Questions tagged [back-emf]

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Feedback from a 100 W laser power supply

I built a 100 W laser cutter from scratch using a controller from a small laser cutter I had before (Open Builds Blackbox 4x). It worked with no problems, but I'm going from a 7 W laser to a 100 W ...
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Why does slow decay decelerate a motor faster than fast decay does in a H Bridge?

I understand how the terms slow decay and fast decay relate to current rather than angular acceleration, but I am currently having a lot of trouble understanding why slow decay decelerates the motor ...
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4 answers
1k views

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 ...
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What could be the cause of a limit in the voltage supplied to a capacitor?

Recently I built a very basic 2-stage coil gun for a school project. Each coil was powered by an electrolytic capacitor. In order to charge the capacitor, the coil connected to an IGBT (insulated-gate ...
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How to calculate torque constant and back EMF constant of a BLDC motor?

I have a BLDC motor to run for a fan. The parameters are as follows: Electrical frequency measured: 61.936 Hz Pole pairs: 8 Line voltage measured: 70.365 V RMS Line voltage peak: 99.51113732 ...
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1 answer
104 views

Confused about back EMF protection in maglock circuit

Straight upfront...electrical engineering is not my forte. However, I am trying to help a client with a particular issue and I'm hoping this community can provide some invaluable insight. They have a ...
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4 votes
3 answers
1k views

Weird speed issues with brushed DC motors in parallel?

So I have a simple system where I want to run eight large DC brushed motors (for wheels) in parallel, which should give them all the same voltage, and they should independently change rpm depending on ...
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1 answer
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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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4 answers
653 views

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 &...
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Why is one of my MCU (Bluepill) digital pins broken/not working?

Sorry for the noob question. I'm working on an ESC circuit, first I want to work on a very simple ESC circuit without Back-EMF detection like in this video https://www.youtube.com/watch?v=kAaknXe_JSk&...
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1 answer
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Why is a DC motor's back EMF constant for a given RPM

I was trying to prove this mathematically from the definition of EMF being the change in magnetic flux over time. Starting with $$ \Phi=BAcos(\theta)$$ Then differentiate w.r.t time (assuming B field ...
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3 answers
152 views

Constant Voltage Applied to Inductor

I'm seeking clarity on understanding what happens when a constant voltage is applied to an inductor. I gave this explanation in another thread and it was regarded as wholly misguided in the following ...
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2 answers
126 views

Inductor Back EMF Direction Relative to Changing Current

I have spent a lot of time thinking about Faraday's law and common explanation as given on wikipedia does not sit well with me. I may be confused. My concern is entirely with the wording of this ...
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1 answer
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Will reducing the back EMF on a running motor increase its torque? [closed]

Will placing a diode across a DC motor after it has started running reduce or even remove the back EMF to allow the motor to achieve higher torque at higher RPMs? I know the motor will begin heating, ...
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1 answer
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Rated drain to source voltage of a power MOSFET sustaining back EMF of solenoid

I have an H-bridge that is using 4 n-channel MOSFETs with max rating of 500 V 100 A drain to source driving a large inductor/actuator reliably. I'd like to find a cheaper MOSFET since the 100 A is ...
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3 answers
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H-Bridge Problem: Vgs dropping with increased motor speed

I am developing an H-bridge for use with 48VDC brushed motors. The bridge is implemented with discrete DPAK N-channel MOSFET transistors driven by an HIP4081AIBZ. I have not yet fitted RC snubbers ...
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1 answer
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Can back EMF from a solenoid trip a circuit breaker?

I am working on an ignition circuit right now in a Cessna 172, the issue is that when the ignition switch is turned to engage the starter, the circuit breaker supplying power from the bus through the ...
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3 votes
3 answers
565 views

Gate driver burning and snubber design for half-bridge transformer driver

IR2113 floating channel digital-input half-bridge transformer driver Dead time is properly set Channel supply VPP 20-60 V, gate bias supply 15 V Operation frequency 15-100 kHz, operation mode PWM or ...
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2 answers
432 views

Understanding back EMF measurement in brushed DC motors

I have been doing some preliminary research for a project and am trying to understand how sensor-less speed control of brushed DC motors can be done by inspecting the back EMF. Where I am at with my ...
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What are the effects of self-inductance in a DC armature?

So, I just stopped to think that, for the armature coils, the current passing through them varies with time due to commutation. The voltage applied to different conductors in the armature varies ...
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3 answers
67 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 ...
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1 vote
1 answer
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How can I reduce the power dissipated across this MOSFET without affecting avalanche?

previous and very relevant question here. I want to reduce or remove entirely the heatsink that is attached to my switching MOSFET. It heats up due to the back-EMF generated by the large inductor that ...
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Is it possible to regulate the amount of counter torque in a generator?

I have a question for a machine I am working on, The machine is used to pre-tension steel wire ropes for maritime uses, the wire rope sits on a drum with a 2m diameter. The tension has to be ...
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2 answers
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Current Voltage Curve of a motor

I have a question that has been bugging me for a while. I have an 48 W EC-fan with nomimal Voltage 24 V (voltage range 16-30V). I wanted to plot the current-voltage line of the motor so I thought of ...
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2 answers
387 views

Grounding Ignition Coil Using IGBT ckt....Not Working + Can't Understand?

I am a hobbyst, and recently been working on a small project of my own, Creating a rev limiter of my own. Following is my circuit which will explain a lot about what I am trying to do. First of all ...
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Is regenerative braking always suitable for an EV regardless of battery chemistry?

