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Author Topic: The Back emf misnomer  (Read 32469 times)

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The CEMF/BEMF is both in series and in parallel so you are both right and wrong!  Now that might sound daft but as always it depends on how you look at it and what you see.  We usually draw circuits with the source on the left and the load on the right both standing up from the common ground along the bottom and connected across the top.  Then you see them in parallel.  But you could also draw it with both the source and the load across the top in series, with the LH and and RH end of this series both connected down to ground.  Then you see them in series.  From the parallel viewpoint the polarity arrows both point in the same direction (say upwards) and that is Tinman's view.  From the series viewpoint the polarity arrows point in opposite directions.  For solving a closed circuit where you wish to determine the current produced by the various EMF's you must follow the series viewpoint around the circuit and sum the various EMFs using those polarity arrows. 
 

Personally I consider counter EMF and back EMF to mean the same thing, but Tinman has used references to suggest that they apply to different circumstances.  I have suggested that simple resistance produces a "counter" or "back" EMF proportional to current in order to illustrate the offending series/parallel viewpoints.  However the accepted wisdom is that these EMFs are proportional to the rate-of change of magnetic flux.  (As an aside Mr Lenz doesn't help when he talks about induced current and not induced voltage.)  Perhaps it would be better if we used a common term like MIEMF (magnetically induced emf) for all these situations, then we would not be wasting energy on arguing which term is correct.  I don't think you can say that one reduces and one adds to the AC signal without specifying the circuit you are referring to.  It is common in most AC circuits for both addition and reduction to happen at different parts of the cycle.
Smudge

Smudge,  Thank you for your most informative posts.  As I said above to Brad I am not a so called expert, I don't profess to be an expert in anything,  I just have a lot of knowledge in many things and probably not all correct. I do defer to your knowledge as I do look at you as the expert here.  If I have offended you or Brad in any way I sincerely apologize that is not my intention, yes I am a bit gruff, sorry, as an old biker I tend to talk a bit ruff and yes at my age I still ride my harley when ever I can. I hope this has helped people that don't have a handle on it and for me it has been fun.  Have a good day and again Thank you.
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
   

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Smudge,  Thank you for your most informative posts.  As I said above to Brad I am not a so called expert, I don't profess to be an expert in anything,  I just have a lot of knowledge in many things and probably not all correct. I do defer to your knowledge as I do look at you as the expert here.  If I have offended you or Brad in any way I sincerely apologize that is not my intention, yes I am a bit gruff, sorry, as an old biker I tend to talk a bit ruff and yes at my age I still ride my harley when ever I can. I hope this has helped people that don't have a handle on it and for me it has been fun.  Have a good day and again Thank you.
Room

Hi Room

Dont know if you are interested or not,but i have provided a close up(time expanded) scope shot view of T=0

You will note that once the coils self capacitance charges,and the current begins to fall,the CEMF value is higher than that of the applied EMF,and we now see current flowing back into the source(area between green lines).

But as i said,it depends on how accurate you want to be,and how close you want to look.


Brad


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Hi Room

Dont know if you are interested or not,but i have provided a close up(time expanded) scope shot view of T=0

You will note that once the coils self capacitance charges,and the current begins to fall,the CEMF value is higher than that of the applied EMF,and we now see current flowing back into the source(area between green lines).

But as i said,it depends on how accurate you want to be,and how close you want to look.


Brad

Hi Brad,
Just so I am on the same page, this is a scope shot of just T=0 not the entire time period is that correct.  You are saying the first peak is the self capacitance of the coil charging after which the rest of the total time period T1-T5 is then the normal looking curve.?  So what this means is there is a spike of current charging the internal capacitance before the normal curve is started if one looks close enough.  OK I can see how that can occur I just can't say I have ever seen it before, but I am not saying you are wrong.  I would like to see the entire curve T0- T5 as well as the expanded T=0 screen shot of this coil just to observe it all, interesting coil or is this from a motor?

And yes it does look like the voltage is higher then source at that point, So are you saying that the internal capacitance charging current is creating the initial maximum CEMF/BEMF at T=0 ?
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
   

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Hi Brad,
Just so I am on the same page, this is a scope shot of just T=0 not the entire time period is that correct.  You are saying the first peak is the self capacitance of the coil charging after which the rest of the total time period T1-T5 is then the normal looking curve.?  So what this means is there is a spike of current charging the internal capacitance before the normal curve is started if one looks close enough.  OK I can see how that can occur I just can't say I have ever seen it before, but I am not saying you are wrong.  I would like to see the entire curve T0- T5 as well as the expanded T=0 screen shot of this coil just to observe it all, interesting coil or is this from a motor?

And yes it does look like the voltage is higher then source at that point, So are you saying that the internal capacitance charging current is creating the initial maximum CEMF/BEMF at T=0 ?
Room

Hi Room

Yes,that is an expanded view at T=0,and the normal curve you see starts after the initial charge up of the coils self capacitance.

If you look at the current and voltage trace closely when viewing the normal curve on a scope,you can actually see the spikes at T=0.

