# Does a coil with CW and CCW turns split its B field?

1. Mar 12, 2016

### Chris Fuccillo

Single Electro magnet with split field
Single core with separated counter clock wise and clock wise turns

My question: I’m not worried about field strength at the moment, I am just trying to make sure that the field will develop in this manner? Note: Please see picture.

If you take a ferrous material core rod radius r and length L, then you wind the wire CCW half the distance, then you switch and wind the other half of the core rod CW. The CCW wire windings will never cross the CW wire windings, if that happens you get non induction windings. The CCW turns are on the left of the rod and the CW are on the right. Note: Please see picture

Last edited: Mar 12, 2016
2. Mar 12, 2016

### Staff: Mentor

It will develop in that way, but it will be very weak.

3. Mar 12, 2016

### Chris Fuccillo

Thank you and this will bring my next question

Now that we know the field will develop as in the picture, I want to look as strength of the B field. I know the overall field will be week, I am more interested in the individual fields B1 and B2 respectively

Can B1 and B2 be calculated individually with the standard formulas if I use the area and number of turns in one of the sections? example CCW section has 10 turns and its magnetic path “Lm” is just area under the CCW turns of my core material falls under diamagnetism, the magnetization M is often proportional to the applied magnetic field such that: B= µ*H

H field: H = N*I/Lm

N = turns

I = Current

Lm = magnetic path

Note: H is in A/m

Then

B field: B= µ*H

µ = permeability of core

H = H field in Am

Note: B= B field in Tesla
Note please reference picture in original post

4. Mar 12, 2016

### Staff: Mentor

It cannot, and the field will depend on details of the transition region. If one coil has significantly more windings than the other, then you get a single coil with the normal field behavior to a good approximation. If you have the same or a very similar number of windings, things get complicated.

5. Mar 12, 2016

### Chris Fuccillo

Each coil will have the same number of windings. The transition area will leave the minimum x distance required with no windings between the CCW and CW turns to allow a region of magnetic domains in the material with no windings to allow the fields to exit the core. The goal is to have B1 and B2 be equal or as close to equal as possible. If there is a change to how you would calculate the B1 and B2 fields besides H field: H = N*I/Lm and B field: B= µ*H could you point me in the right direction?

6. Mar 13, 2016

### Staff: Mentor

Where is the point of that setup?
To a good approximation, you get the sum of the magnetic field of the two coils, using that formula. But that sum is exactly zero. The remaining field you get is only from deviations from that formula. And those deviations are complicated.

7. Mar 13, 2016

### Chris Fuccillo

First off thank you again so much for going through this with me. It helps talking with others that understand magnetics because I am doing a few things that are not standard lol.

Ok I get that the sum of B1 and B2 fields should equal approximately 0 and the overall field is only the deviations but the physical fields B1 and B2 exist and each will have a value correct? Also it’s just the resulting field over the entire coil B1+B2 = 0 correct? B1 and B2 are also their own independent fields?

Imaginary numbers basic Example “T = Tesla” “Bt = B total for entire coil”

Basically If Bt = B1+B2 “B1 = 1T→” and “B2 = 1T←” so “1T→ + 1T← = 0”

If the B1 section of coil has a third independent magnetic field to interact with that we will call B3 also make B3 = 1T and let’s say B3 is a permanent ring magnet for ease of the example and sits around the B1 section of coil “IE the coil is through the center of the ring magnet”. The B1 and B3 fields will have their own interaction independent of B2 based on the values B1 and B3 correct?

Last edited: Mar 13, 2016
8. Mar 13, 2016

### Staff: Mentor

Splitting the magnetic field into components B1 and B2 is completely arbitrary. Only the sum is a physical quantity you can measure.

Adding a third magnetic field just means you'll get the field of the third component, with tiny additional components from B1+B2.

9. Mar 13, 2016

### Chris Fuccillo

I might need to clarify a little more my goal is the magnetic force between B1 and B3.

