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# How to calculate the inductance value?

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#### wccheok

##### Member level 1
How to count inductance?

Hi, i hv found alot about the inductance calculation formula. But i cant found the formula i need. Any one who know how to calculate the inductance value by given the information like below?

L=9turn, 0.15mm wire, 4.5mm diameter coil

what are the inductance at above?

Thx for helping

Re: How to count inductance?

Isn't this good enough?

Re: How to count inductance?

Hi wccheok,

If you have got a headache from the calculations, then consider a small software which can do the number-crunching for you, see induct30.exe self-extacting file at this site: http://sss-mag.com/swindex1.html (scroll down to about the middle of the that page).
This software is reasonably precise and includes the user' addition of the needed lead lengths. From its INDUCT.BAS file you can see the equations used for calculation if you wish.

Run it first in a separate empty directory and it self-extracts into 3 small files (the induct.exe will run in the DOS window of your Windows system.

You can compare results with calculations from formulas and from this software (in this case use very short lead lengths in the software to do meaningful comparisons).

rgds
unkarc

Re: How to count inductance?

If you're looking for another program that will do the calculations for you, you might want to try Mini-ring kern calculator at **broken link removed**. It will calculate both toroid as well as air core values. The help file that accompanies the program gives a good explanation of the calculations performed. I have found it to be very accurate and the price is right - FREE

Mike

Re: How to count inductance?

Inductance of a single-layer close-wound air-cored coil.
Calculations to give the inductance of a single-layer close-wound air-cored coil are extremely complex, but a good approximation is given by the following formula provided that these assumptions are adhered to:

Wire diameter is less than 10% of the coil diameter.
Wire is close wound in a single layer.
The coil's length is 0.4 to 3 times the diameter.

The formula is often called Wheeler's Formula .. (see picture below) ..

Where:

L=inductance, in uH
d=coil diameter, in inches
b=coil length, in inches
N=number of turns

Regards,
IanP

Re: How to count inductance?

Hi all, 1st of all thx for u all for trying helping me. =p
I have found one formula which is L= (N²µA)/ l
which N is number of turn, µ is permeability, A is cross section are in meter squared and l is the length in meter.
Can this formula used?
may i know wat is d Vaccum/ Air permeability?

IanP, is tht u gv me once info is the rule of making a inductance?

Wire diameter is less than 10% of the coil diameter.
Wire is close wound in a single layer.
The coil's length is 0.4 to 3 times the diameter.

Re: How to count inductance?

µ(vacuum)=4Π • 10(-7) Henry/meter .. (-7) to the power of -7 ..

Both formulas are derived from quite a complex equasion that you most likely wouln't like to know about, so there are certain conditions impose on them ..
After all you always tune a circuit by changing coil's geometric shape (length), so if the calculated inductance is within <10% of the real value, you would be more than happy about it ..

Regards,
IanP

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