# Questions tagged [magnetics]

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

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### Ethernet coupler implementation on PCB - whether to use magnetics (transformer) or not?

I need to implement a sort of coupler on a PCB which has other things running, but without any connection to an Ethernet circuit (see drawing). One end of this 'coupler' connects (using a suitably ...
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### Estimation of open-circuit inductance from the leakage inductance

The title may not reflect the problem I explained below. Please feel free to update. For a power supply application, I designed a transformer with a primary turns of 15 and a secondary turns of 4+4 (...
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666 views

### Is magnetic flux in a transformer proportional to voltage or current?

Consider a transformer. I put a constant sine wave AC voltage through the primary circuit and a resistor on the secondary circuit. I know that the secondary voltage is proportional to change in ...
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2k views

### How accurate is my phone's magnetometer?

I'm trying to build a linear motor, for which purpose I bought this large permanent magnet. The website claims it has up to "13,500 Gauss", which is 1.35 tesla. However when I put my phone ...
65 views

### Question when obtaining magnetic flux density B

I am trying to obtain the magnetic flux density B of a toroidal transformer with one winding around the core. I am injecting a voltage in the terminals of the winding, and I am measuring this voltage ...
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### Is this PFC choke design correct?

I would really appreciate it if you could check this inductor design, if there are any mistakes, or if it can be improved. I'm designing a $50\,\mathrm{\mu H}$ PFC choke for a totem-pole bridgeless ...
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### How is slope compensation implemented in the UC3843?

I was reading about slope compensation in the datasheet of UC3843 and I have watched this tutorial on youtube which gave me a general idea and overview about what slope compensation is. Now regarding ...
108 views

### Magnetic field in a tape

This is a theoretical question. Let's guess we have an unknown magnetic tape cassette, no brand, no numbers or other signs. The question is: do tools exist, that are able to analyze the magnetic field ...
1 vote
65 views

### How does a Current Injection clamp work from a physics persepective?

Current injection clamps are normally described as a transformer with a single turn secondary, which is all fine and good, but the construction of a transformer is different from a current clamp. ...
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### Can I deduce the saturation current of a transformer from the rated wattage and maximum frequency?

I have an SMPS transformer EE10, but am not sure about the saturation current it has, I tried doing some internet research, all what I can get is this so far : I am trying to deduce the saturation ...
29 views

### Measurement bias of Hall sensors with moving permanent magnets

I want to measure the magnetic flux density produced by a moving permanent magnet. In my case, the magnet would move left and right alternatively at speed of 10 mm/s, with a constant vertical distance ...
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108 views

### Energy stored in a saturating inductor

We all know that the energy stored in an ideal inductor is $E=\frac{1}{2}LI^2$. However, real inductors with a ferromagnetic core don't have constant inductance. Particularly, when a specific field ...
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### Inductance after core saturation

Looking at the datasheets of some drum core inductors, at higher currents the inductance drops significantly due to ferrite core saturation. But it seems inductance asymptotically approaches a value ...
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### Why are common mode chokes used in Ethernet magnetics

I’m trying to understand the reason the common mode choke is required in Ethernet magnetics. To understand, if we look at the schematic, with the common mode choke (horizontal coils) removed, we are ...
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### Does hysteresis still occur if saturation is not achieved in a core?

When looking at a BH curve, what happens if the H field is raised to some level below saturation. For example we apply an H field that is only half way to saturation. On a BH plot this will trace a ...
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### Inductance Computed As Length in Historical Document

In "Formulas and Tables for the Calculation of Mutual and Self-inductance.", many equations compute the inductance of an arrangement as a length. For example, Equation 95, on p. 150, states,...
1 vote
129 views

### What are sources of extra low frequency magnetic field in a car with IC engine? [closed]

ELF analyser (16 Hz - 2 kHz) shows a magnetic field around 300- 2000 nT (at some position exceeding that) in car when petrol or diesel engine work. When RPM increase from idle to 2500 RPM, magnetic ...
100 views

### Transformer losses due to eddy currents. Why these losses are compensated by the transformer?

Here is my understanding of a transformer. Let's assume that we have the following ideal circuit, in which a coil is wrapped around a core and there are no core losses⎯excuse my crude drawing.         ...
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### Magnetic Force Equation

Is there any equation where I can take a metal with a given volume/mass, with a certain amount of magnetic flux in it (in teslas) and find out how much force (in newtons) it exerts a given distance ...
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2k views

### How can single phase induction motor's direction be reversed?

My house has a ceiling fan which has 2 wires which are connected to a capacitor, and Iam able to control the velocity and direction. After looking about these motors on the web I found out its ...
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### Magnetization of an Electric Guitar String

I'm trying to calculate the magnetic field generated by electric guitar strings of various gauges. The strings are made of some ferromagnetic material (pure steel or pure nickel). They are magnetized ...
49 views

### If I have two magnets repelling each other, will they always form a peak in the middle?

If I have two identical magnets, aligned so they repel each other a distance of X apart and at a height of Z I have Hall effect sensor, the peak of the magnetic field sensed will be at the distance X/...
71 views

### Energy stored in a magnetically coupled circuit

In the circuit shown, inductors $$L_1,L_2$$ are magnetically coupled with the mutual inductance being $$M$$. The red dots are for dot convention. Normally,the energy stored in such a circuit is \...
1 vote
143 views

### How does all (well most of) the flux in the primary side get into the secondary side in a transformer?

I had a follow up question to this: How does a magnetic material "confine" a magnetic field? In the above question, it asks how the magnetic flux is "confined" by the core. The ...
319 views

### Equation for the force created by a solenoid

I'm trying to make an electro-magnet and I want to figure out what core and wire I need using math instead of trial-and-error. I want it to produce ~1.5 newtons of force at ~1.5 inches from the magnet....
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### Characterize ferrite cores, e.g. core losses

How can I characterize ferrite cores? I can measure saturation, but how can I measure core losses so I can decide what frequency to run them at? I could charge a primary winding to a certain current, ...
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### Finger magnets and MRI

A few years ago in the biohacking community there was a phase where people (mostly engineers) were having small magnets embedded in a fingertip in order to sense magnetic fields. I was slightly ...
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### Are 10GBASE-T ethernet magnetics modules compatible with 1000BASE-T?

