The Back emf misnomer

Author Topic: The Back emf misnomer (Read 57080 times)

Topic Options

TinMan

Re: The Back emf misnomer « Reply #75 on: 2018-08-20, 15:22:27 »

Group: Elite Experimentalist
Hero Member

Posts: 4727

Quote from: Room3327 on 2018-08-19, 17:49:01

Brad I am not going to continue the argument, and it would seem that one of us needs to go back to school. As no one has taken your side in this, I would reconsider WHO needs to go back to school. I don't know where you got your erroneous information, but I like you, so I tried to be diplomatic with you on correcting your erroneous ideas but that time has passed. Get your act together and quit confusing everyone on this subject.
Room

Room

I have read your last few posts,and i can tell you now--it is not me that should look more into this.

Reading one of your positions on this,i see you believe that a coil placed across a battery is a series connection,and that is where i am making my mistake.

I can assure you that it is not me making the mistake here,as a coil placed across a battery is a parallel connection. To help you understand this,first you must understand the difference between series and parallel connections.

In a series connection,the components are connected so as they all have the same current flowing through them.
Series connected circuits normally require a minimum of two components plus the source--in this case a battery.
A parallel connection is where the circuit components are connected to the source so as they all have the same potential difference across them as the source. An inductor placed across a source-such as a battery,will at all times have the same potential difference across it as that of the battery.

If you place a resistor across a battery,it is a parallel connection,as the potential difference across the resistor will be the same as that of the battery
If you place a capacitor across a battery,it is a parallel connection,as the potential difference across the capacitor will be the same as that across the battery--providing no ohmic losses through the connecting wires.
And the same applies for an inductor placed across a battery--parallel connection

Quote: Many people do not know the difference between CEMF and BEMF and think they can interchange them whenever they want.

There is not a lot of difference.
CEMF is normally used in relation to AC or solid state devices,such as a voltage being dropped across an inductor.
BEMF is normally used in reference to the generating action of an electric motor-such as a PM DC motor-->but not limited to.
Both relate to magnetic fields cutting through conducting loops(coils),and producing a voltage that is of the same polarity to that which created it.

Quote: The CEMF is not at it's highest at the moment the switch is closed It is at it's lowest.

Im sorry Room,but that is also incorrect.
At T=0 to the first time constant,is when the CEMF is at it's highest value,which is why the current flow through the coil during the first time constant is at it's lowest.
The instant a voltage is dropped across a coil (T=0),is when the rate of change of the magnetic field is at it's greatest--this is why the CEMFs value is at it's maximum at this time,and why the current flow is at it's minimum--the potential difference between the applied EMF and the CEMF is at it's smallest value.

Quote: It doesn't first block current it first allows the current and then as the CEMF develops it slows it down untill the coil is fully charged,

Once again,that is incorrect,and in actual fact completely opposite to what happens.
The CEMF at T=0 is at it's highest value,and so the potential difference between the applied EMF and CEMF is at it's lowest value,and so very little current can flow.
As the magnetic field being built by the inductor starts to close in on it's maximum value,and rate of change reduces,the current flow through the coil starts to increase,due to a lower CEMF value.

Quote: In BEMF before the EMF is removed (example) current is flowing left to right through a coil from negative to positive. So the left end of the coil is neg. and the right end is pos. ( its connected to source Positive current flow is neg. to pos.) so now the source is removed from the coil and we start the bemf cycle, in order for the BEMF to aid or give back its energy the coil must release it in the same direction it was flowing. Which means the coil now becomes neg. on the right and pos. on the left --It reverses In order to keep current flowing in the same direction neg. to pos.

Once again,BEMF and inductive kickback are being mixed up.

Once again-BEMF is not inductive kickback.
An example of BEMF--
A PM DC motor produces BEMF.
BEMF is the self generated EMF within the motor.
Once again,the BEMF produced is of the same polarity to that of the source.

Inductive kickback--
When a voltage is dropped across a coil,the magnetic field being built starts at the core(if it has one),cuts through the conducting loop's,and then into free space.
When the source is removed,the magnetic field collapses from the surrounding free space,through the conducting loop's,and back into the core. During this process,the coil now becomes the source. The magnetic field is now collapsing from free space,through the conducting loops,back into the core. This is why the voltage inverts across the coil--the magnetic field is cutting through the conductive loops in the opposite direction. It is also why the current continues through the coil in the same direction.

Inductive kickback has nothing to do with CEMF or BEMF.

I hope that helps explain where you are making your mistakes.

Brad

---------------------------

Never let your schooling get in the way of your education.

