diyAudio Member
Join Date: Jul 2004
Location: Scottish Borders

Is the first formula?
A = sqrt(W) / K
where W is the input power in Watts and K is 0.0086 for EI.
The answer in mm^2 (sqmm)
Is the second formula?
Turns/Volt = 10^9 / [ K' * B * f * A]
where K' = 4.44 for sinewave, B = 780mT for EI to stay cool and avoid the saturation knee on high mains voltage, f = mains frequency, A = core area in sqmm
Inserting values into that first equation gives the same answer as: Watts = 31 * [Core Area (in square in)]^2
using 100W and 1160sqmm = 1.8sqin
Inserting values into the second formula for 4.44, 780mT, 50Hz, 1160sqmm,
gives 5T/V
resulting in 1145T for 230Vac @ 100VA
Whereas, John's first formula result in 892T for 230Vac with 1160sqmm. This seems to confirm that Johns' first formula has assumed B=1000mT = 1T
Have I got this correct?
__________________
regards Andrew T.
Last edited by AndrewT; 20th November 2011 at 11:49 AM.
