Tesla's "COIL FOR ELECTRO-MAGNETS".

[MileHigh]

I am assuming a lot of you know the Hyperphysics web site.  It's a great resource.

http://hyperphysics.phy-astr.gsu.edu/hbase/hph.html
http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/indcur.html#c2
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/indsol.html#c1

Here is something to ponder:  When you look at a coil, you can separate it into individual loops of wire.  Each loop will generate a magnetic field that looks like the familiar toroid that extends out to infinity.  So you simply add the magnetic fields together from each loop to get the true magnetic field generated by the coil.  The only tricky thing to remember is that the magnetic field is represented by a vector that has both magnitude and direction.  Therefore all of the additions are vector additions.

And when you strip it down to it's bare-bones reality, that's all there is.

If there is a core inside the coil, then each loop will tend to have more of the magnetic flux it generates travel through the core.  If the windings are many layers thick, the outer windings see a core that is further away with some "air" in between.  Since the "air" is much less conducive to the passing of magnetic flux than the core, almost all of the magnetic flux generated by the outer loops will also travel through the core.   So there is very little difference between a loop that's wrapped directly around the core material and an outer loop that's effectively 1/2 inch away from the core.  Both loops will contribute a nearly equal amount of magnetic flux through the core.  Naturally the outer loop will contribute a bit less because a very small amount of flux will flow through the "air gap."

You can use the terminology "lossy" for the outer loops in the sense that a very small amount of the flux they generate does not flow through the core.  So that's arguably "lost" flux.

What that means is many "exotic" coil winding schemes are exercises in futility.  I know I am using somewhat strong terms but it's true.  All the circuit cares about with respect to a coil is its inductance.  You can wind a coil in many fancy ways.  ZeroFossilFuel made "hemisphere" coils.  No doubt the magnetic field pattern generated by the hemisphere coils will be a bit different.  You can visualize it in your head, each loop creates the toroidal magnetic field pattern.  Some are larger than others and they are also offset from each other.  Big deal, you add up all of the magnetic field vectors and you are still left with an inductor, or an electromagnet.  If you plug the coil into an electrical circuit, the shape and the winding pattern of the coil means essentially nothing.  All that the circuit sees is that the coil has an inductance.  We are going to assume that the capacitance of the coil is minuscule and irrelevant and does not affect the operation of the circuit.

Now, think of some exotic coil winding configuration being used as a drive coil in a pulse motor.  Same deal, all the pulse motor cares about is that the coil has a certain inductance and generates a magnetic field.  Think of all the pulse motor clips with exotic drive coil winding schemes and break them down in your mind into individual turns, and add the magnetic field generated by each turn to get the final field generated by the coil.

What's the point?   The point is that if you are working with coils, just a regular coil winding on a spool of some diameter and some length and some number of turns will be fine.  All exotic coil winding configurations ultimately are not that much different from you basic standard cylindrical coil that you can see anywhere.

Think of a pancake coil and do the same thought experiment were you look at it turn by turn.  If you have never done that thought experiment and do it now you will realize that there is a significant amount of flux self-cancellation going on in a pancake coil, much more than a standard coil.  The larger outer windings will work against windings in the middle of the coil in the "air gap" betwween the two windings.

My favourite "bad boy" coil is a Rodin coil.  Ultimately, there is not a single thing that a Rodin coil can do that a regular coil cannot do better.  A regular coil will always be able to do what a Rodin coil can do with less wire, so a regular coil is more efficient from a materials point of view.  Think about how much self-cancellation there is going on in a Rodin "starship" coil.  The points of the star are useless and do nothing for the coil.  When you think of it, the adjacent star points are engaging in flux cancellation with their neighbouring star points.  So at least that aspect will reduce the inductance of the "Rodin starship" coil.

Perhaps the funky coil windings in a Rodin coil give it more self capacitance and for some unusual reason you want that.  BFD, just put a super tiny capacitor in parallel with a regular coil.

Anyway, that's for you guys and girls to contemplate.  Coils are basic circuit building blocks or electromagnets.  There is no real reason to investigate all sorts of exotic winding techniques.  Likewise some people believe that a coil's windings have to be perfectly neat.  A messily wound coil and a neatly wound coil will be virtually identical.

Wow, that was a big posting!

