Electrical Engineering Stack Exchange
Electrical Engineering Stack Exchange

Questions tagged [back-emf]

167 questions
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4 answers

How to choose a flyback diode for a relay?

A diode is put in parallel with a relay coil (with opposite polarity) to prevent damage to other components when the relay is turned off. Here's an example schematic I found online: I'm planning on using a relay with a coil voltage of 5V and…
Nate
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How does an inductor store energy?

I know that the capacitors store energy by accumulating charges at their plates, similarly people say that an inductor stores energy in its magnetic field. I cannot understand this statement. I can't figure out how an inductor stores energy in its…
Andrew Flemming
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How can I measure back-EMF to infer the speed of a DC motor?

I'm interested in measuring the back-EMF of a motor to determine a motor's speed because it's cheap and requires no additional mechanical parts. How can I measure the back-EMF when I'm driving the motor?
Phil Frost
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Why should I worry about a motor causing my supply voltage to shoot up when the back-EMF can't exceed the supply voltage?

I have heard people say that in motor control circuits, one must take precautions to keep the motor from feeding back into the power supply, causing the supply voltage to rise, consequently breaking things. But how can this be? Unless some external…
Phil Frost
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Do solenoids exhibit back EMF like motors?

I just purchased some pinball machine solenoids and was experimenting with them; DC resistance is about 30 ohm, they actuate at about 30 volts, and they hold at about 6. I tried controlling them with 10A relays and found that the a relay sometimes…
supercat
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Torque relationship to speed in a DC motor

I have a conceptual doubt about torque-speed relation in a DC motors. It's probably a gap in my thinking but I'm posting this question anyway. Torque and speed in a DC motor are said to be inversely proportional. But doesn't an increase in torque…
Vineet Kaushik
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Electrical behavior of holding magnets when you pull them apart

I'm going to buy a holding electromagnet and a strike plate to hold some things, and I want to design my circuit (arduino-controlled) not to fry like bacon. I'm aware that since a holding magnet is an inductor, I should use a flyback diode and…
Ed Krohne
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Switching inductive loads without flyback diodes

I came across a commercial design which switches coils using N-channel MOSFETs (two in one MOSFET in a SOIC package). It surprised me a bit that there were no flyback diodes in parallel to the coils. I talked to the designer, and he said that the…
bask185
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Inferring back emf from oscilloscope

I have this stepper motor with unknown back EMF / RPM. There are 200 steps/rev (i.e. 1.8deg step angle), and 8mH "phase inductance", but I'm not sure if that's enough to calculate back EMF. I hooked up one of the parallel windings from each phase…
abc
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Do I need back EMF protection for a small brushless cooling fan?

I am designing a PCB, and I want to add cooling to the project. To accomplish this I have added a connector for small (40mm x 40mm) brushless cooling fan that will draw off an existing 12V supply from a DC/DC SMPS. Do I need to add any back EMF…
flimsy
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Fast coil decay

I have circuit where I need to fire electromagnetic actuator fast. If I need to go faster strike I need to increase voltage. But what about freewheeling inductor energy. In circuit A the energy is "shorted" with diode and current decay is pretty…
eSlavko
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"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 gets going, a current will be induced by the…
Daniel Nilsson
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Using a large resistor instead of a flyback diode

In a video lecture a professor is explaining how to prevent an electric arc caused by the switching operation in an RL circuit. Here is the section (at around 18:26) where he explains it: https://youtu.be/FYDLG_A2P1I?t=1106 I know that a flyback…
user16307
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Won't the back EMF from the relays hurt the LEDs?

In this ULN2803 based relay driver schematic, why won't the back-EMF from the relays hurt the relay status LEDs?
VAN
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4-20mA ADC, HV DC measurement & DC/DC PSUs schematic validation

Hello i am designing a small Li-ion battery charger based on an custom generator which produces 36v DC output and i have designed a PCB that controls the whole procedure and logs the measured data to an SD card using an esp32. I also have a 4-20mA…
geocheats2
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