Inductor/coil B field calculation help

[Salvador12]

I am trying to figure out why can't I come to a meaningful result in Teslas in my calculation for B field strength in my core/airgap?
My figures are ,
Permeability of core = 3500
Permeability of airgap =

length of magnetic circuit =

cross section =

Here is my calculation , i calculate Phi (the flux) in Webers and then I use the formula for B in Tesla but I seem to get weird results, what am I doing wrong?

 

[FvM]

Looks correct. B = 6.2 mT. Expectable due to the large air gap.

 

[Salvador12]

@FvM here is something I dont understand.

https://calculator.swiftutors.com/reluctance-calculator.html

When I calculate using this calculator supplying my input parameters it gives me the values seen in my original post in At/Wb.
When I do the calculation myself on paper using the formula shown in the link I get different results , why?
I am using the same values for circuit length and cross sectional area as in my original post.

Where is the problem ?


Also my results using the calculator from the link seem suspicious, I had a cross area of 0.0004 m2 a circuit length of 0.08m and airgap of 2mm and core permeability of 3500 and for 10 turns of wire passing through 1Amp I got a result of about 12mT field ,
now I calculated a second circuit that also has 3500 permeability of core but 1mm airgap and 0.0002 m2 cross sectional area with a length of 0.05m and using the same 10 turns with 1 Amp of current I still get about 12.5mT of field strength.
Seems weird because my cross sectional area has halved , my airgap is half of the original and my cirucit length is smaller by about 1/3.
Can you please take a look and help me out ?

 

[Easy peasy]

Don't forget you have to calc the R of the air gap and the R of the core separately and then add them to get the total magnetic R ( Reluctance ) ...

 

[Salvador12]

Yes @Easy peasy I did just that, did you checked the calculation ?

 

[Easy peasy]

for 1A, 10T, 2mm gap on 400mm^2 core, 6.2mT seems about right, what is it you are trying to design ... ?

 

[Salvador12]

Nevermind, I was tired yesterday and forgot the decimal place in the magnetic flux calculation where I divide ampere turns with total reluctance , windows small calculator shows the e sign while google's larger one shows the whole number ,

I am just trying to see how much turns, amps one needs to make an electromagnet for a faraday disc


copper has mag. permeability of about 1 so even when the gap is just 1mm wide that low permeability really seems to destroy the strength of the field in the core quite fast. I either have to severely increase the amps or turns but increasing turns is not that great for AC as it increases the impedance of the coil