Solenoid Best Adjustment Part 2

The curve below is from "Performance & Design of Alternating Machines" by M.G.Say.

You write that you have a solenoid 50 cm long. So the magnetic path (circuit) length through solenoid round and back must be one metre at the least.

You have 3 amp x 200 turns = 600 A-t for 1 metre path = 600 A-t/m.

Look at curve, 600 A-t/m will only get about 1.4 Tesla in iron. Any gaps in air require 800 A-t per millimetre per Tesla.

Look at X 100 curve at top - you need about 400 x 100 = 40000 A-t per metre for 2 Tesla in iron - or cast steel, supposing it is close to "42 quality".

An air gap of 5 cm with your coil in it would need an extra 800 x 50 x 2 Tesla = 80000 A-t, added to nearly 40000 A-t to magnetise the 95 cm of iron in the magnetic circuit, total 120000 A-t.

It seems you have errors in your assumptions about A-t needed to get very strong magnetic fields. If you want a strong field, it is best to minimise the magnetic path length.

I think you did not catch my question . What I am trying to say is I took a solenoid and then i cut a cross section in the middle of solenoid and insert my coil there. I don't need 50 cm air gap. I am trying to create a magnetic field that would be strong when i put the coil at middle of the two poles. That is 25 cm. Buy if I use the conventional method then it was not getting enough because the .Magnetic field produced by a solenoid will change with cube of distance . And I have covered all the 50 cm solenoid with wire expect the space or cross sectional area where I would insert my coil. I am using only one wire. So the space that would be created , in that air gap flux will travel. And hence I have created flux at 25 cm from the two poles. But I understood your magnetic field calculation too. Thank you very much .

If you want a motor then the method from 160 years of experience is to make the rotor of iron to minimise the air gap as shown in Rixter's post #2.

It was not clear if you wanted a strong field for experiment, or a linear motor or a rotary motor. Rotating motors are based on a toroid, not a solenoid. A solenoid is a bad start because the path outside coil in air is long.

Now I cut out a piece enough to accommodate the coil . But I cut it from the middle and not the whole cross section area . Then i inserted the coil there . I have not cut it all the way through . Just enough so that my coil is inserted .

If I understand you correctly, this will not work. The flux will go through the core and not through the hole in the core. The cut has to go all the way through. It's like soldering a wire across a resistor, current will not flow through the resistor.

You need something more like this:

This is a motor and not a generator, but the design is the same. If the rotor were inside the coil, there might be a little more flux, but most of the flux will stay in the iron core, and putting it inside the core might make it harder to build.

Make the air gap around the rotor as thin as possible and the rotor, of course, needs an iron core. There should be no iron around the rotor to shunt the flux.

Well what if I make a tunnel and insert my coil then?

And also if what you are saying is true then can I manipulate the flux? I mean I can use variable cross sectional iron ore to produced more flux at less space . Like I make the cross sectional area less so as the flux passing through the iron ore becomes more concentrated . When it becomes more concentrated then i use a small space where I can get high flux in small space. Would it work? And again thanks for your help.

Exactly, flux lines never end. The flux density is greater if the core cross section is smaller. You want all of your flux to go through the coil. The change in the amount of flux through the coil generates the voltage. The amount of flux through the coil changes as the rotor rotates.

To accurately analyze the magnetic field produced by a current one should understand the mathematics expressed by Ampere's Law, the mathematics of three dimensional Calculus. The solenoid equation you are familiar with identifies the magnitude of the uniform field strength inside the solenoid. Outside of the solenoid the field non-uniform field strength and direction is more accurately expressed by the Biot-Savart Law, notice that the magnitude reduces by the square of the distance away from the magnetic source. Placing a fixed coil inside the magnetic field of another coil is the fundamental of making a transformer. Understanding a transformer requires the use of Faraday's Law. Placing a movable coil inside the magnetic field of another coil is the fundamental of making an electric motor. Understanding the mechanical force of a motor requires the use of the Lorentz Force Law. All of these equations were accurately combined into the highly cryptic Maxwell's Equations.

One thing you've not made clear to me at least is what is your goal, are you trying to make a motor, a transformer, electron beam deflection or what?

Its about a generator . And nice explanation . Thanks

http://www.hk-phy.org/energy/power/print/act_ac_gen_e.html

It would be really helpful if you could submit a drawing of what you are proposing. Each of us develops some kind of mental image of what you are attempting to describe, but I'm willing to bet that no two of us have even close to the same mental image.

It would also be helpful if you told us something about what you are trying to accomplish. It is not even clear whether your solenoid is to have AC or DC, although your frequent mentioning of 3A of current seems to imply DC, which could be continuous or pulsed. Is this to be some form of motor, or some form of generator, or something else entirely?

The <...cost...> depends upon the availability of materials locally, the amount of time needed in their assembly (which has a value) and vendor prices for those things. It is not something any CR4 reader other than the original poster could possibly answer. Further, given the location on the planet is not specified, the money-currency of the <...cost...> is also indeterminate.

CR4 doesn't do <...cost...>!

Reading the detail here and in the previous post, I can conclude that your knowledge in the field is equivalent to a basic high school level. And the only reasons I can think of why you are doing this is either because you are being paid (with public funds) for something you do not know how to do, or you want to be the next Albert Einstein (making discoveries without being in the field).

There are a few reasons I doubt you can do a lot in this area.

1. Magnetics have been around for a while, and our ancestors are way smarter than we are. We are lucky technology has simplified engineering, but it has not always been like this.

2. You must not saturate cores. When you reach saturation it overheats, burns the isolation, increasing Eddy currents and heats up even more. At 770ºC the Curie temperature, the electric steel is not magnetic anymore. So it will be like if you did not have a magnetic core.

3. I am telling you this because "Now I cut out a piece enough to accommodate the coil ." is pointless. It is not a matter of how to generate incredibly high magnetic field in a magnetic core. The issue is that you cannot magnetise at more than a few teslas without damaging your equipment.

Please go to university and do a related course if you want to research on an engineering field. Otherwise there will be people like Thunderf00t, who can show your research is totally useless with only some basic calculations.

Just what is this solenoid/electromagnet/alternator, or whatever it is called, supposed to be doing, please?

I am trying to attach a photo as suggested by some members . But the photo is not be able to uploaded in this site . I don't know why. And yes as suggested by ivanaov, I am not a electric engineer , that's why I need help on this project . And I am trying to build a generator.

If you are trying to upload a photo, JPEG format is the most reliable. The site will not accept .png or many other formats as they come directly from the camera. Export the photo in .jpg format from whatever photo viewing software you use, and in a reasonably high resolution. Then click on a "Reply" button in CR4, type any text you want, then click on the camera icon in the toolbar at the top of the edit window. Click on "Browse", and navigate to wherever the exported photo was saved. Select the photo, then click on "Submit". Wait a few seconds, and it should appear in your reply.

I am trying . I tried in jpg format . But its not uploading . I don't know why. I have click the picture from my mobile camera and now i am trying to upload it but can not.

You have transferred the photo from the camera to the computer, haven't you.?

If the computer is a Mac, then I can probably help you further; otherwise, probably not!

No I have not. I trying to upload it from mobile

Raj,

CR4 cuts the file size and resolution of pictures, if you try to send a big file and modern cameras have many pixels.

For hand-drawn diagrams, I convert to black and white and .png type. This usually minimises file size - I always try .jpg, sometimes smaller than .png.

Then call it a generator, and not a solenoid.