Something ive been thinking about for some time.  It fits the topic because it is involved with the transformer function.


If we have a rod core, with say the primary on one end and a secondary on the other, where the pri and sec are not overlapped, when we put an ac input to the primary, loading the secondary should have the secondary producing an opposing field to the primary. No?

So with a toroid core, with primary on one side of the core and the secondary on the other side, when the primary induces the loaded secondary, and the secondary produces an opposing field, there is no longer a loop of field in the core as there should be both windings having their N pole fields facing each other in the core, and likewise the S pole fields opposing at the other end of the core in the open face of the core between the ends of the primary and secondary windings.

So it wouldnt be that the core is just saturated by increasing continuous loop of field in the core, it is sort of separating the core field holdings and we should be able to see field leakage N at one side of the core between the 2 windings ans S at the other during a half phase of operation, and the opposite happens at the open spaces of the core between the 2 windings.

Maybe im just tired. If it is so, it would seem we didnt know that before?

Mags

One more thing and i gotta git

Im just trying to straighten this out in my head so Im not lost in that area. And if what I think is correct, there may be something good here. Got an idea.

Now lets say we have a primary and secondary wound overlapping the whole core. Wind the sec first all the way around 1 time, 1 layer. Then wind the primary over top of that as a secondary layer, all the way around once.  Now we add an AC input to the primary and its field is in the core in a loop, changing polarity for each phase of the AC input. Fine and dandy, I agree on that. Now load the secondary. It will produce and opposing field compared to the primary and they should be canceling in the core, depending on the currents for each. 

If that the case, then when the primary and secondary  are able to produce equal amounts of field opposing each other, then there would be littlle field in the core as compared to just the primary with input and sec not loaded.

Strange. Sort of belittles the meaning of saturation of the core, in my mind as to what I thought it meant, when the max in and out are achieved and fields cancel at full power compared to what I had normally thought, and there is more flux in the core at idle with no load on the sec?

K. Im nuts  Need sleep

Mags

One more thing and i gotta git

Im just trying to straighten this out in my head so Im not lost in that area. And if what I think is correct, there may be something good here. Got an idea.

Now lets say we have a primary and secondary wound overlapping the whole core. Wind the sec first all the way around 1 time, 1 layer. Then wind the primary over top of that as a secondary layer, all the way around once.  Now we add an AC input to the primary and its field is in the core in a loop, changing polarity for each phase of the AC input. Fine and dandy, I agree on that. Now load the secondary. It will produce and opposing field compared to the primary and they should be canceling in the core, depending on the currents for each. 

If that the case, then when the primary and secondary  are able to produce equal amounts of field opposing each other, then there would be littlle field in the core as compared to just the primary with input and sec not loaded.

Strange. Sort of belittles the meaning of saturation of the core, in my mind as to what I thought it meant, when the max in and out are achieved and fields cancel at full power compared to what I had normally thought, and there is more flux in the core at idle with no load on the sec?

K. Im nuts  Need sleep

Mags

Mags here is a link to a good guide for transformers. The clipping below explains what your post above says.

http://sound.westhost.com/xfmr.htm

Preface
One thing that obviously confuses many people is the idea of flux density within the transformer core. While this is covered in more detail in Section 2, it is important that this section's information is remembered at every stage of your reading through this article. For any power transformer, the maximum flux density in the core is obtained when the transformer is idle. I will reiterate this, as it is very important ...

For any power transformer, the maximum flux density is obtained when the transformer is idle.

The idea is counter-intuitive, it even verges on not making sense. Be that as it may, it's a fact, and missing it will ruin your understanding of transformers. At idle, the transformer back-EMF almost exactly cancels out the applied voltage. The small current that flows maintains the flux density at the maximum allowed value, and represents iron loss (see Section 2). As current is drawn from the secondary, the flux falls slightly, and allows more primary current to flow to provide the output current.

Total system resonance is not a prerequisite for resonant electronic circuits. Where on earth did you get that idea from.?

