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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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29 views

How do I determine what magnet to use at a specific distance for a reed switch?

I have a reed switch that shows a 10AT to 15AT operate range on the data sheet. I need to determine if specific magnets will fire the switch, and at what distance. The magnets I'm looking at though, ...
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1answer
30 views

Is it possible to influence the working behaviour of a simple dc motor with an outside electromagnet?

I am using a simple DC-Motor 9V like this one. Now, I am curious about what influence an outside magnet / magnetic field would have on the working behavior of this motor? I would like to use the ...
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24 views

HR911105A or similar integrated magnetics for POE

Is it ok to use this RJ-45 socket for low power POE application (just to power the uC)? The only available datasheet : https://www.google.com/url?sa=t&source=web&rct=j&url=http://www....
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35 views

Magnetic Linear Positioning with no magnetic disturbances at all

I recently saw a machine where it used a hall sensor or a magnetometer for linear positioning (the sensor is wrapped in some opaque protection so I don't know what it actually is which is the real ...
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31 views

What to do with unused Ethernet magnetic center taps on POE?

I'm using a MAGJACK GIG PDJACK 1X1 CLASS 4 (Molex # 0857914020 - Link: https://www.digikey.com/products/en?keywords=WM9656-ND) to run POE on a 100MBit network connection. I thought this was a nice ...
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1answer
107 views

Compass-Needle steering PCB

I'm trying to think of the easiest/best way to steer a compass needle using a PCB. Specifically, placing a PCB of some kind under a compass (assume no shielding between the PCB and the compass) and ...
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3answers
103 views

How critical is the magnetics circuit diagram in a magjack RJ45?

I'm looking at an example circuit diagram from ST, and it use sa 48F-01GYDXNL part that I can't find anywhere. It's a gigabit ethernet jack with magnetics, and the datasheet shows a circuit looking ...
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1answer
69 views

Can I swap TX+ and TX- (and RX+ and RX- ) using ethernet magnetics?

I am building ethernet connectors and a switch into a product. There is a requirement to include PoE which I haven't done before. This has required the use of a new magnetics chip to expose the two ...
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1answer
43 views

measuring ac voltage drop across a resistor with a solenoid in series with it

I wanted to measure the phase difference between the current (magnetic field due to the solenoid) and the system response. I am doing this by measuring the voltage drop across the resistor in series ...
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1answer
51 views

10/100Mbps Magnetics with 10/100/1000 PHY

I have a SOC that has a KSZ9031RN PHY, that is a Gigabit PHY. But I'm going to use only in 10/100 Mode with 4 wires. Gigabit PHY datasheet recommends a magnetic for Gigabit Ethernet, that are ...
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1answer
85 views

Possible to have too much magnetics in Ethernet

I have a question regarding magnetics topology on an ethernet 1000base t channel. I'm working on a project where I have a board (board 1) with MAC, PHY, and magnetics. I have another board that mates ...
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2answers
64 views

Charging a capacitor with a ferromagnetic generator

I am doing my internship and the company is making a ferromagnetic generator which indeed uses magnetic transition to create a flux and finally EMF. I am assigned to design a circuit which takes the ...
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20 views

High speed switching electromagnet control circuit

I am not very familiar with high speed switching magnets, and need help finding a control circuit that has adjustable frequency and duration for High Rate Switching Electromagnets, with a digital ...
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1answer
43 views

Increase emf received from a coil without changing flux source

I have a situation where I'm trying to increase the amount of power received by a coil. To my understanding, I can increase the emf (voltage) by doing one of 4 things: Increase the number of coils (\$...
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52 views

What defines the maximum primary current of a (sensor-only) current transformer?

