# Toroidal electromagnets

• linear_shift

#### linear_shift

Okay, I have been looking the web over for some toroidal (doughnut) electromagnets for a project I am working on. Any ideas on where to get some? I need about 8 to run off of 110 VAC (10A) or 12 VDC (220A). Inductive force is not important. Inner OD should be about 3 inches or so. Danke (no umluat, can't find char map, grrr...).

Well, first of all, a "toroidal electromagnet" is an oxymoron. All of the B field that you would generate from driving the coil would be confined to the magnetic material of the toroid.

What are you trying to do with this electromagnet?

Welcome to the PF, BTW.

Well, I am looking to make a "projectile launcher" (not really, just don't want to break the secret, I'll tell in time). Fyi, it does have poles, just not N-S up-and-down, like a bar (instead just one side of toroid to the other). Think back to the old kiddo magnet kits, I just need an electromagnetic verision with a 3" inner OD. I'm thinking the specific name was an inducer? Hint, hint, it is akin to a magnetic transformer or car fuel injector.

Okay, if you want to use electromagnetic energy to launch a metal projectile, that's called a "Railgun", not a toroidal electromagnet (which is still an oxymoron -- Quiz Question: Why is that an oxymoron?).

Here is a reasonable wikipedia.org page about Railguns:

http://en.wikipedia.org/wiki/Railgun

You need to search for solenoids, not a toroidal wound electromagnet. That is indeed an oxymoron.

A few short sections of solenoidal wound cores could make a very nice linear motor.

Okay, I guess I worded it wrong, I'm kind of reaching with a "toroid." What are you guys describing a toroidal electromagnet as? I'm thinking of it as a doughnut wound around the side with wire. Were you thinking wound on the inside or something? Now that I think about it that is ridiculous as there would be no poles: the field would try to wrap around like a bar but magnetize the torus at every point canceling the field outside of the torus (give me a bit of a break, I'm a hobbyist just starting out, prior to this, though still doing it, I was mainly an amateur astronomer). Heh, heh. Oy, embarassing :P Okay, so know we have it: solenoid. So, where could I buy a solenoid with a 3" inner OD (mabye make it out of steel piping?)? Oh, and just fyi, its still not a "rail gun" per se, you'll find out ;)

It sounds like you figured out why we didn't think the term toroidal electromagnet made sense...

Now that I think about it that is ridiculous as there would be no poles: the field would try to wrap around like a bar but magnetize the torus at every point canceling the field outside of the torus

That's correct. A toroid (yes, a donut with wire wrapped around the dough part in a coil) confines its self-generated B-field to the magnetic donut of material itself. The B-field does not get outside the toroid in order to be used for external purposes (like accelerating an object with magnetic forces). The only things you use a magnetic toroid for are as an inductor (with one coil of wire looping around part or all of the toriod), or as a transformer (with multiple coils of wire).

What was wrong with the Railgun link that I posted? If you want to make a "projectile launcher", that would seem to fit the bill, eh?

Ok, cool. Not the railgun though, I'm looking more at the Gauss gun. This I could make myself. This does not have to induce much mass, however (very little it fact). Hint: its not even a gun per se, or a weapon of any sort (intentionally anyway), I'm not into that. And no its not a particle accelerator, that's ridiculous (by conventional means anyway). Think about it for a sec :)

Oh and btw, this may sound like a stupid question but does making a solenoid require *unvarnished* wire as opposed to *varnished* wire (help help the noob :P )?

Oh and btw, this may sound like a stupid question but does making a solenoid require *unvarnished* wire as opposed to *varnished* wire (help help the noob :P )?

Okay, I don't have a clue anymore about your main question, but at least I can answer this one. The wire needs to be insulated when you wind a magnetic coil (probably obvious), in order to avoid shorting coil-to-coil and lowering the magnitizing inductance because of the shorts. But the voltage gradient from adjacent coil to adjacent coil is not very high, and you usually want to stack the wires as close as possible to each other for magnetic efficiency reasons, so the thinner the insulation on the wires the better.

So magnet wire is usually coated with the varnish style insulation, and comes in several thicknesses. "Single Build" wire has the thinnest varnish insulation thickness, and is used when you don't need much voltage delta capability, and can accommodate the higher capacitance you get with the thinner insulation. Double Build and Triple Build wire are used for higher "HiPot" standoff voltages and lower capacitance transformer constructions.

Okay, so thinner varnish, check. Thanks guys. Sorry about the weird sentence/logic construction, seems to happen everytime I post to new forums (happened on Slashdot when I posted there the first time), don't know why exactly... :\$