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Raj Mohit
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Solenoid Best Adjustment

07/28/2017 2:57 AM

Hello everybody . I am trying to find a method , best method to contain the heat losses from a solenoid . I am using the solenoid as a electromagnet so as I can create north and south pole . I need to create a magnetic field of 750 T. Number of turns 100. Current is 3 A. Length is 10 cm. Now the coil that will rotate in the magnetic field created by the solenoid it will produce a emf in the coil and I have attached the coil or DC current directly to the solenoid. Like in a DC series motor. Now here I need to use a high resistance as I want to maintain my current to 3 A . And for that when I calculated then it comes to be 9 k ohm. That's very high. Heat losses alone only were above the requirement. Given by the formula I2 *R.

I wanted some help regarding this. I wanted to know what can I do to make such a system viable .I wanted to know how can I keep the heat loss minimum and current at desired level at the same time. Any help is appreciated . Thanks a lot.
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#1

Re: Solenoid best adjustment

07/28/2017 3:04 AM

Redesign: the same number of turns of a lower-resistance wire with a lower voltage applied to it to maintain 3A, perhaps?

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#2

Re: Solenoid best adjustment

07/28/2017 3:37 AM

3A into 9kΩ will require a 27kV supply rated at 81kVA!

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Raj Mohit
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#4
In reply to #2

Re: Solenoid best adjustment

07/28/2017 3:41 AM

Yup you get that right . That's the data I am getting . That's why I posted this question . I need to regulate the data. Thanks for your comment .
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#5
In reply to #4

Re: Solenoid best adjustment

07/28/2017 3:44 AM

Well, that's nonsense. See #3⇓.

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#6
In reply to #5

Re: Solenoid best adjustment

07/28/2017 3:47 AM

Not nonsense . It is a research by which a large magnetic field needs to be generated in a small space . But on doing that I totally forgot to count the losses and all. And now I am counting it. Regulating the data . I thought of other methods too.
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#8
In reply to #6

Re: Solenoid best adjustment

07/28/2017 4:27 AM

Well, the numbers are nonsense. See #1⇑.

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#10
In reply to #6

Re: Solenoid best adjustment

07/28/2017 4:45 AM

That's not a <...solenoid...>. That's a "heater".

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#3

Re: Solenoid best adjustment

07/28/2017 3:40 AM

90Ω per turn? That's very strange <...wire...> or a very large <...electromagnet....>.

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#27
In reply to #3

Re: Solenoid best adjustment

07/28/2017 11:20 AM

I think he missed several decimal places when picking up the resistivity per km of the wire, Oh well, back to the sand board.

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#7

Re: Solenoid best adjustment

07/28/2017 3:57 AM

Dude, just get an SMPS.

You have them for labs, PC controlled, applications specific, and with other options.

I work at a Company where we them at high voltage (up to 3kV or more) and high power (MW and more) for very specific applications, but I doubt that you will need any of those with 3A. Unless you mean 3kA...

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#9
In reply to #7

Re: Solenoid best adjustment

07/28/2017 4:29 AM

That doesn't look as though it is rated at 81kVA.

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#11
In reply to #9

Re: Solenoid best adjustment

07/28/2017 4:47 AM

He DOES NOT NEED an 81kVA power supply.

First of all, this is DC, where power is measured in Watts rather than Volt Amps.

Second of all, he needs a current source of 3A. He thought that it would be a good idea to make it with a voltage supply and a resistor. And for this application there are better solutions.

Right now I have on my desk a TTi CPX400 which can provide up to 120V 20A. He needs only 3A, so even the CPX200 would be more than enough.

If higher voltage is required by the coil, it should be further specified.

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#12
In reply to #11

Re: Solenoid best adjustment

07/28/2017 4:53 AM

Quite.

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#13
In reply to #7

Re: Solenoid best adjustment

07/28/2017 4:57 AM

Thank you for your help. I will search in the net about it . Thanks a lot.
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#15
In reply to #13

Re: Solenoid best adjustment

07/28/2017 5:04 AM

OK. Here's a start:

https://en.wikipedia.org/wiki/Ampere-turn

https://en.wikipedia.org/wiki/Ohm%27s_law

https://home.cern/about/updates/2013/11/test-magnet-reaches-135-tesla-new-cern-record

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#14

Re: Solenoid best adjustment

07/28/2017 5:03 AM

"... . I need to create a magnetic field of 750 T. ..."