A simple am radio receiver is a compound circuit (a total system) that relies on tunable resonance in one minor portion of the total circuitry only, that is, the tunable antenna system, which resonates in 'tune' with the radio carrier frequency being 'tuned' for. The rest of the circuit need not display any resonant activities whatsoever. The rest of the compound circuit is designed to separate the amplitude variations in the carrier signal (the audio frequency signal that's superimposed on the carrier) from the carrier frequency itself (for which the antenna system has been tuned to resonate with), and then amplify the separated electrical audio frequency, before converting it to sound via the speaker.
Resonance is not required in the separation, amplification and conversion stages of the circuit.
Cheers

Yes,. you are correct, that in standard practices, total circuits are NOT designed to be resonant.
And as long as the feedback is blocked from interfering with the resonant portion of the circuit,
then it should operate properly.

However, I would argue that these are not truly resonant.
only partially resonant.
What I am talking about are circuits designed to be entirely resonant, among each of its' parts.

If we go back to the mechanical example.
whether just a simple mechanical oscillator, operating at resonance,
or the large bridge that tears itself apart.....

Suppose for an instant, we placed some sort of "dampeners" against these oscillations, to siphon off some of the built-up energies.
rather than creating situations that simply disrupt and dissipate it.

Would this be a better scenario, than just letting the build-up energies go to waste?

If your answer be a yes or a no,
think about how this would apply to the electronic analogy.

Oops.

Thanks farmhand.   Its been buggin me for some time. We see all these diagrams/drawings of toroid and other closed core transformers that do not depict this. And the idea that the core would leak due to an over abundance of field when the transformer is working hard, calling it over saturation.

Ok. Question answered in the best way.

Thanks again

Mags

yes. In fact, in engineering, the self-resonant frequency of the ferrite inductive core is understood to be
the frequency at which saturation peaks at a maximum (with no oversaturation) in the minimum time.
It is kind of a funny way of looking at things, but this is what occurs at that freq.

When the ferrite reaches saturation, it can hold no more field. (all else is wasted EMF radiation)
 When the switching occurs right at this point, the resultant field collapse is precisely timed with the oscillations.
1/2T + 1/2T = T

In the case of undersaturation - there is a shorter charging time of the core material (or correspondingly weaker field)
clean waveforms can be transferred in this case, however it is not "resonant" with the ferrite.

In the case of oversaturation - there is a longer charging time of the core material, and a shorter discharge.
this leads to an imbalanced (asymmetrical) waveform. Also not "resonant" with the ferrite.

There are certain nodal frequencies in the case of undersaturation, where resonance can occur.
Not the case with oversaturation.

These conditions are in addition to what has been stated about the resonant frequency of the ferrite in previous posts.
It is not often looked at from this perspective, except by those that manufacture ferrite materials.

Was going through my toroid cores. If you take a ferrite bead, most have seen, a medium dark grey, and use an ohm meter, you dont get any resistance reading. So they would appear to have the least amount of eddy currents and would be best for high freq operation. At least ones available locally or from a scavenged device.

Some cores do have continuity. Ones that are coated in various colors, if you scrape away some of the coating in 2 different places then measure, you would be surprised at what you find. Some may be 0ohm. Some like one I just checked, 214ohm, one at 1.4mohm.  Ones that measure very low down to 0ohm, you can see they are shiny after scraping the coating, like if it is just solid iron. Probably used for low power/freq requirements.

So Im going for the known 'ferrite' core this round. Will do 11 turns, windings on opposite sides of the core.  I have a bunch of the blue coated 1.4mohm cores that I want to try something leaning towards EMjunkys opposing coils by winding 2 identical transformers, but one has 1 winding wound in the opposite direction to see it that affects things with the circuit. Naturally I will have to reverse the polarity connection on the EMj winding to make it work. But just interested in what might happen, if it affects freq, etc.

Mags

Mags:

Yes, the colored ones are powdered iron.  I always got better results with ferrite...with a high permeability if possible.  It all depends upon the goal.

Bill