I will get you a series of scope shots,where i expand the time durations a bit more each screen shot of the same event/pulse of the inductor when i get home from work today.

I will see if i can find a coil with a higher value self capacitance,and clean up the waveforms a bit.


Brad


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Hi Room

Yes,that is an expanded view at T=0,and the normal curve you see starts after the initial charge up of the coils self capacitance.

If you look at the current and voltage trace closely when viewing the normal curve on a scope,you can actually see the spikes at T=0.

I will get you a series of scope shots,where i expand the time durations a bit more each screen shot of the same event/pulse of the inductor when i get home from work today.

I will see if i can find a coil with a higher value self capacitance,and clean up the waveforms a bit.


Brad

Hi Brad,
Great, we can look at one piece at a time.
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
   

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Hi Brad,
Great, we can look at one piece at a time.
Room

Hi Room

I didnt make it to the bench last night,had some mechanical repairs to do on the wife's car.
Will try again tonight.


Brad


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

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Hi Brad,
Great, we can look at one piece at a time.
Room

Hi Room

Below is a scope shot from T=0.
For this test i use a MOT,as the inductance value is high,and gives a better indication of what i am showing.

In the first shot,you see the normal current curve(blue trace),and the voltage trace (yellow)
If you look carefully at the first(non expanded)pic,you will notice a thin blue trace at T=0. It stands out quite well when using a MOT.
So keep an eye on the time per division setting on each scope shot,and the voltage per division on the last scope shot,where i dropped it down to 100mV P/D

So the scope shots below are all of the same scope shot,but where i froze the scope shot,and expanded the time on each.

The first is at 10uS
The second at 1uS
The third at 200nS
The forth at 50nS
On the forth shot,the V/PD was raised to 100mV,and that is over 10 ohms.
So within the first 50nS from T=0,we have a current of 40mA.

This is my area of current research.
Something very interesting happens in this area when using a bifilar wound coil,and that i will show tomorrow night.

Brad


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

Below is a scope shot from T=0.
For this test i use a MOT,as the inductance value is high,and gives a better indication of what i am showing.

In the first shot,you see the normal current curve(blue trace),and the voltage trace (yellow)
If you look carefully at the first(non expanded)pic,you will notice a thin blue trace at T=0. It stands out quite well when using a MOT.
So keep an eye on the time per division setting on each scope shot,and the voltage per division on the last scope shot,where i dropped it down to 100mV P/D

So the scope shots below are all of the same scope shot,but where i froze the scope shot,and expanded the time on each.

The first is at 10uS
The second at 1uS
The third at 200nS
The forth at 50nS
On the forth shot,the V/PD was raised to 100mV,and that is over 10 ohms.
So within the first 50nS from T=0,we have a current of 40mA.

This is my area of current research.
Something very interesting happens in this area when using a bifilar wound coil,and that i will show tomorrow night.

Brad

Brad,

Nice!  O0

Pm
   

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Posts: 383
Hi Room

Below is a scope shot from T=0.
For this test i use a MOT,as the inductance value is high,and gives a better indication of what i am showing.

In the first shot,you see the normal current curve(blue trace),and the voltage trace (yellow)
If you look carefully at the first(non expanded)pic,you will notice a thin blue trace at T=0. It stands out quite well when using a MOT.
So keep an eye on the time per division setting on each scope shot,and the voltage per division on the last scope shot,where i dropped it down to 100mV P/D

So the scope shots below are all of the same scope shot,but where i froze the scope shot,and expanded the time on each.

The first is at 10uS
The second at 1uS
The third at 200nS
The forth at 50nS
On the forth shot,the V/PD was raised to 100mV,and that is over 10 ohms.
So within the first 50nS from T=0,we have a current of 40mA.

This is my area of current research.
Something very interesting happens in this area when using a bifilar wound coil,and that i will show tomorrow night.

Brad

I agree with partzman very nice,  and Yes I think you are right and that large current peak at T=0 must be self or internal coil capacitance, What else could it be?  Is it SM's 'kick' ? I don't know but very interesting, are you working on something that keeps the 'KICK' and stops the rest of the cycle, it makes me wonder about ELI voltage leading current in an inductor although you can see it in the rest of the cycle but like you say right at T=0 must be internal capacitance, so what is this project you are working on I am very curious?
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
   

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Good work Brad!  Well illustrates that there is not
a perfect inductor or capacitor in the Real World.

The instant that power is applied to the inductor
a very sharp transition occurs which has very high
frequency composition.  At those frequencies, which
are far above the self-resonant frequency of the
inductor, the internal capacitance of the inductor
will dominate.

You've given us Proof Positive.

I suspect the transient response of the Capacitor is
quite similar.  At the first instant of transition it
could be expected that the capacitor's internal
inductance would dominate. But only very briefly.

The questions of "When does an inductor look like
a capacitor?"
and "When does a capacitor look like
an inductor?"
have been answered.
« Last Edit: 2018-08-30, 22:59:26 by muDped »


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Posts: 383
Hi Brad,

Isn't this the problem Tesla worked on early in his career,  At the moment of switch closure on motors and generators they were zapping people and Tesla fixed it for Edison and never got paid.  How did he fix it I forget?
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
   
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Simply stunning! so close to solution for many devices including TPU  O0
   

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To all here.
ATM i am exploring this area,and carrying out hours of research in this area of capacitive coupling between primary and secondary coils within transformers,where the two winding are wound either one atop the other,or bifilar type.