.

Ah, that wouldn't 750 Teslas, would it?

I feel pretty safe in predicting, whatever you build, it isn't going to get anywhere near 750 Teslas.

Strongest man made magnets can get to around 100 Teslas.

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#17
In reply to #14

Re: Solenoid best adjustment

07/28/2017 5:13 AM

That order of magnitude agrees with the internet.

I looked up the magnetic field for his setup and it should achieve 0.00376991T. +5 orders of magnitude lower lol

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#19
In reply to #14

Re: Solenoid best adjustment

07/28/2017 6:30 AM

Thanks for the info. I will keep it in mind. Thanks you very much. I am actually trying to create a magnetic field which can is as strong that when you rotate a coil at a distance of say 15 cm from the electromagnet then it can produce at least 60 Hz depending that the revolution of coil is 60. Per sec. I am also looking at ways by which I can increase the number of coil and increase the produced ac quantity . But that would come in voltage and my further explanation would required a whole lot of another forum . Thanks .
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#26
In reply to #14

Re: Solenoid best adjustment

07/28/2017 11:02 AM

Here is a handy table of magnetic field strengths:

List of orders of magnitude for magnetic fields

Factor (tesla)

SI prefix

Value (SI units)Value (CGS units)Item
10

−18

attotesla5 aT50 fG

SQUID magnetometers on Gravity Probe B gyroscopes measure fields at this level over several days of averaged measurements[2]

10

−15

femtotesla2 fT20 pGSQUID magnetometers on Gravity Probe B gyros measure fields at this level in about one second
10

−12

picotesla100 fT to 1 pT1 nG to 10 nG

Human brain magnetic field

10

−11

10 pT100 nGIn September 2006,

NASA found "potholes" in the magnetic field in the heliosheatharound our solar system that are 10 picoteslas as reported by Voyager 1[3]

10

−9

nanotesla100 pT to 10 nT1 µG to 100 µGMagnetic field strength in the

heliosphere

10

−7

60 nT to 700 nT600 µG to 7 mGMagnetic field produced by a

toaster, in use, at a distance of 1 ft (30 cm)[4]

100 nT to 500 nT1 mG to 5 mGMagnetic field produced by

residential electric distribution lines (34.5 kV) at a distance of 100 ft (30 m)[4][5]

10

−6

microtesla1.3 µT to 2.7 µT13 mG to 27 mGMagnetic field produced by

high power (500 kV) transmission lines at a distance of 100 ft (30 m)[5]

4 µT to 8 µT40 mG to 80 mGMagnetic field produced by a

microwave oven, in use, at a distance of 1 ft (30 cm)[4]

10

−5

24 µT240 mGStrength of

magnetic tape near tape head

31 µT310 mGStrength of

Earth's magnetic field at 0° latitude (on the equator)

58 µT580 mGStrength of Earth's magnetic field at 50°

latitude

10

−4

500 µT5 GThe suggested exposure limit for

cardiac pacemakers by American Conference of Governmental Industrial Hygienists (ACGIH)

10

−3

millitesla5 mT50 GThe strength of a typical

refrigerator magnet[6]

10

−2

centitesla
10

−1

decitesla150 mT1.5 kGThe magnetic field strength of a

sunspot

10

0

tesla1 T to 2.4 T10 kG to 24 kGCoil gap of a typical

loudspeaker magnet.[7]

1 T to 2 T10 kG to 20 kGInside the core of a modern 60 Hz power transformer

[8][9]

1.25 T12.5 kGStrength of a modern

neodymium–iron–boron (Nd2Fe14B) rare earth magnet. A coin-sized neodymium magnet can lift more than 9 kg, erase credit cards.[10]

1.5 T to 3 T15 kG to 30 kGStrength of medical

magnetic resonance imaging systems in practice, experimentally up to 11.7 T[11][12][13]

9.4 T94 kGModern high resolution research

magnetic resonance imaging system; field strength of a 400 MHz NMR spectrometer

10

1

decatesla11.7 T117 kGField strength of a 500 MHz

NMR spectrometer

16 T160 kGStrength used to

levitate a frog[14]

23.5 T235 kGField strength of a 1 GHz

NMR spectrometer[15]

