Electromagnet Noob Question - Page 1
Forum section: electronics / beginners

author: electromateria
author_rank: Regular Contributor
timestamp: August 15, 2021, 07:22:24 pm
content: https://en.wikipedia.org/wiki/Oersted%27s_law"Ørsted's law is the physical law stating thatan electric current creates a magnetic field."If an electric current automagically creates a magnetic field why do we use insulated wire coils in motors? What's the purpose as opposed to using a coil of regular copper wire?Are there any good BLDC motor designs that don't use insulated wire?

author: TimFox
author_rank: Super Contributor
timestamp: August 15, 2021, 07:31:24 pm
content: The reason why magnetic fields are typically more important than electrostatic fields in practice is that by using insulated (or non-touching) wires wound into coils, you can use the same current over and over again to increase the “ampere-turns” and get a larger field. Uninsulated wires shorting out to each other would give you only one turn.

author: IanB
author_rank: Super Contributor
timestamp: August 15, 2021, 07:37:27 pm
content: Same as Tim said, if you don't use insulated wire, what prevents a short circuit?

author: Gregg
author_rank: Super Contributor
timestamp: August 15, 2021, 08:27:02 pm
content: Magnetomotive force is measured in ampere turns. If you make a coil of uninsulated wire it becomes a dead short in essence zero turns. Even if you have infinite current there still won’t be any more of a magnetic field than a single non-coiled conductor. Infinity times zero is still zero except in the minds of a few over unity nutcases. See the dodgy technology thread for discussion of some of the nutcases out there.

author: electromateria
author_rank: Regular Contributor
timestamp: August 15, 2021, 08:59:46 pm
content: Thanks for the answers. I'm still confused though, probably because my knowledge of physics is the same as someone who never went to schoolAn electric current going through a plain copper wire creates a magnetic field. Is that statement true? If so it means the field is just extremely weak and almost non-existent right? Once you insulate that wire and coil it up, for some reason outside my understanding the field powers up like crazy.Do you guys know any good books on electromagnetism?Preferably something an uneducated, semi-retarded person like me can understandMaybe a kids book that gives lots of experiments as well as an overview of the principles.

author: rstofer
author_rank: Super Contributor
timestamp: August 15, 2021, 09:20:51 pm
content: Quote from: electromateria on August 15, 2021, 08:59:46 pmElectromagnetism comes up in a course named "Field Theory" which, in my case, was the final and most difficult class in an undergrad BSEE program. Four simple equations, known as "Maxwell's Equations" cover just about everything.Here they are:Enjoy!What you want to think about it the magnetic field created in the motor caused by the winding current. A DC motor, for example, will have a certain physical construction such that the rotor current creates a magnetic field that drags the rotor around until the commutator changes to another winding.A more detailed explanation showing how the magnetic field around the wire is concentrated with multiple windings.https://en.wikipedia.org/wiki/Electromagnet

author: Gregg
author_rank: Super Contributor
timestamp: August 15, 2021, 09:44:26 pm
content: Any conductor carrying current has a magnetic field associated with it; but you specifically mentioned coils. Each conductor of a coil adds to the magnetic field in the center of that coil. That’s the very simple explanation; from there all sorts of things like core material and eddy currents become significant.For your coil of uninsulated wire the magnetic field would be similar to using a copper pipe as a conductor; the magnetic field in the center is essentially zero.If you are really interested in this stuff, look up things like right hand rule and left hand rule for magnetic fields associated with conductors. For books; a local library is a good source as well as any used book stores in your area. Thrift stores often have books really cheap and technical books don’t exactly fly off the shelves.A good attitude, asking well prepared questions and willingness to learn will serve you well on this forum.