I am designing a board with a 1000BASE-T ethernet PHY and I want to use a discrete magnetics module since I will be using a non-standard connector. However, I am constrained with space and I found a ...
1 vote
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### Transformer design and calculations

I am trying to find correct way of determining the transformer parameters. I provided a simple schematic of a PSFB (phase-shifted full bridge) converter below. How do we determine thr primary ...
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1 vote
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### Core demagnetisation - What is the condition?

Consider forward converter topology. What is necessary for core to be successfully demagnetised? Does the magnetising current has to reach absolute zero amps, or even little negative is advantage? How ...
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### Would a electromagnet be used to detect the presence of a permanent magnet?

I was wondering if there is any way I could use an electromagnet to detect the presence of a permanent magnet. I am specifically thinking of using a planar type small coil. Maybe use a core or ...
2k views

### How to design a 12V to <100mV 15A DC-DC converter?

My project requires a constant current source of at least 13A for a minimum of 1s (preferably capable of longer such as 5s). The primary use of this current is to produce a B-field. The current would ...
507 views

### How Should I Model Eddy Currents in a Magnetic Core?

simulate this circuit – Schematic created using CircuitLab I'm primarily a VHDL and DSP guy, so I apologize in advance if this question is dumb. I have wire wrapped around a magnetic core. The ...
1 vote
192 views

### Electromagnet design and powering it up? (Fault prevention of DC supply for a small coiled Electromagnet)

I want to create an array of multiple electromagnet which I will be controlling using a microcontroller. I will have around 100 such magnets lined in a squared grid 10x10. Only three or five at a time ...
126 views

### Problem acquiring B-H curve

I'm trying to acquire the BH curve of a toroidal current transformer in saturation, having the primary and secondary current. The formulas I am using are: B = (1/NsS) Integral(Vs(t)dt) H = (Ip*Np)/l \$...
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1 vote
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### Ethernet Magnetics Polarity Swapping

Can I on the same pair (for Example A) to swap polarity on opposite side of transformer/magnetics? Update 1: Currently i use cross-over method to make lanes shorted and more easy to layout. Update 2:...
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### Boost Inductor Design for three phase Diode Bridge Rectifier for PFC operation

I am doing a simple DCM based control for power factor correction. Please see the topology below . Specifications are as below: 1.) Power 5KW 2.) Input Voltage is 415V L-L Nominal 3.) Inductor ...
159 views

### Does winding a solenoid around a copper pipe reduce the net magnetic flux at all?

I want to wind an air core solenoid around a copper tube. One end of the solenoid is soldered to the copper tube. (See picture above). Will a magnetic field be induced in the copper tube that cancels ...
1 vote
211 views

### How is the holding force of this electromagnet so large?

I am designing a system that uses the magnetic force to fix an object in its place. I plan to connect an I-core to my object and fix it to a fixed C-core by letting a magnetic flux flow through both ...
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### Design Ethernet capable board without RJ45 socket

I have been tasked to design the schematics of a board of an ECU which provides 4-pin Ethernet on its 58 pins connector, for a 100Base-T implementation; I have been mandated the use of TI's DP83822 ...
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1 vote
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### I am wondering if magnets can be safely used to connect power from one to the other? [closed]

I am thinking of trying to create a extension cord that can be taken apart or separated as needed. And rejoined at any length of cord but connected only through magnetic connections. So I'm wondering ...
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### Why are induction motor cores laminated to prevent eddy currents?

The permeable iron alloy cores of induction motor rotors are formed from thin laminated sheets, designed to prevent eddy current flow and thus "reduce losses", but isn't the whole point of ...
72 views

### Any information on magnetic braking with copper?

I have an engineering project where I have to design and build a model of a drop tower from a theme park. The tower itself can be no taller than 40cm. I plan to use magnetic braking with copper to ...
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### Does operating an iron core near its saturation field reduce performance?

I am sizing an iron core for an electromagnet, and I am uncertain if there are disadvantages to operating close to the saturation flux density. If the saturation field is X, would it be better (more ...
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1 vote
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### How Far Should Mu Metal Be From An Inductor to Leave Its Internal Behavior Unchanged?

I have an air core inductor. Since its magnetic field will be large, and it will turn on and off rapidly, I assume it will make a lot of noise. I don't want that noise to disturb the PCB's nearby, so ...
72 views

### Magnetics part with and without auto-transformer

I have 2 magnetics part. One magnetics is this (Circuit A configuration magnetics) & the other magnetics is this When I use the Halo part, the ethernet link is not up. But when I just replace the ...
1k views

### Why do metal finders not use any sensors other than search coils?

I was wondering why metal finders do not use any other sensors to recieve the magnetic signal instead of search coils. I have been looking at MEMS sensors used as digital compasses, for example. As ...
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### Is there any practical purpose of placing read only memory (ROM) chip near a hard drive?

Premise: a PCB file has ROM chips (I think they are masked ROMs?) placed beside standard 3.5" HDDs, which has lead me to a few questions. While the product is off, I understand that the magnets ...