magnetic fields

A lot of the math for AC machines was perfected and published at the beginning of the twentieth century. Check out the published works of Charles Steinmetz and N. Tesla. Their work allowed optimal machines to be built without testing every conceivable prototype.

Tesla was more secretive and jealous of his patents, so you may not find as much technical detail in his published works.

Voice coils spring to mind. That is a linear motor. You can salvage some parts from a hard drive to play with one. The older and bigger, the better. If you could track down an IBM 3330 voice coil assembly you would have something worth doing some work with. (coil the size of an oat meal can and magnets like paving bricks, 3" stroke). On the other end of the scale is a regular speaker. If you couple this with a lot of coils and a controller you have a linear accellerator that you can shoot like a gun

On Thu, 03 Apr 2008 15:16:29 -0500 snipped-for-privacy@aol.com wrote: | On 3 Apr 2008 18:31:50 GMT, snipped-for-privacy@ipal.net wrote: | |>I'm on a quest to find a good book that covers information about magnetic |>fields as it applies to power and/or radio engineering. For power, this |>would be things like generators, motors, and transformers. For radio, it |>would be a lot about antennas. Right now my preference is for the power |>side of this. |>

|>Doing searches through Amazon and B&N I find many books about things like |>motors and transformers. But pretty much everything is about how to do |>things like install, maintain, and repair them, or select them for various |>applications. There are some that cover the theory, but they did not look |>to be the best choices. I am interested more in things like the design of |>devices like generators, motors, and transformers, with respect to how the |>magnetic fields are used and shaped, particularly for specialized devices |>handling non-ordinary needs. A typical motor, for example, just turns a |>rotor, and has a classic axial construction. I'm interested in unusual |>things like non-rotary motion devices (electric pistons, for example) as |>well as unusual rotor motion devices, such as ring motors that have no axis |>at all. The focus I am looking for in an ideal book is on the design or |>the exporation of designs for a wide variety of devices, with an emphasis |>on how the magnetic fields are shaped and operate, whether coupling to |>electric windings, or interfacing with mechanical motion of any kind. |>

|>Pure electromagnetic or magnetodynamic theory is not the interest. Nor is |>the manufacturing, selection, installation, maintenance, or repair of such |>devices (though something that focused on the very unusual devices might |>provide some insight into their design). | | Voice coils spring to mind. That is a linear motor. | You can salvage some parts from a hard drive to play with one. The | older and bigger, the better. If you could track down an IBM 3330 | voice coil assembly you would have something worth doing some work | with. (coil the size of an oat meal can and magnets like paving | bricks, 3" stroke). On the other end of the scale is a regular | speaker. | If you couple this with a lot of coils and a controller you have a | linear accellerator that you can shoot like a gun

I'll hunt around in my basement to see if I have some old 3330's I'm no longer using :-) Actually, the 3350's looked like more awesome magnets.

Right now I'm focusing on looking for the information on how magnetic fields are engineered for various things including this. Yes, a voice coil is a very good example of a specialized magnetomotive device.

One interest I would have is substituting a magnetically driven device like this (which a voice coil could very well work) for the escapement of a clock as a means to electrically control an otherwise mechanically operated clock. One approach would be a mechanical escapement that is driven magnetically to overpower the gear forces. Another idea is to make a gear that instead of teeth, has alternating magnetic bars, and just drive it entirely from the field of two coils.

A couple years ago I mentioned the idea of making toothless gears by having alternating magnetic bars in each "wheel" that engage each other magnetically. The same wheel can be the rotor of a permanent magnet syncronous motor, too, by driving it from a sufficient number of electromagnetic windings. One of the things I want to explore is the diversity of winding shapes that can be used for doing such things, either for motor drives, or as a generator to either produce power from some primary mover, or to sense motion (which could also be done optically in a powered system).

I have no one particular goal at this time, other than to learn more about the way magnetic fields can be constructed. Maybe this will inspire some creative idea.

On Thu, 03 Apr 2008 19:54:31 GMT Beachcomber wrote: | | |>On 3 Apr 2008 18:31:50 GMT, snipped-for-privacy@ipal.net wrote: |>

|>>I'm on a quest to find a good book that covers information about magnetic |>>fields as it applies to power and/or radio engineering. For power, this |>>would be things like generators, motors, and transformers. For radio, it |>>would be a lot about antennas. Right now my preference is for the power |>>side of this. | | A lot of the math for AC machines was perfected and published at the | beginning of the twentieth century. Check out the published works of | Charles Steinmetz and N. Tesla. Their work allowed optimal machines | to be built without testing every conceivable prototype. | |

| | Tesla was more secretive and jealous of his patents, so you may not | find as much technical detail in his published works.

The math will help. I'm also looking for geometric ideas. That is, how can a magnetic field be shaped in different ways for unusual devices, either in the form of motive interfaces or electrical interfaces.

Consider, for example, a pair of steel wires spiraling around each other. A current in one of them (steel isn't the best conductor, but is usable) should induce a magnetic field in the other. Now consider what if at the looped around end, they switch such that on the 2nd pass, the current is now going through the "other" wire. Both should now have current AND a magnetic field, I would think (since it is effectively one wire). Now to figure out how to get the current into this wire without breaking the magnetic field. Something else coupling to it would seem right. Maybe a separate copper wire (everything being insulated or separated) running along side? Maybe a current transformer? Not that there is anything useful that could ever be made from this; it's just exploratory ideas.