TinMan	Re: The Back emf misnomer « Reply #76 on: 2018-08-20, 15:31:13 »
Group: Elite Experimentalist Hero Member Posts: 4727	Quote from: Room3327 on 2018-08-19, 17:49:01 Brad I am not going to continue the argument, and it would seem that one of us needs to go back to school. As no one has taken your side in this, I would reconsider WHO needs to go back to school. I don't know where you got your erroneous information, but I like you, so I tried to be diplomatic with you on correcting your erroneous ideas but that time has passed. Get your act together and quit confusing everyone on this subject. Room Well some of us are confused,that is for sure. This is the very reason i booted this thread up again. I can assure you that my ideas are not erroneous,and i can prove every statement i have made on the bench without fail-i have been doing it for many years now Room. I can show you in real experiments on the bench the value of the BEMF produced within a DC motor,and give you an exact percentage of that BEMF to that of the applied EMF. I can show you the very same with pulsed coils,where the value of the CEMF throughout the 5 time constants can be calculated exactly,and a percentage given of the CEMF in relation to that of the applied EMF. Can you do the same? Brad --------------------------- Never let your schooling get in the way of your education.

Room3327

Re: The Back emf misnomer « Reply #77 on: 2018-08-20, 17:58:43 »

Group: Experimentalist
Hero Member

Posts: 571

Quote from: TinMan on 2018-08-20, 15:22:27

Room

I have read your last few posts,and i can tell you now--it is not me that should look more into this.

Reading one of your positions on this,i see you believe that a coil placed across a battery is a series connection,and that is where i am making my mistake.

I can assure you that it is not me making the mistake here,as a coil placed across a battery is a parallel connection. To help you understand this,first you must understand the difference between series and parallel connections.

In a series connection,the components are connected so as they all have the same current flowing through them.
Series connected circuits normally require a minimum of two components plus the source--in this case a battery.
A parallel connection is where the circuit components are connected to the source so as they all have the same potential difference across them as the source. An inductor placed across a source-such as a battery,will at all times have the same potential difference across it as that of the battery.

If you place a resistor across a battery,it is a parallel connection,as the potential difference across the resistor will be the same as that of the battery
If you place a capacitor across a battery,it is a parallel connection,as the potential difference across the capacitor will be the same as that across the battery--providing no ohmic losses through the connecting wires.
And the same applies for an inductor placed across a battery--parallel connection

What I am saying is THE CEMF is in SERIES with the source not the inductor there is a difference.

Quote: Many people do not know the difference between CEMF and BEMF and think they can interchange them whenever they want.

There is not a lot of difference.
CEMF is normally used in relation to AC or solid state devices,such as a voltage being dropped across an inductor.
BEMF is normally used in reference to the generating action of an electric motor-such as a PM DC motor-->but not limited to.
Both relate to magnetic fields cutting through conducting loops(coils),and producing a voltage that is of the same polarity to that which created it.

There is a tremendous difference between the two, CEMF occurs when the current is rising and opposes the rise and BEMF occurs when the current is falling, neither do the two work the same or cause the same phenomena. Have you ever seen a high voltage spike occur with CEMF can you grab the CEMF and bottle it up in a capacitor as you can with BEMF. They are, again, two distinctly different things.

Quote: The CEMF is not at it's highest at the moment the switch is closed It is at it's lowest.

Im sorry Room,but that is also incorrect.
At T=0 to the first time constant,is when the CEMF is at it's highest value,which is why the current flow through the coil during the first time constant is at it's lowest.
The instant a voltage is dropped across a coil (T=0),is when the rate of change of the magnetic field is at it's greatest--this is why the CEMFs value is at it's maximum at this time,and why the current flow is at it's minimum--the potential difference between the applied EMF and the CEMF is at it's smallest value.

Before the switch is thrown there is no potential there anywhere in the circuit HOW can CEMF be at it's maximum when it only occurs when current flows and the CEMF is created by that current flow.

Quote: It doesn't first block current it first allows the current and then as the CEMF develops it slows it down untill the coil is fully charged,

Once again,that is incorrect,and in actual fact completely opposite to what happens.
The CEMF at T=0 is at it's highest value,and so the potential difference between the applied EMF and CEMF is at it's lowest value,and so very little current can flow.
As the magnetic field being built by the inductor starts to close in on it's maximum value,and rate of change reduces,the current flow through the coil starts to increase,due to a lower CEMF value.

