"i think the more important observation is most of the no load loss is the iron core."
No....That is not quite what I have found.
With a torroid, I can get a 200w to 20 watts drop, and they are big ones.... thats 10:1
Without the inductor, the figures are about the same ... ie an EI transformer with high leakage, and a torroid with the same ratings, will be about the same 200 watts loss at idle. These are 40 pounders or more.
The inductor will lower the toroids idle by 10:1 in this case, it will not lower the EI by more than 2:1 for good cores, and virtually NO difference for poorer cores.
So I figure it is the leakage making the difference in how the core will react with the inductor... not the mass of the core...lowering the flux by over winding is a given.. so can be ignored for this case...... although with big torroids, I just rewind with bigger copper and so the copper loss does not go up for the extra turns..... and we are talking 3v/turn or more@50hz, so it does not take much extra length to add a few volts here and there.
If thats true, and the leakage is the key... then what would that effect, and why only 18uf or so makes so much difference, not 2.7mh ( tried that too ), which really would have squashes a bit of the HF from seeing the cores.
Thats why I think the switching losses are being altered, and that they are altered to the extent that they can help tight transformers, and make little or no difference to poorer EI transformers..... once mine gets down to 20 watts or so, I think it is iron losses from the massive core/s.
Would be interested in boBs take on this .... but thats what I see as the key to low idle losses..... otherwise use a small transformer until the power rises and switch in more in parallel to handle the loads...... BUT this won't help overall efficiency with higher power.
The headline idle losses are lower, but switching losses will occur when the second bigger transformers would start to conduct.
Using a good big one gives efficiency across the whole range.
............oztules
EDIT: from post #9.. this:
"
There is no changing in frequency like yours, there is no noticeable change in any parts of the wave form.... except, if we go to 1us/div we see a ringing lasting for about 1us.
It has about 8-9 wobbles before it zero's out.
When I short the inductor out, this ringing has the same number of wobbles, but about half the magnitude, and the current drops by over 1/2 an amp... that looks to be the culprit.
"
should read nmore like this "
There is no changing in frequency like yours, there is no noticeable change in any parts of the wave form.... except, if we go to 1us/div we see a ringing lasting for about 1us.
It has about 8-9 wobbles before it zero's out.
When I short the inductor out, this ringing has the same number of wobbles, but twice the magnitude, and the current increases by over 1/2 an amp... that looks to be the culprit.
"