author: electromateria
author_rank: Regular Contributor
timestamp: August 15, 2021, 11:59:50 pm
content: Quote from: rstofer on August 15, 2021, 09:20:51 pmThat first video was way too fast, and totally out of my depth, I have about 30 tabs open of things I need to research nowthe second video was much easier to follow and I found it really helpful. I think I'll make a simple electromagnet out of a bolt and play around with it.Is there a way for hobbyists to view magnetic fields digitally? Through some kind of device?Quote from: Gregg on August 15, 2021, 09:44:26 pmI had access to a really good book store pre-covid but I think it's shut down now unfortunately.You reminded me I have a 700 page book on electrical engineering, but I've been scared to even open it again after reading the first 25 pages. I didn't retain almost anything about atoms / nucleus / electrons so I lost some motivation. I'll give it another look tonight, and if it's too advanced or technical I'll try to find a more basic one.

author: rstofer
author_rank: Super Contributor
timestamp: August 16, 2021, 12:35:28 am
content: That's OK, I don't understand the math behind Maxwell's Equations either. I figure only about 3 people actually understood it and all 3 are dead. Maxwell, Feynman and, maybe, Einstein. The rest of us are guessing.This stuff is supposed to be a hobby. Simple solutions are fine and the detailed math is seldom required. Skip over the particle physics stuff and get to DC circuits. That's where most of the work is done and, someday, you should move on to AC circuits. In my view, most of the hobby has migrated to uC projects and most of those seem to involve the Arduino with the Raspberry Pi coming on strong.Here's Dave's playlist re: DC Circuits.https://www.eevblog.com/category/eevblog-official-releases/tutorials/Khan Academy has a good program specifically for EE but is math based. Digilent has a Real Analog series that is mostly math based. There are DC circuits tutorials all over the internet.AC circuits get a lot more involved but there are tutorials so that's a lot better than when I had to take the class back around '71.Sometimes you just need to experiment and measure things. It is actually worth the time to build up some resistor networks and measure branch currents and node voltages. Then see how the readings compare with the math. Don't just take the lecturer's word for it!There are lots of books on the subject and there is a 'sticky' re: Primers at the top of the forum. Most people recommend The Art of Electronics but I think Forrest Mims books are more approachable. "Getting Started With Electronics" by Mims might helphttps://www.amazon.com/s?k=forrest+mims&ref=nb_sb_noss_1Don't make it more work than it needs to be.

author: denelec
author_rank: Regular Contributor
timestamp: August 17, 2021, 08:59:14 pm
content: Quote from: electromateria on August 15, 2021, 11:59:50 pmI've never heard of a magnetic field digital camera.But you can easily buy a magnetic viewer film.It's a plastic film that reacts to magnetic fields when you place it on a magnet.

author: gcewing
author_rank: Regular Contributor
timestamp: August 18, 2021, 04:03:36 am
content: The insulation is there so that the turns don't all short together.The reason for using multiple turns is that the magnetic field from a single turn of wire, for everyday currents, is rather weak. With many turns, the fields from the individual turns add up to give a strong field. Getting the same field from a single turn would require an enormous current.

author: james_s
author_rank: Super Contributor
timestamp: August 18, 2021, 05:18:59 am
content: You will get a magnetic field any time you run current through a conductor, but if you wind a bunch of turns of bare copper you will have a short circuit, and the magnetic field will be along the axis of the most direct path for the current to take, which will not be where you want it in the middle of the coil.The classic way of visualizing a magnetic field is to use iron filings on a sheet of paper. The film someone else mentioned is less messy though, it consists of two closely spaced sheets with the gap full of very fine iron filings.

author: Terry Bites
author_rank: Super Contributor
timestamp: August 18, 2021, 03:25:28 pm
content: The magnetic field created is proportional to the current and the number of turns. If the turns are not insulated from one another, you just have one fat turn. AKA a short circuit. So no, you cant make a BLDC motor from bare wire, ever! Forget Maxwell, field theory and all the nut job comments.

author: james_s
author_rank: Super Contributor
timestamp: August 19, 2021, 01:57:24 am
content: It's not even one fat turn if the wire is all bare, you'll have a loop with the two wires feeding it connecting at some points, and if they are adjacent to one another the short there will be the most direct path and bypass the whole loop.