The Magneformer-lenzless transformer ?

[MileHigh]

Magnetics and transformers and materials, it's a pretty big subject if you are hard core.  I am too tired to comment on previous postings right now, but let me mention something interesting.  I saw this thread on a science forum but didn't try to read it, it looked like way like too much work and my interest level was not high enough.

The subject was what happens in the magnetic core of a transformer under normal operation.  It's not so obvious.  Think of a good quality fairly large 1:1 transformer.  You put a nice pure 60 Hz sine wave into it and there is a resistive load.  We don't really need to worry about values.

Here is the thing:  The primary current creates magnetic flux in the core.  But the secondary also reacts in perfect synchronicity and its current also creates an equal and opposite magnetic flux in the core.  Since we know that flux in one direction can be cancelled by equal flux in the opposite direction, then what is going on in the core?  If there is no net flux in it, what's happening?  What are the magnetic domains doing?  Are they flipping or not flipping?

We know that each coil in the transformer is creating a "blast of flux."  But between the two blasts there is a kind of mutually assured destruction going on and there is no flux.  It's almost like electrons and holes in a diode smashing into each other and self-annihilating (in a figurative sense).

I honestly have never read up on this subject at all.  I just saw the subject line and it got me thinking.

MileHigh

[tinman]

Magnetics and transformers and materials, it's a pretty big subject if you are hard core.  I am too tired to comment on previous postings right now, but let me mention something interesting.  I saw this thread on a science forum but didn't try to read it, it looked like way like too much work and my interest level was not high enough.

The subject was what happens in the magnetic core of a transformer under normal operation.  It's not so obvious.  Think of a good quality fairly large 1:1 transformer.  You put a nice pure 60 Hz sine wave into it and there is a resistive load.  We don't really need to worry about values.

Here is the thing:  The primary current creates magnetic flux in the core.  But the secondary also reacts in perfect synchronicity and its current also creates an equal and opposite magnetic flux in the core.  Since we know that flux in one direction can be cancelled by equal flux in the opposite direction, then what is going on in the core?  If there is no net flux in it, what's happening?  What are the magnetic domains doing?  Are they flipping or not flipping?

We know that each coil in the transformer is creating a "blast of flux."  But between the two blasts there is a kind of mutually assured destruction going on and there is no flux.  It's almost like electrons and holes in a diode smashing into each other and self-annihilating (in a figurative sense).

I honestly have never read up on this subject at all.  I just saw the subject line and it got me thinking.

MileHigh

MH
The flux in the secondary wouldnt be equal or opposite. Not equal due to ohmic losses,nor opposite. It would be a weaker field,and of the same field-apposing yes-opposite no. This is where transformer loss comes from.If one end of the transformers primary builds a north field,then the secondary field would be a north field aswell at that end-this is an apposing field,as opposite would be south. There is no equal in the magnetic fields either,as there is heat produced.If it was a 1 to 1 transformer,and was equal,then we would get out what we put in. But as we know we dont get out from the secondary what we put into the primary,we know the magnetic field isnt equal in both winding's.The output is less,and if we add the heat energy created by ohmic resistance to the output,we then have an equal amount of energy to that of what we put in.

[Farmhand]

I think this paper is fairly close to the mark for the layman's needs.

Although it's not second nature to most of us it's not rocket surgery either, if we look in the right places the info is around.

I recommend that anyone interested in transformers and not already trained to read the entire paper from start to finish a few times and use it for reference.
Of course transformers that vary from the efficient power transformer he talks about will behave differently it's a good starting point especially if we want to design our own transformers to use.

Transformers - The Basics (Section 1)
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.

It is not important that you understand the reasons for this right from the beginning, but it is important that you remember that for any power transformer, the maximum flux density is obtained when the transformer is idle. Please don't forget this .

3.   How a Transformer Works

At no load, an ideal transformer draws virtually no current from the mains, since it is simply a large inductance. The whole principle of operation is based on induced magnetic flux, which not only creates a voltage (and current) in the secondary, but the primary as well!  It is this characteristic that allows any inductor to function as expected, and the voltage generated in the primary is called a 'back EMF' (electromotive force). The magnitude of this voltage is such that it almost equals (and is effectively in the same phase as) the applied EMF.

Although a simple calculation can be made to determine the internally generated voltage, doing so is pointless since it can't be changed. As described in Part 1 of this series, for a sinusoidal waveform, the current through an inductor lags the voltage by 90 degrees. Since the induced current is lagging by 90 degrees, the internally generated voltage is shifted back again by 90° so is in phase with the input voltage. For the sake of simplicity, imagine an inductor or transformer (no load) with an applied voltage of 230V. For the effective back EMF to resist the full applied AC voltage (as it must), the actual magnitude of the induced voltage (back EMF) is just under 230V. The output voltage of a transformer is always in phase with the applied voltage (within a few thousandths of a degree).

For example ... a transformer primary operating at 230V input draws 150mA from the mains at idle and has a DC resistance of 2 ohms. The back EMF must be sufficient to limit the current through the 2 ohm resistance to 150mA, so will be close enough to 229.7V (0.3V at 2 ohms is 150mA). In real transformers there are additional complications (iron loss in particular), but the principle isn't changed much.

