Determining transformer coupling factor (k) from measurements.

[sjb741]

Suppose there are two air-core coils. Same count of turns (say 1 turn) but different geometries. Primary P, secondary S.
For example, maybe P is circular with diameter 0.1m and S has diameter 0.3m.

(1) By measuring Lp with coil S open (or distant), then measuring again with coil S in "the designed position" (and shorted), is it valid to calculate coupling k as follows? My concern is the coils have different geometries.

k = sqrt(1 - Lx/Lp)
where
Lx is primary inductance with S closed
Lp is primary inductance with S open

[Question: Does the validity of the calculated k value require the coils are parallel?]
Reference is here


(2) If instead I simply have the data I(P) and I(S): With only that data, can I calculate "k"?

 

[D.A.(Tony)Stewart]

[Question: Does the validity of the calculated k value require the coils are parallel?]
Reference is here

The equation does not care, but you will degrade k, when they are not parallel or coaxial.

(2) If instead I simply have the data I(P) and I(S): With only that data, can I calculate "k"?

That is correct, but will k vary with load resistance?