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Calculation of magnetic field

by keith03
Tags: calculation, field, magnetic
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Jan22-10, 07:34 PM
P: 32
I have been working on a generator. I would like to double check the "guidelines" given to me. I need to calculate the magnetic field density and stregnth at given distance away from the magnet surface (pole). I also need to calculate B as they decay to the side.

I have circular magnets on a 1/4" steel disk. They are N48 grade, 1" in diameter, and 1/4 " thick. They are placed at 30 degree intervals around a circle. I need to insure that my diameter is appropriate such that the flux between the magnets at any given diameter of the disk is appropriate. I will also need to know what the flux is at a given distance away from the pole of the magnet.

I would appreciate it if any formulas are provided, that you tell me how you got it.
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James Leighe
Jan25-10, 04:28 PM
P: 230
Seems relatively simple but I can't picture what your talking about... draw a picture in mspaint or similar maybe?

Also, what is the strength of the magnets? What kind of magnet?

Here is the wiki on magnetic fields: ''
That includes the equations you are going to need to use.
Bob S
Jan25-10, 05:44 PM
P: 4,663
Here is an on-line calculator for magnetic fields from neodymium magnets:
This field calculator is most accurate if there are no other magnets, steel, or current-carrying coils in the vicinity.

Bob S

Feb2-10, 12:15 PM
P: 32
Calculation of magnetic field

I need to use the formulas. None of the five online calculators that I have found agree, and also, I will need to graph the field density at an angle from the poles. I want to make a graph of the field. Picture a Round (coin shaped) magnet on a table of steel. The coils will pass from the extereme "left" of the magnet. (no field present), over the top of the magnet, (center of field), and then to the extereme right. (no field present). I need to place the next magnet such that the field from the first magnet ends exactly where the field from the second magnet begins. Hope this helps. I am assuming that cos might account for the angle?? Hope this helps clarify what I am looking for.
Per Oni
Feb3-10, 10:09 AM
P: 262
Quote Quote by keith03 View Post
I need to place the next magnet such that the field from the first magnet ends exactly where the field from the second magnet begins. Hope this helps.
Surely there’s not a particular point where the field of the first magnet “ends”?
If you place 2 of your magnets, similar poles up, at a certain distance apart then there will be a zero field at a very small midpoint region.

To get an idea of this field first measure it. I’m using a very cheap probe (A1302 Allegro) which will output 1.3mVolt/Gauss. But whatever you are using, detecting zero field when measuring a single magnet will only indicate the sensitivity of your measuring device. The more sensitive your probe the further apart you will find some magnetic field.
Feb9-10, 10:39 PM
P: 32
Although effective, I need the calculated portion to relate to a prototype. I am using extreme examples in my last post to get a point of what I trying to describe across. I will determine when the field is at a unusable point. lets call that "0" It could be 1800 gauss. I just need to get a good idea of what I am even working with. That is where this calculation comes in. I dont want to spend any more money on tools. There has to be a way to calculate this.

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