There are many texts that cover the basics of what you want. The older ones do put emphasis on magnetic "paths" and optimisation of them (basically- keep air gaps to a minimum and work the iron just below the knee of the B-H curve) and all do deal with the whole business of force production -whether in solenoids, motors or whatever, in terms of energy balances. These are generally at the junior to graduate EE university level. Unfortunately, they do require some basic calculus at the minimum. Some lower level texts do cover much of this for simple situations such as loudspeakers. The basic concepts apply to the things that you want to explore. For example, winding shapes/locations may or may not be important depending on what the winding is intended to do but often simply become a case of what is practical for the purpose.

Try looking for texts on "electromagnetic energy conversion" rather than "motors". I also may be able to send you some notes in pdf or word form- with your correct address.

| There are many texts that cover the basics of what you want. The older ones | do put emphasis on magnetic "paths" and optimisation of them (basically- | keep air gaps to a minimum and work the iron just below the knee of the B-H | curve) and all do deal with the whole business of force production -whether | in solenoids, motors or whatever, in terms of energy balances. These are | generally at the junior to graduate EE university level. Unfortunately, | they do require some basic calculus at the minimum. Some lower level texts | do cover much of this for simple situations such as loudspeakers. The basic | concepts apply to the things that you want to explore. | For example, winding shapes/locations may or may not be important depending | on what the winding is intended to do but often simply become a case of what | is practical for the purpose. | | Try looking for texts on "electromagnetic energy conversion" rather than | "motors". | I also may be able to send you some notes in pdf or word form- with your | correct address.

One thing I am curious about is shaping the magnetic field. Normally if I have one simple winding, I'm going to have a certain rather common field shape looping inside the coil and back outside of it all around it. And the field would have a highest density somewhere near the coil (exactly where is one thing to know) and gradually decrease in density as the distance grows. But if I insert additional coils, there will be a combined effect of the fields. In much the same way as multiple elements of a radio antenna can shape the emission pattern, this is what I want to learn about for magnetic fields. Suppose I want a field that has a particular shape in a certain cross section? What if I want a field that is relatively flat in density up to a point and then falls off rapidly? This goes to things like minimizing the effect and coupling of the field in certain directions, while maximizing it in others, with or without shielding. Or maybe "active shielding" which could be in the form of added small coils to cancel out some of the field in certain places where it is undesired. Or maybe "controlled shielding" which could be those added coils being energized or not depending on immediate needs as determined and controlled by a special driving circuit (or computer).

OK, I guess that wasn't _One_ thing :)

More thoughts:

And ... the magnetic field of the Earth itself would be something to learn more about. I do know a nearby electromagnetic field strong enough can overtake the Earth's field at that point and control a compass needle.

I've heard that some transformers are made with steel wires instead of steel plates as the core. Do they have to be "insulated" from each other?

What are the advantages and disadvantages of winding coils separately on different sides of a square core vs. both windings over each other or even mixed together around the center bar of the core?

I asked last year about a motor idea where the stator was driven in one direction and instead of having permanent magnets on the rotor, it was driven with a rotating electromagnetic field, too (have as many phases as might be useful, 3, 6, 12, etc), and in the opposing direction. The idea was to get a syncronous motor with the rotor going at twice the speed as one with simple permanent magnets would. Coupling the power into it might be a trick to make it practical.

I would expect this stuff to be junior/senior EE, at least for power track majors. All the EE I ever took in school was a couple courses, one in audio electronics, and one in digital design. I didn't have the in-depth curiosity for other stuff as I do now.

My email can be derived from my signature, or by removing appropriate the "-news-nospam" part from the posting header email. PDF is easiest for me to view.

------ It appears that you are considering "air core" situations and the approach to the questions that you pose would require some form of field mapping rather than an analytical approach. Very messy. The basic Maxwell's equations would apply but in such cases, numerical analysis would be needed. At one time, there were plotting tanks for 3D analysis and "teledeltos" paper (conducting) for 2D cases. These are resistive analogs and equipotentials could be plotted- following this, field lines could be plotted on the basis of "curvilinear squares" (i kid you not). THe same techniques apply to stream flow, electrostatic fields,etc. but now are done through computer programs.

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Yes- for the same reason that the normal laminations are insulated from each other. This is done to reduce eddy current losses.

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------------- There is always some leakage inductance so that ideally it is best to have the coils as close to each other as possible to minimize the flux that leaks or doesn't couple both windings. It is pretty awkward to mix the coils together (particularly for higher voltages) so it is best to have the windings one on top of the other, and often the windings are split so that each leg of the transformer has half of each winding. Spacing between windings and between winding and core will depend on insulation needs and cooling requirements. EHV windings will be actually be wound on "pancakes" because of insulation needs as well as capacitance distribution.

------ I remember that discussion. It seems that what was needed was that the field of the rotor, as seen by the stator had to be at synchronous speed.

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------------ That would be the level but a lot of the transformer design has been developed and optimised in industry.

Ok- I will dig up and modify some old notes and get them off to you. Some deal with magnetic forces and others deal with induction and synchronous motors.