Back EMF

[PoorFish]

Greetings Folks

Can anyone give a nice and simple explanation of this baby!!

Thanks in advance

P

 

[The Godfather]

Usually from a DC supply across a coil or a relay, when the supply is broken.

The emf is dependent on the Inductance of the coil, the Voltage may well exceed the incoming voltage that was applied.

(Back-EMF is the electric potential difference that opposes the current that induces it. )

Don

 

[M107]

Back emf (if the old college notes are right) is an induced voltage in a circuit/coil, that opposes the applied voltage.

Such as that produced in the armature of a DC motor as the armature rotates & cuts the magnetic field of flux.

 

[M107]

Took to long to dig out the old notes:_|

 

[The Godfather]

The back emf, is often a problem in electronic circuits.

A diode is usually fitted across the coil to absorb the voltage.

The Godfather

 

[PoorFish]

Thanks for swift responses

So is back EMF just a given fact that happens in coils

 

[The Godfather]

Thanks for swift responsesSo is back EMF just a given fact that happens in coils

In a word yes.

Don

 

[PoorFish]

So shall I just accept that and stop doing my head in.....

or to put it another way

do I really need to understand this to any further depths!!!!

 

[The Godfather]

So shall I just accept that and stop doing my head in.....or to put it another way

do I really need to understand this to any further depths!!!!

You do need to understand this, because the back emf is (sometimes) destructive to the circuit that drives it.

(unless measure are taken to suppress it)

Don

 

[PoorFish]

So I maybe jumping slightly ahead of myself but from your earlier response you mentioned diodes regulating the back EMF when attached to the coil....I imagine this is something that I will come across as my course will progress.

one other point though, i

I thought that the back EMF would work against the supply EMF and therefore the EMF/voltage total would be reduced

 

[The Godfather]

So I maybe jumping slightly ahead of myself but from your earlier response you mentioned diodes regulating the back EMF when attached to the coil....I imagine this is something that I will come across as my course will progress.one other point though, i

I thought that the back EMF would work against the supply EMF and therefore the EMF/voltage total would be reduced

In a AC Motor/Generator.

Sorry PF, my references where aimed at the DC issues (a relay for example).

regards

The Godfather

 

[SPECIAL LOCATION]

Dunno if this helps at all...

Counter-electromotive forceFrom Wikipedia, the free encyclopedia

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The counter-electromotive force (abbreviated counter emf, or CEMF ) [1] is the voltage, or electromotive force, that pushes against the current which induces it. CEMF is caused by a changing electromagnetic field. It is represented by Lenz's Law of electromagnetism. Back electromotive force is a voltage that occurs in electric motors where there is relative motion between the armature of the motor and the external magnetic field. One practical application is to use this phenomenon to indirectly measure motor speed and position [2]. Counter emf is a voltage developed in an inductor network by a pulsating current or an alternating current [1]. The voltage's polarity is at every moment the reverse of the input voltage [1][3].

In a generator using a rotating armature and, in the presence of a magnetic flux, the conductors cut the magnetic field lines as they rotate. The changing field strength produces a voltage in the coil; the motor is acting like a generator.. (Faraday's law of induction.) This voltage opposes the original applied voltage; therefore, it is called "counter-electromotive force". (by Lenz's law.) With a lower overall voltage across the armature, the current flowing into the motor coils is reduced. [4]

[edit] Efficiency

If it is assumed that a motor is 100% efficient with no friction or windage losses, the speed of the armature will increase until the back electromotive force is equal to the applied electromotive force, i.e. there will be no net electromotive force, no current flow and hence, no net force. The armature will spin at a constant rate, of its own accord.

from:-

Wikimedia Error

 

[The Godfather]

Thankyou SL, but the OP wanted a simplistic approach, that he could get his head round.

Horses Head Award, for you

Don & His Boys

 

[PoorFish]

thsnks Mr Godfather

ill let it all sink in for a bit...that usually helps.

we hadnt touched on the effects on DC .

Im sure its all to come

Regards

PF

 

[The Godfather]

The Don is pleased.

The Godfather

 

[NozSpark]

thsnks Mr Godfatherill let it all sink in for a bit...that usually helps.

we hadnt touched on the effects on DC .

Im sure its all to come

Regards

PF

It's easier to get your head around with DC circuits as it's to do with collapsing magnetic fields, LH rule, RH rule, blah, blah, blah

 

[The Godfather]

Indeed so, Nozspark.

Don

 

[SPECIAL LOCATION]

Thankyou SL, but the OP wanted a simplistic approach, that he could get his head round.Horses Head Award, for you

Don & His Boys

I thought the bit I'd highlighted in bold was a simple bit?

Back electromotive force is a voltage that occurs in electric motors where there is relative motion between the armature of the motor and the external magnetic field.

and that electrical C&G's would be more AC related?? ?:|

Can't recall a fat lot of DC during my C&G's................. ?:|

but perhaps me memory's going?Blushing

Can I pick the horse... ?

Not the brown one..

The black one please:|Applaud Smiley

looks like I shall be put on stable cleaning duty again next week by Admin! ?:| :_|

Sorry P Feeney if I have confused matters for you. :x

 

[The Godfather]

For you SL.

YouTube - Godfather - Horse Head

Don & His Boys

 

[batty]

For you SL.YouTube - Godfather - Horse Head

Don & His Boys

Whats his problem if he had the whole horse in there he would have something to worry about.

Batty