JT> Actually, increasing turns would probably make it worse unless
JT> it's the extra winding impedance you're relying on?

JB> That had me wondering too, but I don;t really understand power
JB> transformer design, turn ratios are the limit of ability to
JB> design transformers. 

 Iron saturates rather quickly. For a given core size, more turns
means less flux density and less iron losses (less saturation). The
field coil in a synchronous motor is the same.  Of course, the power
is reduced, but iron-loss drops a lot faster than power. For 10% less
power you can drop losses, and motor-noise, by half.

 Most motors (and transformers) are run in iron-saturation using
temperature rise as the limit (60C max). It's an art to screw the
maximum output for minimum cost, and a beginner often crosses the
line.

 A transformer is not easy to design. First you pick a core, then the
turns, the turns ratio, then wind it up to see that the wire fits in
the hole, load it up to make sure the volts are right, and run it to
measure temperature rise...

 It's too big a fiddle... but it is possible to design the whole
thing on paper, temperature rise and all, and get it right first time.
If you try to fiddle it, you'll never get it right.

 SMPS are even worse, because wire-losses are almost unpredictable.  

Regards,
Bob

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