Questions tagged [magnetics]

Important to inductors, transformers, generators, motors, magnetic fields, inductive heating, magnetic storage, permanent magnets

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1k views

How does a hall effect wheel speed sensor work?

I have been researching how a wheel or crank speed sensor works in vehicles and am having a hard time finding a hard truth. I think I understand how it works simply. That the sensor detects a change ...
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1answer
107 views

Difference series resonant and LLC DC/DC converter

What is the exact difference between a series LC resonant converter and an LLC converter. From a topological perspective, they seem to be exactly the same. I believe that for an LLC, also the ...
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3answers
2k views

Does this experiment show that Kirchhoff's Law hold when there's a changing magnetic field involved in a circuit?

In this video, the electrical engineer and youtuber Mehdi Sadaghdar (ElectroBOOM) disagrees with another video from professor Walter Lewin. Basically, professor Lewin shows in an experiment that if ...
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1answer
264 views

Proper connection of choke coil in ethernet magnetics

I need to use the medical ethernet magnetics by Pulse HXU6200NL (it is the only 2MOPP medical-certified PoE magnetics I can find). These are of the rather common transformer/choke coil topology. My ...
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2answers
153 views

Double ethernet magnetics for a passive medical application

I am designing medical data acquisition equipment that requires moderately fast data transfer. As part of the design we are using a custom 100BASE-T PoE architecture (and cabling) to the data ...
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2answers
51 views

Optimizing magnetic field force of a coil

For a personal project, I've done a redesign of Samy Kamkar's MagSpoof project. Basically, it is possible to use an electromagnet, h-bridge, and microcontroller to trick a magnetic card reader into ...
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1answer
129 views

What is the purpose of perpendicular “smaller” magnets in between the main magnets in a rotor of a motor? had never seen this before. Do they help?

I am trying to build my own generator at home for fun, I saw on a video in youtube https://www.youtube.com/watch?v=YsSm65DAcCg where the guy placed smaller magnets in between the main magnets of the ...
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3answers
358 views

Wireless power transfer - Inductive vs. resonant mode

When talking about how wireless power transfer is done, the standards (e.g Qi) distinguish between inductive and resonant mode. (Link) They claim that when the units are in very close proximity it is ...
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1answer
188 views

Cable Side and Physical Side of a PoE Magnetics

I am reading the datasheet of PoE Magnetics. I am not able to understand which side belongs to cable side and which belongs to ...
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1answer
299 views

Dolby HX PRO implementation on existing tape recording deck

I'm experimenting the implementation of Dolby HX PRO's IC into an old stereo Fostex tape deck to improve high frequency and headroom capabilities. HX PRO works as a dynamic processor with the BIAS ...
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0answers
54 views

How strong is the field of a magnetic strip on a credit card?

How strong is the field of a magnetic strip on a credit card? In other words, at the typical distance of a read head, say 0.001" how strong is the magnetic field from the stripe? (Note this is NOT a ...
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2answers
144 views

Detecting very small magnetic movements

I am looking for techniques and methods to detect very small linear magnetic movement caused by a bar magnet. Imagine a bar magnet that can produce yaw and pitch but with extremely low frequency and ...
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2answers
83 views

Is there a way to make an experimental magnetic head?

I recently had a magnetic stripe on my bank card fail and I was curious to find out the exact nature of the corruption which would require scanning the surface of the stripe and determining its ...
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0answers
218 views

In an induction cooktop, what happens to the coils resistance when there is no pot? Does it vary between pots? How does the appliance respond?

An induction cooktop (or an induction rice cooker) uses a copper coil with a high-frequency alternating current going though. The magnetic flux heats any iron-alloy pot placed above. But what ...
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2answers
48 views

Can I create a continous gap in iron powder cores?

