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Questions tagged [magnetics]

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

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25
votes
6answers
26k views

What is the difference between the magnetic H field and the B field?

Wikipedia provides a mathematical explanation. Can I get the intuitive one? I'd like to, for example, understand a ferrite datasheet. These usually have graphs of H vs B, and the definition of ...
20
votes
3answers
1k views

Do magnetics connectors exist?

Conventional connectors, where the plug and socket have metal parts which touch, suffer from the following problems: Limited mating cycles or expensive plating. Impedance mismatch (relevant for high ...
19
votes
2answers
6k views

Magnetometer dynamic calibration

I am working on a Magnetometer AK8975 being a part of an IMU. Which seems to be very tricky for me. This chip gives a 3D vector as output describing earth's magnetic field at any place on earth or ...
16
votes
4answers
4k views

Why does magnet wire need to be insulated?

What is it about having multiple coils that enables the magnetic field? Why can't I just have one big wire or threaded wire on a motor? Sorry, it's kind of a baby question but I couldn't find the ...
16
votes
4answers
28k views

What is the difference between a transformer and a coupled inductor?

Transformers and coupled inductors seem very similar. Is there a difference in construction? Or only in use? This question asks something similar, but the answers don't address my question: Coupled ...
16
votes
1answer
502 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. ...
14
votes
5answers
3k views

Why are reed switches made in glass tubes?

Why are reed switches made in glass tubes? Reed switches sense magnetic fields, and glass is not the only material not affected by a magnetic field. They can use plastic for example. Why are most of ...
14
votes
12answers
4k views

Tracking rotation with extremely high accuracy

I would like to track the angular position of a fairly slow motorized rotating arm (direct-drive; see illustration below) -- but require angular accuracy of under 0.05°, and similar resolution. As @...
14
votes
2answers
4k views

How does this iPhone app measure the power flowing through an AC appliance cord?

My electric utility released an iPhone app called "DTE Insight" which (among other things) measures the amount of power flowing through an appliance's power cord by asking you to hold the cord against ...
13
votes
2answers
6k views

Ethernet Without Magnetics?

How / can you connect Ethernet devices together without magnetics? How do you wire it up? What sorts of practical limitations are there on doing this? To clarify, I'm not trying to connect two ...
13
votes
3answers
2k views

Does Shielding “Electrically” shield “Magnetically” too?

I know it sounds like a newbie question but I can't wrap my mind around it. An electromagnetic field is electric + magnetic field. So this means that when shielding an equipment offensively, for ...
12
votes
5answers
3k views

Can a transformer work if the core is not circular?

I am trying to build a transformer to convert 12V AC power to 5V AC. Here is what I have right now: I haven't adjusted the coil ratio yet but I tried it just to see if there would be any output and ...
12
votes
3answers
5k views

Why is inductance (L) proportional with turns-square (N²)?

We start from the Maxwell's Equation $$ \mathbf{\nabla} \times \mathbf{B} = \mu \mathbf{J} + \overbrace{\mu \epsilon \dfrac{\partial \mathbf{E}}{\partial t}}^0. $$ We take surface integration of ...
12
votes
3answers
821 views

Electrical Machines based on Electric Fields

Our teacher asked us this question during the lecture for Power Electromagnetics. We know that Electric Fields and Magnetic Fields are easily transformable into one another. And they are used greatly ...
11
votes
2answers
1k views

Why do most flyback converters / LED drivers operate under 100 kHz?

Most of the LED drivers and flyback converters I have come across operate in the 60-100 kHz range. Is there any particular reason behind this - example - ferrite cores not being able to handle higher ...
11
votes
3answers
529 views

How is the state of a bit position on a hard drive measured?

Firstly, I am not the EE type, but I do have a petty good foundation on physics work on a pretty low level. I was wondering what mechanism it is that measures the magnetic indentation on hard drive ...
10
votes
2answers
2k views

Very small transformer powering a microwave oven

I have recently cannibalized a 6 year old microwave oven. I was very surprised to find the following beast at the electrical entry of the oven: The reason: this small 1:1 isolation transformer was ...
10
votes
3answers
11k views

Magnet that needs power to turn off? Inverse coil?

