Mutual Inductance

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Hi forum!

I have a RM5 core with 2 inductors in it such that one inductor(winding) is between 1-2 and other is between pins 6-2. So pin2 is common.

The inductors are in series but since they are wound on same former, I guess there should be some mutual inductance between the two. Now if I measure the inductance between pins 1&2 and then pins 2&6 and finally between pins 1&6. What I have observed that there is an inductance of 16mh between 1-2, 164mh between 2-6 and 280mh between 1-6( although I was expecting around 180mh, it means there is some Mutual Inductance).

Am i right to assume that since for coupled indcutors,

L(eq) = L1 + L2 +/- 2M

Where M= mutual inductance. USing this equation with + sign and above values, I get M=50mh. Is this anyway correct?

Thanks
 
Your measurements sound right to me.

On a pot-core, you're going to get almost perfect mutual coupling between the windings, so as L is proportional to turns(squared), then 16mh will be 4a turns, and 164mH will be 12.8a turns. (a is a constant depending on the Al of the core).

So if you series the windings to give 16.8a turns you would expect to get (16.8)*(16.8)=282mH. which is pretty close to what you are measuring.
 
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