Questions tagged [emf]
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105
questions
-1
votes
1answer
40 views
Wireless charging shielding requirements
I have a project where I want to throw a charging coil into the wonderful mix of tiny parts but the problem is, I also need an accelerometer/magnetometer roughly right beside said coil. I believe I ...
8
votes
3answers
891 views
How should I understand back-EMF in an inductor?
I have a circuit made of a MOSFET that pulls the lower side of an inductor to ground while the other side is connected to a DC voltage source as follows:
Then it is very simple to describe what's ...
8
votes
4answers
581 views
Why does analysis indicate that ground lifts do not fix ground loops?
Note: "Ground loop" in this question refers to a ground loop caused by linked magnetic fields. (Sometimes ground loop refers to slightly different scenarios.)
Recently I've been looking into ...
0
votes
0answers
39 views
Identifying strange readings from Arduino EMF detector
Intro and knowledge self assessment
Full disclosure, I'm an amateur, and my knowledge of electronics is cursory, and I'm more into computer science. But I bought an knock off arduino kit, and decide ...
1
vote
4answers
84 views
Motor Noise Reduction + PWM
I'm trying to suppress EMF coming from a brushed DC motor that I am running. I've tried using 0.1uF capacitors across the motor leads as discussed here: https://www.pololu.com/docs/0J15/9.
It works ...
0
votes
1answer
99 views
Is it normal to have around 40 V in your body, when touching your plugged, ungrounded laptop?
I have had bilateral shoulder pain and then both arms and hands pain for around 7 mounts, which got much worse when I started working from home, with my laptop.
The ultrasound of shoulder muscles ...
0
votes
3answers
53 views
Do switches induce voltage spikes in the AC power grid?
I know that DC inductive loads create back EMF when turned off and that's why we use a freewheeling diode.
Does this also true for AC inductive loads and AC loads in general?
I know we can't use a ...
1
vote
1answer
62 views
Isn't the voltage reading in this image wrong?
The conductor is moved from top to bottom through the B-field. Shouldn't the reading be negative on the volt-meter?
Right-hand-rule gives that the positive charges experience a force towards us. Then ...
2
votes
2answers
104 views
How is it that the induced EMF in an alternator is in quadrature with the main flux?
Looking at the simplified diagram of an alternator, the flux "linked" with the conductor is maximum at 90, 270 degrees, is also when induced EMF is maximum. So isn't the main flux in phase ...
-1
votes
1answer
123 views
A misunderstanding with Faraday's experiment with iron ring
I am learning about electricity and magnetism, and have got some misunderstanding about Faraday's experiments with iron ring.
If iron can conduct electricity, why is electricity inducted only while ...
0
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0answers
82 views
Where are the sensors of the EMF/RF meter on the circuit board?
In the attached photo you can see the PCB of a simple EMF/RF meter.
This meter shows, at the same time, the values of the electric field,
magnetic field, and power density (see small illustration on ...
0
votes
2answers
38 views
EMF and voltage on inductor
What is difference between EMF given as \$\epsilon=-L\frac{dI}{dt}\$ and voltage on inductor \$V=L\frac{dI}{dt}\$? In circuit analysis is \$V\$ used as the voltage on inductor, and why is it equal to \...
0
votes
2answers
49 views
Permanent magnets inside electric motor create stress
I am trying to do a simple project, a brushed DC motor, in my free time to check what I learn in lessons in real life and I've encountered something I didn't think of before while studying the EMF ...
2
votes
2answers
184 views
How exactly does a basic EMF sensor work?
Halloween is coming up, and inspired by the simplicity of this project, I'm asking for a more technical explanation (and / or resources to do that) - this seems to be either missing or too obvious to ...
1
vote
1answer
35 views
What will be the graph of flux of coil 2?
In the following picture current is flowing through coil 1. Let's assume that current is increasing linearly in coil 1. Then emf induced in 2nd coil be will constant and having some negative value. ...
0
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0answers
2k views
Elaborated difference between static and dynamic EMF
I have seen two sources have contradicting takes on static and dynamic induced EMFS.
One source says that Static EMFs are produced by the circuit and magnetic field both being stationary. Dynamic EMFs ...
