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Andy

Fri Feb 06 2015, 05:07PM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
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Posts: 874

Signifaction, maybe something like this, or a sprial coil with the primary on the outside.

1423242475 4266 FT168825 Img 20150207 060718

This foumla is confusing me, its for mutal indtuance.
M =Uo*Ur*N1*N2*A/l

If you throw in these values, it produces a stupid value
1.2*10-6*100*50^20*3.2*10-5/0.3 = high value

Was thinking have 50 turns and 20 of that in parallel on a 3.2mm welding electrode, how could the mutual inductance be so high?

Edit
Did a test, five turns with ten in parallel and a voltage divide with primary of a mot, got 4 volt which should make 1500mH if the mot is 300mH, that was on a welding rod :)

Edit
At 2H and 20 p =1024H
At 0.2H and 20 p = 1.02e-7 H

As long as one inductor is 1.1 Henery above it should work, otherwise it will get worse.

Andy

Sat Feb 07 2015, 08:43AM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
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Thanks Dr Slack found some info at

the flyer links look interesting, for rail gun data, a speed of 45km/sec was produced :)

Signification

Sun Feb 08 2015, 06:35AM

Registered Member #54278 Joined: Sat Jan 17 2015, 04:42AM
Location: Amite, La.
Posts: 367

One thing I was reminded of by the thread Andy poster (and of which my response was largely based) was a few years ago when the things that could be said about capacitors (when supercapacitors were not rated in 1000's of farads) were limitet to "standard capacitance" magnitudes. Now, assuming the future holds a similar possibility for "superinductors / ultrainductors" I was just imagining (perhaps dreaming of) a new type of low cost kilohenry (kH) even MH inductors.

I recall when people somewhat unfamiliar with capacitors asked experts "ridiculous" questions concerning a capacitor's limitations. Now, given the present circumstances, the answers and replies to these inquiries have been virtually reversed.

Dr. Slack

Sun Feb 08 2015, 08:42AM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

Signification wrote ...

One thing I was reminded of by the thread Andy poster (and of which my response was largely based) was a few years ago when the things that could be said about capacitors (when supercapacitors were not rated in 1000's of farads) were limitet to "standard capacitance" magnitudes. Now, assuming the future holds a similar possibility for "superinductors / ultrainductors" I was just imagining (perhaps dreaming of) a new type of low cost kilohenry (kH) even MH inductors.

I recall when people somewhat unfamiliar with capacitors asked experts "ridiculous" questions concerning a capacitor's limitations. Now, given the present circumstances, the answers and replies to these inquiries have been virtually reversed.

Supercapacitors were made possible by having a super thin dielectric, albeit one that is made chemically and breaks down at 2.something volts.

Aiming for super inductors or ultra inductors is aiming too low, because we already have infinite inductors, at least inifnite retention time if not infinite inductnce value, which are made possible by windings having zero resistance. OK, admitted, at the moment you need at least LN2 cryo, but people are hopeful of higher temperatures being possible, even room temp sometime? Watch that space.

Antonio

Sun Feb 08 2015, 01:12PM

Registered Member #834 Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644

Superconducting wire does not make infinite inductors, unless with infinite size too. Large magnetic fields destroy superconductivity, and if magnetic cores are used, they have a limit on the magnetic field too.

Uspring

Sun Feb 08 2015, 05:33PM

Registered Member #3988 Joined: Thu Jul 07 2011, 03:25PM
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Posts: 711

I wonder about the mechanical stress on high power inductances. A typical example would be a coin shrinker coil. They usually explode, when energized.

Andy

Mon Feb 09 2015, 08:09AM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874

Uspring, hopefull not :) , im thinking if it reachs the tipping point of 1.1H, the voltage picked up by stray magnetic feilds will proable arc between the turns in the coil.

Just updating the foumla for three or more coils
L = (m11+m22+m33)+(m12+m13+m23)+(m21+m31+m32)

M12 = sqrt(l1*l2)
M13 = sqrt(l1*l3)
M23 = sqrt(l2*l3)

Kolas

Sat Feb 14 2015, 08:16PM

Registered Member #102 Joined: Thu Feb 09 2006, 08:15PM
Location: Raleigh, NC
Posts: 169

Not only are the volts per turn an issue but with higher current densities, another very prominent force comes into play. Assuming you could somehow overcome the resistance vs wire size vs magnetic field strength vs total size there are still the Lorentz forces that will try to torque and tear the coil apart upon rapid retrieval of stored magnetic energy.

Andy

Sun Feb 15 2015, 06:30AM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874

I should be constructing a protype, it will be made of mild steel 1cm dia rod, with a straight trianglish shape with four sides 0.3meters the short side and 1.4 meters long side, with 50 parallel layers.

The reason for steel, high perm, strength of struct, cheap money wise, and low resistance for price, with size not being to large.

Just wondering is the reason way 0.5 is times LI2 because half the energy goes back into the coil that made it, to rejiuce the power that can be extracted.

Was thinking of free wheel diode or a rc snubber, trying to stop current being produced when the coil closes, a snubber does it by sim( zero voltage change), but is current still flowing.

klugesmith

Tue Feb 17 2015, 11:57PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

Read about the flyback converter topology, and how the ferromagnetic core needs an airgap if it is to store significant energy.

Magnetic field energy density is BH/2, generally proportional to the square of magnetic flux density.
For 1 tesla in air, the number to remember is 400 kJ/m^3. Dimensionally the same as pressure, 4 bar = 60 psi, the attraction between magnetic pole faces at 1 tesla. At 2 teslas it's 1.6 MJ/m^3 = 240 psi.
In steel with a relative permeability u=1000, the energy density for same B is 1000 times smaller.

Coin shrinking enthusiasts cite stored energy levels on the order of 10 kilojoules.
A HV capacitor storing that much, say 200 uF at 10 kV, would be about as heavy as you or me.
How about an inductor, say 2 henries at 100 amps? Or 200 H at 10 A, etc., using different wire gauges but needing the exact same winding volume and copper mass?

Such an inductor could take the form of a cyclotron electromagnet producing 1 tesla in 25 liter volume between the poles, or 2 T in 6 liter volume. I bet the yoke and pole pieces would weigh more than a ton. If resistive, the windings would dissipate the stored energy in seconds, unless continuously powered. Kind of like water-dielectric HV capacitors, which self discharge in milliseconds even with perfectly deionized water.

I figure solenoids for human-body MRI scans store more than 10 kJ, but not by orders of magnitude.

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