I've been doing a lot of reading on different motion control approaches both for hardwire industrial motion, as well as EV applications. While I've skimmed a few IEEE papers that sought to study the ...
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BLDC back-emf measurement

I am trying to make a sensorless control system for a BLDC, using "Trapezoidal control", see here: https://www.ti.com/lit/an/sprabz3/sprabz3.pdf?ts=1610192643720&ref_url=https%253A%252F%...
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1 answer
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BLDC Y-shaped motor with Hall sensors generating different combination of back EMF on windings with different direction?

I have a BLDC Y-shaped motor. I connected the Hall sensors and winding to a logic analyzer to see the combination of back EMF on thr windings. My intention is to eventually create a commutation table ...
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2 answers
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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 \...
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158 views

Back EMF protection of a bi-directional inductive load

I have been researching this subject for some time now and I found three ways to deal with this issue but I can't make up my mind on which one is the best for my application. I have a high torque 12V ...
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2 votes
4 answers
402 views

Can measuring back EMF spikes damage the oscilloscope?

I want to measure the voltage across an inductor as soon as I disconnect one of its terminals to visualize how back EMF changes with and without a fly-back diode. From videos on Youtube: https://www....
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AGC (automatic gain control) circuit for brushless phase measurement?

Intro: I am projecting a Brushless motor driver which relevant specs here are basically: use with 6v to 60v. To make it work the circuit's microcontroller needs to analyze the signal that comes from ...
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1 answer
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Differentiating Equation containing modulo operation

(DC motor Single Loop setup) I have the equation for flux containing mod operation of the angle as an independent variable. the graph: The textbook then directly derives the derivative of flux for ...
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1 vote
1 answer
344 views

Back EMF in sensored BLDC motor

In hall sensor based BLDC motor, motor is controlled by feedback of hall sensor. At a time only 2 stator pole pairs will be excited and 3rd pair will be ideal. So in third pair Back EMF will be ...
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1 vote
0 answers
222 views

BLDC motor simulation

I would like to simulate BLDC motor in programming language other than Matlab or Simulink, but have problem with several equations and inverter output. BLDC motor scheme is following: After searching ...
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2 answers
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What happens if the BEMF generated while going downhill is higher than the supposed applied voltage to the motor terminal by the inverter?

If a brushless DC (BLDC) motor is moving fast ( the case of ebike going downhill,) what happens if the back EMF (BEMF) generated while going downhill is higher than the supposed applied voltage to the ...
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1 answer
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Blackout Protection for H Bridge with Synchronous Rectification

I'm designing an H-bridge motor controller with synchronous rectification similar to the Ti Stellaris RDK-BDC24 link here. Synchronous rectification has the promise of handling the back-emf from a ...
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2 answers
893 views

Relationship between torque and back-EMF voltage | BLDC motor modeling

I want to simulate an BLDC motor, so I am studying corresponding mathematical model. My problem is that I am little bit confused by the torque equation. \$e_a\$, \$e_b\$, \$e_c\$ - Back-EMF voltages (...
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1 vote
1 answer
187 views

Is it must to have freewheeling diodes for ULN200x when used with dc motor?

I need to eliminate the MOSFET drive circuit from my PCB by replacing uln2004 or uln2803, should I still keep the back EMF diode across the dc motor? motor supply 5V current 70mA
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  • 497
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2 answers
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Using back emf for charging window-blind controller battery

Let me start: I have no clue of electric engineering. However, I built an automated window blind controlled by my home automation. It consists of a stepper motor, motor controller board, an ESP8266 ...
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2 votes
2 answers
590 views

Operation of Induction Motors and their Back EMF [duplicate]

I'm trying to reconcile the physical steps that go into the operation of an AC induction motor. Looking online, I either find broad and general explanations that I already know and understand, or very ...
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2 votes
8 answers
819 views

Inductor with AC source

When an AC source is connected with an inductor we have a continuous change in voltage and current across the inductor. According to Farady and Lenz law we will get an equal and opposite voltage ...
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1 vote
2 answers
205 views

Why does the measured back-emf decrease when R is shorted in this circuit?

In the following circuit I move an iron rod back and forth inside a solenoid (represented by Rsol and Lsol) and measure voltage fluctuations across the terminals. I do this under two scenarios: with ...
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1 vote
1 answer
739 views

Back EMF protection on bidirectional DC motor controller

I am trying to design a circuit using the TB67H450FNG,EL motor driver ic to control a 6v dc motor that will be run bidirecitonal and run in 1 second pulses. due to being bi directional I am unsure of ...
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3 votes
1 answer
257 views

Solenoid and mechanical damping, options for ways to minimize

I have an iron rod supported by a coil spring that vibrates vertically within a solenoid coil. The solenoid has a 5 ohm dc resistance. There is no physical contact between the coil and rod. As I ...
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1 answer
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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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1 vote
1 answer
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Back EMF in a transformer with an external power source to the secondary coil

When discussing an ideal transformer, Wikipedia says “varying flux at the secondary winding induces a varying electromotive force (EMF, voltage) in the secondary winding due to electromagnetic ...
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1 answer
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How do we reduce or nullify the back current from the wheel motors of the modern electric vehicles?

As expected, this EMF opposes the voltage of the source that created it; that is, the motor becomes a generator as soon as it is turned on, and the opposing (or counter, or back) EMF will increase ...
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1 answer
1k 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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2 votes
2 answers
301 views

Phase difference between resistor and inductor voltage in an RL AC circuit

In my textbook, it is given that \$\mathcal {E} = -L\frac{\Delta I}{\Delta t}\$. The graph of resistor voltage (\$V_R\$) and inductor voltage (\$V_L\$) in a series RL AC circuit is given similar to ...
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