0
votes
1answer
124 views
Mesh to block or reduce wireless cell signals
I want to block or reduce the amount of wireless cell signals coming into my house through my window(s) by using some type of mesh (screen). I could use a sheet of metal but then I wouldn't be able ...
6
votes
3answers
683 views
Measuring back EMF induced current with multimeter
I have built a solenoid with copper.
It is 19 cm long, it has 64 turns and the radius is 1.5 cm.
To trigger back EMF, I use a permanent magnet that has the same surface as the cross sectional area of ...
1
vote
0answers
24 views
EMF radiation from an open AC circuit
When I pass my EMF radiation meter near an electricity cable (a cable that is connected to the home mains), it shows me that there is a radiation.
But if there is an extension cable for example, and ...
1
vote
2answers
43 views
Motional Emf confusion
I know that in motional emf V=Blv where B,l,and v are perpendicular to each other. When one of them isn't, then there would be no emf. What formula supports this?(mathematical evidence)
Can anyone ...
0
votes
1answer
27 views
How will equivalent EMF and resistance of cells be calculated
In the image, three cells are arranged in a circuit. But the cell in the centre is installed such that the positive terminal is connected to the positive terminal of one cell and the negative terminal ...
-2
votes
1answer
335 views
Harrington rod from spinal fusion might be acting like a human EMF antenna [closed]
In 1994, I had a spinal fusion surgery to correct Scoliosis which was a result of my medical condition, Spinal Muscular Atrophy Type II. I've used a wheelchair my entire life. Because my upper body ...
0
votes
2answers
246 views
Should I be worried about a surge protector near my pillow
I have just realized how close my surge protector appears to be to my pillow. It is about 20-30cm away. Should I be worried about any EMF/radiation/something else? The surge protector itself is new ...
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votes
1answer
90 views
Which EMF frequncies provide power to field powered implants? [closed]
What EMF frequencies provide power to field powered implants? There are in ear phones and some implants which obtain power through EMF fields. They produce sound in the ear and some other implants are ...
0
votes
1answer
49 views
How do I calculate the regulation of the generator in a Ward-Leonard system?
I have a DC motor with independent excitation, power by a ward-leonard system. The nominal voltage applied to the motor is 250 V. I have to calculate what regulation(%) to apply to the generator so ...
1
vote
1answer
44 views
Question: AC Voltage and Current variables
So I know how alternating current is produced, but I'm curious to what determines the voltage and amount of current moving within the wire.
Does the frequency of the alternations give more voltage/...
0
votes
1answer
42 views
Grabbing EMF meter magnifies signal 10fold
I have a Tenmars tm‑195. Holding it in my hand arm's length, still, I read \$2 \mu W / cm^2\$. In exactly the same spot, without me holding it, I read 10 times lower, \$0.2 \mu W / cm^2\$. I can ...
0
votes
0answers
41 views
Shield EMF from power cable with aluminium foil
There is a big electric cable behind a wall. On the other side, I read around \$2 \mu W / cm^2\$ of EMF at distance about 3 feet from wall.
Is there any way to shield this using aluminium foil? I ...
1
vote
1answer
72 views
Is it normal for 24" LED monitor to emit 1000 odd mV/m?
I have a 24" LED monitor, we have a cell phone tower on a building next to ours, so we bought an EMF meter to see if there was any high radiation from it. Throughout the house, the radiation was above ...
0
votes
1answer
116 views
How to calculate the emf with flux density given instead of flux
So I have the following question
What is the emf in a coil of 2000 turns and c-s area 10cm2 when a flux density of 0.4T density in it is reversed, i.e. in a time of 20ms. Also what would be the the ...
1
vote
1answer
109 views
Is there a way to measure or predict how much a 10.5 microns Aluminum foil attenuates EMF radiation? [closed]
Is there a way to measure or predict how much a 10.5 microns Aluminum foil attenuates EMF radiation? And at what frequencies?
Is it enough to use as Faraday shield?
0
votes
1answer
777 views
Back EMF of an H Bridge
I am building a H bridge to control a motor in the middle.
As an example, when power is fully removed (24V... 80V in the picture below), there is some back EMF that will drive the 24V input rail.
...