I have never heard of such thing. But it would really suit my needs. I'm inventing a device and during it's operation, it should be able to catch an iron object any time (with a permanent magnet). ...
10
votes
2answers
6k views

Saturation current of my inductor not agreeing with formulas

I have wound my first inductor and I have verified the inductance with 2 methods. However, when I test its saturation current, its much lower than the formula gave me: \$B_{peak} = \dfrac{V\cdot T_{...
9
votes
4answers
17k views

Does magnetism affect SD cards?

Would a strong magnet have any effect whatsoever on a thumb drive (I'm assuming not) or on an SD card? It seems unlikely, but I'm hoping someone can give me a definitive answer, since I'd rather not ...
9
votes
5answers
3k views

How big a magnet do I need to wipe my portable HDD?

According to this article, I need a really big magnet to wipe the data off my HDD. Thing is, I don't know how strong a "laboratory degausser" is, so I'll ask it in my own terms: I have a pair of ...
9
votes
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 ...
9
votes
2answers
7k views

Ethernet: how important is the magnetics topology?

I have some Ethernet issues with a set of boards (6/10 are bad). They're possibly just assembly house mistakes... but I'm very concerned about my magnetics jack. I could have sworn I saw a example ...
9
votes
2answers
3k views

How can this layout be improved? (Gigabit Ethernet with discrete magnetics and POE)

Answer: No there is nothing majorly wrong with the layout, it turns out that the ethernet transformer was out of spec by 0.2dB on Insertion loss, when paired with the PHY IC we are using. Question ...
9
votes
2answers
2k views

How to check whether a component can work in strong magnetic fields?

I want to design my PCB to operate nicely even when we place it next to a neodymium magnet. How to check whether my component can work in such condition without shielding? Edit: I haven't face any ...
9
votes
1answer
2k views

Ethernet: distance from PHY to magnetics

I am confused as to the preferred placement of Ethernet PHY and magnetics. I thought that in general, the closer the better. But then SMSC/Microchip app note (http://ww1.microchip.com/downloads/en/...
8
votes
4answers
815 views

How to track motion of a moving ovendoor

At work, we are measuring various parameters to test out a newly designed oven prototype. To make things more efficient, I am trying to create an electronic setup to automate the measurement, in ...
8
votes
2answers
1k views

Using the audio input port as a voltmeter

I'm a physics undergraduate currently studying electromagnetism. I have no experience at all with playing with electronics. I'm trying to see the effect of a changing magnetic field on a closed ...
8
votes
1answer
1k views

Differences between a planar coil and coplanar waveguide to create a local 1D AC magnetic field

Coplanar waveguides (for example picture look here) are often used in research to create a local in-plane magnetic field. Now if compared to a planar microcoil like this, driven by a AC voltage in ...
8
votes
3answers
7k views

Which type of Ethernet magnetics should I choose for PoE?

I'm trying to find a suitable PoE MagJack for use with my Phy, KSZ8051MNL. The problem is that I can't find one with the same suggested magnetics topology. The closest one I can find has one extra ...
7
votes
2answers
1k views

How do I determine safe distance from a choke to prevent accidental coupling?

In most of my power converter applications, I end up with a choke of some description, somewhere in a steel chassis. I have seen and heard tell of situations where the choke couples to the steel of ...
6
votes
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 ...
6
votes
1answer
3k views

How does Ethernet magnetics work?

If you refer to Figure 14 of http://www.analog.com/media/en/technical-documentation/application-notes/EE-269.pdf. There are 2 transformers on each data pair. Can someone help explain how they work? ...
6
votes
1answer
261 views

Where are Ćuk converters

According to "the art of electronics" (p 651) and other internet sources, the ćuk switch converter has the most desirable properties: continuous input and output current waveforms, boosting and ...
6
votes
1answer
9k views

Permanent magnets near wifi device

Background I have a small circuit that consists of a microcontroller operating on 14Mhz and a wifi module. This circuit is enclosed in a small plastic box. I am considering gluing a few magnets on ...
6
votes
2answers
729 views

What are the physical mechanisms of core loss, and how can they be minimized?