At T=0 there is no current flow and NO CEMF, where would the CEMF come from if there was some at T=0 (grab it quick sounds like free energy to me)

Quote: In BEMF before the EMF is removed (example) current is flowing left to right through a coil from negative to positive. So the left end of the coil is neg. and the right end is pos. ( its connected to source Positive current flow is neg. to pos.) so now the source is removed from the coil and we start the bemf cycle, in order for the BEMF to aid or give back its energy the coil must release it in the same direction it was flowing. Which means the coil now becomes neg. on the right and pos. on the left --It reverses In order to keep current flowing in the same direction neg. to pos.

Once again,BEMF and inductive kickback are being mixed up.

Once again-BEMF is not inductive kickback.
An example of BEMF--
A PM DC motor produces BEMF.
BEMF is the self generated EMF within the motor.
Once again,the BEMF produced is of the same polarity to that of the source.

Inductive kickback--
When a voltage is dropped across a coil,the magnetic field being built starts at the core(if it has one),cuts through the conducting loop's,and then into free space.
When the source is removed,the magnetic field collapses from the surrounding free space,through the conducting loop's,and back into the core. During this process,the coil now becomes the source. The magnetic field is now collapsing from free space,through the conducting loops,back into the core. This is why the voltage inverts across the coil--the magnetic field is cutting through the conductive loops in the opposite direction. It is also why the current continues through the coil in the same direction.

Inductive kickback has nothing to do with CEMF or BEMF.

Inductive kickback is the SAME thing as BEMF these two are interchangeable.

I hope that helps explain where you are making your mistakes.

I hope that helps explain where you are making your mistakes.

Brad

---------------------------

"Whatever our resources of primary energy may be in the future, we must, to be rational, obtain it without consumption of any material" Nicola Tesla

"When bad men combine, the good must associate; else they will fall one by one, an unpitied sacrifice in a contemptible struggle." Edmund Burke

muDped

Re: The Back emf misnomer « Reply #78 on: 2018-08-20, 18:29:34 »

Group: Tinkerer
Hero Member

Posts: 3055

We mustn't overlook the importance of the
electro-magnetic field and how it generates
by induction whatever voltage is developed
within the inductor to resist or oppose changes
in current flow. That is the 'magic' of the
Inductor and its amazing properties.

The electro-magnetic field represents stored
energy. As the intensity of the magnetic field
changes a force is generated to oppose either
an increase in the level of current flow or a
force to sustain that level of current flow when
it tends to decrease.

The abrupt cessation of current flow is the
foundational characteristic of the DC Transformer
at the heart of the Switch Mode Power Supply,
which is able to either Buck or Boost as desired.

It is unfortunate that the language and terminology
of the technical world can become corrupted by
uneducated "builders" who create their own lingo
to explain their often incorrect theories. This lingo
catches on within the "builder" community who
proudly demonstrate their disdain for 'conventional
theory,' and so it goes...

Those who don't know the language create their own.

---------------------------

For there is nothing hidden that will not be disclosed, and nothing concealed that will not be known or brought out into the open.

forest

Re: The Back emf misnomer « Reply #79 on: 2018-08-20, 19:15:25 »

Sr. Member

Posts: 478

What I can say? I think mistake is to consider EMF when you have to watch how current and fields interract. But you are more experienced od course

CITFTA

Re: The Back emf misnomer « Reply #80 on: 2018-08-20, 19:44:00 »

Group: Experimentalist
Hero Member

Posts: 782
Believing in something false doesn't make it true.

https://en.wikipedia.org/wiki/Counter-electromotive_force

These are the accepted definitions used by those trained in electronics.

---------------------------

Just because it is on YouTube does not make it real.

Room3327	Re: The Back emf misnomer « Reply #81 on: 2018-08-20, 20:57:47 »
Group: Experimentalist Hero Member Posts: 571	Quote from: CITFTA on 2018-08-20, 19:44:00 https://en.wikipedia.org/wiki/Counter-electromotive_force These are the accepted definitions used by those trained in electronics. I disagree with what it says in line one, It is saying Back EMF "is the electromotive force or voltage that OPPOSES the change in current which induced it". Back EMF does not oppose the current which induced it, it AIDS it but if you believe CEMF and BEMF are the same thing, then I am talking about Inductive kickback.. I think Wikipedia is wrong as they so often are but I can work with that too. Now if I'm wrong and I could be and CEMF and BEMF (Why would there be two names for the same thing in electronics?)are the same exact thing fine then call, what I call BEMF, Inductive kickback. It still doesn't change what I have been saying all along about how the two work. CEMF is NOT at it's maximum when or before the switch is thrown. it's at it's minimum, the CEMF is in series with the source not parallel etc. If I am wrong, I will admit it and apologize, if I am right I will expect the same from those who disagree with me. Room --------------------------- "Whatever our resources of primary energy may be in the future, we must, to be rational, obtain it without consumption of any material" Nicola Tesla "When bad men combine, the good must associate; else they will fall one by one, an unpitied sacrifice in a contemptible struggle." Edmund Burke

