Why Ian, in your effort to elect Gerald your new best
friend, you completely failed to notice how he
calculated the number of turns in his primary!

-----gerald's method----

Ex108/4.44 x f x B x A x K.

120 x 108/4.44 x 60 x100,000 x .95 = 418 turns on the primary

-----gerald's method----

Now, I bet I know why you missed it; because, being as you are
a self professed nonengineer, you probably didn't know that
engineer speak for voltage is "E".

But just so you won't miss out, the "120" above is 120 Volts RMS,
and the "60" is 60Hz, and the "100,000" is a number of lines of
flux that Gerald picked based on the core loss he was hoping
to achieve.

And surprise, out of the equation (that has no mention of current)
comes 418 turns of primary.

Another silly little thing you will notice about the above
equation, is it is completely independent of the current in
the transformer winding! Gerald would get the same number
of turns for the same flux in the core if the primary drew
1A fully loaded, or 101A... or 1001A.

The funny thing is it is the same equation I use when I design
transformers. I sometimes look it up in the "ITT Reference Data
for Radio Engineers", sometimes in RDH4, sometimes in "Electronics
Engineers' Handbook"... It is always the same??? It never uses
current??? It MUST be wrong!

If you re read Gerald's article, you will notice that the only
use he had for current was in calculating the wire size used
in his windings. He also used the current to calculate the
Trise of his windings. You know, I^2 R and all that.

Gerald, didn't willy nilly transform equations, like you have
suggested, he left them the way they are most useful....the
way he found them.

-Chuck


Ian Iveson wrote:
Your entire post [below] demonstrates exactly what I mean. If you
transform equations willy-nilly you can end up very confused about
the direction of causality in a given practical context.

See Gerald's excellent illustrative example.

cheers, Ian

"Jim Adney" wrote in message
...

On Sun, 6 Jul 2003 16:33:27 +0100 "Ian Iveson"
wrote:


Equations can be rearranged. You can just as easily say that
voltage heats resistors but it would be a highly misleading
confusion of dependent and independent variables in most

contexts.

You seem to be arguing that

P = Isquared * R

is a more correct form and that

P = Vsquared/R is less correct.

How about P = I * V?