Questions tagged [emf]

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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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8 votes
3 answers
1k 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 ...
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8 votes
4 answers
793 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 ...
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7 votes
5 answers
5k 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 ...
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7 votes
3 answers
29k views

What are the consequences of connecting two motors in parallel?

I am using two DC motors rated at 36V and maximum current draw of 5A. To reduce the number of motor-controllers, I am planning to connect them in parallel. The two motors are required to run at the ...
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6 votes
3 answers
868 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 ...
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6 votes
3 answers
19k views

How do DC motors work with respect to current, and what consequence is the current through them?

Motors in general have always been a difficult subject that I cannot fully wrap my head around. Considering DC motors, what determines the rate at which the motor spins? It was my understanding that ...
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6 votes
1 answer
270 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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5 votes
1 answer
387 views

Ideal Op Amp and its Input Voltage

In an ideal operational amplifier, I understand that the inputs draw no current (due to infinite impedance). So, in the example below, the value of Vp would equal the value of the EMF (because there ...
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  • 116
4 votes
2 answers
2k views

Harvesting Back EMF Possible?

Let me start by saying that I am not talking about the free energy or "overunity" idea of back EMF. When searching around for information I can only seem to find information from free energy sites, ...
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4 votes
3 answers
3k 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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4 votes
2 answers
374 views

Detect multiple corn bags through wood with a sensor

I'm working on a project for school, and wondering what options I have for detecting the corn bags through a piece of wood. More specifically, we are creating an automated cornhole scorer. Sources ...
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3 votes
4 answers
2k views

Does free electrons from the conductor itself flow or electrons inside the battery flow?

I am new to electronics. I read electricity works this way: some atoms have more electrons than protons. These free electrons flow through a conductor such as a copper wire. However, to induce flow of ...
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3 votes
1 answer
214 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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  • 432
3 votes
2 answers
115 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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2 votes
2 answers
8k 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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  • 317
2 votes
3 answers
951 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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2 votes
4 answers
1k 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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2 votes
2 answers
168 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 ...
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2 votes
2 answers
250 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 ...
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2 votes
1 answer
88 views

Why does the emf depends on the material of the electrodes? Why is the emf independent of the distance between electrodes and amount of electrolyte?

Concise Physics mentions that: The emf (electromotive force)of a cell depends on 1) the material of the electrodes and 2)the electrolytes used in the cell.However it is independent of the a)the shape ...
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2 votes
2 answers
129 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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2 votes
1 answer
126 views

EMF in an Open Circuit?

Lets assume we have a wire passing a magnetic field, it is know that EMF is induced due to the magnetic field, what if the wire is not connected to a circuit what happens? Is there ay voltage in the ...
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  • 465
2 votes
2 answers
2k 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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  • 131
2 votes
2 answers
106 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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2 votes
2 answers
2k views

Can ground plane EMIT noise?

I have 3 separate grounds in my project: AGND - Analog ground is very quiet, very small relatively smooth currents PGND - Power ground used for power bypass caps and power supply related circuitry is ...
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  • 1,410
1 vote
2 answers
2k 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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  • 11
1 vote
4 answers
12k views

Reduce interference over 3.5 mm to cassette tape adapter

I have one of those cheap 3.5mm > cassette adapters, to use in my car. I've purchased high-end ones (around $40) and I've purchased cheaper ones like this ($20) but I always get static/feedback from ...
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  • 121
1 vote
3 answers
93 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 ...
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  • 11
1 vote
1 answer
3k views

Emf interference on arduino and breadboard , using 74HC595 shift register, how to prevent it?

I’m using a 74HC595 chip (shift register) NPX semiconductors, connected to and arduino board. Basically the shift register switches on and off 8 leds in sequence. Everything seem to be working, code ...
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  • 135
1 vote
1 answer
105 views

Back-EMF Concepts (Confusion)

I am trying to understand the current and EMF relationships in a brushless motor. Can someone tell me if this explanation is correct? Specifically, I'm interested in what is happening as the rotor ...
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  • 575
1 vote
1 answer
84 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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1 vote
2 answers
433 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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  • 487
1 vote
1 answer
2k views

Can I tell the voltage of High Power Transmission lines by its Type?

I am moving to Foster City, CA and am looking at an apartment about 550 feet from these power lines: https://www.google.com/maps/@37.562322,-122.27068,3a,75y,153.58h,99.44t/data=!3m6!1e1!3m4!...
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  • 113
1 vote
2 answers
346 views

Best way to convert a voltage output from a circuit into graph software

Looking to convert a voltage output from a circuit in order to show a voltage/time graph. From my knowledge I would have thought the best way to transmit the data would be to use the mic input on the ...
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1 vote
4 answers
171 views

Microcontroller 24V digital output

For a microcontroller generating a 20mA industrial digital output. What kind of setup is best? I'm considering: Microcontroller pin driving a low current N-FET to pull a 24V signal to ground. But ...
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  • 25
1 vote
4 answers
148 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 ...
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1 vote
1 answer
63 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 ...
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  • 217
1 vote
1 answer
426 views

Noise from stun-gun based butane torch ignition spark is locking up ATmega328 microcontroller

I have a stun gun (http://www.amazon.com/VIPERTEK-VTS-989-Heavy-Rechargeable-Flashlight/dp/B00FPE6UN2) which I am using to create a large 1/2" electrical arc through the air to remotely ignite a ...
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1 vote
1 answer
146 views

What electric field strength in the range 50MHz to 3.5GHz should be considered "natural"?

If we were to measure the electric field strength of the earth's surface in the range 50MHz to 3.5GHz (in the absence of any man-made transmitter), what value should be considered "natural"? The next ...
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  • 113
1 vote
2 answers
125 views

Magnetic field shielding for electronics?

I am looking at an issue where a PCB design that is powered by a couple of CR2032 batteries will shut off all of a sudden in the presence of strong magnetic fields (around 15-40mT). However, when the ...
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1 vote
1 answer
40 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. ...
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1 vote
1 answer
46 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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1 vote
1 answer
75 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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1 vote
1 answer
126 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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1 vote
1 answer
338 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 ...
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  • 133
1 vote
1 answer
578 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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  • 883
1 vote
2 answers
3k views

Induced EMF in a transformer

In a transformer a sinusoidally varying voltage is applied to the primary coil of the transformer which give rise to a time varying flux which induce another sinusoidally varying EMF in the primary ...
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1 vote
1 answer
76 views

Do external EMFs affect in some way a capacitor?

I Know that inducters are affected by external magnetic fields .The affect depends on the construction of the inducter . What I would like to know is how capacitors are affected by external ...
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1 vote
1 answer
96 views

Do short circuits between transformer windings cause noticeable change in EMF?

I am looking into developing a sensor system to be placed within a transformer. This sensor system in theory, should be able to detect any unprecedented change in EMF within the transformer enclosure. ...
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