CITFTA	Re: The Back emf misnomer « Reply #82 on: 2018-08-20, 21:17:11 »
Group: Experimentalist Hero Member Posts: 782 Believing in something false doesn't make it true.	HI Room, A simple thought experiment clearly shows you are correct about CEMF being zero at the instant a voltage is applied. Just ask what causes the CEMF to be generated? It is generated by the current flowing through the turns of the coil. So until there is some current flowing there can be NO CEMF. So at the instant voltage is applied the CEMF is zero. In the language of experimenters BEMF can mean anything. For those of us actually trained in electronics it is the opposing voltage generated in the motor windings because those windings are moving through a magnetic field. However you will find many people that actually work in the field that also call this force CEMF. No one that I am aware of that has actually worked or been trained in electronics calls the inductive kick-back BEMF. As some of you have agreed on it is not the same thing at all. I am basing my answers on over 50 years of actually working in electronics in an industrial environment and actually having earned a degree in electronics. Everyone is entitled to their own opinion as to what they want to call things but it only adds confusion to those trying to actually learn the proper terms. It also caused some major misunderstandings about what someone may be trying to say. Respectfully, Carroll --------------------------- Just because it is on YouTube does not make it real.

Room3327	Re: The Back emf misnomer « Reply #83 on: 2018-08-20, 21:24:11 »
Group: Experimentalist Hero Member Posts: 571	Quote from: CITFTA on 2018-08-20, 21:17:11 HI Room, A simple thought experiment clearly shows you are correct about CEMF being zero at the instant a voltage is applied. Just ask what causes the CEMF to be generated? It is generated by the current flowing through the turns of the coil. So until there is some current flowing there can be NO CEMF. So at the instant voltage is applied the CEMF is zero. In the language of experimenters BEMF can mean anything. For those of us actually trained in electronics it is the opposing voltage generated in the motor windings because those windings are moving through a magnetic field. However you will find many people that actually work in the field that also call this force CEMF. No one that I am aware of that has actually worked or been trained in electronics calls the inductive kick-back BEMF. As some of you have agreed on it is not the same thing at all. I am basing my answers on over 50 years of actually working in electronics in an industrial environment and actually having earned a degree in electronics. Everyone is entitled to their own opinion as to what they want to call things but it only adds confusion to those trying to actually learn the proper terms. It also caused some major misunderstandings about what someone may be trying to say. Respectfully, Carroll Agreed, Thank you. I have worked in electronics for 56 years. Room --------------------------- "Whatever our resources of primary energy may be in the future, we must, to be rational, obtain it without consumption of any material" Nicola Tesla "When bad men combine, the good must associate; else they will fall one by one, an unpitied sacrifice in a contemptible struggle." Edmund Burke

gyula

Re: The Back emf misnomer « Reply #84 on: 2018-08-20, 22:51:36 »

Group: Tech Wizard
Hero Member

Posts: 1242

Hi gentlemen,

Someone wrote the text below that I quote and I agree with it.

Inductors react against a change in current. Applying a voltage to its terminals will produce a current that will then create a magnetic field like any other wire. An inductor is called as such because its magnetic coupling is high. In other words, the magnetic field it creates will have an effect on the element itself. If the magnectic field varies with time (which is the case when you just applied a voltage to the inductor terminals), an electric field will be induced within the wire the counter the change in magnetic field. This E-field will tend to "stop" the current that would normally be present without the inductance effect. Thus current "lags" behind voltage. Too quick of change in current creates an e-field that decreases dI/dt.
You can see an inductor like a wheel that is free to spin due to the flow of a river. If the flow changes too quickly, the wheel, due to its inertia, will tend to keep spinning for a moment. The same is true if the water of the river goes from steady to flowing in a short instant."

Reference https://www.physicsforums.com/threads/why-does-current-lag-behind-voltage-in-inductor.479918/

To me the appearing E-field sounds to be the CEMF and it must be at its maximum value when a voltage is just applied across a coil because otherwise the current would not be near to zero just just pico or nano seconds later the t=0 moment. And the CEMF must be reducing to zero within roughly the 5L/R time duration when the coil current reaches it maximum value, defined by Ohm's law.

