McLyman approach - area product, watch out, he uses Teslas, probably a closet commie,

Apparent Power Pt=P in + P o

P in = P o /

*n* where

*n* is xfmr eficiency some algebra>

Pt = P o /

*n* + P o

**Pt = P o ( 1 / ***n* + 1 )Pt = I o x (E o + V d ) x ( 1 /

**n**Pt = .250 x (15 + 2) x (1/0.95 +1)

Pt = .250 x 17 x 2.0526 =

**8.72** now Area Product (wind window area x core x section)

Ap= (Pt x 10^4 / K Bm f Ku Kj)^1.16

K=4.44 for sine wave Bm= 1.2 Tesla f = Hz Ku = .4 (what % copper in window)

Kj = 366 (current density for 25 Degrees C operation)

Ap= (8.72 x 10^4 / 4.44 x 1.2 x 50 x 0.4 x 366)^1.16

Ap = 2.23^1.16 =

**2.543**pick core from chart: looks like 21 EI which has a 0.5 tongue or 13 mm we have a match.