0
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0answers
100 views
Hall effect current sensor and proximity to EMI
I am preparing to layout a PCB. I have an ACS723, that I want to use to sense the current going through a relay. In addition to the relay I have a Meanwell IRM-12-20 to supply ac to dc voltage to the ...
1
vote
1answer
276 views
Pancake Coil Magnetic Field Strength
I am trying to measure the magnetic field strength of a pancake (flat) coil. I know the turns, inner radius, current, and frequency from an AC input and am trying to measure the magnetic flux so I can ...
3
votes
2answers
84 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 ...
0
votes
1answer
243 views
How does DC braking stop an AC motor without considering current direction?
When a motor is coasting to standstill, if I apply a DC voltage across the windings I will brake that motor... We'll at least that's what I've read.
Now here's the thing. With reverse current ...
2
votes
2answers
6k views
Why is the air gap between the stator and rotor on a motor kept as small as it is?
Between the stator windings and rotor is a small air gap. What would happen if this gap were larger than it is? Surely the magnetic field set up by energizing the stator windings would still cut the ...
-1
votes
1answer
47 views
How Does Resistance Affect EMF Measurements?
I have very little electrical engineering knowledge, but am working on a simple Arduino project that detects electromagnetic fields. The original project specifies that three 1M resistors should be ...
0
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2answers
111 views
Does 20 Millegausse near outlet with nothing plugged in suggest faulty wiring?
Meterk EMF meter showing 20+ millegausse near two outlets only. Both outlets have nothing plugged in. Possible live and neutral wires faulty?
-1
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3answers
4k views
EMF - Dangerous uT levels? [closed]
Live in 7 floor apartment building directly above electrical room for entire building and old elevator. Noticed static electricity or excessive charge and have been investigating. Measured EMF ...
1
vote
1answer
396 views
DC Shunt Motor Load Loss
I have three DC shunt wound motors in series. Each motor has a coupling to a transmission. I am trying to work out (mathematically, as opposed to intuitively), what happens if the coupling was to drop ...
0
votes
2answers
358 views
How do I connect a four way key in a potentiometer?
I asked this question in Physics stack exchange and had an answer, but I couldn't understand it well. A comment said this stack exchange was a better fit for the question.
Question:
How do I connect ...
0
votes
0answers
120 views
Why aren't homopolar generators more commonly used?
In particular with the advent of HVDC(high voltage direct current). Using mercury(metal), the resistive losses can be greatly reduced. There has even been some experimental research into neon plasma ...
0
votes
1answer
176 views
What happens in a generator so that we get a sinusoidal voltage as an output?
I read this online, " For a travelling magnetic field in a circle, the induced magnetic field in the armature of the generator will be sinusoidal. That's why the generated voltage is a sinusoid, ...
-4
votes
1answer
270 views
Are headphones with EMF measurement of 10,000 milligauss harmful to me?
I used a EMF detector app on my phone and measured the EMF output on my wired headphones. It measured around 10,000 milligauss on one part of both ear cups. Since wearing these headphones on my head ...
-1
votes
3answers
4k views
What is the SI unit of magnetic force?
As derived from F = qvB sinθ, what is the unit of magnetic force, and why?
Edit: I mistakenly asked about magnetic field before. -- I'm asking the magnetic force.
0
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1answer
79 views
EMF from power lines [closed]
My new house flat is near an overhead power line. It's a steel structure so it's the higher energy lines. The line is about 1200 feet away at the closest point, I guess that is fairly far and you'll ...
1
vote
1answer
14k views
Calculating a voltmeter reading
I'd like to preface with saying that I'm quite new to this.
Given emf E = 9 V, and that both resistances are equal, R = 1 kΩ, ...
0
votes
2answers
217 views
Strategies to reduce EMF radiation
During a long-term, almost six month long, data acquisition in a proximity of scanning electron microscope I have found a significant source of magnetic field noise, which is altering the results. I ...
-1
votes
1answer
304 views
Stepper Driver signal noise problem (Ground Loop)
I have an BluePill board (Arm Cortex M3 Dev. Board). Also a a4988 stepper motor driver. BluePill is powered from usb of my PC. Stepper motor driver is powered by external power supply which is 220V -> ...