Gyula

PS Room, I wrote to in Reply #74...

muDped	Re: The Back emf misnomer « Reply #85 on: 2018-08-20, 23:31:01 »
Group: Tinkerer Hero Member Posts: 3055	Since I do have a copy of The Radio Amateur's Handbook (1970) I looked into the terminology in their article about Inductance. Interestingly, the terms used there are induced e.m.f. and back e.m.f. No mention at all of Counter emf. I also have a copy of Electricity and Magnetism by Norman E. Gilbert (3rd Edition 1950) where the terms used are Induced emf and Back emf. Back emf in this book includes self induced inductor emf and motor induced emf. In his description of how Induction Coils work Gilbert used the term Induced emf to describe what we now call 'kickback' or 'flyback.' The Allied Dictionary of Electronic Terms published by Allied Radio, Chicago, Illinois (6th Edition 1962) defines Counter emf and Back emf to include normal inductor action as well as what we now know as kickback. The voltage developed within a motor is called Induced emf. I'm unable to locate my Navy training manuals but I recollect that we used Counter emf extensively. It seems that whatever terminology we learned was very much dependent upon where we studied. --------------------------- For there is nothing hidden that will not be disclosed, and nothing concealed that will not be known or brought out into the open.

TinMan	Re: The Back emf misnomer « Reply #86 on: 2018-08-21, 00:32:54 »
Group: Elite Experimentalist Hero Member Posts: 4727	Quote from: CITFTA on 2018-08-20, 21:17:11 HI Room, A simple thought experiment clearly shows you are correct about CEMF being zero at the instant a voltage is applied. Just ask what causes the CEMF to be generated? It is generated by the current flowing through the turns of the coil. So until there is some current flowing there can be NO CEMF. So at the instant voltage is applied the CEMF is zero. In the language of experimenters BEMF can mean anything. For those of us actually trained in electronics it is the opposing voltage generated in the motor windings because those windings are moving through a magnetic field. However you will find many people that actually work in the field that also call this force CEMF. No one that I am aware of that has actually worked or been trained in electronics calls the inductive kick-back BEMF. As some of you have agreed on it is not the same thing at all. I am basing my answers on over 50 years of actually working in electronics in an industrial environment and actually having earned a degree in electronics. Everyone is entitled to their own opinion as to what they want to call things but it only adds confusion to those trying to actually learn the proper terms. It also caused some major misunderstandings about what someone may be trying to say. Respectfully, Carroll Carroll Here is another thought experiment When dose an electric motor draw the least amount of current? 1-when it starts and RPM is at it's lowest,hence BEMF is at it's lowest value--or 2-when RPMs have reached there maximum,and the BEMF is at it's maximum. 3-is the greatest rate of change of the magnetic field taking place at 1 or 2 ?. 4-is the polarity of this BEMF the same polarity to that of the source-or of the opposite polarity? Brad --------------------------- Never let your schooling get in the way of your education.

TinMan	Re: The Back emf misnomer « Reply #87 on: 2018-08-21, 03:17:05 »
Group: Elite Experimentalist Hero Member Posts: 4727	Quote from: gyula on 2018-08-20, 22:51:36 Hi gentlemen, Someone wrote the text below that I quote and I agree with it. Inductors react against a change in current. Applying a voltage to its terminals will produce a current that will then create a magnetic field like any other wire. An inductor is called as such because its magnetic coupling is high. In other words, the magnetic field it creates will have an effect on the element itself. If the magnectic field varies with time (which is the case when you just applied a voltage to the inductor terminals), an electric field will be induced within the wire the counter the change in magnetic field. This E-field will tend to "stop" the current that would normally be present without the inductance effect. Thus current "lags" behind voltage. Too quick of change in current creates an e-field that decreases dI/dt. You can see an inductor like a wheel that is free to spin due to the flow of a river. If the flow changes too quickly, the wheel, due to its inertia, will tend to keep spinning for a moment. The same is true if the water of the river goes from steady to flowing in a short instant." Reference https://www.physicsforums.com/threads/why-does-current-lag-behind-voltage-in-inductor.479918/ To me the appearing E-field sounds to be the CEMF and it must be at its maximum value when a voltage is just applied across a coil because otherwise the current would not be near to zero just just pico or nano seconds later the t=0 moment. And the CEMF must be reducing to zero within roughly the 5L/R time duration when the coil current reaches it maximum value, defined by Ohm's law. Gyula PS Room, I wrote to in Reply #74... Very correct Gyula. Some believe it is the current flowing throgh the coil that creates the magnetic field,when in fact it is the increasing electric field that creates the magnetic field. You simply cannot have a moving/expanding electric field without a magnetic field. 1-A voltage is dropped across a coil 2-An electric field starts expanding through the coil. 3-The expanding electric field produces a magnetic field. 4-The magnetic field cuts through the winding,producing a CEMF. 5-This CEMF,which is of the !!same!! polarity to that of the source,reduces the potential difference between the coil and source,thus by ohms law,reduces the amount of current that can flow through the resistance of the coil it's self. This can all be shown on the bench to be true,and the numbers add up to be exact. Brad --------------------------- Never let your schooling get in the way of your education.