MileHigh

[Farmhand]

Nice post MileHigh, and to add, neatly wound coils look nice and take up less space but they get hotter easier and take longer to cool because of a lack of airflow through the windings. Wrapping the outside of the coils with tape also allows heat to build up, I don't think a bit of warm is bad for coils unless they get actually too hot or radiate unwanted heat to other things, sealing up a coil (like with tape) can show better if it is dissipating energy through heat, by making it more noticeable. Bottom line with neat coils is they take up a lot less space when trying to fit stuff in a box.

What about aluminium wire, why can't we use insulated aluminium wire to make coils ? It's a lot less weight. What is the lightest core material with the best qualities ?

What do we need to make the lightest high energy electromagnet/motor coils we can make, like for applications in bicycles and such things ?

Cheers

[Magluvin]

I am assuming a lot of you know the Hyperphysics web site.  It's a great resource.

http://hyperphysics.phy-astr.gsu.edu/hbase/hph.html
http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/indcur.html#c2
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/indsol.html#c1

Here is something to ponder:  When you look at a coil, you can separate it into individual loops of wire.  Each loop will generate a magnetic field that looks like the familiar toroid that extends out to infinity.  So you simply add the magnetic fields together from each loop to get the true magnetic field generated by the coil.  The only tricky thing to remember is that the magnetic field is represented by a vector that has both magnitude and direction.  Therefore all of the additions are vector additions.

And when you strip it down to it's bare-bones reality, that's all there is.

If there is a core inside the coil, then each loop will tend to have more of the magnetic flux it generates travel through the core.  If the windings are many layers thick, the outer windings see a core that is further away with some "air" in between.  Since the "air" is much less conducive to the passing of magnetic flux than the core, almost all of the magnetic flux generated by the outer loops will also travel through the core.   So there is very little difference between a loop that's wrapped directly around the core material and an outer loop that's effectively 1/2 inch away from the core.  Both loops will contribute a nearly equal amount of magnetic flux through the core.  Naturally the outer loop will contribute a bit less because a very small amount of flux will flow through the "air gap."

You can use the terminology "lossy" for the outer loops in the sense that a very small amount of the flux they generate does not flow through the core.  So that's arguably "lost" flux.

What that means is many "exotic" coil winding schemes are exercises in futility.  I know I am using somewhat strong terms but it's true.  All the circuit cares about with respect to a coil is its inductance.  You can wind a coil in many fancy ways.  ZeroFossilFuel made "hemisphere" coils.  No doubt the magnetic field pattern generated by the hemisphere coils will be a bit different.  You can visualize it in your head, each loop creates the toroidal magnetic field pattern.  Some are larger than others and they are also offset from each other.  Big deal, you add up all of the magnetic field vectors and you are still left with an inductor, or an electromagnet.  If you plug the coil into an electrical circuit, the shape and the winding pattern of the coil means essentially nothing.  All that the circuit sees is that the coil has an inductance.  We are going to assume that the capacitance of the coil is minuscule and irrelevant and does not affect the operation of the circuit.

Now, think of some exotic coil winding configuration being used as a drive coil in a pulse motor.  Same deal, all the pulse motor cares about is that the coil has a certain inductance and generates a magnetic field.  Think of all the pulse motor clips with exotic drive coil winding schemes and break them down in your mind into individual turns, and add the magnetic field generated by each turn to get the final field generated by the coil.

What's the point?   The point is that if you are working with coils, just a regular coil winding on a spool of some diameter and some length and some number of turns will be fine.  All exotic coil winding configurations ultimately are not that much different from you basic standard cylindrical coil that you can see anywhere.

Think of a pancake coil and do the same thought experiment were you look at it turn by turn.  If you have never done that thought experiment and do it now you will realize that there is a significant amount of flux self-cancellation going on in a pancake coil, much more than a standard coil.  The larger outer windings will work against windings in the middle of the coil in the "air gap" betwween the two windings.

My favourite "bad boy" coil is a Rodin coil.  Ultimately, there is not a single thing that a Rodin coil can do that a regular coil cannot do better.  A regular coil will always be able to do what a Rodin coil can do with less wire, so a regular coil is more efficient from a materials point of view.  Think about how much self-cancellation there is going on in a Rodin "starship" coil.  The points of the star are useless and do nothing for the coil.  When you think of it, the adjacent star points are engaging in flux cancellation with their neighbouring star points.  So at least that aspect will reduce the inductance of the "Rodin starship" coil.

Perhaps the funky coil windings in a Rodin coil give it more self capacitance and for some unusual reason you want that.  BFD, just put a super tiny capacitor in parallel with a regular coil.