Take the Coilcraft CS1200L for example, which states the sensed current maximum is 35 A. This limit doesn't seem to be defined by the wire size which can fit through the hole (5 mm) as you can pass > ...
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2answers
84 views

Stacking M.O.T. to create an E-E core

I just came across this site looking for answers on some questions I have concerning microwave oven transformers (M.O.T.). I am currently going into my third year as an E.E. student and I am trying to ...
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0answers
48 views

Question about Biot Savart Law using vectors

This is a Biot savart law question using vectors and I tried this question and I want to check my answer is correct or not. And please show me the correct answer if wrong. I uploaded my Answer. ...
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1answer
51 views

Sending flyback current to another inductor using crossed diodes

So, here is the context. We have two electromagnets (modeled as R1 and L1, and R2 and L2), their state is dictated by a microcontroller which sends PWM to Q1 and Q2. The signal sent to Q1 and Q2 is a ...
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2answers
116 views

Bob Smith termination for Ethernet magnetics

I know that Bob Smith termination is recommended for Ethernet differential pairs. Please refer the below image for Bob Smith termination resistor placement. As far as I know, Bob Smith terminations ...
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2answers
104 views

Why is the the permeability of a ferromagnetic material given as B/H not it's slope dB/dH?

I was going through my Electromagentics book by Sadiku where it was mentioned as a point that permeability of ferromagnetic material is given by the ratio of B(magnetic flux density) to H(magnetic ...
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1answer
116 views

Should Ethernet MDI Pairs all be Length Matched (Inter-Pair) before going into magnetics?

I've been trying to find information for the above question and I can't seem to find anything. I have 1000 BASE-T lines coming from an Ethernet cable to a PCB mounted connector. I'm pretty much ...
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0answers
43 views

Are magnetically tunable surface acoustic wave devices commercially produced?

I have been reading up on studies of magnetically tunable surface acoustic wave devices, in general they note the relative velocity change or in some cases a frequency shift if it is part of an ...
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1answer
33 views

GbE Phy(88E1543) with POE+ PSE(LTC4266) design (POE+ magnetics? RJ45 with Integrated magnetics?)

I'm trying to understand how i can inject power to a 4 bank RJ45. I want to use these parts : - LTC 4266 4 ports PSE (802.3 at compliant for GbE, in type1 class3 for 13W at each port) - Marvell ...
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3answers
131 views

How can an induction motor be “self starting”

I read that all you need to start an induction motor is to apply the AC voltage, and with time the slippage decreases. How does this happen magnetically? If a rotor, connected to a moderate sized ...
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1answer
29 views

Field geometry of external magnetic core?

If there is a coil with an external core, would the polarization of the magnetic field inside it be the opposite of an internal core? For example, in the image: If DC current were applied to the ...
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1answer
63 views

At what frequency is a transformers rated impedance measured

Where transformers have a specific impedance rating for the the primary/secondary, what frequency is this measured at? For example, this transformer is rated at 40MHz - 860MHz with an impedance of 50/...
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2answers
100 views

Wireless Electricity Transmission model not working. Why?

I made wireless electricity transmission model using the principle of magnetic inductive coupling to transfer electricity between two separate coils. The model is very simple, known to everyone and ...
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2answers
100 views

Electrical model of a transformer

I would like to know what is the inductance (circled in red) of this part of this model? Is the value infinite? And only the inductance (circled in blue) is the value of the inductance of the ...
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56 views

Tuning antennas

I am working in a biomedical implant. I have to design an antenna for the wireless power transmission. The frequency that I am using is 13.56 MHz. I used some antennas found in some articles but when ...
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0answers
82 views

Can an inductor lose its characteristics permanently after short saturation?