So B1 would apply no magnetic force against B3? the overall field strength can be just B3 that’s not what I'm looking for, what I am actually looking for there to be force between B1 and B3

So if B1 and B2 were independent coils(electromagnets on 1 core) turned on as opposite magnetic polarities and B3 was still around B1 there would be no force interaction between B1 and B3?

p.s I love your avatar :)

10. Mar 13, 2016

### Staff: Mentor

Fields do not apply forces against each other.
Fields can apply forces against moving charges. The force the coil 3 would feel would be nearly zero, as the forces due to "coil 1" and "coil 2" cancel to a very good approximation. The wire along coil1 and coil2 would feel some force.

What is the overall point of the questions? Is there some problem you want to solve?
:)
It is an artist's impression of 1SWASP J140747 b

11. Mar 13, 2016

### Chris Fuccillo

The artist did a nice job J I have a lot back ground on my work computer that are artist rendering of deep space

I want to apply magnet force on a free floating permanent ring magnet B3 that has 1 or multiple electromagnet ie: core and windings that generate B1 and B2 field through the center of the ring magnet to induce motion of the ring magnet. Much like a coil gun would work except being on the outside of the coil instead of in the center. I only wish to move the ring magnet about 15 to 30 mm depending on other variables.

I was also hoping a split coil would be easier to wind, than having to rout return paths for the wires if it has to be individual coils. that is if I could get the same effect from a split coil. tolerances and spacing are important :)

Last edited: Mar 13, 2016
12. Mar 13, 2016

### Staff: Mentor

If you want to apply a force on B3, then your coil design is pointless. Removing the core would probably increase the effect. You also have to break the symmetry, as a permanent magnet needs an inhomogeneous magnetic field to feel a force.

13. Mar 13, 2016

### Chris Fuccillo

In short making individual coils for electromagnets then to develop B1 and B2 is the best way to proceed? The core material is required to develop the field and lower the current needed for the electromagnet. There is less and 0.1mm separating the OD of the coil windings and ID of the permanent ring magnet.

14. Mar 13, 2016

### Staff: Mentor

Probably.

15. Mar 13, 2016

### Chris Fuccillo

that is how the system is designed now with individual electromagnets currently, I was just hoping a split coil might have been possible because it would get rid of the timing requirement and having to rout wire inside the core or notching the core to rout the wire so that its flush with the core material.

I was hoping the split field would mimic the individual electromagnet fields where there is separation between the CCW and CW turns. I think I am still a little confused as to why the split coil would not work. Below I added the ring magnet B3 at position X on the coil and its field direction in the picture below. The field is opposite that of the B1 field. I just have a hard time seeing why the B1 section of the coil which creates the B1field that develops in that area and the B3 fields would not exert force on each other and cause B3 to travel when the coil is turned on while B3 is on the B1 side of the coil? B1or B2 itself are not homogenous and B1+B2 make the total B field that is homogenous?

16. Mar 13, 2016

### Staff: Mentor

Splitting the cables doesn't make a difference. Splitting the core does.
A permanent magnet in a homogeneous field won't experience a force. In which direction should that force go?

17. Mar 14, 2016

### Chris Fuccillo

So if I split/cut the core in half and use a spacer of nonmagnetic material then I can wind the B1 and B2 coils as drawn with the CCW and CW winding with the single wire, then the permanent magnet will experience force? This way B1 and B2 are individual coils on individual cores correct. It is ok to bond the 2 coils together as long as there is a gap/spacer making it so that it is no one solid core but two individual?

18. Mar 14, 2016

### Chris Fuccillo

I wanted to say thank you again for your help.

I am going to start changing my physics model when I get home tonight to see the differences with the core split with a gap and the CCW/CW windings. The single wire makes it a lot easier to construct the prototype thankfully :) I have been cutting strips of core material and bonding them together for a while now. Unless you point some thing else out that keep will me from getting force on the B3 permanent magnet now that I will be splitting the core and making individual coils for B1 and B2?
Note: Though both B1 and B2 will be identical except for polarity.

19. Mar 14, 2016

### Staff: Mentor

The force will be tiny, but at least better than with a complete coil.

I don't think this discussion is progressing. You overcomplicate the situation before you understand the basics. Why don't you study the interaction of a single coil with a ring magnet first?