# Electromagnet Coil Question.

1. Nov 5, 2007

### mgibson

I am designing an electromagnet and need a strong field strength. I have came across a few different ways to wire the coil and am curious which way produces the strongest dipole electromagnet. The coil is to be wound around a cylindrical steel core. The first way is what I think is the most common. Just a coil starting at one end and wound to the opposite end and then back to the beggining end, and then repeated for however many coil layers. The other method is to wire from one end to the opposite end, then bring the wire back to the starting end and wire back to the opposite end. Then repeated as many times as layers wanted. So the main difference is in method 1 the coils are going back and forth and in method 2 the coils are going in one direction then brought back and repeated. Hopefully that makes sense.

So my question is, which method would produce a stronger dipole electromagnet?

Any help would be greatly appreciated! Thanks!

2. Nov 5, 2007

### Midy1420

the only problem that i can think of off the top of my head is that using your first method it seems you will canceling out magnetic field. If the wire is running in the one direction on the way up the current in that direction will created a magnetic field going one direction lets say up. If you wind the same wire back down beggining at the end the current will be flowing in the opposite direction and switching direction of the magnetic field. It seems that would be deminishing what you are trying to set for. I would try to use as many coils allowing wound in the same direction. (I hope that made sense)
Best solution I can think of is to use thin wire and wrap it very very tightly. The magnetic field produced is proportional to the number of coils.
Hope Im not just making things up. good luck

3. Nov 5, 2007

### tc_kid

Agreed, clockwise windings will result in a magnetic field which moves in the same direction as your current. anticlockwise windings result in a magnetic field moving in the opposite direction as your current so if you continued winding in the same direction back to the start it will cancel out the magnetic field) you could however wind backwards to the start if you were to change the direction of your windings...

4. Nov 5, 2007

### mgibson

Thats what I thought at first. But after reading a couple "how to coil" documents they said to coil like method one. Which didnt make sense for the same reasons you guys are saying. I will probably experiment with both ways, and see which produces a stronger field. Thanks for your help!

5. Nov 5, 2007

### marcusl

So long as you always wind in the same sense, it doesn't matter which approach you take. You'll get the same field each way. There is a slight difference in the inter-turn capacitance (there's an entirely different way to wind high frequency coils), but that makes no matter to you for a DC electromagnet.

6. Nov 5, 2007

### tc_kid

by winding in the same sense do you mean keeping the field in the same direction by swapping winding directions? otherwise i dont understand....

...oooh high frequency coils...(thinking of my TC)

7. Nov 5, 2007

### NoTime

The coiling they are talking about all goes in the same direction.
The pitch(slant) of the winding will reverse (if you are being neat and not just scramble winding) but the core is always being turned in the same direction. The minor change in pitch here has no significant effect since the current vector is still going in much the same direction.

The two 90 degree bends needed to bring the wire back to the start end just adds extra length (and resistance) to the wire. It can also change the field pattern if there are enough of these crossovers since there is a corresponding 90 degree change to the current vector.

Last edited: Nov 5, 2007
8. Nov 5, 2007

### mgibson

So should I be coiling it as described in method 1? Or does it not really matter which way I do it? The coil is always being wrapped around the core in the same direction, their are no bends in the wire, just a continuous coil from one end to the other, and then back.

If I have a steel cylindrical core, how should I wind the coils (and coil layers) to produce a very large field strength?

If a steel bolt about 3 inches long, and 3/4 inch in diameter is fully saturated by being the core of an electromagnet, how strong can its maximum field strength be? Can this strength be compared to the strength of an equally sized neodymium permanent magnet? How much current and turns of wire would this take? Is it even possible?

Thanks everybody for all your input.

9. Nov 6, 2007

### tc_kid

you've lost me now....

10. Nov 6, 2007

### stewartcs

I think the confusion is that you are thinking that the direction of current flow is reversing...it is not. Just the direction you are winding is reversing. There is a slight change in flux due to the small "slant" as NoTime indicated, but the magnetic field is still in the same direction. The "sense" that marcusl was referring too is just that; keep the magnetic field in the same direction, i.e. from N to S (or whatever).

11. Nov 6, 2007

### NoTime

This thread may be of some intrest

12. Apr 16, 2008

### Mindstormed

Sorry for beating a dead horse here, but I have a similar problem with coil windings and didn't quite understand what was said. Supposing a bolt is standing up on it's cap on the table. The coil would be wound clockwise & down the shaft towards the cap. Once the cap is reached, remaining in the same clockwise direction, the wire is wound back up the shaft for the 2nd layer. Once the top of the shaft is reached, the same process repeated in a clockwise direction. Is thiscorrect?

Also, I have a ductile iron (soft iron) core that is 1" dia, 1.5" tall, with a bottom plate 1/4" thick and 5.5" diameter. I've got enough #10 gauge magnet wire to cover the entire plate (about 20 outward layers) and intend to lift 5000+ lbs for just a few seconds. I think I may have made a big mistake choosing such a tiny core and never heard about saturation before doing so! So is this still salvageable? I can get discount on a 12v@25a battery, or a used 12v@80+a battery.... which would work best? Annnnd, what would be an ideal core diameter for the same sized bottom plate and same gauge wire?

13. Apr 17, 2008

### Redbelly98

Staff Emeritus
He doesn't mean to reverse the direction of the turns, i.e. clockwise vs. counter-clockwise. That is obviously wrong for the reason you said, and nobody would recommend doing that.

He is talking about direction in terms of winding from end #1 towards end #2, or vice-versa.

Hope I am making sense :-)