36.2 T362 kGStrongest continuous magnetic field produced by non-superconductive resistive magnet.

[16]

45 T450 kGStrongest continuous magnetic field yet produced in a laboratory (

Florida State University's National High Magnetic Field Laboratory in Tallahassee, USA).[17]

10

2

hectotesla100 T1 MGStrongest pulsed non-destructive magnetic field produced in a laboratory,

Pulsed Field Facility at National High Magnetic Field Laboratory's, Los Alamos National Laboratory, Los Alamos, NM, USA).[18]

10

3

kilotesla1 kT100 MGStrongest (pulsed) magnetic field ever obtained in a laboratory (

Z machine, Sandia National Laboratories in Albuquerque, New Mexico)[19]

10

6

megatesla1 MT to 100 MT10 GG to 1 TGStrength of a

neutron star

10

6

megatesla2.2 MT22 GGStrongest pulsed magneitc field created by destrutive measurements in

Jablikia , Russia).

10

8 - 1011

gigatesla100 MT to 100 GT1 TG to 1 PGStrength of a

magnetar

10

53

N/A2×10

29 YT

2×10

33 YG

Planck magnetic field strength

https://en.wikipedia.org/wiki/Orders_of_magnitude_(magnetic_field)
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#28
In reply to #26

Re: Solenoid best adjustment

07/28/2017 12:07 PM

Z machine or Z pulsed power facility.....

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#16

Re: Solenoid best adjustment

07/28/2017 5:05 AM

I am wondering why the numbers do not match. I have some experience having to minimise magnetic flux in magnetic components, since regulations require less than 0.5mT outside the equipment. And we have thousands of amps.

So I just used an online tool to calculate the induction you would be getting, and I have NO clue how you are getting those 750T. According to this even with a few kA you would get only 3T. So either the tool is wrong or there is a catch. Can you explain?

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Raj Mohit
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#18
In reply to #16

Re: Solenoid best adjustment

07/28/2017 6:22 AM

Yeah sure mate . Just remove the permeabity of there. And put 0.25 there. I am using iron core as a substitute . The permeability of iron core is according to this site

https://en.m.wikipedia.org/wiki/Permeability_(electromagnetism)#Values_for_some_common_materials

Is 0.25. putting that to it and then calculating it . You get the Tesla. And yeah I know I need to account for losses . And by the way I used the same site for my calculation haha.

Thanks .
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#25
In reply to #18

Re: Solenoid best adjustment

07/28/2017 10:55 AM

Iron has a high permeability only until all the iron atoms get lined up. Once the field is stronger than the saturation point, the permeability of iron is no better than free space. (You cannot extrapolate using the online tool!)

Extremely strong magnets do not use iron cores.

Magnetization curves of 9 ferromagnetic materials, showing saturation. 1.Sheet steel, 2.Silicon steel, 3.Cast steel, 4.Tungsten steel, 5.Magnet steel, 6.Cast iron, 7.Nickel, 8.Cobalt, 9.Magnetite[1]

https://en.wikipedia.org/wiki/Saturation_(magnetic)
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#20
In reply to #16

Re: Solenoid best adjustment

07/28/2017 6:56 AM

It's anealed in H
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Raj Mohit
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#21
In reply to #16

Re: Solenoid best adjustment

07/28/2017 7:06 AM

Ah ha! Now I see where I was doing the mistake. I mistook and took the wrong permeability data. The research was about simple iron core which has a permeability of 0.0063 . Have to now do the calculation all again .

But it's fun so

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#23
In reply to #21

Re: Solenoid best adjustment

07/28/2017 7:45 AM

Then rather more than 3A is going to be needed. Start winding the coil with lacquered 12mm copper rod instead!

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Raj Mohit
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#24
In reply to #23

Re: Solenoid best adjustment

07/28/2017 8:10 AM

Yeah I re do the calculation . I used 0.0063 and the number of turns changed to 300 at 20 cm and 4 A current . The induced emf came out to be 1360.8 V . The magnetic field came out to be 37.8 T. The resistance came out to be 340.2 ohm. And heat loss to be 5443.2 joules . Mama Mia I am going to lose my job with this figure haha.

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#29
In reply to #24

Re: Solenoid best adjustment

07/28/2017 12:31 PM

There is no way you will get 37.8 Teslas from 4 x 300 or 1200 ampere-turns! (See #25). Your iron core saturates long before then.

