Magnet Density?!

[GreenTeam]

o/   <--- me waving at all
  with a pmg using neodyms, how dense can they be placed on the magnet rotor?
I ask because I see a trend lately with some of the hyper high tech alts and motors - energy densification
I have seen some designs online that are super teensy and I imagine that the magnets are right beside each other!
Why do we not do that hear?
Or use a axial hallbach array?

[bigrockcandymountain]

My motor conversion is pretty much 100% magnet coverage on the rotor surface.  I used 84 pcs 1-1/2" x 1/2" x 1/4 thick n42 magnets.  I wish I had taken some pictures before assembling it. 

[electrondady1]

i always built with 50/50 magnet density using square mags but the Dans (original owners of this site) ended up going with 60% magnet density  using round magnets.  i reason you want a greater distance between the magnets on an individual rotor than you want between the magnets faces between rotors . Taking into account the stator thickness and the two air gaps,  should be a smaller  space than between any two mags on a rotor. You want all the flux moving through the coils. you could checkout Hugh Piggott at Scorage wind to see what density he uses.

 

[Mary B]

Keep in mind those modern motors are using computer controlled coil winding machines and CNC made bobbins...

[GreenTeam]

i always built with 50/50 magnet density using square mags but the Dans (original owners of this site) ended up going with 60% magnet density  using round magnets.  i reason you want a greater distance between the magnets on an individual rotor than you want between the magnets faces between rotors . Taking into account the stator thickness and the two air gaps,  should be a smaller  space than between any two mags on a rotor. You want all the flux moving through the coils. you could checkout Hugh Piggott at Scorage wind to see what density he uses.

I want to actually have magnets alot closer together. My stator is 9.4 or so mm thick, and I am hoping to have a 1 mm gap between stator and magnets.
I think I have a very sturdy bobbin finally, almost the EXACT dimensions of my magnets im using. They are longer than they are wide.

i ask because i am trying to figure out if i can fit 16 magnets on this little metal disc im using for a magnet rotor. I know before everyone points out how small it is, how low the output will be! Im having fun and i want to master it before i move on to the big stuff.

[MagnetJuice]

Hey Green Team, nice work.

A permanent magnet motor and an axial flux alternator are related to each other but they are different. Similar to the relationship between humans and apes. In some ways they look alike, but there are some major differences between the two.

Concerning the halbach array, that is an interesting arrangement that could be useful in the creation of a monopole that could be used to create a magnet motor. A magnet motor would be a self-powered motor. It would rotate by using only the power of the magnets. It is considered the holy grail of inventions that would solve the energy crisis in this planet. But the halbach array is not useful for an axial flux alternator.

For an axial flux alternator, those magnets in your picture are a bit too close to each other. If you put them closer than that, there would be a lot of flux leakage. Flux leakage is when the magnet flux jumps from one magnet to the magnet next to it. You don’t want that, that is wasted power.

Ideally, the magnet flux should flow through the coils to the magnet of opposite polarity on the rotor that is on the other side of the stator. When the flux goes through the coils, it produces voltage, that’s what you want.

You are doing OK. What you have there is a nice little system that you can use to learn from.

Keep us posted on your progress. If you have questions, just ask.

Ed

[GreenTeam]

Hey Green Team, nice work.

A permanent magnet motor and an axial flux alternator are related to each other but they are different. Similar to the relationship between humans and apes. In some ways they look alike, but there are some major differences between the two.

Concerning the halbach array, that is an interesting arrangement that could be useful in the creation of a monopole that could be used to create a magnet motor. A magnet motor would be a self-powered motor. It would rotate by using only the power of the magnets. It is considered the holy grail of inventions that would solve the energy crisis in this planet. But the halbach array is not useful for an axial flux alternator.

For an axial flux alternator, those magnets in your picture are a bit too close to each other. If you put them closer than that, there would be a lot of flux leakage. Flux leakage is when the magnet flux jumps from one magnet to the magnet next to it. You don’t want that, that is wasted power.

Ideally, the magnet flux should flow through the coils to the magnet of opposite polarity on the rotor that is on the other side of the stator. When the flux goes through the coils, it produces voltage, that’s what you want.

You are doing OK. What you have there is a nice little system that you can use to learn from.

Keep us posted on your progress. If you have questions, just ask.

Ed

  Thank you!

[Adriaan Kragten]

The optimal orientation of the magnets of an axial flux PM-generator depends also from the amount of fluctuation of the rectified DC voltage which you allow. If there is no iron in the coils, there is no concentration of the magnetic flux through a coil. So in this case, the voltage is simply generated by a copper wire moving in a certain magnetic field. If you use rectangular magnets and trapezium shaped coils as it is often done, there is a part of the rotation where a tangential wire is moving through a constant magnet field. This means that the generated voltage is constant. Next the tangential wire comes in a region where there is almost no magnetic field and the voltage will then be almost zero. So the voltage fluctuation is not sinusoidal but has about a block shape. A rectified three phase current built up from these block shaped voltages may have rather high peak values. If you take round magnets and round coils, the fluctuation of the voltage is more fluent and looks much more like a sine wave. This gives a rectified current with only a small fluctuation (for rectification of a 3-phase current see public report KD 340). An example of a simple 8-pole PM-generator with 8 circular magnets and 6 circular coils is given in public report KD 679.

[GreenTeam]

Is it possible to use a magnet field line viewer to see if the magnetic energy is not going through the circuit and just jumping to the magnet beside it? Has anyone ever built one and used it?.
i am going to use a vodka mickey bottle and finely ground steel wool in water and try it i geuss....
Dont know what im looking for yet though.....