Neo magnets

The important thing is not so much the shape of the magnet as such, but the shape of the field it produces and the orientation of that field.

The ultimate objective in any case is for the coil windings to cut as many field lines as possible, as fast as possible, in order to produce the most electricity for a given coil/magnet combination.

As we don't know your magnet's field orientation with respect to the coil, it's gonna be a bit tough to give you a specific, optimal solution to your problem.

Is your 'trapezoidal' magnet a true 3D trapezoid (a prismatic, polyhedral shape) or are you using the term when you really mean 'truncated cone?' If your magnet is a (truncated) cone, is the field oriented along the axis or does it have some other orientation?

Hi,

Your information is too vague to give you any definite answers, but I can give you a few items you need to consider in order to proceed.

First, there are a variety of basic magnetic materials (Strontium Ferrite, Neodymium, Alnico, Samarium Cobalt), and within those basic groups, several grades of differing strengths and coercivity. Each has a number and each has a list of general parameters defining it. Without knowing your design goals and operating conditions, its hard to know which would be best for you.

Secondly, for each type of material, there are guidelines for length versus surface area to give the optimum energy per mass of material.

Third, not only the shape and orientation of the magnets are important, but the entire magnetic field geometry, and the quality of the steel. Too little steel or too little magnetic conductivity and the whole design becomes less efficient. Various steels have different points where they saturate magnetically, so you need to consider the geometry and steel quality carefully.

In the final assembly of wire and magnetic field, the number you are interested is the B x L product, or the magnetic energy times the length of wire in that field. It can be calculated instantaneously at any given point in time or orientation (much simpler), or it can be calculated given their relative positions (more difficult, but more accurate).

The good news is there are variety of tools available to perform magnetic FEA (finite element analysis) and give you a 'snap shot' prediction of cause and effect, and save a lot of time and money before you spend money on pieces and parts. Some of the software is costly, but some, more basic analysis software is free.

Here's one for your reference, but there are other solutions you can find by entering 'magnetic analysis software' in most popular search engines.

http://www.freebyte.com/cad/fea.htm

My best advice is to do some quick research before you spend time and money on models and prototypes of whatever you are building. There is a lot to consider, and it can be the difference between disappointment, and a great first step.

Good luck ... tell us more ... and keep us posted on your success.

(and join CR4 so you can get email responses automatically when someone takes the time to answer you )

Indeed there are a lot of factors to the principal of magnetic-induction.

To increase the efficiency of an inductor then shape of the coil should definitely be rectangular so that the longer-sides should run along in parallel with the axis of the magnetic-field but in 90degrees with respect to its direction.

The longer-sides will be cut by the magnetic-field during rotation and act like effective captors of the magnetic-field therefore, they should be as long as possible in order to increase the effective capture area of your coil-wire by the magnetic-field.

The shorter sides of the coil-wire, which fall on the ends of the magnetic-field, they only serve as links between the longer-sides as they are in parallel with the direction of the magnetic-field therefore, they do not generate effectively.

A car alternator's individual induction loops are only covered about 50% effectively (i.e. in right angle) by the magnetic-field due to their square shape.

So, if you wanna make sure your coils are the least efficient then make them round shaped!

When you start working out the geometric shape of a round inductor then you'd realise that a very-small portion of the entire length of the coil-wire falls perfectly in perpendicular to the magnetic-field.

It is different if you use it as an electro-magnet because then the shape does not matter as far as creating the magnetic-field is concerned. (However, its shape may still become a concern if you wanna effectively capture most of its magnetic-energy.)

I would also recommend you to read upon about this as much as you can about the principle of induction. There are a lot of factors DCaD he mentioned and are equally important!!!

Thanks for your input.

My understanding from all the comments from people like yourself is that the long sides of a coil produce the most current(volts) when a magnet is passed over them. If that is the case then, would it be better to have very long coils and long magnets ,(as long as possible) radiating out from the center of the rotar and stator discs.

hi miik999,

I don't know if you referring to me but I'll take the initiative anyway to answer back.

Try to get the coils designed so that most of its length will be cut by the magnetic field. The physical size of your coils will be determined by the voltage and by the expected current. (The voltage will affect the length and the current will affect the diameter of your coil-wire.)

Naturally, the Neo magnets should be the full length of the coils. And I don't know what device you're designing but obviously the stronger the magnets the better. You should also remember to keep the magnetic-length of the stator-core as short as possible. I assume you're making an Alternator and not a Generator or Dynamo as they used to call it?

Also make sure you leave enough vent-holes.

One last thing!!! The permanent magnet excited generators RMS output voltage will be determined by the rev as there's no voltage regulator. If freq. control is important as well as the output voltage then you may have a problem to conveniently control these two at the same time. You may have to adopt a mechanical arrangement besides rev control.

the answer here is ones with corners as this will aloow you to use the corner vortexes. the more corners you have to pass over the wire the more you will excite the wire and make more power.

read this

Howard Johnson - The Secret World of Magnets (Spintronics)

this is a interesting read

Reading the comments to date there is a practical aspect that has not been discussed, assuming that the author's goal is to build a rotor as part of a generator. The author's question is general, but a generator might be the goal.

Trapezoidal magnets and coils are more efficient in real estate usage if a rotor is being built as part of a generator. The coils are be laid out in a circular pattern on the rotor, and the diameter of the circle is defined by the number of coils needed to generate the desired number of poles and phases needed (a coil is a pole and wiring a minimum of 3 poles together creates a phase, and most generators are 3 phase requiring a minimum of 9 coils or "poles").

Trapezoidal coils require a smaller layout diameter than circular coils because more coils per circular inch can be placed vs circular coils. This can significantly reduce the overall diameter requirement of the rotor. When designed for highest efficiency the long edges of the coils will be parallel to the coil next to it. Think of radial lines radiating from the center of a circle out to the circunference. The optimal trapezoid design would have its edges parallel to those lines so that the edge of one coil would be equally spaced along its length from the coil next to it.

Also, use of trapezoidal coils and magnets makes field changes quicker because the long side of the magnet passes over the long side of the coil resulting in a faster coulped field risetime. Using circular coils and magnets the field change gradually increases and gradually decreases as the magnet moves past the coil. At higher rotor RPMs the peak coupled field into the circular coil may decrease due to inefficiencies of the coil, wire, spacings, etc. The same inefficiencies are also present in the trapezoidal coils, but due to the faster rise time of the coupled field the peak field coupling is still achieved at higher RPMs.

There are many websites about generator design, usually refering to there usage in wind turbines. The vast majority, particularly higher power ones, use trapezoidal coils and magnets.

Of course if you are only trying to generate electricity by waving a magnet over a coil then either shape will do. It all depends on what you are trying to achieve.

All the advise given in the forum is very useful, but the best way to learn is to experiment, make small improvements, and test again.

Hope this helps.