TinMan	Re: The Back emf misnomer « Reply #88 on: 2018-08-21, 03:38:12 »
Group: Elite Experimentalist Hero Member Posts: 4727	Quote from: CITFTA on 2018-08-20, 21:17:11 HI Room, A simple thought experiment clearly shows you are correct about CEMF being zero at the instant a voltage is applied. Just ask what causes the CEMF to be generated? It is generated by the current flowing through the turns of the coil. So until there is some current flowing there can be NO CEMF. So at the instant voltage is applied the CEMF is zero. Respectfully, Carroll And that is where the mistake is being made. It is the electric field that is producing the CEMF,not the current flowing through the coil. This is why voltage leads current in an inductor. This is why voltage across a secondary in a transformer is alway in phase with the voltage across the primary of that transformer. The EMF across the secondary is produced by the electric field of the primary-not the current flowing through it. Some ask why i booted this thrrad up again?. Well,by now,im guessing you can see why. Brad --------------------------- Never let your schooling get in the way of your education.

muDped	Re: The Back emf misnomer « Reply #89 on: 2018-08-21, 04:28:35 »
Group: Tinkerer Hero Member Posts: 3055	My Navy manuals are in storage somewhere. Here's a copy of one that is very similar. ------------------------ Navy Course Chap 13.pdf (1005.49 kB - downloaded 168 times.) Navy Course DC Motors Chap 15.pdf (1302.89 kB - downloaded 156 times.) « Last Edit: 2018-08-21, 06:14:26 by muDped » --------------------------- For there is nothing hidden that will not be disclosed, and nothing concealed that will not be known or brought out into the open.

TinMan	Re: The Back emf misnomer « Reply #90 on: 2018-08-21, 07:49:45 »
Group: Elite Experimentalist Hero Member Posts: 4727	Quote from: muDped on 2018-08-21, 04:28:35 My Navy manuals are in storage somewhere. Here's a copy of one that is very similar. Thanks for those papers muDped I only hope those here will take the time to read and understand them. Brad. --------------------------- Never let your schooling get in the way of your education.

TinMan	Re: The Back emf misnomer « Reply #91 on: 2018-08-21, 09:07:33 »
Group: Elite Experimentalist Hero Member Posts: 4727	Quote from: Room3327 on 2018-08-20, 21:24:11 Agreed, Thank you. I have worked in electronics for 56 years. Room Many smart men once said heavier than air machines could never fly. That statement was often made by the same people that watched birds flying over head. I have been dabbling in electronics for maybe 10 years on a hobbiest basis. Dose your 56 years mean you know better than me?,or maybe you have been looking at it all wrong ? I am mostly self taught,and if something dose not sound right,i search for the truth on my bench--and i find the correct answers. To you i may be an amature,but i stand by what i say. Brad --------------------------- Never let your schooling get in the way of your education.

TinMan	Re: The Back emf misnomer « Reply #92 on: 2018-08-21, 13:23:59 »
Group: Elite Experimentalist Hero Member Posts: 4727	author=muDped link=topic=1585.msg69278#msg69278 date=1534786174] Quote It is unfortunate that the language and terminology of the technical world can become corrupted by uneducated "builders" who create their own lingo to explain their often incorrect theories. This lingo catches on within the "builder" community who proudly demonstrate their disdain for 'conventional theory,' and so it goes... Those who don't know the language create their own. I see in the thread below muDped,that you also use the term flyback. http://www.overunityresearch.com/index.php?topic=1580.0 Quote: If the forward voltage characteristic of the diode is greater than the supply voltage (1.5 Volts max in the example) then there will only be a small leakage current. But, your point is well taken; I would much prefer that all output measurements be made across the coil winding directly and isolated from the supply rather than as its shown which places the coil during flyback in series aiding with the source cell so that whatever voltage appears across the load is the sum of Vsource and Vflyback. --------------------------- Never let your schooling get in the way of your education.

