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14 votes
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"Where" does back EMF appear in motor?

The back EMF is generated in the wire that makes up the coils of the motor. When a wire is swept sideways thru a magnetic field, a voltage is generated along the length of the wire. Spin the motor ...
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13 votes
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Why is the air gap between the stator and rotor on a motor kept as small as it is?

Air has a much higher reluctance (the magnetic equivalent of resistance) than the magnetic materials used in the motor. The smaller the air gap is, the lower that reluctance, and thus the higher the ...
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9 votes

Thermal EMF (seebeck effect) on PCBs

The Seebeck effect is always there, and has nothing to do with the quality of the PCB fabrication process. Copper is copper, and exhibits a certain Seebeck effect. Unless you have a very sensitive ...
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8 votes

Why the LED stays on all the time in this very simple circuit?

Why? What could be the cause of that? The 2N2222 collector leakage current is 10 nA. So, T1 might be presumed to deliver 10 nA to T2's base. This gets amplified by T2's beta (about 100) to 1 μA. That ...
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7 votes

What are the consequences of connecting two motors in parallel?

A simple PWM controller will cause each of two similar motors connected in parallel to run at approximately the same speed (with some minor change on each due to loading). That is because the ...
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7 votes

Thermal EMF (seebeck effect) on PCBs

Yes, and it can be an issue when trying to build metrology grade instruments. Typically you see this stuff sweated about by people like Keithly and Keysight when designing 7 digit volt meters where ...
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7 votes
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How should I understand back-EMF in an inductor?

UPDATE: I reran the simulation with a 10 µH inductor and got the following: which seems indicative of behaviour similar to reverse recovery in a diode, maybe the body diode itself, but I don't think ...
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6 votes

Measuring back EMF induced current with multimeter

I don't think you can make any kind of meaningful measurements of short events while using a multimeter. Multimeters react slowly. The resistance of the coil is of less importance than the impedance. ...
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5 votes
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Produce current

No. Your approach is not good. You are trying to create energy out of nothing. This is against the law (of conservation of energy). The flaw in this case is that you are only imagining the force ...
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5 votes
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Harvesting Back EMF Possible?

Normally, like you say, the little bit of energy saving isn't worth the complexity. But yes, this can be done. In fact, this is the basis for how boost converter and flyback power supplies work. In ...
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5 votes

Zener diode for solenoid

First place is to think about what an inductor (the solenoid) does: It opposes any change of current, by doing whatever is necessary to keep the current flowing, at the same A, and in the same ...
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4 votes
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Emf interference on arduino and breadboard , using 74HC595 shift register, how to prevent it?

This is either a decoupling problem, or an unconnected wire. As the commenters have said, you'll need to add some capacitors. Fit them as physically close as possible to the 74HC595's power pins (your ...
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4 votes

Are headphones with EMF measurement of 10,000 milligauss harmful to me?

The ability to measure something, with your phone app for instance, makes it far easier to worry about it. Consider the mass experiment that is being done now, has been ongoing for the past few ...
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4 votes

EMF - Dangerous uT levels?

You are about 5 orders of magnitude (100000 fold) below the fields used in an MRI machine. These are the ones they're quite happy to use to image healthy people. Contrast this with Xray machines, ...
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4 votes
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Mesh to block or reduce wireless cell signals

Mesh attenuates in the range 10dB to 50dB. For anything more than that you'd need sheets of 1mm to 2mm thick, made of copper or steel. It is not true that holes smaller than the wavelength block or ...
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4 votes
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Could the electromagnetic field (EMF) from a power station disrupt wireless signals?

Not generally. Power stations generate signals at 60 (50) Hz, while 'wireless' signals start from AM radio (~ 1 MHz) up to many GHz. A sensitive radio will have a front-end filter that prevents any 60 ...
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3 votes
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Reduce interference over 3.5 mm to cassette tape adapter

Looks like this will stay open, so: It sounds like you are getting RF interference from your cell phone. There's a few ways to go at it. Simplest and cleanest is to get a split ferrite bead, make a ...
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3 votes
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Can I tell the voltage of High Power Transmission lines by its Type?

You can determine the voltage imposed on the wires. This is done by looking at the insulators holding the wires off the tower. The more discs, the higher the voltage. Those look like pretty high ...
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  • 7,868
3 votes

Why isn't number of loops included in the EMF equation?

It is there, where you find it depends on how you define the flux. If you consider \$\phi\$ to be the flux through a single loop, then the definition of the EMF must be N times the single loop flux. ...
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3 votes

How do I reduce the Counter EMF?

Since it is a small motor and you are thinking of using an L293D you could use the chip to brake the motor before reversing it. If you disable the pair of half-bridges that is driving the motor it ...
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3 votes

Safety advice for best EMF detector and body shielding for UHF RFID reader

From the Wikipedia dBm article, there is a table with some examples of devices with different power levels: 33 dBm: Maximum output from a UMTS/3G mobile phone (Power class 1 mobiles) ...
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3 votes
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Best way to convert a voltage output from a circuit into graph software

The line-in and microphone inputs certainly can be used as a recording interface to the computer. The only difference physically between the line-in and mic inputs is their sensitivity; line-in can ...
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  • 12k
3 votes

Electromotive force of a battery

Think of a battery like this: V1 is the voltage produced by the chemical reaction in the battery. This is the EMF you are asking about. However, real batteries have this annoying problem of some ...
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3 votes

"Where" does back EMF appear in motor?

You can simplify things by removing the battery from that diagram, and turning the motor by hand, as a generator. As the armature turns, the wires cut through the magnetic field, and a voltage is ...
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  • 142k
3 votes

"Where" does back EMF appear in motor?

Think of it like a generator; you spin the rotor and an output voltage is produced. This voltage is in series with the rotor coil. It makes no difference if instead of manually spinning the motor you ...
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  • 384k
3 votes

AC Circuit Having Only Capacitor

Current in the capacitor is proportional the rate of voltage change across it (proportional to how quickly the voltage across the capacitor is changing). The faster the voltage change (frequency of an ...
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  • 12.3k
3 votes

Question about Stepper Motors

Yes, you can do that, but then the control logic will lose track of the actual position of the motor. It would be better to provide manual "jog" inputs to the controller so that you can make the ...
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  • 165k
3 votes

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

With two identical coils wound around a magnetic core when you apply a voltage to one coil, the same voltage appears across the terminal of the other coil. This is because the primary voltage sets up ...
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  • 384k
3 votes

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

Short answer, lightning carries so much energy in the form of electromagnetic waves, it can create current in objects a few km's away. Lightning can create electric fields that are more than 100kV/m ...
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