Anyway, that's for you guys and girls to contemplate.  Coils are basic circuit building blocks or electromagnets.  There is no real reason to investigate all sorts of exotic winding techniques.  Likewise some people believe that a coil's windings have to be perfectly neat.  A messily wound coil and a neatly wound coil will be virtually identical.

Wow, that was a big posting!

MileHigh

"What that means is many "exotic" coil winding schemes are exercises in futility."

Wow. You really dont want us to mess with these coils do you.? Im not going to fight here, but I will respond as I see fit.

The first thing Im seeing with the bifilar is it takes on a charge much faster than a normal coil. With a coil that has more turns, the resistance is higher, sure, and the inductance is higher also. But it doesnt seem to act like a large inductor does with with an uphill climb in current due to high impedance. So it seems that the difference is that the bifi takes in current quicker and produces the magnetic field to its max much quicker, possibly instantaneously as compared to a normal coil of the same dimensions. This is far from just adding a cap across a coil. Will do some vids as I get things set up to see things more clearly.


"All the circuit cares about with respect to a coil is its inductance"

Thats not true. If there is capacitance in the coil, it should be ignored, right? If we were to put a cap across a normal coil as you say, if we pulsed it like in a pulse motor, the very first thing the circuit sees is the capacitance and the circuit charges it before much happens in the coil. But in the bifi, the charging of the capacitance happens through the windings of the coil, and since the capacitance neutralizes the self inductance till the capacitance of the coil is fully charged. Talking a DC pulse of course.


"If you plug the coil into an electrical circuit, the shape and the winding pattern of the coil means essentially nothing."

If we wound a random ball of wire, and a nice neat coil of the same wire and length, there are many differences between them.


"We are going to assume that the capacitance of the coil is minuscule and irrelevant and does not affect the operation of the circuit."

Why exactly should 'we' 'assume' this? What if we didnt?


"Think of a pancake coil and do the same thought experiment were you look at it turn by turn.  If you have never done that thought experiment and do it now you will realize that there is a significant amount of flux self-cancellation going on in a pancake coil, much more than a standard coil.  The larger outer windings will work against windings in the middle of the coil in the "air gap" betwween the two windings."

Personally I dont think the pancake is a good choice for a pulse motor driver or pickup coil. If the magnetic field of the magnet cuts only a mall portion of the coil at a time, like passing only a section of windings as it passes, the inductance of the rest of the coill works against current flow. Its better to have the windings bundled up so that the field 'cuts' all and as much of the windings on one side of the coil as possible. Even better to have an opposite magnet field cutting the other half of the coil at the same time to avoid the inductance hindering currents to flow quickly. Look at the windings of an alternator and look at the gaps in the core where the magnetic field is 'dragged' through in order to 'cut' the windings to induce current flow. They are not wound on spools wound in a circle. They are wound lengthwise and the portions of the windings that are not in a position for the magnetic fields of the rotor(with field core inside) to 'cut' them, are very short and bend around to the next core gap. So most of the coil in the alternator, both sides at the same time are being induced by the rotor with little left virtually untouched by the rotors passing field where the windings bend and turn into the next core gap.

These cores are what many motor builders should concentrate on in order to make the best use of controlling how the fields cut the windings as a gen coil and controlling and condensing the drive fields also. I Have a reply for Farmhand to one of his posts today in the confirming delayed lenz thread, where ill show the inside of my bike motor and another little treasure that I found from spare parts at work from a VW Touareg that I will be working with soon.

When we make pulse motors with 1 drive coil, if we dont capture and direct as much of the field of the coil to the rotor, then we are wasting energy. If we have 1 coil and not using the back end of the coil we are wasting a lot. That 1 coil can be configured to apply both ends of the coil to the rotor using core materials and the rotor will essentially act like 2 coils were used instead of 1. Doing this will give more rotor torque and speed using the same single coil.


"There is no real reason to investigate all sorts of exotic winding techniques."

Welp, Im gunna do it anyhoo. 



"Likewise some people believe that a coil's windings have to be perfectly neat.  A messily wound coil and a neatly wound coil will be virtually identical."

Can you provide a good link that describes what you are saying in the above quote?
Thane uses messy wound coils from what I hear.


Mags

[MileHigh]

Magluvin:

Good luck in your investigations and I will make a few comments.

The first thing Im seeing with the bifilar is it takes on a charge much faster than a normal coil. With a coil that has more turns, the resistance is higher, sure, and the inductance is higher also. But it doesnt seem to act like a large inductor does with with an uphill climb in current due to high impedance. So it seems that the difference is that the bifi takes in current quicker and produces the magnetic field to its max much quicker, possibly instantaneously as compared to a normal coil of the same dimensions. This is far from just adding a cap across a coil. Will do some vids as I get things set up to see things more clearly.

