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Author Topic: Question regarding flux speed and transformer operation  (Read 5782 times)

void109

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Question regarding flux speed and transformer operation
« on: July 21, 2010, 06:00:55 PM »
I've been thinking about transformers and flux, and I wanted to share some thoughts and questions to see if anyone would kindly clarify some issues.

Nothing travels faster than the speed of light (supposition), including flux.  So flux can only travel at roughly 1 foot per ns.  In a transformer when you pulse the primary, it induces a magnetic field which induces current on the secondary.  The secondary then induces its own magnetic field in opposition to the primary.  I think this is what we call BEMF and a manifestation of Lenz law?

All of the transformers I have seen are relatively small.  Given the speed limit on flux - wouldn't simply having a sufficiently large transformer core along with a sufficiently short pulse on time and dead time, avoid the penalties mentioned above?

Thanks in advance!

mscoffman

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Re: Question regarding flux speed and transformer operation
« Reply #1 on: July 21, 2010, 10:48:07 PM »

Signals in magnetic fields are probably a lot like electrical
signals. The signal wave front has to pass back and forth
several times at the speed of light between the source and
the load before the energy of the signal becomes unavailable
at the source and is available at the load. This is how the
real world implements conservation of energy "accounting" in
relativistic systems. It's really the basis of Quantum Mechanics
in physics, and all part that pesky "Real World".

A Pulse also has TIMOWTDI - theres more than one way to do it.
If the pulse isn't accepted magnetically it can always become
active as EMF and radiate as a radio wave.

:S:MarkSCoffman

void109

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Re: Question regarding flux speed and transformer operation
« Reply #2 on: July 22, 2010, 03:26:09 AM »
I'm feeling often of late, that I really should step back from all of this gadgeteering in OU research and spend a year studying physics and quantum mechanics.  I get the impression that much of what I feel is mysterious and new is actually well understood and documented.

I did notice you said "probably a lot like", instead of "is a lot like".  I have a reel of metglas tape I picked up off of ebay awhile back.  I may wrap a large magnetic track, large enough that I can use small pulse times (a magnetic circuit that is meters in diameter and pulses that are < 1 ns) and test the notion.

gyulasun

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Re: Question regarding flux speed and transformer operation
« Reply #3 on: July 22, 2010, 11:04:45 PM »
...
  In a transformer when you pulse the primary, it induces a magnetic field which induces current on the secondary.  The secondary then induces its own magnetic field in opposition to the primary.  I think this is what we call BEMF and a manifestation of Lenz law?

Yes.

Quote
All of the transformers I have seen are relatively small.  Given the speed limit on flux - wouldn't simply having a sufficiently large transformer core along with a sufficiently short pulse on time and dead time, avoid the penalties mentioned above?

Your question brings up in my mind a very interesting answer on getting around Lenz law. I managed to find it in the Sweet-VTA yahoo group, see this link:
http://tech.groups.yahoo.com/group/Sweet-VTA/message/4583

If someone cannot see it, here is the text, first the question, then the answer:

-----------------------------------------------------------------------
Really confused about Lenz Law
>
> Hey Yall,
>
> I'm really confused about Lenz's Law. If you place a solid permanent
> magnet through a coil, the coil will produce a magnetic field that
> opposes the magnetic field of the magnet. But, isn't this simply due
> to the fact that magnetic fields flow in a circle from North to South
> pole? Inside the structure of the permanent magnet, magnetic field
> lines flow from South to North, but outside the magnet they loop back
> around and flow from North to South. What gives?
>
> If we placed a coil through a hollow cylindrical permanent magnet,
> wouldn't induction produce a magnetic field that sucks the coil in,
> at least so far as center of the hollow cylinder?
>
> Confused,
> Ed
--------

Re: Really confused about Lenz Law

Only the imaginary lines of magnetic flux looping around the outside
of a magnet will cut across external conductors and create a current
flow in them which will then have its own opposing magnetic field.

see: http://micro.magnet.fsu.edu/electromag/java/lenzlaw/index.html

for a demo.

But you can get around Lenz's law. If you have a single small loop
inside a conductive cylinder or sphere and the distance from the loop
to the outer conductor wall is X and you apply a microwave signal to
the loop such that a 1/4 wave length of the signal equals X then the
normally opposing magnetic field from the current induced in the outer
conductor will be aiding rather than opposing the magnetic field of
the loop by the time it propagates back to the loop.

Lenz's Law only applies at distances much smaller than the wavelength
of the signal involved. The higher you go in frequency, the more time
delay and so the more phase shift across distances between original
signal and counter EMF signals until an opposing signal becomes an
aiding signal.

