Questions tagged [emf]

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29 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 ...
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1answer
39 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/...
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1answer
39 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 ...
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0answers
36 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 ...
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1answer
69 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 ...
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1answer
37 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 ...
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1answer
87 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?
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1answer
58 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. ...
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0answers
37 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 ...
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1answer
73 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
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2answers
67 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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1answer
114 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 ...
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2answers
1k 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 ...
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1answer
45 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 ...
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2answers
105 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?
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3answers
408 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
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1answer
214 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 ...
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2answers
148 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 ...
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0answers
76 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 ...
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1answer
74 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, ...
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1answer
169 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 ...
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3answers
897 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.
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1answer
65 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 ...
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1answer
2k 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, ...
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2answers
119 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 ...
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1answer
167 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 -> ...
0
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1answer
156 views

PC monitor flickers/resets when washer motor switches on or off [closed]

My room is next to our laundry and I've recently got a new PC monitor. I've noticed each time the motor in the washing machine is switched on or off, my monitor flickers/resets. The monitor is 32" but ...
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1answer
45 views

Cancelling Ripple With A 7555

Friends, I did this once but don't remember the detail. A very sensitive circuit which switches a relatively heavy load. I used a 7555 IC to momentarily blank out any ripple or instability caused by ...
6
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1answer
120 views

Sparks on grounded metal bodies on lighting strikes in the nearby (two miles)

I have a strange phenomenon in our mountain cabin, on the Italian alps: lightning strike on the nearby (not so near: < 2 miles) causes audible / visible sparks on: electric / fire wood water ...
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0answers
69 views

EMF - DC Permanent Magnet Motor

I am using FEMM to design a dc permanent magnet rotor. I am trying to calculate the EMF that is induced to the rotor. Since each coil has a different position, the induced emf will be different. In ...
2
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3answers
332 views

Circuit approximation of Induction in guitar pickups

I was trying to learn the way basic guitar circuits work, the other day, and I stumbled upon a thing that I couldn't fully understand. According to this site, a simple guitar circuit can be made as ...
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1answer
35 views

What is the canonical form based on sinus of the autoinduced EMF in a coil

I am stuck with this exercise as I can't really find the expressions I need in order to solve this. Please help me & guide me theoretically, so I can finish this. Deduce the canonical form based ...
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1answer
50 views

Using 2 Tank Circuits to Determine the Position/Direction of a Wire

I am building a robot that uses 2 LC tank circuits with some gain and analog filtering to determine the position of a "Track Wire" that has an AC current of a specific frequency traveling vertically. ...
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2answers
683 views

Zener diode for solenoid

I am new in electronics and this is old subject but still. I started new Arduino project where I control 4 solenoid valves independently via Arduino 4 chanel 5 V Relay module. From the beginning I put ...
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1answer
144 views

A simple motor using Copper coil

This is a simple motor made with a magnet, a battery and a copper coil. I am curious to know how can it be explained using physics. I know that the copper is diamagnetic but not enough that it can ...
2
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1answer
183 views

Is there an actual need for the concepts “emf” and “back emf”?

Given a two-terminal element where you can only measure the voltage across terminals \$v(t)\$ [\$v_{ab}(t)\$] and the current \$i(t)\$ defined as entering the positive [a] terminal, there doesn't seem ...
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2answers
1k views

Thermal EMF (seebeck effect) on PCBs

Can poor PCB fabrication process / assembly, and the type of solder used cause thermal EMF (seebeck on PCB) problem? Is it affected by the type of the material used? For example, quality of plating, ...
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2answers
81 views

Using an analog temperature sensor near 3-phase 150V , 40A Motor Controller?

I'm looking for suggestions on what type of temperature sensor to use. I need to have it attached to the heat sync of a 150V, 40A 3-phase motor controller. The motor controller is in a enclosed space ...
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3answers
96 views

Question about coil emf

Hi I am a Korean student studying physics. Recently I was solving a physics problem about coil emf and I have a question. As you see in this circuit and the graph, when you close the switch the emf ...
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1answer
136 views

Question about Stepper Motors

I have a need to sometimes manually turn the lead screw on a stepper motor controlled CNC system (which I have not purchased yet). So IF I put a switch in the wires of the stepper motor and open the ...
2
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2answers
1k views

Relating DC motor with the Fleming right hand rule

I am studying DC motors and I know that what the direction of the rotation will be given by the left hand rule. If I compare the right and left hand rule, if I point the thumb and the first finger ...
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3answers
677 views

AC Circuit Having Only Capacitor

In my book, it is written that at any instant, PD across the Capacitor Plates = Applied EMF ---------(1) Assuming that it's a pure Capacitor of Capacitance C, I think if Voltage across Capacitor ...
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3answers
1k views

basic differences between voltage and emf?

what are the basic diff between the emf and voltage? is it that the voltage of a battery is emf and voltage is potential diff between two points,and also please give me some suggestion how to take ...
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3answers
2k views

What properties of metal makes make them suitable as EMF shielding material?

What properties of metals make them effective at shielding against EMF, and which metals are typically used? How does Aluminium, Steel, Copper and Lead compare?
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5answers
3k views

“Where” does back EMF appear in motor?

I've been trying to understand EMF, specifically back EMF in electrical motors, such as for example a setup like this: Say that we apply a voltage to the brushes. I understand that once the rotation ...
2
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2answers
88 views

Why is the outlet ground voltage different from grounded Macbook voltage

Measuring on A/C with a digital voltmeter: Measurement One I connect the ground lead to earth on a 3-prong plug, And hold the other lead with my thumb and forefinger, And observe that I register ...
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2answers
160 views

Electromotive force of a battery

The definitions of electromotive force of a cell that i have studied include: 1.When no current is drawn from a cell,i.e., when the cell is in open circuit, then potential difference between the ...
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1answer
75 views

Measure EMF Radiation from High Altitude Balloon

I'm participating in a competition which involves building a probe that will be attached to a weather balloon. It will probably rise up to an altitude of 30 km. I am thinking of measuring EMF ...
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1answer
892 views

RC filter in a simple PWM motor drive

I was looking at a friend's design for a simple PWM motor drive and I'm trying to figure out what's the use of some components. Here's the schematic: I get what most parts are for: power supply fuse ...
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3answers
88 views

DC Motor EMF re-usage?

I have 2 questions: 1 - The Brushed DC motor variety has a type when one turns the shaft manually it free runs with no friction or resistance at all, and then another type which feels like a mild ...