I was testing a SMPS (boost) where I had an overcurrent due to overload for a few seconds. The inductor saturation current is 2A. Although I could not measure the current, I am quite sure that the ...
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0answers
38 views

Is there risk to using magnets on an enclosure that would have 1-2A wire assemblies leaving the enclosure

Would there be a reasonable risk to using magnets to close a large enclosure panel which has 3 motor drivers with wire assemblies that leave the enclosure to drive stepper motors? The motor drivers ...
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25 views

Confusion regarding the right hand thumb rule

I am confused regarding the use of the right hand thumb rule . There is two use cases for this rule : 1- The first when the thumb points in the direction of the current the fingers points in the ...
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1answer
45 views

Shape of a core for use in a solenoid

I am currently designing an electromagnetic accelerator meant to accelerate a spherical nickel-plated NdFeB (neodymium) projectile along a circular tube, in a similar manner to a particle accelerator. ...
3
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1answer
70 views

Detrimental impact of magnetic field on PCB and battery?

We are developing a small consumer electronics product consisting of a small 4-layer PCB along with a few PDM microphones and BLE chip/ an antenna, as well as a LiPo battery. We are locating a small ...
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1answer
110 views

Replacing a magnetic speaker with a non-magnetic one

I need to mount a speaker next to a magnetic compass. Any suggestions? I have a becker radio which comes with a traditional 4 ohm moving coil magnetic speaker. Due to space limitations I don't really ...
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2answers
96 views

Does this coil topology work at high frequencies?

I have a cast iron wok and an induction hob. My understanding is that a ~24kHz AC in the hob's coil causes heating in the wok due to eddy currents from the varying magnetic field. Sadly, the iron ...
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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 ...
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2answers
77 views

How do I convert the units of a moving magnetic field to volts?

Copper wire wrapped around an iron core produces current when a strong magnet is moved in its vicinity. I gather the "magnet movement" part is expressed in units of "weber" (kg⋅m2⋅s−2⋅A−1) or perhaps ...
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0answers
31 views

Magnetic Field Strength Measurement at Extreme Temperatures

Hi I have just been given a project at work and we are magnetically stress testing DUTs at extreme temperatures going from -40 Degrees Celsius to 200 Degrees Celsius, I need to come up with a way that ...
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1answer
84 views

Questions on Inductor Selection guide from TI [closed]

I have been researching on Selecting inductors for Buck Application and came across an Application report from TI. I have few questions which are listed below: On ...
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2answers
76 views

A contradiction regarding flux conservation

Consider a simple circuit Initially switch S was opened till steady state is reached and then it was closed. My understanding regarding inductors is that you can't have a SUDDEN change in current ...
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1answer
71 views

Ethernet magnetics [duplicate]

I am working on a system prototype which includes two ethernet switches (KSZ9896) to provide Ethernet Gigabit connectivity between several devices (let's call them slaves, from now on); every slave ...
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2answers
139 views

“Electromagnet 5kg DC 3V 5V 6V 12V” - what do these multiple voltages mean?

I wanna buy an electromagnet from aliexpress and many of them are lifter magnets and have 6V, 12V, 24V and 5kg. So if i choose the 6V option does that mean the magnet can lift 5kg at 6V? Why would ...
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1answer
40 views

Does waveform shape affect transformer eddy current loss as frequency changes but peak voltage is fixed?

I'm trying to figure out how eddy currents change with frequency. While learning about this its occurred to me that eddy currents might be impacted differently as frequency changes, if the voltage is ...
3
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1answer
181 views

What impact does winding tightly versus loosely have on transformer performance?

To make it simple (and actually, directly relevant to what I am working on): what impact does winding tightness have on transformer performance? Lets assume typical laminated EI / EE 60hz transformer, ...
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1answer
48 views

Measuring a magnetic pulse using a coil, and circuit adjustments

I have the following circuit, I am using it to create a pulsed magnetic field, in the coil. I am trying to measure and verify the magnetic field in the coil. I am testing it with 40 V to drive the ...
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2answers
102 views

Determining magnetic flux density of a closely wound toroidal coil

I am using David K. Chengs's Fundamentals of Engineering Electromagnetics book. In chapter 5/question 5.2, there is a given closely wound toroidal coil, and it asks what is the magnetic flux density ...
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2answers
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
103 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 ...