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Author Topic: Measuring Amps on output coils  (Read 27366 times)

TinselKoala

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Re: Measuring Amps on output coils
« Reply #30 on: March 23, 2015, 08:44:06 AM »
Sigh. WIKI is your friend.

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Superconducting magnets have a number of advantages over resistive electromagnets. They can generate magnetic fields that are up to ten times stronger than those generated by ordinary ferromagnetic-core electromagnets, which are limited to fields of around 2 T. The field is generally more stable, resulting in less noisy measurements. They can be smaller, and the area at the center of the magnet where the field is created is empty rather than being occupied by an iron core. Most importantly, for large magnets they can consume much less power. In the persistent state (above), the only power the magnet consumes is that needed for any refrigeration equipment to preserve the cryogenic temperature. Higher fields, however can be achieved with special cooled resistive electromagnets, as superconducting coils will enter the normal (non-superconducting) state (see quench, above) at high fields.
Superconducting magnets are widely used in MRI machines, NMR equipment, mass spectrometers, magnetic separation processes, and particle accelerators.
One of the most challenging use of SC magnets is in the LHC particle accelerator.[7] The niobium-titanium (Nb-Ti) magnets operate at 1.9 K to allow them to run safely at 8.3 T. Each magnet stores 7 MJ. In total the magnets store 10.4 GJ. Once or twice a day, as the protons are accelerated from 450 GeV to 7 TeV, the field of the superconducting bending magnets will be increased from 0.54 T to 8.3 T.
The central solenoid and toroidal field superconducting magnets designed for the ITER fusion reactor use niobium-tin (Nb3Sn) as a superconductor. The Central Solenoid coil will carry 46 kA and produce a field of 13.5 teslas. The 18 Toroidal Field coils at max field of 11.8 T will store 41 GJ (total?).[clarification needed] They have been tested at a record 80 kA. Other lower field ITER magnets (PF and CC) will use niobium-titanium. Most of the ITER magnets will have their field varied many times per hour.
One high resolution mass spectrometer is planned to use a 21 Tesla SC magnet.[8]

http://en.wikipedia.org/wiki/Superconducting_magnet

Low-Q

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Re: Measuring Amps on output coils
« Reply #31 on: March 23, 2015, 09:05:49 AM »
Yes, it's a good one and leads-out much thought and speculation.

One question that immediately arises is this: Does the magnet always wind up rotating in the same direction or sense?
No... it does not. It can rotate in either direction once it gets started.

I have also done the experiment using a larger disc magnet, about the size and shape of a US quarter-dollar coin, completely
wrapped in copper foil. My thinking was that this should help to equalize any thermal gradient across the magnet. It still rotates.

The superconductor is a YBCO type, melt-textured and sintered, prepared according to formulae and directions from Eugene Podkletnov.
I assume the coolest side of the magnet change location as it "wobbles" so in a way this magnet starts to rotate due to difference in temperature. Its a lag in the temp.change, always delayed, causing the phenomenon.

My guess.

Low-Q

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Re: Measuring Amps on output coils
« Reply #32 on: March 23, 2015, 01:01:12 PM »
Ref. post 31. The coolest side of the magnet are getting temporarily demagnetized. I wonder if this rotation would happen if you put styrofoam between the magnet and the liquid nitrogen - insolateing the magnet somehow...

Vidar.

Low-Q

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Re: Measuring Amps on output coils
« Reply #33 on: March 23, 2015, 03:50:00 PM »
Ref. post 31-32. Cooling a magnet makes it more magnetized. So this is a heat engine based on magnetism :-)

verpies

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Re: Measuring Amps on output coils
« Reply #34 on: March 24, 2015, 03:23:52 PM »
There is no magnetic field surrounding a super conductor.
Yes there is, if a superconductive ring was made superconductive (frozen) WHILE a non-zero external magnetic flux was penetrating it.
Such superconducting ring will generate the magnetic flux penetrating its hole even when the external flux source is removed.