The iron powder core material, as you may know, has a continuous air gap in its structure. However, do you think it is possible to add a continuous air gap (for example 1mm) to the iron powder cores? ...
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1answer
80 views

Toroid coating got scratched

Will there be any performance effect if the torroid coating gets scratched?
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1answer
855 views

Magnetic field in the air gap of a transformer core

I am trying to calculate the magnetic field, Hg, and have been looking these formulas. I would like to know if I am on the right track, as something is not working out for me. From these with a ...
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0answers
70 views

Can a CM choke saturate due to the leakage inductance?

On a 3-phase common-mode choke, if the three currents sum to zero, then it will theoretically never saturate. I understand that the leakage inductance stores energy in the core. Can the three phases ...
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3answers
51 views

Magnetic field direction

How do I know the direction of magnetic field produced by a bar magnet, assume a electron present side to the magnet ?
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2answers
988 views

Increase the pulling force of a solenoid with a permanent magnet [duplicate]

I have a number of solenoids I would like to use in a project. The problem is that they're not quite powerful enough so I've been trying to come up with ways to increase the their pulling force ...
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1answer
59 views

Calculating the magnetic flux density in cylandrical coordinates near a neodymium disc magnet

I am looking for an analysis of a disc magnet, I have heard there are 2D analaysis and 3D. Could someone point me in the right direction of a paper or some academic text on the matter. I don't mind ...
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1answer
40 views

90 degrees phase shifted magnetic fields

If we have a closed magnetic circuit with two primary coils and one secondary coil wound on it. The primary coils are wound such that unlike poles are adjacent. Both primary coils are using rectified ...
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2answers
76 views

Do MRI magnets oscillate due to parasitic capacitance?

Moved here from SE Physics. Do MRI magnets oscillate during charging or even during persistant mode due to parasitic capacitance? What problems can this cause? I am planning a low temp ...
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3answers
137 views

Why is the magnetic field around a bar magnet represented by iron filings?

Why would we use iron filings to display a magnetic field interaction and then teach this as the unaffected field of a magnet? Iron affects the field itself. This is analogous to an observer ...
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1answer
72 views

Simple Stepper motor for my experiment?

To graduate (Grade 12 or Year 12), I need to do an self-thought experiment in Physics. I decided to do something about stepper motor because I learned that they use this type of motor for robot arms. ...
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3answers
273 views

Circuit approximation of Induction in guitar pickups

I was trying to learn the way basic guitar circuits work, the other day, and I stumbled upon a thing that I couldn't fully understand. According to this site, a simple guitar circuit can be made as ...
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2answers
681 views

Metal detector coil SHIELDING?

Many designs of coils, of metal detectors, are shielded (Faraday shield). Should this be used in a gravity-fed detector (like the sketched one)? What's the shield for? NOTE: The coils are arranged ...
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61 views

Calculation of stray magnetic field from substation transformers

Say I want to assess the magnetic field attributed to some substation equipment and the cables in the substation area. Calculating the contribution from the cables and busbars are for my purposes done ...
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1answer
217 views

Transformer Output waveform

If input to a transformer is square/triangular, draw its output voltage waveform. This problem was asked in one of my recent interviews, please help me with this problem.
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311 views

Relationship between brushless coil inductance and back EMF as a function of phase angle

In general, does the inductance across the coils of a brushless motor have the same waveform as the back EMF? That is, if back EMF is sinusoidal, should I expect the inductance to be sinusoidal [with ...
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69 views

Falling Marble Sensor

I'm really building a sort of Rube Goldberg machine that students will assemble in order to guide a falling ball down through a series of gates/openings, where I need to detect when they're successful ...
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2answers
242 views

Saturating magnetic field in an inductor without heating

I am building an RL series circuit with a toroidal inductor that I am winding on my own. The toroid is made of steel (low carbon, I believe, but not 100% sure) and has about 280 turns of 22 gauge wire....
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1answer
60 views

Strong H fields: electronic items susceptible to thier damaging effects and how to shield them

This is another question related to magnetic fields. I'm trying to determine the thickness of copper foil that would be required to shield common electronic items from H fields of about 133 A/m over ...
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1answer
75 views