When you say "charge" I am assuming that you mean current flowing through the coil to energize it.  If we assume that a series bifilar coil gets the inter-coil capacitance charged right away (which would have to be verified), and we are really simplifying things here, it's still impossible to escape the fact that it takes electrical work to energize the coil and build up the magnetic field.  There seems to be a train of thought that somehow a series bifilar coil allows the coil to energize very quickly, seemingly implying that this can be done at very little energy cost.  It's simply impossible, to build up a magnetic field takes electrical work.  That work ends up being stored in the magnetic field.  The stored energy is 1/2 L i-squared.  Note for a flywheel it's 1/2 MoI omega-squared - the same formula.

There is just no "jailbreak" for energizing a coil, be it a regular coil or a series bifilar coil, which as we know is just a different winding pattern for a regular coil.  Beyond that, I am not aware of any serious analysis of this on YouTube or elsewhere.  I don't want to be a party pooper, but to the best of my knowledge this issue simply never comes up in the real world.

The true actual dynamics of how a series biflar coil actually will actually react is not trivial at all and is probably beyond the capabilities of most forum experimenters.  It's possible that your testing will show something, and it's just as easily possible that the effects will be so small that it will be hard to discern what is causing them.

For example, look at this Spice model and analysis of a transformer:
http://fmtt.com/Transformer%20SPICE%20Model%202-14-08.pdf

This image is called, "Fig. 1. Equivalent circuit of single-phase power transformer windings."
http://ars.els-cdn.com/content/image/1-s2.0-S037877961000060X-gr1.jpg

So if you are going to get "hardcore" the actual modelling of how series bifilar coil works and reacts to an outside stimulus could get incredibly complicated.

I suppose the question is is it worth the trouble?  Perhaps just an A-B comparison between two coils with the same number of turns, one regular, one series bifilar would be a good test.   Supposing you notice a tiny current inrush on the series bifilar when you energize it and you don't see that with regular coil.  Like I already said, there is no magic bypass for the energy it will take to energize either coil.

So this possible tiny current inrush, does it mean anything?  Can you do anything practical with it?   That's the real question.

The theme behind my posting is to try to recognize what's relevant and what's not relevant when you experiment.  That is an important basic fundamental skill worth learning.  Do you spend hours and hours doing some kind of special winding for a coil or do you spend 20 minutes and just wind an ordinary coil, or do you buy a spool of wire at the electronics store and have an "instant coil?"

MileHigh

[Magluvin]

What about aluminium wire, why can't we use insulated aluminium wire to make coils ? It's a lot less weight. What is the lightest core material with the best qualities ?

What do we need to make the lightest high energy electromagnet/motor coils we can make, like for applications in bicycles and such things ?

Cheers

Ugh!!! just tried to post the pics of my bike motor. And I lost a long post. The files were too much to post and when I went back to pull some pics and post them in another post it was all gone. Ugh!!!

heres the pics, will post the text in a bit. Spent an hour sizing and writing. Ugh ugh.

Ok figured it out. Some pics were not resized.

Ill condense my post here.

The bike motor is asymmetrical where the coils fire off at different times for smooth torque and reduce cogging. I want to replace the bikes control board with an Arduino to reduce the restrictions programmed in. Different number of mags vs coils.
The last 2 pics are of the main parts of an alternator from a 2004 5L twin turbo Touareg. it has permanent magnets!!  Never seen that before. And I can configure it like the bike motor to be a motor. Its asymmetrical also but just a different number of elements. Ill use this to test and try the Arduino as a controller before I build for the bike.

Removing the core of the bike motor is a serious effort. Putting it back in I will have to make a jig. Were talking a lot of force here. Squash finger like grape. Mr Miagi said. 

Also the alternator is a sweet setup to mess around with otherwise. Using motors that are already made and modding them will give the advantages of premade framework to control the flux efficiently within the motor. Making motors with 1 round coil that doesnt even take advantage of the back side of the coils fields and is extremely inefficient. Lots of waste of input. This goes for motors and gens. Its ok for comparison testing and gathering field collapse, but not much torque or gen activity from the motoring part. RC motors are great bases to work with. Larger motors are probably easier to rewind and less costly is many ways. The RC motors can get pretty expensive for such a small package. Some are reasonable.

Had a lot more in the lost post but I gota git.

Mags