That's got to be mighty fine (small gauge) wire to have a resistance of 1.14 ohms per turn. Use bigger wire! Check out the table at this site. (ohms/MFT means ohms per 1000 feet).

Joules is energy, you should calculate power in Watts, which is Joules/sec. 340.2 ohms x 4 amps x 4 amps = 5443.2 Watts.
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#30
In reply to #29

Re: Solenoid best adjustment

07/28/2017 12:38 PM

Thank you . You really helped me a lot. Thanks a lot. Understand about your saturation talk . I will surely keep that in mind. Thanks for your help.

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#33
In reply to #30

Re: Solenoid best adjustment

07/28/2017 4:34 PM

Here is a simple explanation of a solenoid.

To generate a strong magnetic field is a small region, (up to about a Tesla), you need a magnetic circuit made of a ferrous material (e.g. iron) with an air gap. The narrower the air gap, the more intense the field.

http://www.encyclopedia-magnetica.com/doku.php/air_gap

Here is a simple explanation. A magnetic circuit is analogous to an electrical circuit. Instead of a battery, you have ampere turns. Instead of electrical current, you have flux. (Like electrical current, flux is constant around the magnetic circuit.) Iron has very low resistance to magnetic flux (i.e. high permeability) and is analogous to wires in an electric circuit. Almost all of the resistance in the circuit is the air gap (which has low permeability). So, the narrower the air gap, the lower the total (magnetic) resistance, the greater the flux.

Iron has very low resistance to magnetic flux (i.e. high permeability) and is analogous to the wires in an electrical circuit. Almost all of the resistance in the circuit is the air gap (which has low permeability). So, the narrower the air gap, the lower the total (magnetic) resistance, the greater the flux.

You can increase the flux in the air gap by increasing the ampere-turns until the iron gets saturated. Once this happens, the iron no longer provides a low resistance path for flux.

https://www.electrical4u.com/magnetic-circuit-with-air-gap/

I hope this is helpful.

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#34
In reply to #33

Re: Solenoid best adjustment

07/28/2017 4:49 PM

It is refreshing to go back to the basics. Huh.

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#22

Re: Solenoid best adjustment

07/28/2017 7:45 AM

You have not explained why you need a 27 kV supply to maintain 3 amps in a solenoid. What is solenoid [9 kohm?] winding resistance or does "coil" inside solenoid give back-emf which affects some tight tolerance on solenoid current?

There are electronic circuits which can regulate current with varying output voltage
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#31

Re: Solenoid Best Adjustment

07/28/2017 2:22 PM

Well, I'd say one (or more) of the assumptions you posted here are wrong. The one that jumps out and screams *ERROR* is the 750T ("T" as in Tesla) field strength! Do you mean 750G ("G" as in Gauss) which would be 0.075T -- a far more realistic value.

I believe you could then solve for the diameter of the 10cm (length) solenoid and achieve a physically plausible size, and a reasonable power dissipation in the coil.

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#32

Re: Solenoid Best Adjustment

07/28/2017 4:01 PM

You are NOT going to produce 750 Teslas. The record field is only 91.4 T.

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#35

Re: Solenoid Best Adjustment

07/28/2017 11:54 PM

There are several problems associated with trying to generate a 750 T field. Forget about using any core - all magnetic materials saturate at fields of 2-3 T even when using flux concentration techniques, and the effective incremental permeability drops to about 1. All higher-field electromagnets use an air core. Also, magnetic forces on a simple solenoid begin to exceed the yield strength of any conductive materials once you reach about 0.35 Megagauss (35 T). There is an outward pressure ("magnetic pressure") that acts on the inward-facing surface of the conductor, along with an axial force that squeezes the windings closer together. The larger, and usually more problematic, are tensile forces that apply huge hoop stresses on the windings. The outward pressure on the winding, P (in atmospheres), scales approximately as 4*H2 where H is the field in Tesla. A 500 T field will generate ~100X greater force on the winding than a 50 T field.

The only way to generate fields greater than about 50 T is to use pulsed magnets. These are typically single-turn thick loops driven by a short current pulse that ends before the coil self-destructs, or a single-use coil or loop, sometimes augmented by an external explosive that temporarily counteract the outward pressure on the coil. Another approach established a field inside a current loop, and then the loop diameter is rapidly reduced, compressing the trapped field (flux compression). Fields above 100 T usually require some type of flux compression technique.

