Questions tagged [magnetics]

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

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1answer
29 views

Will using magnetic base test indicators with breadboards cause electrical interference?

The situation leading to the question In the Quick Tips #8 // Precision Helping Hands YouTube Video, a "helping hands" with various names such as "Magnetic Base Adjustable Metal Test Indicator Holder"...
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1answer
218 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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1answer
30 views

Magnetometer moving along a line with different measurement?

I am testing on a magnetometer and found that moving the magnetometer along a straight line within the range around 1m, and the measurement varies. From what I understand, moving magnetometer along a ...
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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 ...
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1answer
119 views

Short range wireless pulse transmission in wind anemometer

I have an old windmil-type anemometer, something like this: (Illustrative image, the real unit is 40+ year old soviet-made device with presumably no operational active components inside) My project ...
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0answers
39 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
32 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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28 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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37 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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3answers
122 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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0answers
41 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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1answer
72 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
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? ...
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1answer
87 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
44 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
832 views

Modeling A Current Transformer in FEMM

I would like to accurately design and model a current transformer in FEMM. I'm hoping this will enable me to accurately estimate the secondary current in a current transformer, including it's phase ...
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1answer
390 views

Appropriate models to model magnetic components in LTspice and what are the pros and cons?

I'm looking for appropriate models to model magnetic components, mostly transformers and perhaps for chokes as well, for use in LTspice. I've heard briefly of some models, like Jiles-Atherton-model (...
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1answer
62 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
86 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
65 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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0answers
21 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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2answers
96 views

UAV-towed gradiometer: magnetic signal decay with water depth

I want to use an unmanned aerial vehicle to tow an airborne gradiometer. Goal is to detect historic anchors buried in the sea floor. What is the effect of (sea)water depth on the magnetic signal? Any ...
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1answer
300 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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2answers
2k views

Air gap in switching power supply transformer

An article I have read regarding switching power supplies (https://sound-au.com/articles/smps-primer.html) says that push-pull, half-bridge, and full-bridge switching supplies don't use an air gap in ...
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1answer
44 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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3answers
822 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 ...
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0answers
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
103 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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1answer
860 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
49 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
54 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
131 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
107 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
135 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
36 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
139 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
110 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
105 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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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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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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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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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
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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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). ...
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1answer
49 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. ...