If this is all to confusing, don't worry about it. Unless you intend to devote your career to transformer design, the information is actually of little use to you, since you are restrained by the 'real world' characteristics of the components you buy - the internals are of little consequence. Even if you do devote your life to the design of transformers, this info is still merely a curiosity for the most part, since there is little you can do about it.

4.   Interesting Things About Transformers
As discussed above, the impedance ratio is the square of the turns ratio, but this is only one of many interesting things about transformers ... (well, I happen to think they are interesting, anyway  ).

For example, one would think that increasing the number of turns would increase the flux density, since there are more turns contributing to the magnetic field. In fact, the opposite is true, and for the same input voltage, an increase in the number of turns will decrease the flux density and vice versa. This is counter-intuitive until you realise that an increase in the number of turns increases the inductance, and therefore reduces the current through each coil.

I have already mentioned that the power factor (and phase shift) varies according to load, and this (although mildly interesting) is not of any real consequence to most of us.

A very interesting phenomenon exists when we draw current from the secondary. Since the primary current increases to supply the load, we would expect that the magnetic flux in the core would also increase (more amps, same number of turns, more flux). In fact, the flux density decreases! In a perfect transformer with no copper loss, the flux would remain the same - the extra current supplies the secondary only. In a real transformer, as the current is increased, the losses increase proportionally, and there is slightly less flux at full power than at no load.

MIT Lecture - Inductance.
http://www.youtube.com/watch?v=UpO6t00bPb8

A transformer designed to be efficient can be made to behave like a Thane Crimes transformer just by increasing the applied frequency.  And it will behave woefully. See link.
http://www.youtube.com/watch?v=Zxde9qga79c  Please bear in mind I am no expert and I get things wrong and say the wrong thing at times, but the video shows some stuff in my opinion. I made it quite some time ago. I know a little bit more now. It still makes me laugh, I think I am a funny guy, no ?

..

[MileHigh]

About the issue of the relative permeability of a magnet, it may be possible to have a magnet that still retains a high relative permeability if it is only partially magnetized.

Yes permanent magnets are almost fully saturated magnetically, many FE tinkerers are not aware of that and when they use magnets in a "closed" magnetic circuit where permanent magnets are used to "close" the magnetic path, they actually build an "air gap" into the circuit at places they insert the permanent magnet(s).

Note the attached graphic showing how you can control how strong the nominal flux in the magnet is if you travel up and then down the BH curve and choose your path carefully.  You can back off on the externally applied field strength and then slide down to a flux density level that is about 50% strength.  The trick is to know what your maximum externally applied field strength is to then back off and settle around the 50% flux density level.  Where I am uncertain is about the choices and associated properties for the core material.  How well will the material retain its partial magnetization if you wrap a coil around it and pulse it?   But at least in theory there is a recipe for doing it.

When it comes to the various types of commercial magnets you play with, I would assume that when they "bang" them to magnetize them, the flux density in the magnet is nearly or is 100% strength - they are fully saturated.  So does that imply that the relative permeability is very low in both directions because the magnetic domains are 100% "occupied?"

With a lot of care I would assume that you could demagnetize a commercial magnet and then give it a flux density level of 50% by yourself.  You would have to carefully tip toe up and then down the BH curve.

If anyone wants to do some reading "BH curve" and "tape head demagnetiser" would be a good launching pad.

MileHigh

[gyulasun]

....
When it comes to the various types of commercial magnets you play with, I would assume that when they "bang" them to magnetize them, the flux density in the magnet is nearly or is 100% strength - they are fully saturated.  So does that imply that the relative permeability is very low in both directions because the magnetic domains are 100% "occupied?"

Yes it does imply. Ferromagnetic materials intended for permanent magnets are magnetically "hard" materials with very high coercivity value, this means that once magnetized to a certain strength they tend to stay at that magnetized level, you cannot control its magnetization as readily and easily as in case of a soft ferromagnetic material. For such hard materials, when the H field is reduced back to zero (or even to an opposite value), the B field in the material does not get reduced but it remains 'remanent' at a certain level.

Here is a link to show the BH curve for a strong and a not so strong permanent magnet,  I refer to Figure 3:  http://www.electronenergy.com/magnetic-design/magnetic-design.htm   

By the way the formula for a BH curve is B=u*H and u (u=permeability) has to be close to unity in case of a material with very wide hysteresis curve.

With a lot of care I would assume that you could demagnetize a commercial magnet and then give it a flux density level of 50% by yourself.  You would have to carefully tip toe up and then down the BH curve.

Yes that would be a hard and arduous task for sure. I would suggest a much easier solution using the so called electro-permanent magnet which includes a soft and a hard magnetic core combination, the soft core serves for a normal electromagnet and the hard core is in fact a normal permanent magnet. By changing the current in the electromagnet the resultant combination of the PM and that of the electromagnet gives a variable and strong magnetic field: http://en.wikipedia.org/wiki/Electro-permanent_magnet 
You surely remember the Hildenbrand or the Flynn setups etc: all such magnetic circuits add magnetic flux from permanent magnets to that of electromagnets, albeit not always in a linearly controllable way but by switching. See these products:
http://www.magnets2buy.com/acatalog/Electro-magnets.html

Gyula