TinMan	Re: The Back emf misnomer « Reply #93 on: 2018-08-21, 13:38:03 »
Group: Elite Experimentalist Hero Member Posts: 4727	Quote from: CITFTA on 2018-08-20, 21:17:11 No one that I am aware of that has actually worked or been trained in electronics calls the inductive kick-back BEMF. As some of you have agreed on it is not the same thing at all. Respectfully, Carroll That is correct Carroll Inductive kickback is caused by an abrupt interruption of current flow from the source. BEMF is produced while the coil is connected to the source. The two are totally different. Brad --------------------------- Never let your schooling get in the way of your education.

TinMan	Re: The Back emf misnomer « Reply #94 on: 2018-08-21, 14:17:32 »
Group: Elite Experimentalist Hero Member Posts: 4727	author=Room3327 link=topic=1585.msg69277#msg69277 date=1534784323] Quote What I am saying is THE CEMF is in SERIES with the source not the inductor there is a difference. No,the CEMF is in parallel with the source EMF,as the CEMF has the same polarity across the coil as the source EMF. This is why it is said that the CEMF apposes that of the EMF-->positive of the CEMF to positive of the applied EMF. Quote CEMF occurs when the current is rising and opposes the rise and BEMF occurs when the current is falling, CEMF is the self induced EMF within inductors. The CEMF is at it's greatest from T=0,and falls as the rate of change of the magnetic field decreases. BEMF is the self generated EMF within electric motors. The value of the BEMF is at it's lowest when the motor is first switched on,and at it's highest value when the motor reaches running RPM. The BEMF is produced due to the coils of the rotor cutting through the fields of the permanent magnets--referring to a PM DC motor here. Quote neither do the two work the same or cause the same phenomena. They both work the same,in that they both reduce the current due to lowering the potential difference between the applied EMF and BEMF/CEMF The greater the rate of change of the magnetic field in relation to the coils,the greater the value of the CEMF/BEMF. Quote Have you ever seen a high voltage spike occur with CEMF can you grab the CEMF and bottle it up in a capacitor as you can with BEMF. They are, again, two distinctly different things. Once again,you have mixed up BEMF with inductive flyback/kickback. They are not the same thing--not even close. https://www.precisionmicrodrives.com/content/ab-021-measuring-rpm-from-back-emf/ Quote: Back electromotive force (back EMF, BEMF) is a voltage that appears in the opposite direction to current flow as a result of the motor's coils moving relative to a magnetic field. It is this voltage that serves as the principle of operation for a generator. https://www.sealevel.com/support/what-is-flyback-voltage-and-what-should-i-do-about-it/ What is flyback : A “Flyback Voltage Spike” occurs when the supply current to an inductive load such as a solenoid is interrupted. Quote Before the switch is thrown there is no potential there anywhere in the circuit HOW can CEMF be at it's maximum when it only occurs when current flows and the CEMF is created by that current flow. Well of course nothing will happen until the switch is closed. T=0 represents the very instance the switch is closed. Current flow dose not create the CEMF. The CEMF is created by the electric field produced by the applied EMF. Get your self a transformer,and drop an AC voltage across the primary. Now,will the secondaries voltage be in phase with the primaries voltage or current? As most of us know,the secondaries voltage wave form will be in phase with the primaries voltage wave form,and the primaries current wave form will be 90* behind. This clearly shows you that it is the primaries electric field that is inducing the EMF across the secondary coil--not the primaries current flow. We also know that a moving or changing electric field is accompanied by a magnetic field--you cant have one without the other. It is this magnetic field that cuts through the coil windings,creating the CEMF--not current flow. Quote At T=0 there is no current flow and NO CEMF, where would the CEMF come from if there was some at T=0 (grab it quick sounds like free energy to me) One would think that after 56 years of working electronics(as you claim)you would know your statement to be wrong. It is as i stated above. At T=0,the CEMF is at it's greatest value,and this value is only slightly less than that of the applied EMF value. This is why very little current flows at T=0--the potential difference between the applied EMF and CEMF is at it's lowest. The CEMF value is high,because at T=0,the rate of change of the magnetic field is at it's greatest. This is the same as an electric motor spinning at it's maximum RPM. Quote Inductive kickback is the SAME thing as BEMF these two are interchangeable. As i have stated many times before,and provided links that show you the difference,the two are very different. Quote I hope that helps explain where you are making your mistakes. As i stated before,it is not me making the mistakes here--regardless of your 56 years in electronics,verses my 10 years of dabling on the bench. Brad --------------------------- Never let your schooling get in the way of your education.

forest	Re: The Back emf misnomer « Reply #95 on: 2018-08-21, 17:29:43 »
Sr. Member Posts: 478	You only need very fast scope 4-channel and a coil to check all this and end this topic.

