# Solenoid layers

1. Apr 28, 2005

### Serj

I want to make a very powerful one stage solenoid. The pipe is only so long , so if I wrap the wire evenly I will only acheive a fixed number of turns. If I wrap the same wire of that one with the current flowing in the same directon I should get twice as many turns altogether. The problem is I dont know how one should wrap more layers of the same strand of wire over the first layer. Do I wrap the wire from one end to the other and then wrap it from that end to the other. Or do I wrap it from 1 end to the other and then wrap a new wire over that and simply connect the same charge ends together?

2. Apr 29, 2005

### willib

That is a good question..from my expierence , most soleniods are wound with one strand of wire from end to end , back and forth till you run out of wire..
you can absolutely wrap more than one layer , that is the only way to get more power from your solenoid..
you are using magnet wire correct? how thin/thick is your wire..?

3. Apr 29, 2005

### willib

4. Apr 29, 2005

### TimeKeepsMeUpAtNight

Back and fourth? I am just curious as I am just learning all this stuff but it would seem to me that the current would oppose it self being that it would be coiled in multiple directions.

5. Apr 29, 2005

### willib

Not true ,he is wrapping the coil around a pipe , in the same direction..around n around..by back and forth i meant from end to end..

6. Apr 29, 2005

### Serj

I'm using insuated copper wire approximately .5 mm in diameter (judging by eyesight, havent actually measured it yet). My teacher said it could be used for the purpose of making a solenoid.

Yes, I am going to use a plastic pipe. Although I might use a copper pipe because plastic is very thick andI am afraid if the core is placed in a thick PVC pipe it wont work as well.

The problem is what do I do with the wire once I get to the end of the pipe? I am planning on making several layers of wire until the wire is 1 cm thick. I've got plenty of wire (a bucket weighing about 70 lbs.).

7. Apr 29, 2005

### sepulker

TimeKeepsMeUpAtNight:

Back and fourth? I am just curious as I am just learning all this stuff but it would seem to me that the current would oppose it self being that it would be coiled in multiple directions.

-No. Remember the fourth Maxwell Equation: Ampere's Law, which translates into Biot-Savart's Law (also analogus to Columb's Law):

dB = (mu/4pi) * (I*dL X r)/(R^2)

where dB is the vector magnetic flux density, mu is the magnetic permittivity, I is current through an infinitely long wire, r is a vector radius of the magnetic field, R is the magnitude of r, and dL is the length density of the wire at a point. The X is a cross-multiplier.

IN OTHER WORDS:
If you are looking at a vertical wire, and current is flowing "up" the wire, then the magnetic field will appear in a counterclockwise fashion around the wire. Think of grasping the wire with your right hand... If the current is flowing in the direction of your thumb then the magnetic field will appear in the direction of your fingers.

If you wrap this same wire in a clockwise coil, then the magnetic field contributions will cancel out everywhere except the center, and will be directed away from you.

Now, when you wrap a coil, you are disregarding the thickness of the wire itself. The closer the wrappings, the more ideal your magnetic field distribution will be in the center of the solenoid. However, the direction of the field depends on the direction of the CURRENT, not the WINDINGS. Feeding the wire back to the beginning causes more distortion then winding it back in the opposite direction.

This is why wrapping a solenoid in a "ping-pong" fashion is standard.

8. Apr 29, 2005

### willib

Just reading this i see how hard it is to explain..
let me try again..
Say you are winding clockwise around your plastic tube,and you finish one layer , you would then continue winding clockwise back towards your starting point.. the key word is towards .. ok??
copper tubing is not a good idea even though copper will pass a magnetic field , all the solenoids i have seen , are wound on plastic..

9. Apr 30, 2005

### sepulker

Yes, "you would then continue winding clockwise back TOWARDS your starting point"... all in the clockwise direction. Key word is clockwise.

Ferrite cores are used for a lot of solenoids and all flyback transformers found in TV sets. Ferrite is used because it has a high magnetic permiability (concentrates the magnetic field), but is also conductive. You can use any type of core you wish as long as your windings are properly insulated.

10. May 9, 2005

### Serj

I made a solenoid today and when I turned on the power the core was pulled to the center of the solenoid ,not the other end.