have show, the next magnet ( opposite polarity ) should be just touching the outside of the right leg of the coil. As the mag rotor rotates the legs of the coil will be over opposite polarity magnets. it is that change in polarity in the coil legs

Could this be an angular setting

[MagnetJuice]

I think there is some confusion here.

The way I understood is that the OP, malofito, placed 4 magnets on a disc made out of plywood and spun the disc with a drill to find out how much voltage a single coil can put out.

He tested two coils, one at a time, to find out the difference in voltage output between the two coils.

He is NOT building a generator with this setup.

That is why at the beginning, he said:

"Hello don't mind the miniature generator prototype... I'm testing coils..."

Ed

[JW]

The way I understood is that the OP, malofito, placed 4 magnets on a disc made out of plywood and spun the disc with a drill

why doesn't he use a steel disk? there are multiple magnets

I would mention that this typically is measured on a lathe and a single coil. [/quote]

https://www.fieldlines.com/index.php?topic=127284.0

[electrondady1]

there is a relationship between the size of an individual magnet and the center of a coil .
there is a relationship between the width of the coil leg and the width of the magnet.
As i mentioned earlier, if a magnet is under the center hole of the coil  then the next magnet should be just to the right of the right leg of the coil.
So, as the mag disk rotates further, there should be one magnet under the left leg and another magnet (opposite polarity) under the right leg of the coil.
 as JW suggests the magnets should be on a steel disk thick enough to contain the flux.
the diameter of the steel disk should be such that you can lay your magnets out with the proper spacing
i have always used  50/50 spacing on my mag rotors, that being the width between mags at their closest point is the same as the width of the magnet
i recall flux was in favor of mag spacing to be 1/2 the with of the magnet at their closest point .

if your building a dual rotor alternator the flux density will double and the output of your coils will double when you add the second rotor

[Adriaan Kragten]

There is a big difference in axial flux generators built by individuals and axial flux generators built by the Chinese company Hefei Top Grand. Hefei Top Grand uses magnets with the shape of a trapezium and therefore the distance in between adjacent magnets is constant. The distance is taken rather small and the wires of the stator are therefore in between the magnets of the armature for a long part of the time. So a voltage is generated in the wires of the stator for a long part of the time.

If you use rectangular magnets, the distance is smaller at the inside than at the outside. If the distance is chosen large at the inside, the wires of the stator are not in between the magnets for a long part of the time and then no voltage will be generated. So the variation of the voltage in one phase is far away from a sine wave. If three of those voltages are rectified, there might be a rather large pulsation on the DC current and therefore also a rather large pulsation on the torque. I have chosen for circular magnets and circular coils and a distance less than half the magnet diameter in my 8-pole axial flux generators because then the variation of the voltage in one phase is more sinusoidal (see drawings at the end of public report KD 679).

The angle in between the left and the right leg of a coil must be chosen the same as the angle in between two adjacent armature poles. However, this is only possible for the heart of the legs. So for the inner wires of a coil the angle is somewhat too small and for the outer wires of a coil the angle is somewhat too large. This means that there is some difference in the voltage generated in one turn of a coil depending on its position.

[MattM]

The poor man's alternative to trapezoid magnets, IMO, would be trapezoidal magnetic conductors between coil legs.  Hence the premise that iron filings in the fill improves generation.  Obviously, both would be even better but one or the other is the biggest initial gain.  There is always a point where cost outweighs the benefit.  Iron filings are easier to come by than perfect magnets.

Since the filling would be uniform, it seems like one could pre-cast iron fillings before final assembly.

[mbouwer]

But trapezoidal magnets are also offered right?

[malofito]

I think there is some confusion here.

The way I understood is that the OP, malofito, placed 4 magnets on a disc made out of plywood and spun the disc with a drill to find out how much voltage a single coil can put out.

He tested two coils, one at a time, to find out the difference in voltage output between the two coils.

He is NOT building a generator with this setup.

That is why at the beginning, he said:

"Hello don't mind the miniature generator prototype... I'm testing coils..."

Ed

Exactly, well I did test them using a mini vawt 6 inch diameter x aprox 15 inch tall, i made with pvc pipes and used a fan to spin it.