This is called "flux freezing" and can be used to attract a soft ferrite to a superconducting ring - just like a magnet would.

P.S.
Conversely, when such superconductor is "frozen" with magnetic flux absent, then it will continue to exclude any external flux, should such appear in its vicinity.  In other words, a superconducting ring maintains the flux level, which existed in its hole when it was "frozen".

verpies

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Re: Measuring Amps on output coils
« Reply #35 on: March 24, 2015, 03:36:16 PM »
If I recall correctly there is no magnetic field inside a superconductor. 
Leaving aside "flux pinning" inside type II superconductors, that concept gets a little murky when a superconducting ring is considered.  Does the hole in a superconducting ring constitute an "inside" or "outside" ?

verpies

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Re: Measuring Amps on output coils
« Reply #36 on: March 24, 2015, 03:47:59 PM »
And once this field is poled into the super cooled material , you believe a current is now flowing through that material?-without a voltage potential?
Yes and I find it very annoying when people try to apply voltage and EMF concepts to shorted coils - this is not necessary because coils are inherently current devices (while capacitors are voltage devices, btw). 

Yes, you can do it, as long as a coil has some resistance, that keeps dissipating coil's energy (that's what Faraday's law is about) but it is like fitting a square peg into a round hole with shorted superconducting coils...

tinman

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Re: Measuring Amps on output coils
« Reply #37 on: March 24, 2015, 10:17:17 PM »
Yes and I find it very annoying when people try to apply voltage and EMF concepts to shorted coils - this is not necessary because coils are inherently current devices (while capacitors are voltage devices, btw). 

Yes, you can do it, as long as a coil has some resistance, that keeps dissipating coil's energy (that's what Faraday's law is about) but it is like fitting a square peg into a round hole with shorted superconducting coils...
Although you believe a coil is a current device,the current/voltage value is dependant on resistance. The higher the resistance,the lower the current,and higher the voltage-disregarding the super conductor of course. The same applies to capacitors. Capacitors can deliver extreem currents across low resistive loads,while the voltage across that load may be low.

Now,what is the difference between a super conducting ring(that has only an internal magnetic field once a current is sent through it,and the good old room temperature PMH ?

verpies

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Re: Measuring Amps on output coils
« Reply #38 on: March 25, 2015, 01:07:47 AM »
Although you believe a coil is a current device,the current/voltage value is dependant on resistance.
An ideal inductor has no resistance.  Working in terms of voltage with inductors is only needed to account for their imperfections -  resistive "energy leaks".

Also, a natural state for an inductor is when it is shorted and a natural state for a capacitor is when it is opened. 
With ideal components, there is no energy leakage out of them then.

When you do something unnatural for them, e.g. open an energized coil or short an energized capacitor, then all hell breaks loose.

Now,what is the difference between a super conducting ring (that has only an internal magnetic field once a current is sent through it) and the good old room temperature PMH ?
Do you mean this by "PMH" ?

tinman

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Re: Measuring Amps on output coils
« Reply #39 on: March 25, 2015, 02:35:46 AM »
An ideal inductor has no resistance.  Working in terms of voltage with inductors is only needed to account for their imperfections -  resistive "energy leaks".

Also, a natural state for an inductor is when it is shorted and a natural state for a capacitor is when it is opened. 
With ideal components, there is no energy leakage out of them then.