Energies of the fields in a plane wave, attenuated and unattenuated

This is a combination of two of my previous questions (question 1 and question 2) which are related. I'm trying to learn both how energy is carried in the electric and magnetic components of a plane ...
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1answer
319 views

EMI difference between Ferrite (powdered iron) and Iron

In an EMI application where I'm applying a snap on style ferrite core around a cable. What's the difference / benefit of the typical powdered iron type and just using a similarly sized piece of iron ...
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2answers
92 views

Energies carried by electric and magnetic fields in plane waves

This is a newbie question. I'm trying to understand what I think must be a very basic concept with an obvious answer, but I want to be sure. Do plane wave electric and magnetic fields of equal ...
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3answers
76 views

The electric and magnetic components of far field EMR and shielding thereof

This is a newbie question. I'm pretty sure of the answer, but I would like confirmation. I found this thread in this forum that came close to what I was looking for, but I think my question is ...
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2answers
108 views

Magnetic Locks mods [closed]

What about magnetic locks? Two questions.. Does armature plate need be exact size as magnetic mate? Id like to get a bigger one milled so i dont have to use lasers to check perfect alignment. ...
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1answer
96 views

magnetic hall effect sensor

I'm currently working on building a density based traffic light model. I want to use the magnetic hall effect sensor to detect the number of the cars passing, so the idea that I have is to place the ...
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0answers
40 views

Any deleterious effect from very strong, close magnets on NiMH cells over time?

This question probably isn't a perfect fit for this SE, but I did find this question: Will placing a strong magnet near my electric skateboard Li-Ion Battery pack damage or discharge it? This is a ...
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1answer
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Ethernet magnetics - PHY side center tap isolation

I am designing a PCB that will use a Microchip KSZ9896C 6-port Gigabit Ethernet Switch. In the datasheet (section 7.2) they state that : "the four transformer center tap pins on the KSZ9896C chip ...
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1answer
176 views

Why transformers Secondary magnetizing inductnace and Secndary inductace are Not Considered while doing filter calculation for output ?

Why transformers Secondary magnetizing inductnace and Secndary leakage inductace are Not Considered while doing filter calculation for output ? Why most transformer datasheet only mention ...
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1answer
498 views

What is the relationship between field strength and efficiency in a DC motor?

This refers to a DC motor with permanent magnets. What is the relationship between the efficiency of the motor and the magnet field strength?
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1answer
503 views

Why can my bare PCB be magnetized?

I am working on a magnetic sensors design and noticed that my measured magnetic field bias shifts over time. I have studied the bare PCB and measured that it can be magnetized with a strong magnet. ...
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4answers
3k views

Why do Rogowski coils work for measuring current?

Rogowski coils measure current by completing a loop of coils around the conductor seen below. This makes sense, but question 1: This is a current transformer, and transformers couple, so in this ...
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1answer
45 views

What is the difference in working of an GMR readhead vs an EMR one?

As I understand it, a GMR readhead works by stacking magnetic and non magnetic layers, passing a current through them and measuring the total resistance. Then a 4 point measurement is used to remove ...
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0answers
57 views

Can I create a uniform magnetic field with an n52 magnet?

I want to build a ribbon speaker and I've read that one of the greatest sources of distortion in these types of speakers is the non uniform magnetic field along the length of the magnet. I've also ...
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3answers
103 views

Boost converter Inductor Current

In a boost converter during switch on time inductor build magnetic field and during off state magnetic field collapse.My question is during off satte inductor is connected to source voltage,so why not ...
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1answer
57 views

electromagnet's strength

So i know that these following things will affect the strength of an electromagnet: Amperage going through the wire, the amount of coils of wire, and the ferromagnetic core. I also know the poles of ...
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1answer
62 views

Net-Zero Magnetic Fields in a Three-Phase Motor

When a three phase motor in running and you clamp an amp-meter around all three of the phase wires, you should expect to read zero because the magnetic fields cancel each other out. I'm having ...