I actually made a coil recently with the same inner size of the magnet, but used #18 wire... 3/8 thick but produced less output 0.15-0.25v, not sure if its because it is not tight enough, made a bigger coil winder but I think i need to fix some things on it.

[Adriaan Kragten]

There is an optimum distance in between rectangular magnets for a 3-phase winding if it is wanted that the rectified DC current is as constant as possible. If the magnets have a width b this distance is 1/2 b at the pitch circle of the magnets. The voltage is only generated when a leg of a coil is in between the magnets. So the voltage in one phase is generated during 2/3 of the time and the voltage U is constant during this time if the magnetic flux in between the magnets is constant. So this means that the voltage is +U for 0° < alfa < 120°, that it is zero for 120° < alfa < 180°, that it is -U for 180° < alfa < 300° and that it is zero for 300° < alfa < 360°. If three of those voltages which have a phase angle of 120° with respect to each other are added by a 3-phase rectifier, you will get a constant DC voltage of +2U (if the voltage drop over the rectifier diodes is neglected).

If the distance in between the magnets is taken larger than 1/2 b, there will be periods for which the DC voltage is supplied by only one phase and so the DC voltage will vary in between +U and +2U. If the distance in between the magnets is taken b, the period for which the DC voltage is +U will have the same length as the period for which the DC voltage is +2U. The DC current will vary in the same way as the voltage if the load is a resistance or a battery and this results in strong pulsation of the torque which will make the generator noisy at high rotational speeds.

If the magnets are lying on a circle there will be a short period for which a wire is only partial in between the magnets, So the voltage will not change as fast from zero to +U or from zero to -U as for a pure block voltage but this effect can be neglected if the magnets are not very long in relation to the diameter of the pitch circle.

So a certian magnet configuration requires a certain coil configuration for an axial flux PM-generator with a 3-phase winding. The voltage in a coil should be generated by two adjacent armature poles and therefore it is useless to test a coil if it is influenced by only the magnets of one pole.

[electrondady1]

" it is useless to test a coil if it is influenced by only the magnets of one pole."

exactly.

[MagnetJuice]

Hi malofito,

Other users here have commented and given you some good information. Most of them have built their own systems and they know what they are talking about, but I think that you are not yet able to understand it all.

I think that you are where some of us were many years ago. I remember when I first learned that passing a magnet over a coil could generate 'electricity', so I wound a coil and started moving a magnet over it, and I could see the needle in the old analog voltmeter jumping. That was exciting. We all have to start somewhere.

I am going to keep it simple. I hope that you will gain some knowledge from this.

Voltage from the coil depends on many things.

1 - Number of turns. If a coil has 50 turns and produces 1 volt, doubling the turns to 100 will produce 2 volts. That is only if the magnet is thick enough. Thin magnets, like the ones that you are using, will not double the voltage in the coil.

2 - The thickness of the coil wire affects only how much current (amps) can safely flow through it. Wire thickness doesn’t affect the voltage, only the number of turns does.

3 - The speed that the magnet passes over the coil affects the voltage. If the speed (RPM) is 100 and produces 1 volt, 200 RPM will produce 2 volts.

4 - Magnet strength. N-45 Neodymium is stronger than N-42. N-52 is very strong and produces the most voltage.

5 - Magnet area. If a magnet is 2 x 1, it will produce two times the voltage than a 1 x 1 magnet can produce.

6 - Magnet thickness. The thicker the magnet, up to a point, the more voltage it will induce in a coil. The flux from a thin magnet cannot reach all the way through the coil; therefore, it will not induce a lot a voltage. If the magnet is thin, adding more turns to the coil will have little effect on the voltage produced.

7 - Distance from magnet to coil. The closer the magnet passes over the coil, the higher the voltage will be.

On an axial flux alternator, you get the best performance when there are steel plates on both sides of the coil and both plates have magnets on them. You can reduce the cost by placing magnets on only one plate.


.


If you have magnets on both plates, you will get be about 40% more power (watts), than having magnets on one plate only.

There has to be plates on both sides of the coil to complete the magnetic circuit. The plates must be steel (ferromagnetic). They cannot be stainless steel, aluminum or wood.

I hope that will get you started on your journey.

Ed