Smudge

Re: The Back emf misnomer « Reply #96 on: 2018-08-21, 20:19:06 »

Group: Professor
Hero Member

Posts: 1953

Just got my PC working again after moving house and I note the disagreement between two individuals here. I see them making opposing statements that are completely opposite yet they are both correct from their different perspectives or viewpoints. I'll elaborate on that in a later post but I will say that it took me a long time to work out why you don't get a 180 degree phase shift across a transformer, and it all comes down to perspective. We say that there is a voltage drop across a resistor but we don't talk of a voltage drop across an inductor. We are taught that V=-L*di/dt (note the minus sign) but also that V=omega*L*i (note the absence of a minus sign) and that second V is the AC voltage drop across the reactance. So voltage drop is a sort of back emf and that also applies to resistors. Apply a voltage to a resistor and clearly the polarity of the voltage across the resistor is the same as the that of the supply as seen by an external viewer. But now take an internal view going around the circuit and what is the polarity as seen by a moving electron? In the battery the polarity is in the same direction as the current, in the resistor it is in the opposite direction. So we could say that the resistor creates that opposing polarity, but we don't, we call it voltage drop.
Smudge

muDped	Re: The Back emf misnomer « Reply #97 on: 2018-08-21, 21:12:54 »
Group: Tinkerer Hero Member Posts: 3055	After just reviewing texts and manuals from the past (1945 onward) it seems that there is no standardization in the definitions of the various terms we've been discussing. They are used interchangeably by the various authors and authorities to help explain the concept of induced voltage by a changing magnetic field which always opposes the change. Perhaps the concept is more important than the necessity to label the various aspects with rigid terminology. 'Kickback' and 'flyback (a TV term)' seem to be more recent additions to the group of terms. It seems there is freedom to utilize whichever term suits ones' fancy to describe each aspect of 'induced voltage.' --------------------------- For there is nothing hidden that will not be disclosed, and nothing concealed that will not be known or brought out into the open.

partzman

Re: The Back emf misnomer « Reply #98 on: 2018-08-21, 21:31:35 »

Group: Experimentalist
Hero Member

Posts: 1858

Well, perhaps we've been taught wrong all these years!

For a different view, look at Miles Mathis' theory on photons being the field particle rather than electrons.

http://milesmathis.com/updates.html

Regards,
Pm

Room3327	Re: The Back emf misnomer « Reply #99 on: 2018-08-21, 21:40:00 »
Group: Experimentalist Hero Member Posts: 571	Quote from: Smudge on 2018-08-21, 20:19:06 Just got my PC working again after moving house and I note the disagreement between two individuals here. I see them making opposing statements that are completely opposite yet they are both correct from their different perspectives or viewpoints. I'll elaborate on that in a later post but I will say that it took me a long time to work out why you don't get a 180 degree phase shift across a transformer, and it all comes down to perspective. We say that there is a voltage drop across a resistor but we don't talk of a voltage drop across an inductor. We are taught that V=-Ldi/dt (note the minus sign) but also that V=omegaLi (note the absence* of a minus sign) and that second V is the AC voltage drop across the reactance. So voltage drop is a sort of back emf and that also applies to resistors. Apply a voltage to a resistor and clearly the polarity of the voltage across the resistor is the same as the that of the supply as seen by an external viewer. But now take an internal view going around the circuit and what is the polarity as seen by a moving electron? In the battery the polarity is in the same direction as the current, in the resistor it is in the opposite direction. So we could say that the resistor creates that opposing polarity, but we don't, we call it voltage drop. Smudge That's not a quote above in red I expected to hear, but I am listening. My knowledge of this matter was taught to me by engineers in the R&D department that I worked for at a transformer manufacturing company. We designed and wound all types of transformers for the OEM market and our own products, I can only guess that motors and generators, which I have not worked with, may have some differences from ordinary transformers and inductors that I don't know about, but it is hard to imagine Brad and I are seeing things from opposite ends and yet we are both right? Thank you for your reply. Room I thank everyone who posted on this maybe one day we can all be on the same page with this topic if we keep at it. --------------------------- "Whatever our resources of primary energy may be in the future, we must, to be rational, obtain it without consumption of any material" Nicola Tesla "When bad men combine, the good must associate; else they will fall one by one, an unpitied sacrifice in a contemptible struggle." Edmund Burke