Table 7.2b on page 310. For E55 core (E55/28/21), Ab is listed as 2.800. I downloaded Ferroxcube data sheet. My caluculated winding area is 3.755 sq cm. The table value of 2.800 is 74.5% (~75%) of calculated value. In practice, the entirety of the winding area cannot be used, but I found no reference in the text as to how the 2.800 value (or any of the other bobbin areas) was derived. Maybe it is there and I missed it?

 

Tried with authors?

Did with different books in the past.

 

The answer is to be found on the bobbin dimensions sheet which I discovered was on e552821.pdf data sheet. Authors apparently assumed core would be used with plastic bobbins; a reasonable assumption. Some of the other sources for determining power use Aw which is the core winding area. Two of the three bobbins that fit the E55/28/21 core have specified minimum winding areas of 2.77 and 2.78 sq cm. The other has 2.5 sq cm.