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

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How to work out the magnetomotive force?

I don't know which formula to use for this past exam, there are so many. I was thinking of the formula: f = HL? But then I don't know the equation symbols for flux density and what a BH curve is. ...
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54 views

Where can I find correct documentation of old floppy drive formats?

I have an old drum machine with an ancient proprietary 3.5" SONY floppy disk drive with no information on the device itself that I have seen. The performance is spotty and it's very picky about disks. ...
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2answers
24 views

Potential lose of time-dependent currents in presence of static magnetic fields

A time-dependent current (either DC or AC) that creates a changing magnetic field around the wire, in absence of other materials, only lose current in heat proportional to ohmic resistance of wire ...
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51 views

Proximity activation

My boss wants me to implement a system that only lets "allowed users" to use the machineries in our shop. Since I am an IT, I do not have any idea how to process this. I came with the idea to ...
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2answers
36 views

Can a planar transformer replace a laminated transformer for 50Hz AC conversion?

I have seen planar magnetics transformers even with isolation up to 20 kV. However those devices seem to be designed for DC/DC conversion in 100 kHz range. I am wondering whether low frequency ...
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1answer
24 views

Hall-sensor replacement for reed switch

I have a device in which a reed switch is encased in potting compound. (So impossible to identify.) My problem is, that for my application the switch is too slow. I am considering replacing it with a ...
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1answer
31 views

questions on shielding static magnetic field

It seems that using ferromagnetic materials is the easiest way to shield static magnetic field. But is it still working in strong field strength(up to 5T)? Another question is that are mu-metal ...
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2answers
53 views

Flux in transformers

I have found it very difficult to find what actually happens with primary and secondary generated flux in transformers, I understand the normal transformer theory but it doesn't add up in reality! I ...
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1answer
83 views

How do electric and magnetic fields affect electronic circuits?

I have come across those requirements: "The equipment shall not be susceptible to DC magnetic fields of up to 60 μT." "The equipment shall not be susceptible to electric fields of up to 140dBuV/m ...
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70 views

POE external Magnetics Alternative to magnetic RJ45 jack ieee803af

I can't use a magnetic jack for this POE PD (ieee803af), because we use another connector (M12). Looking for components to replace the internal magnetics, I found that almost all components and ...
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1answer
48 views

Inductor Core Loss: Volt-uS vs. Irms vs. Switcher Frequency

For DC to DC application, I see these charts often for inductors, but I don't understand what they actually mean. What does this chart mean, and how does it relate Volt-uS, Irms, & Freq? Edit: ...
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137 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 ...
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64 views

Why is HV kept open in OC test of transformer?

Why is HV kept open in OC test of transformer? Also, why is LV shorted in SC test of the transformer? (Generally this is preferred - why?)
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1answer
47 views

Create a vest to detect contact

I want to make a laser hunt type game with my son using Nerf Guns. I can modify the Nerf bullet to put some sort of device on the top of the bullet (obviously something not too heavy). It would be ...
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1answer
58 views

Magnetic contact circuit

Which is the best circuit for using a magnetic contact for turning on a LED strip? I would like to turn on a strip led with 12V 7A battery, but: 1 - if I use only the magnetic contact it will be ...
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67 views

Extend an rj45 Jack

I want to extend the Ethernet port (of my raspberry pi) using a short bit of cable plugges in into the Ethernet Port and solider to another rj45-jack. In the jack I have here, are some built-in coils ...
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1answer
46 views

Which is the best material to create a magnetic field?

I'm trying to create a magnetic field and I'm also trying to induct electricity wirelessly to a light bulb. What I have to do is create a round coil but I'm not sure what is the most conductive ...
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1answer
34 views

3 axis magnetometer issue in one axis

I have several 3-axis magnetometers mounted on breadboards, and they all read correctly in the x and z directions. The Y direction is very strange; when turned to read ...
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1answer
72 views

Motor without magnetism [duplicate]

Every electric motor I know, takes electricity and converts it over a magnetic field, for generating movement. Is it possible to generate significant movement, based only only on electrons movement? ...
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194 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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2answers
154 views

How build coil for respiratory magnetometer or find a better option (hall effect)?

I am trying to build an respiratory magnetometer. This device is no longer widely used even thought it was well liked. The reason it is no longer used is due to the fact that the coils used in it were ...
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1answer
39 views

How to determine the minimum proximity of magnet to an AC line for no electrical impedance?

As the title says, I am wanting to calculate the minimum proximity for a magnet to be near a AC line for no electrical impedance. My scenario is this: I have a theoretical device like MagSafe ...
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1answer
40 views

Mitigate the effects of magnetic induction heating in a three phase AC system

To mitigate the effects of magnetic induction heating in a three phase AC system, it is common practice to group the conductors and to keep them in the same raceway. Also, three phase power is ...
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192 views

Magnetic equivalent circuit with permanent magnets

I am fighting to understand how permanent magnets are inserted in magnetic equivalent circuits. In the image below is an example, at the left, the physical representation of an Iron core with a ...
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1answer
49 views

Bit persistence on a Hard Disk Drive

I was wondering if there was a time limit to the "persistence" of bits on a hard drive, a classical SATA for example. If I'm correct, bits are written by a magnetizing head in some cells on the hard ...
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1answer
62 views

Magnetic flux outside a solenoid perpendicular to the direction of axis of solenoid

I know that using straight forward Biot-Svart law it is possible to calculate field inside a solenoid or at a point on an axis away from the circular coil. Now is it possible to calculate the Flux ...
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1answer
222 views

Maximizing force of magnetic mass accelerator

I am planning to build a coil gun to fire small neodymium magnets out of a pipe. For this I am planning to use a large 400 Farad 2.7 Volt capacitor. I am wondering how many coils of wire I should ...
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82 views

Thickness of low frequency Mu shield calculation

I am dealing with a low frequency varying magnetic field, say 10 - 100Hz with a magnitude of 0.8T. It seems shielding at this frequency gets tricky. Even though Mu is capable of doing it, there should ...
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1answer
54 views

Would proximity to water affect a magnetometer

I'm using an InvenSense MPU9150 as a tilt-compensated compass in an autonomous sailboat. I'm trying to decide where to put the the control board, with options being in a dry box on top of the "deck," ...
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1answer
156 views

Can I increase inductance using permanent magnet ?

I know that when I insert a ferromagnetic core inside an air-cored coil, the inductance increases. What if I inserted a permanent magnet with a cylindrical shape into an air-cored coil, does the ...
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1answer
105 views

Why is the Litz Wire twisted?

I understand that dividing a wire into multiple insulated pieces reduce the Eddy Currents, and that reduces the magnetic field inside the wire, which leads to increased skin depth. But why do they ...
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1answer
139 views

Super fast magnetic field by an electromagnet?

Was wondering about the possibility of creating a magnetic field in milliseconds or less? I know it's possible based on certain labs achieving 60-100 Tesla and more. But what about creating a 2 - 5 ...
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3k 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
129 views

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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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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2answers
335 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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4answers
735 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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3answers
118 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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1answer
122 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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1k 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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3answers
157 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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1answer
163 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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292 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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530 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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1answer
235 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 ...
2
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1answer
170 views

Help building electric generator?

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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3answers
584 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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1answer
484 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
743 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
250 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 ...