Toroidal electromagnet question ( really figuring my proplem out)

[StephenDoty]

Hello everyone

I am trying to create a ring shaped magnet. If you coil wire around a toroidal core the magnetic field is only inside the toroid I want the magnetic field to be present around the outside and inside the hole of the toroid, the ring shaped magnet? I basically want the magnetic field of my toroid to be pretty close to the magnetic field of a round cylinder shaped permanent magnet. So is there any way to coil a wire around a toroid or magnetize a steel or iron core so the magnetic field matches that of a circular permanent magnet? Would having two separate wires and criss cross them around the toroid create the field I want? I even tried leaving a good bit of room between coils but the magnetic field was not strong enough to see if the magnetic field is the way I want it. I do not know what else to try. Any advice? I am using AWG magnet wire, the three color pack from Radio Shack, a steel core, a 12v 3 amp dc power supply, and I would like to know how to coil the wire around the toroid to make the field present around the outside and inside the hole of the toroid just like a circular permanent magnet?

Thanks
Stephen

 

[Phrak]

Hold on. First you say you want a field that will be like a round cylindrical magnet. Then you say you want it like a "circular magnet."

Can you be more precise?

 

[StephenDoty]

The circular magnets that you can buy at places like Radio Shack and ACE. It is just a simple magnet that is circular in shape. And it is 3-d so the circular magnet becomes a cylindrical magnet. Its the same thing.

 

[StephenDoty]

I basically want a toroid with an external magnetic field. Would rapping the ring with a few loops of magnetic tape and then coil the toroid with a magnetic wire and use a dc power source create a toroid with an external magnetic field?

 

[Phrak]

Right. A donut, or a toroidal core. The whole idea of a toroid is that most of the flux, H is contained in the core material. So you won't get a lot of leakage flux.

Maybe you're confused as to the direction the field takes. the field loops around inside the core, following the major diameter. The little that there is on the outside is in the same but opposite direction close to each loop of wire. It's the induced electric field that loops around the core like the wires do with an applied AC current.

 

[StephenDoty]

I know it can be done because in my other thread on CR4 forum emc_c said to leave space in between the coils. This worked to a certain extent. The field was not strong at all. I am now wondering if criss-crossing two wires to make a criss-cross coil and connecting them together or if wrapping it with magnetic tape then the magnetic wire coil hooked up to the dc power supply, or if coiling a good number of windings on two sides of the ring and leaving the other two sides clear would make the field I want? Which was shown in my other thread by emc_c picture. I tried emc_c's idea of leaving space between the windings and I hooked it up to a 12 v 3amp dc power supply and it did not attract any metal objects. I am using a steel ring washer as my core. Any ideas as to what I did wrong with emc_c's idea or any ideas on how to create a toroid with an external magnetic field? I do not know what core is used or what magnetic wire was used in emc_c's idea. I am using a steel core and magnetic wire from Radio Shack, the magnetic wire that comes in a pack of three and three different colors, green, red, and clear. Do I need to change any of this to make emc_c's idea or any other idea as to how to make a toroid with an external magnetic field that looks like and is as strong as a bar magnet's field and that attracts metal objects?

Thanks for the help.

here is a link to the idea emc_c had:

http://cr4.globalspec.com/comment/351134/Re-Magnetizing-a-Steel-Ring

 

[Bob S]

Wind the wire around an iron rod (solenoid). The basic formula for the field is

B = u 4 pi x 10^-7 NI where u = mu of iron (about 4000), N = turns per meter, and I = current. B is in Tesla.

 

[StephenDoty]

I did that. But a solenoid does not have an external magnetic field. Any ideas of how to make a toroid with an external magnetic field?

 

[Phrak]

I did that. But a solenoid does not have an external magnetic field. Any ideas of how to make a toroid with an external magnetic field?

Wind it on plastic. Or put an alternating current through it.