When you do something unnatural for them, e.g. open an energized coil or short an energized capacitor, then all hell breaks loose.
Do you mean this by "PMH" ?
Yes-like in the video, although I see laserhacker was a little lost as to why he had to short the coil on the Ecore to get the effect, when the explanation is quite simple.

tinman

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Re: Measuring Amps on output coils
« Reply #40 on: March 25, 2015, 02:47:54 AM »
Yes-like in the video, although I see laserhacker was a little lost as to why he had to short the coil on the Ecore to get the effect, when the explanation is quite simple.
In fact, that video just showed you a continual current flow through a non superconductive coil.

verpies

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Re: Measuring Amps on output coils
« Reply #41 on: March 25, 2015, 09:29:45 AM »
.

verpies

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Re: Measuring Amps on output coils
« Reply #42 on: March 25, 2015, 09:52:39 AM »
Now,what is the difference between a super conducting ring(that has only an internal magnetic field once a current is sent through it,and the good old room temperature PMH ?
The PMH relies on the same effect as a tape recorder to store information - the remanent magnetization of high coercivity ferromagnetic material (...or not a very soft one).  Qualitatively this is no different than the attraction by a permanent magnet.

The difference between the attraction of a soft ferromagnetic keeper by an energized superconducting ring versus by a permanent magnet is that the flux through the superconducting ring always stays constant, while it does not stay constant in case of a permanent magnet  (that's why the LED flashes in this video).
The other difference is that the attraction of a superconducting ring can be "turned off" (by interrupting the electric current in it) while the attraction of a permanent magnet cannot be "turned off" (short of demagnetizing / destroying it, e.g. by exceeding its Curie temperature).

The other operational mode of PMH ( the one with the shorted coil and very soft ferrite) is devoid of magnetic remanence effects and differs from a superconducting ring only in magnitude of the L/R time constant. 
If the PMH does not hold the keeper when the coil is opened or absent, but holds it indefinitely when that coil shorted (or longer that 5*L/R), then it is an anomaly.

There could be a brief discussion about the influence of dΦ/dt on the final level of remanent magnetization in the core, but it will not lead anywhere - been there, done that...

In fact, that video just showed you a continual current flow through a non superconductive coil.
Not a "continual current flow" - more like a LONG one...
Give me the inductance and resistance of that shorted coil and I will let you know whether that time was unusually long or not. ( t  >> 5*L/R ).

MarkE

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Re: Measuring Amps on output coils
« Reply #43 on: March 25, 2015, 10:26:39 AM »
In fact, that video just showed you a continual current flow through a non superconductive coil.
Verpies is right:  The field weakens enough to cause the pieces to separate after a couple of seconds.  That tells us that the current decreases over time.  It does not sustain.

tinman

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Re: Measuring Amps on output coils
« Reply #44 on: March 25, 2015, 05:32:09 PM »

 (short of demagnetizing / destroying it, e.g. by exceeding its Curie temperature).

The other operational mode of PMH ( the one with the shorted coil and very soft ferrite) is devoid of magnetic remanence effects and differs from a superconducting ring only in magnitude of the L/R time constant. 

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Not a "continual current flow" - more like a LONG one...
Yes-bad wording on my behalf.

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The other difference is that the attraction of a superconducting ring can be "turned off" (by interrupting the electric current in it) while the attraction of a permanent magnet cannot be "turned off" (short of demagnetizing / destroying it, e.g. by exceeding its Curie temperature).
This is true some what.While it cant be switched off, an alnico's magnetic field can be flipped quite easly,and without much power to do so.

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If the PMH does not hold the keeper when the coil is opened or absent, but holds it indefinitely when that coil shorted (or longer that 5*L/R), then it is an anomaly.
Do you know why the Ecore keepers will not stay together without the shorted coil?,the answer is quite interesting--odds and evens. ;)

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There could be a brief discussion about the influence of dΦ/dt on the final level of remanent magnetization in the core, but it will not lead anywhere - been there, done that...
Give me the inductance and resistance of that shorted coil and I will let you know whether that time was unusually long or not. ( t  >> 5*L/R ).

The coil in that demonstration was not a good design. There is no need for two sepperate coil's. You need only one coil wound in a partiqular way. My PMH that was the same Ecore design(smaller Ecore),but with a coil wound this certain way,was able to maintain it's bonding for over 11 minutes. I believe a larger gauge wire would have seen this time increase,due to less resistance.

I really think there is something that can be had from the PMH.