Re: total inductance of bucking coils

Brett Holden said the following on 2009-02-05 17:05:

No he is not, that would be me.

YW.

What are you, the Usenet police? I thought maybe you'd have an answer.
Thanks for NOTHING.

What's your application, what do you want to know that for.

You not one of those free energy nuts are you?

I need to be able to calculate the total inductance of two coupled coils
when one coil is wound in reverse. I have a Boylestad's Introductory Circuit
Analysis (old - 6th edition) that has a section covering this but I have run
into a problem because there seems to be some circular reasoning in defining
the equation (#1). (I have used brackets in place of subscripts.)

Inductance of two coupled, bucking coils:
1) L[T-] = L[1] + L[2] - 2M[1,2]

2) M = .25( L[t+] - L[t-] )

3) L[t+] = L1 + L2 + 2M[1,2]

4) L[t-] = L1 + L2 - 2M[1,2]

I can't use subscripts here, so formula 1 is supposed to read:
"total inductance of two reverse wound (coupled) coils equals
inductance L1 plus inductance L2, minus (two times their mutual
inductance)".

OK, if we can define the mutual inductance "M", then all is well.

To define M, formula 2 seems simple enough but introduces two more
variables, L[t+] and L[t-].

In formulas 3 and 4, variables L[t+] and L[t-] are defined, but M is used as
a variable, so I am grasping thin air. Can somebody please help me out?

Also, formula 1 seems to ignore the influence of coeffecient of coupling
between the coils but maybe that is accounted for in equations 3 and 4?
(headache)

Thanks for your help!