George
----------------------------------------------------------------------

Regarding your intention on stepping back from tinkering and starting a study on physics and quantum mechanics: while it is very good to learn on topics like that, you actually do learn while tinkering, so why don't you do both at the same time?  ;)

rgds,  Gyula

void109

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Re: Question regarding flux speed and transformer operation
« Reply #4 on: July 23, 2010, 08:47:34 AM »
Thanks for the reference.  That's what I was thinking, if the wave length is of appropriate size it should reinforce itself until the core material is saturated.  Does that sound logical? my Internet connection has been down all day or I would have worked on this earlier.  My freq gen and scope only resolve to 50 MHz, so I think I'll have to wrap a rather large core to be able to see and measure it, I think I need 0.5 meter between coils for a 299~ MHz signal.  It will need to be a monster magnetic track, or I just need to get a higher resolution scope.

gyulasun

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Re: Question regarding flux speed and transformer operation
« Reply #5 on: July 23, 2010, 01:23:30 PM »
Hi void109,

Perhaps you wished to write you needed 0.25m between coils for a 299..MHz signal ?

The 299..MHz has about 1m wavelength, and a quarter wave is 25cm.
According to the text I quoted above, the flux travels 1/4 wavelength, induces BEMF, the counter flux also travels 1/4 wavelength so that all together 1/2 wavelength is involved which is 180 degree i.e. out of phase, right? 
This out of phase flux is needed because the original BEMF flux is out of phase too just because of Lenz law,  so summing them up you get in-phase flux hence signals.

What I think the problem is what material should be used to carry the flux to 1/4 wave?
Air is the worst flux conductor and whatever higher (higher than 1)  permeability material is considered, it should have low loss in the 300MHz range too. I know of high frequency powdered iron cores that may work at 300MHz though their permeability is between 4 and 10 or so. Suddenly I do not have a better suggestion, will ponder on it later.

rgds,  Gyula 

void109

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Re: Question regarding flux speed and transformer operation
« Reply #6 on: July 23, 2010, 07:06:33 PM »
Thanks for taking time to ponder this Gyula!

The reel of metglas I have is:

http://www.metglas.com/products/page5_1_2_4.htm

I think reading the technical specs that this will not be suited for this test?  It looks like it has very high losses in the Mhz range. :(

I also believe you are correct about the distance required - still being new to this topic I was having trouble wrapping my head around the interactions and I believe my mental imagery of the process was incorrect.  So for a 299..Mhz signal, I'm looking for a 0.5m CIRCUMFERENCE and 0.25m between the primary and secondary coils.

That's a large core!  I have a transformer core on its way here I ordered some month ago, dimensions 150mm x 100mm, which coincidentally works out to a circumference (outer) of 0.5m.  Unfortunately I dont know what type of material it is (from an auction) other than it is manufactured by metglas.

And there's still the problem of not having equipment that will let me view frequencies that high! 

gyulasun

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Re: Question regarding flux speed and transformer operation
« Reply #7 on: July 23, 2010, 09:59:21 PM »
Well, I do not think either the METGLAS core can work above a few hundred kHz (the core loss becomes prohibitive) and unfortunately the large core you are going to receive is in suspect too.

Maybe I am mistaken but for the usual power transformer purposes ferrite manufacturers do not make cores working on higher than a few MegaHertz.
Think of the switch mode power supply cores, nowadays the earlier some ten kHz working frequencies have been shifted up to near 1MHz or slightly beyond that.

There are the so called microwave ferrite materials working up to the 9-10GHz range but normally their shape is disc, triangular or rectangular, although some produce custom shapes like this French firm (found at random):
http://www.temex-ceramics.com/site/en/microwave-ferrites-cermatmenu-29.html
Their so called spinel ferrite may be considered, (see their data sheet) you would have to consult them on toroidal shape possibility, probably they make samples in toroidal shapes to measure and characterize the material, this is normally the procedure when manufacturing.


There are the so called transmission line transformers, they normally have (mainly) toroidal ferrite cores for that purpose and they can cover several hundred MHz range but they consist of tightly coupled twisted wire pairs or coaxial cable lines, do not work in the usual manner power transformers do.  Though they are worth studying...

So the problem is still the material, even if the microwave ferrites could be used, question is their prices if one has to order them in toroidal shape...

rgds,  Gyula

arhitrade

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Re: Question regarding flux speed and transformer operation
« Reply #8 on: July 25, 2023, 08:01:27 AM »
Transformer operation considering the second magnetic field