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0
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2answers
55 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 ...
0
votes
1answer
49 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 ...
0
votes
0answers
45 views

What is wrong with this brushless dc motor commutation

I am trying to understand the working of brushless dc motor. Here is the setup I am referring to: Here is the commutation sequence: And, here is the waveform I get: Many application notes ...
0
votes
0answers
28 views

Permanent magnet DC motor armature current

I'm trying to model a permanent magnet DC motor run off a non ideal voltage source and I just want someone to check my logic and maths. The armature current used in several equations would be found ...
0
votes
3answers
105 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 ...
3
votes
1answer
132 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\$ - ...
0
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2answers
71 views

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 ...
2
votes
1answer
80 views

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 ...
3
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4answers
2k 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 ...
0
votes
2answers
116 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 ...
2
votes
3answers
6k 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.
1
vote
2answers
127 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 ...
1
vote
2answers
525 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 ...
3
votes
2answers
2k 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 ...
7
votes
2answers
217 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 ...
0
votes
2answers
851 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 ...
0
votes
1answer
230 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
-1
votes
1answer
128 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 ...
1
vote
2answers
336 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 ...
3
votes
2answers
418 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, ...
0
votes
2answers
63 views

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 ...
1
vote
1answer
184 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 ...
15
votes
3answers
16k 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 ...
2
votes
5answers
27k 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 ...
-1
votes
1answer
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 ...
2
votes
1answer
829 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 ...
2
votes
2answers
695 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 ...
3
votes
3answers
344 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 ...
14
votes
3answers
4k 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 ...
19
votes
1answer
13k 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 ...
3
votes
1answer
447 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 ...
2
votes
1answer
392 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 ...
2
votes
1answer
5k views

What are the advantages and disadvantages of using signal diodes instead of resistors?

In the past to create voltage dividers or protect against back emf I have used resistors, but reading about signal diodes those situations are given as examples. I can't really comment on the inductor ...
6
votes
2answers
3k views

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 ...