BTW, hobbyists can generate impressive fields using capacitor discharge techniques. For example, during electromagnetic forming of coins ("coin crushing"), we generate peak fields in the 35 - 50 T range using a high voltage capacitor bank discharging through a 10-turn single-layer heavy-gauge magnet wire coil. Inertia basically holds the coil together until after the first current peak (and peak magnetic field) is achieved. After 30-50 microseconds, the coils then explode with the force of a small bomb.

However, achieving a 750 T field is far from a trivial undertaking. The peak field will only exist for microseconds in a relatively small volume. And you'll need to safely handle the resulting explosion when the potential energy in the field is suddenly released as the coil disintegrates.

An interesting article that describes a compound system using a multi-megamp "seed current" in a loop, followed by flux compression, can be seen here. This should give you a feel for some of the challenges that you can anticipate once you venture into fields above 100 T:

http://www.congress-2006.hcei.tsc.ru/cat/proc_2006/shce/Paper_061.pdf

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#36
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Re: Solenoid Best Adjustment

07/29/2017 2:31 AM

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#37
In reply to #35

Re: Solenoid Best Adjustment

07/29/2017 9:44 AM

Nice paper. The paper does not indicate a discharge resistance in parallel with the sacrificial coil as the Physics Girl video shows. I'm curious, does the voltage on the capacitor reverses in a fly-back fashion if the discharge resistance is not there. I suspect it doesn't reverse since the coil inductance disappears before a fly-back voltage can be generated.

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#38
In reply to #37

Re: Solenoid Best Adjustment

07/29/2017 11:04 AM

The bleeder resistor( shown in the schematic in the Physics Girl video) safely discharges any residual charge after the shot. It does not appreciably reduce ringing. If the work coil didn't disintegrate sometime during the first current half-cycle, the main discharge circuit would continue to ring, subjecting the capacitor bank to high voltage reversals (VR) of 95% or more. VR is very stressful to a capacitor's dielectric system. Most energy discharge capacitors are only rated for 10-20% VR. Fortunately, during coin crushing the work coil rapidly disassembles and most of the system energy is then dissipated within the resulting plasma ball before it can reverse charge the bank. Actual voltage measurements show very little VR on the capacitors - typically 10% or less, and ours are rated for 20% VR. However, during can crushing, the work coil is not destroyed, and the VR is about 95%, so the maximum charging voltage is reduced to about 1/2 the rated DC voltage of the capacitors to prevent overvolting the bank.

It's not clear how the scientists in the referenced papers handle ringing in the "seed" circuit since the seed loop must NOT disintegrate until flux compression is complete. The seed circuit would thus be quite oscillatory. However, the capacitor bank is only rated for 10% VR. They may use a crowbar switch across the liner to divert reverse current from the bank, or they may reduce the maximum charging voltage so that the peak-to-peak ringing voltage is less than 110% of the rated DC bank voltage. Or, they may use a higher charging voltage and intentionally overstress the capacitors, accepting reduced lifetime and catastrophic capacitor failures from time to time. Notice the shields used between capacitor bank sections. High-energy capacitor failures can sometimes be quite spectacular.

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#39
In reply to #37

Re: Solenoid Best Adjustment

07/29/2017 2:53 PM

It's unlikely that the circuit is critically damped. Without knowing the capacitance, inductance, and series resistance, it's impossible to know.

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#40

Re: Solenoid Best Adjustment

07/31/2017 11:18 AM

Is this some sort of over-unity device?

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#41
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Re: Solenoid Best Adjustment

07/31/2017 12:01 PM

How can it be over-unity? I don't even see this as a good working coil...

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#44
In reply to #41

Re: Solenoid Best Adjustment

08/01/2017 6:41 AM

Watch this space...

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#42
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Re: Solenoid Best Adjustment

07/31/2017 10:33 PM

What made you think it is a over unity device ?
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#43
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Re: Solenoid Best Adjustment

08/01/2017 6:41 AM

Simple. The absence of any description so far as to what this device, whatever it may be called, is actually there to achieve.

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#45

Re: Solenoid Best Adjustment

08/04/2017 6:36 AM

Why not dump extra energy on earth wires, can be done?
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