Magnetic fields within a toroid inductor.

[Dave45]

I just showed you the secret of the ages and you dont even realize it 

[xee2]

tinman,


I have worked with toroids and magnetic field theory for over 30 years and I have always found the description given in the link suggested by MileHigh


http://www.youtube.com/watch?v=pCSHcftPAIM


to be correct. This is the standard physics/electronic engineering theory approach. The PDF suggested by Magluvin


http://www.overunity.com/13802/magnetic-fields-within-a-toroid-inductor/dlattach/attach/127516/


gives a simpler explanation that is also correct.


These explanations may not be the ultimate truth, but they have been used successfully by physics and electronic engineers for many years.


I recently posted a video you may find interesting about flux cancellation that has experimental tests showing magnetic field cancellation in a toroid (however, I admit it was not easy to understand):


http://www.youtube.com/watch?v=sc9bt5Yo0H8

[Dave45]

Keep on trucken

[MileHigh]

Tinman:

I did a little bit of hunting around and now know that you were looking at the rotor of an alternator (Just like you stated but for some reason it didn't register with me at first).  In the schematics I looked at I did not see any rotors that had two separate energizing circuits for the North and South finger pole electromagnet coils so it's still a mystery to me.  I see how a voltage regulator circuit governs the amount of DC current that goes into the rotor electromagnets via the slip rings and that will then determine the rectified voltage output from the stator windings.

Good doc:  http://www.autoshop101.com/forms/alt_bwoh.pdf

Good graphic:  http://forums.pelicanparts.com/uploads9/mot_alt1168989977.gif

If anything there are lots of diodes, but I can't explain your screwdriver test.  I can only suspect that there are some diodes embedded in your rotor as per the diodes you see that allow the stator to take over the job of energizing the rotor electromagnets once the alternator is spinning.  Perhaps for some reason there are separate circuits to energize the North and South finger poles in the particular rotor you were examining.  However, that still doesn't explain the effect you see when you reverse the polarity.  Although when you think about it, I am assuming that the polarity for the voltage on the slip rings is not supposed to be reversed.

I was the type of kid that opened up everything to see how it ticked.

MileHigh

[poynt99]

I strongly disagree. 

There are fields in that open area.

Mags,
Correct, but it is not a magnetic field.

Lets take the toroid diagram in the vid and make it a transformer. Primary on the left and secondary on the right. Now, if the primary induces a field in the core, how does the secondary get induced if the field is only in the core?    

It's quite easy to understand how, but you first have to understand that a changing flux (B-field) creates a changing electric E-field, which is at 90º. Second you need to be aware that the E-field is present both inside and outside the toroid. Third, you need to understand that it is actually the E-field which is responsible for both self and mutual induction. Fourth, the B-field inside the core is conducted from the primary through to the secondary due to the high permeability core.

The field of the primary has to 'cut' the windings of the secondary.

When using a toroid core, no it is not required. What is required is that the flux created in the core by the primary, must go through the center of the windings of the secondary, the same way you can make a transformer by placing two coils side-by-side on a rod core.

If you put a wire through the very center of the toroid opening,not even touching any toroid windings or the core, you will get current induced into that wire from an input to the toroidal coil. So how can that be, if the field is only in the core? ?

It is not only normal for this to be the result, but it is required. It must occur. But as I mentioned, you must be aware of and carefully consider the E-field in this interaction. When you see this, it is simple and obvious.

Ask questions if you are still not clear on what I'm saying.