Suppose you have an inductor in a boost converter. The core gets hot. Why? What are the physical mechanisms that cause core loss? Eddy currents? Magnetic domains flipping? Coupling to materials ...
6
votes
1answer
3k views

How to choose a reed switch and magnet?

I need to use a reed switch and a magnet on a shaft. When it get turned to a specific degree the magnet will trigger the reed switch. The shaft only turns one way and is turned by hand. The problem ...
6
votes
1answer
651 views

Why are there different Ethernet PHY magnetic configurations?

I'm looking at pcb-mount Ethernet ports like these: I'm seeing a few different configurations of the magnetics within the ports. On a single Wurth data sheet, there are 4: Schematic 2 is the part we ...
6
votes
1answer
201 views

Fine-grained sensing of distance between two permanent magnets

(disclaimer: bit of an electronics newbie here) I have a bunch of little magnet ball-bearings that I was playing around with the other day. I formed them into a strand, then fixed both ends leaving ...
5
votes
2answers
854 views

Homebuilt magnetic tape head

I have seen a lot of projects that use a tape head, but there is very less information about how to build one yourself. Is this possible? I know that basically it is a metal core, with a coil around ...
5
votes
2answers
1k views

What are the specifics of PoE ethernet magnetics

I have a PoE powered design, and it is currently equipped with magnetics not labelled as PoE, HX1188NL. There is also a transformer with a similar topology, HX2019NL. However, the only difference I ...
5
votes
2answers
815 views

How does the length of a transformers core affect its properties?

I often read mentions of a transformer core's "cross-sectional area", of how it affects the transformers VA rating (although I can't find any formulas for that). But I haven't found anything ...
5
votes
3answers
2k views

For remoting 1000Base-T ethernet connector, is it better to remote PHY from magnetics or magnetics from connector?

I'm in need of remoting the gigabit ethernet connector from the main board to a back end board that has all the other connectors. I plan on doing this with a high speed board to board connector (...
5
votes
4answers
2k views

How is the degaussing feature in the HMC5883L 3-Axis Digital Compass chip correctly used?

edit/tl;dr: The set/reset strap driver is an H-bridge circuit to deliver 10 mA of DC current to a strap which temporarily produces about a 1.1 gauss magnetic field offset. A change in the measurement ...
5
votes
2answers
2k views

Sensing magnetic pulses from a rowing boat impeller

I'm a mechanical engineer at uni who has some basic experience in electronics and programming. I'm building a system for my rowing boat to help me with my training. This will give me feedback on a ...
5
votes
1answer
843 views

Winding method of a toroid core

I find some text about the winding of a toroid core as below: But what's the math and physics behind these? BTW: Can someone suggest some good books about the design of an inductor/transformer not ...
5
votes
4answers
2k views

How does a transformer transmit power from the primary to the secondary?

I'm trying to get my head wrapped around transformer operation and in the process regretting the times I snoozed in my Electromagnetics class as a EE student back when I was a lad :) I'm looking for ...
5
votes
1answer
2k views

Magnetic field strength and bldc rotor

As a background to this project, I have taken an off the shelf bldc stator and incorporated it into a small pump, and then built my own rotor using discrete neodymium magnets. At first, everything ...
4
votes
2answers
2k views

Sending data over a magnetic field

I need to find a way to trigger this Hall Effect Sensor with a non-permanent magnet. Does anyone know if an inductor's magnetic field would be strong enough? Or am I going to have to build an ...
4
votes
2answers
4k views

How to properly wind a high frequency / high voltage transformer?

Please, is there any practical tip / caveat I should be aware, when winding a high-frequency transformer? I'm used to wind 50/60Hz transformers and they do work ok, but now I'm trying to make a high ...