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

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Magnet strength in dynamo design

I come from a computer background, and apologies if this question sounds elementary. While designing a dynamo, I came across a problem of how to calculate the the strength of the magnetic field, and ...
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37 views

Is it necessary for EM fields to be dependent & co-exist in static conditions? [closed]

I was having a discussion today with one my colleagues in the lab about the independence and co-existence of EM fields. My argument: In time-varying fields: EM fields are necessary dependent, and ...
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1answer
65 views

Calculation of inductance of rectangle coil

I'm currently working on a project about inductance. I want to calculate the inductance of a rectangle-shaped coil with a pitch different from zero. I tried this by applying the law of Biot-Savart. If ...
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3answers
77 views

How to select and use Strong Magnet together with hall sensor and amplifier?

With reference hall effect IC sensor (hopefully on topic as normal EE work) used together with these silver color magnet, as this example of 20 by 10 mm from ebay, Do they have different ...
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110 views

How do I determine the distance from a magnet using Magnetometer?

I have a triple-axis magnetometer and a magnet, and I am trying to calculate the relative position of the magnet from the magnetometer. The magnetometer outputs the strength of any fields detected in ...
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1answer
52 views

Electromagnet for string vibration

I recently read a lot about guitar sustainers, for those who don't know what are they - it is basically an electromagnet with an amplifier. It takes an input from pickup, amplifies it and then ...
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2answers
262 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 ...
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228 views

Simulating a magnetic field in Spice

I am trying to simulate a circuit that involves pickup coils in Spice. How would one simulate the magnetic fields that the pickup coils can sense? Additionally, how would one get a frequency response ...
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295 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 ...
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183 views

How to design a magnetic vibrator?

I plan to create a magnetic vibrator to shake a small container. What I plan is to buy Two "Magnet Wire 14 AWG Gauge Enameled Copper 1.5lb 118ft 200C Magnetic Coil Winding" a custom made container ...
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2k 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 ...
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107 views

Current source for milliohm loads?

I've been working on a model maglev train as my Grand Hobby Project; something around the H0 scale. The initial idea was to use the Inductrack mechanism to keep it simple. To summarize, a Halbach ...
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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 ...
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80 views

Magnetic shielding

http://www.kjmagnetics.com/blog.asp?p=shielding-materials I understand from the diagrams that the magnetic field is redirected through the shield (and not canceled out.. etc) Suppose I cover one ...
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138 views

Value of inductor

I need to wind an inductor with a value between 47uH - 200uH. I have a 10 mm (in diameter) ferrite core from an RF choke used in an old radio (probably lossy ferrite). The core is 3 cm long (I also ...
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75 views

How does the shape of the coil relate to the magnetic field around it?

I want to know if the shape of the coil affects the path of the magnetic fields around it. The two different shapes that I have are Helical coil and a spiral coil (in a plane).
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374 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 ...
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243 views

Electromagnet duty cycle

I have a project where I would like to use an electromagnet to lift an item for a longer period of time. I was looking at a magnet like this one: ...
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210 views

How to implement a radial encoder with a diametrically magnetized magnet using a hall-effect sensor?

I want to implement a rotary encoder that doesn't use optical sensing or physical contacts. I found the following solution using a diametrically magnetized magnet on the shaft, and a dual axis hall ...
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439 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 ...
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2k 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 ...
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1answer
175 views

How important is the number of cores in RJ45 jacks with magnetics

While searching for RJ45 jacks with magnetics (MagJacks) in Digikey, we found that there is a selection criteria which says "Number of cores per jack". Though we have been using MagJacks previously, ...
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316 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 ...
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106 views

Help building electric generator? [closed]

I am in the process of building an electric generator for the first time, and I have found out most of what I need to do, except the following things. Can I have 2 rows of magnets linked together ...
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1answer
81 views

What does limit transferable power through a transformer?

Assume that there is a transformer as in the image above. The applied primary side voltage \$E_1\$ is always AC. We design the transformer so that the magnetizing flux \$\Phi_m\$ does not saturate ...
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109 views

Back EMF and opposing current of a super conductor?

A 5 meter long super conductor carries 100 Amps, and it passes through a 1 Tesla magnetic field at 0.010 seconds, Is EMF = - (BL) / (t)? And since the resistance of the super conducting wire is zero, ...
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26 views

Average heat generated on thin circular plate in harmonic magnetic field

I have problem with this equation, I have final equation, but I don't know steps, how you get this equation. There are the eddy currents in thin circular copper plate thickness h and radius a, in a ...
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132 views

RJ-45 with magnetics transformer (Ethernet port) connections

I am working on circuit having RJ45 connector with built-in magnetics transformer. The schematic diagram of mentioned circuit shows following connections with Rj45 magnetics connector. At first I ...
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2answers
166 views

How does flux exist in a transformer?

