Back emf Definition and 76 Threads

Help me. I want to use diode for back E.M.F protection.Please help me to select diode which is suitable ,like short circuit recovery time is 9 nano second and ifsm should be 30-90 amp. please also send me surge suppression protection circuit or surge protection device.

i am wondering why in some problem they are regarding back emf of a motor as a constant value that characterizes the motor although current is sometimes variable? i guess the reason is for simplifying the problem, what do u think? can this occur in reality? thanks for helping.

while solving an exercise, i have found that they are considering the back emf of a motor constant although the current is not constant? how comes that? shouldn't it be variable as current varies? they are considering that as E=Ir+E' where E' and r are constants?

1-this is what is written in my book: E= Ir+E' where E' is the back emf, r and E' are constants P(mechanical)=E'*I an electrical motor functions only if the generator connected across its terminals delivers a positive potential difference that exceeds its back emf. So my question is, why are...

Why the back emf of the primary coil always equal to the supply voltage but no greater than supply voltage(because of the large number of coil turns) when no loaded?Or it is a kind of dynamic equilibrium?If yes,how it reach equilibrium? Thank you.

Hey, I'm trying to find a suitable diode to protect against some back EMF in my circuit, but I don't know much about them and so I'm having a really hard time finding one. If someone could look at what i need and then possibly send me a link i'd be so grateful. Requirements: back EMF = 137mV...

Homework Statement Describe with the aid of diagrams how the back emf and induced current vary in a single-coil DC motor over one full rotation of the armature. Give particular attention to the rate of change of flux in the coil and to the direction(s) of the DC and induced current...

Will u tell me what is back emf?

I have always wondered if anyone has ever developed an understanding of why Back EMF happens? All I know is it happens when the the field inside of a transformer collapses at some low frequency during the collapse of the coil when the transistor shuts off creates a huge spike hundreds of...

I searched practically all of the nets and webs and still my questions are unanswered, so I decided to consult y'all. I have previously asked you guys about diode sizing to prevent back emf on a relay and you were very helpful. I am once again calling upon your help. I have some relays in my...

Hi Experts,o:) I am trying to reverse the direction of a spinning dc motor (around 30watts) but not sure how this should be done. I have a logic for the switching of the power polarity to the motor but am worried if back emf would be an issue when the motor is spinning and the polarity...

1. Is there an electric motor of any type that does not produce back emf. 2. Is it possible to design a motor that does not generate back emf. 3.What are the demerits of designing a motor that do not produce back emf. 4. What are the merits of having a motor that generate back emf. 5...

What causes the back emf in motors (brushless DC motors to be exact). First thing is the rotating magnetic field of the rotor, which cuts the stator coils inducing an emf in the opposite direction. This would increase as speed increases. This is just a generator. Second, what about self...

What is the difference between an induced emf and a back emf? (i) i thought they were the same thing? . . .. .

A motor with a brush-and-commutator arrangement has a circular coil with radius 2.5 cm and 150 turns of wire. The magnetic field has magnitude 0.06 T and the coil rotates at 440 rev/min.What is the average back emf? i have tried this Flux=Magnetix Field*Area Flux=0.06*pi*r^2 Here...

So here is the circuit I came up with to represent back emf in a DC motor with rotational inertia. When current is applied to the motor it spins. When it rotates, the motor acts as a generator and creates a voltage (back emf) as shown (sorry for the incorrect notation, I don't know the...

How back emf helps in energy conversion in a motor? hello, I am an engineering student and during the past few days i was searching on the net to clarify my doubts on "motors".So i came across an article and on reading one part of it a doubt arosed in my mind. Q1) "To take a practical...

If i have a series DC motor and at say X rpm it has a back emf of 11.5v and supply voltage of 12v and i increased the supply voltage (keeping rpm the same) would the back emf stay the same? and if not would the diffrence between back emf and supply increase? Thank you.

Ex:At home, you plug an electric drill into an electrical outlet and turn it on. At the moment you turn on the drill, the lights in the room(wired in parallel to the drill) flicker and dim briefly, but then return to normal after a moment. notice that the example is wired in parallel, but in...

Say you had a circuit with a battery and a loop of wire somewhere in the middle of the circuit. The loop of wire is positioned so that it is free to rotate in a uniform magnetic field, and since a current is running through it, a torque will be supplied by the magnetic force allowing it to...

1)When the current through the coil of a motor flows it cases the coil to spin. 2)The spinning motion causes the wires in the coil to cut through the magnetic field. 3)The current induced (back EMF) in the wires by this spinning motion opposes the change that causes it. (Lenz's Law)...

Homework Statement An automobile starter motor draws a current of 1.9 A from a 5.5 V battery when operating at normal speed. A broken pulley locks the armature in position, and the current increases to 8.6 A. What was the back emf of the motor when operating normally? Answer in units of...

Hello, I was just wondering if someone could explain to me why there is a huge spike of current & voltage in a wire when you close and open an electrical circuit. I've noticed these 'kicks' or 'spikes' in wires when runing square waves through them (doesn't seem to occur with sine waves). I...

A motor is designed to operate on 117 V and draws a current of 12.2 A when it first starts up. At its normal operating speed, the motor draws a current of 2.30 A. Obtain (a) the resistance of the armature coil, (b) the back emf developed at normal speed, and (c) the current drawn by the motor at...

hello all!:smile: I have a question about electromagnetism. The question is "Can the back emf ever be greater than the battery emf in RL circuit?" can someone explain this one for me please?

Hey guys my teacher asked us to define back EMF in a motor, I am having a bit of touble understanding all of this can anyone explain it a little. Thanks