# Tagged Questions

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32 views

### Noise suppression on relay Coil

Attached circuit is part of my design. My design use 230VAc line , and SMPS convert it to 3.3V control voltage. In test code we toggle the relay coil at every 1 sec,(relay contact was not connected ...
647 views

### 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://...
87 views

### Calculate Back EMF from Torque Constant

I have a DC motor with a torque constant of 1.05 mNm/A. How do I calculate back emf constant from torque constant (mNm/A)? I have information that is in the maxon catalog.(DCX 10 S metal brush ...
58 views

### Large 3D Printer Heated Bed - High Current Resistive Load - Preventing Back EMF

I have been trying to solve a rather troublesome issue for some time now, and will try to provide as much information as possible. In short, I am powering a 3D Printer and its 12"x12" heated bed by ...
64 views

### Demonstrating back EMF on an inductor in LTSpice

I'm trying to demonstrate back EMF on an inductor in LTSPice with this model: https://dl.dropboxusercontent.com/u/16979265/Draft2.asc I'm expecting the voltage on the inductor to have a negative ...
231 views

### Back EMF of DC motor - protection

Here is schematic that provides polarity inversion and switch off motor if it reaches one of its two end positions: SW1 is On-Off-On DPDT switch with the center position Off. SW 2 and SW 3 are ...
89 views

### A way to cancel/or harness back-emf?

In systems where there is back-emf induced to oppose the applied voltage, or to change it in cases of power converters, is there a direct way to cancel back-emf or harness it back? The simplest way ...
205 views

### Back EMF of an inductor in a DC circuit?

Will an inductor in a DC circuit act as a voltage source and oppose the applied current creating the magnetic field? Or is it because of the steady state direct current there is no change in I there ...
176 views

### How to interpret the equation $e=K_e.\omega_m$ in a BLDC context?

After researching a while on the subject, I noticed that several sources state that the back-emf constant of a BLDC motor satisfies the following equation: $$e = K_e.\omega_m$$ where: $e$ - ...
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### DC Motor: Difference between E and k?

I'm studying for an exam, and have come across a question I don't. really understand The question gives us a back-emf constant and asks for a rated back-emf. Now I know that the back-emf constant is ...
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### Does inductive back-EMF create significant radiated emissions on long load wires?

So, lets say you have a mechanical switch connecting an AC (mains) source to a small inductive load (say, a single speed ceiling fan) via a long wire (1000' of NM). When the switch is turned off, how ...
4k views

### How does inductor store energy?

I know that the capacitors store energy by accumulating charges at their plates, similarly people say that inductor stores energy in magnetic field. I cannot understand this statement. I can't figure ...
128 views

### Short-circuit primary side of a transformer to collect all the spikes at the secondary

Abruptly detaching a power source from a coil produces a back-emf: this is a well known fact. What I would like to achieve, in my experimentation, is to convey ALL the collapsing magnetic field to ...
7k views

### Back Emf of dc motor

I couldn't find the explanation for this query of mine. Why back emf in dc motor is nearly equal to the applied voltage on no-load? I tried to search on the internet but all in vain.
180 views

### Will back emf damage a lithium ion battery?

I am prototyping a battery-operated toy containing a couple of motors - these motors are driven by a pair of h-bridges which are controlled by a micro controller. I'm running this whole thing from a ...
810 views

### H-Bridge flyback diode selection?

I am wanting to make a motor driver using a SN754410 Quadruple Half-H Driver IC. The SN754410 requires external flyback diodes. Here is an example circuit: My question is, how do I choose which ...
4k views

### How to calculate the Back-EMF energy on an Inductor?

The Back-EMF generated by an inductor in Volts is: $V = -L\dfrac{di}{dt}$ Where $L$ is the self-inductance and $\dfrac{di}{dt}$ the rate of current change. Now, let's say I want to store those ...
257 views

### 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 ...
1k views

### Why do AC motors have various back EMF shapes?

I just saw in one of the threads that apparently, a permanent magnet synchronous motor and a brushless DC motor have different back EMF shapes. But why? I thought those two were exactly the same in ...
316 views

### What is the path taken by the back emf current?

! Where will the current flow through? If ON current(back emf "current") will loop through A B and C If OFF current will(back emf "current") loop through x y and z
149 views

### Calculating DC Brushless Motor Position

I am using a brush-less motor in one of my projects and I need a decent method of sensing the motor position so I know what coils to turn on and off. I looked a bit into sensing Back-EMF, but I did ...
406 views

### AVR main loop interference with relay

I'm working on a test program on an ATmega164A that toggles a 12V relay on and off (with no load) through a ULN2003A. For my test program, I'm toggling the relay at 100ms. I've got an IN4001 diode ...
518 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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### EMF due to inductance?

In a DC circuit, current starts to flow, and some time is needed for current to stabilize based on the time constant, there is EMF induced due to current changing over time. As soon as the current ...
210 views

### motor Back EMF phase differences

I am reading though a product manual for an amplifier that I am working with. It says that if you view the motor Back-EMF while it is disconnected from the controller and spun in a clockwise direction ...
25k views

### 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 ...
34k views

### 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 ...
1k views

### How to protect the switching device from back EMF when we connect the inductive load

Why the snubber circuit is necessary for inductive load and not for resistive load. What is the back EMF?. When we connect the inductive load how the back emf affect the switching device. how to ...
1k views

### BLDC speed and position from back-emf

I'm trying to make my own sensorless speed controller and I need to know the speed and the position. What are the basic techniques used to determine the speed and position of a BLDC motor from the ...
779 views

### Filtering Reverse voltage from a coil

I am working on a interface between an Arduino microprocessor and a old electromechanical pinball machine to track the scoring and light up some LED's based upon that. I made a circuit diagram... or ...
367 views

### Back EMF with Octal Driver / inverter

I have a project which I am using an octal driver/inverter (DARLINGTON ARRAYS) to allow a micro controller to control 4 electromechanical relays. I have been experiencing relay failure and driver/...
5k views

### 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 ...
14k views

### 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 ...
483 views

### Why do some transformers hum less or not at all when lightly loaded?

It can be observed that large power transformers hum more under load. For example, when some devices are powered up, there is brief "twang" sound: a loud hum that quickly decays as the filter ...
420 views

### Inductance of a HDD BLDC Motor Phase

So I have set up a little experiment which involves a HDD BLDC Motor, a scope and a multimeter. Pretty simple, I know. Is it possible to determine the inductance of a phase by the voltage the phase ...