What I understand about working principles of ideal transformer: We apply an alternating voltage at the primary side. This creates a flux inside the transformer core (\$\Phi_p\$). Some voltage is ...
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1answer
84 views

Polarity of the induced voltage on inductor for an applied magnetic flux according to the Lenz's Law

I'm trying to visualize the Lenz's Law on a practical inductor. The Lenz's Law says that $$ \mathcal{E} = -\dfrac{\partial \Phi}{\partial t} . $$ Now, assume that there is a magnetic flux inside ...
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60 views

What is the theory behind the coded magnet sensor?

I see that Banner has coded magnet switch. The switch would NOT be active by any magnet but one. Why this happen?
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1answer
103 views

Increasing the surface area of an electro magnet

I am trying to design an electro magnet with a large surface area at the end. The first design used a 1/4" rod wound with magnet wire resulting in about 10 ohms of resistance driven with 12 V. This ...
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3answers
82 views

How to detect non magnetic material?

I want to design a paintball counter. I have a metallic or plastic tube through which a paint ball passes. How can I detect that the ball passed? What kind of sensors do I need? I cannot see the ...
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769 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 ...
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143 views

Will running a DC motor below stall current damage it?

We have DC motors that power wheels on a car. Because of internal friction, the motors will not actually rotate until they are given 50%+ power. However, they do make some neat noises within this ...
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497 views

My DIY solenoid does not work

DESCRIPTION: Hi there, I don't know lot about electricity and I`m having problems with my first solenoid-prototype, I tried to build it watching you tube videos. I have attached the pictures of the ...
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1answer
78 views

When -EMF is induced can we keep current the same?

I'm confused at how Back EMF or (-V, -EMF) reduces current, and conserving the overall power. Let use the following simple example to help my understanding: A solenoid produces a magnetic field B, it ...
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156 views

How internal capacitor stud finders work?

I don't understand how can a non magnetic object like wood be detected using a stud finder For instance, stud finders find wood from dielectric constance, but I don't understand the princible. The ...
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118 views

Magnetic Equivalent Circuit

Is this correct magnetic equivalent circuit for this electromagnet system ? simulate this circuit – Schematic created using CircuitLab And i am trying to solve it like this example, ...
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89 views

RFID + permanent magnet

A project I'm exploring requires placing a permanent magnet in close proximity to an RFID tag (within a cm or so). Can an RFID tag be read when there's a permanent EM field so close to it?
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95 views

Powerful electromagnet?

Is it possible to produce over 1000 lb of magnetic force over a distance of 4 inches(0.101 meters), using an electromagnet? How difficult would it be? Explaining the general spec's of such an ...
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283 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 ...
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66 views

Resources for ferromagnetics

I am looking for experimental data on the experimental strength of magnetic fields inside ferromagnetic materials. Here is what I mean. If all of the magnetic moments of the molecules are aligned in ...
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151 views

Curie temperature

Does a ferrite core (or other material) have their magnetic characteristics changed when they reach curie temperature and goes below it (considering it does not suffer any mechanical damage from that) ...
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134 views

magnetics for ethernet PIC18f

I need to add ethernet connectivity to a PIC18f66j60. The datasheets tells about magnetics. But I know only very little about that. Do you know any surface-mount magnetics suitable for this use ? I ...
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119 views

Need to close or open a circuit (and keep it that way) with magnet

I need to build a circuit that closes when it detects the passing of a magnetic card. It should open again when the card passes again. So I need a simple magnetic reed (like this one). And some kind ...
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2answers
86 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 ...
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190 views

Is it possible to create an external electric field using a toroid?

I would like to create a directional, "external" electric field. For example, a solenoid creates an "external" magnetic field in one direction(coming out of the ends of the solenoid). I would like to ...
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108 views

Electro-magnetism. What's it all about anyway? [closed]

Ok, so am new to electronics. I've been looking up various thing like basic theory, schematics, circuit components, logic gates, and the rest. So all of that (on an extremely basic level anyway), I ...
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80 views

Designing a purely reactive circuit with the following requirements

how would you design a purely reactive circuit with: Infinite impedance in f = 0 Hz and f = 800 Hz Zero impedance in f = 5000 Hz and 11000 Hz At 7000 Hz, has a reactance of 181.85 Ohms How to proceed ...