Tonight i will post some scopeshots of a bifilar transformer,with a 1 to 1 ratio being pulsed with a 1% duty cycle.

Some of you may not believe what you see,but it is real,and may just be the secret to the TPU,or something we have been overlooking all these years.

I believe i have found a way to make electrons flow through the secondary (current in other words)without current flowing through the primary--so no input power as we know it,but output power from the secondary.

ATM i am working alongside another person,who's research is the basis of my indepth research. Once we have solid evidence of a COP+ device,im sure it will be presented. But as it stands ATM,we are still in the primary stages of research.

Brad


Brad


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

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Wow looking forward to seeing it Brad. Is it tonight yet?
   

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Hi Room

Below is a scope shot from T=0.
For this test i use a MOT,as the inductance value is high,and gives a better indication of what i am showing.

In the first shot,you see the normal current curve(blue trace),and the voltage trace (yellow)
If you look carefully at the first(non expanded)pic,you will notice a thin blue trace at T=0. It stands out quite well when using a MOT.
So keep an eye on the time per division setting on each scope shot,and the voltage per division on the last scope shot,where i dropped it down to 100mV P/D

So the scope shots below are all of the same scope shot,but where i froze the scope shot,and expanded the time on each.

The first is at 10uS
The second at 1uS
The third at 200nS
The forth at 50nS
On the forth shot,the V/PD was raised to 100mV,and that is over 10 ohms.
So within the first 50nS from T=0,we have a current of 40mA.

This is my area of current research.
Something very interesting happens in this area when using a bifilar wound coil,and that i will show tomorrow night.

Brad


I used the same 50ns setting at TM, but due to my lower selfcapacitance of my coil the current charge peak
is much lower (20mA or so), see green trace below,  yellow is the voltage (12V SLA) across the coil.

But i fail to see what this has to do with the topic at hand in this thread being the CEMF, BEMF, Polarity etc.

I think as mentioned earlier here, this is a normal capactance charge current of a capacitor, in this case the
self capacitance of a coil.


Itsu
   

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Posts: 494
Hi Brad,

Isn't this the problem Tesla worked on early in his career,  At the moment of switch closure on motors and generators they were zapping people and Tesla fixed it for Edison and never got paid.  How did he fix it I forget?
Room
That always reminded of a champagne bottle I was holding, while a mate was tapping a knife between the cork and bottle as the cork had snapped off. A tiny bit of gas escaped, he moved the knife which shut it of and the the bottle exploded. I was still holding the base but he ended with 4 hours of micro surgery and rehab.
   

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I used the same 50ns setting at TM, but due to my lower selfcapacitance of my coil the current charge peak
is much lower (20mA or so), see green trace below,  yellow is the voltage (12V SLA) across the coil.

But i fail to see what this has to do with the topic at hand in this thread being the CEMF, BEMF, Polarity etc.

I think as mentioned earlier here, this is a normal capactance charge current of a capacitor, in this case the
self capacitance of a coil.


Itsu

If anyone else would like me to discontinue with my findings and research in this thread,please let me know here in this thread.

I will hold off for a couple of days ,until those contributing to this thread let me know.


Brad


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

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Sounds like it deserves its own thread but happy to see it here first :) If you're seeing data that helps me better understand these concepts I'd love to see it. Sounds related to me.
   

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If anyone else would like me to discontinue with my findings and research in this thread,please let me know here in this thread.

I will hold off for a couple of days ,until those contributing to this thread let me know.


Brad

Hmmmm,    did i say that you should discontinue to put your findings and research in this thread?
I don't think so, i just pointed out that the noticed cap charge effect has to my knowledge nothing
to do with the Cemf/Bemf discussion, nothing more.

Itsu
   

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Hmmmm,    did i say that you should discontinue to put your findings and research in this thread?
I don't think so, i just pointed out that the noticed cap charge effect has to my knowledge nothing
to do with the Cemf/Bemf discussion, nothing more.

Itsu

But i fail to see what this has to do with the topic at hand in this thread being the CEMF, BEMF, Polarity etc.

To me it sounds like you are saying that what i was showing has nothing to do with the topic of this thread--so why is it here?.

Anyway,a new topic has been started,so as to keep this one on track.

Thread name is T=0


Brad


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

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Since you asked, its there because i think it has nothing to do with the topic in this thread, simple.

That is what i was saying, NOT that you should discontinue to put your findings and research in this thread, those are your words.

Itsu
   

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Seems some rocket scientist bumped this old thread at OU.com,so i had a read through it.

I found a post made by Poynt99 in this thread relating to BEMF and inductive kickback.

Hope you dont mind me posting your explanation here Poynt?

Quote: Perhaps a simple way to distinguish between bemf and inductive kickback (IK) is to ask yourself, "does the effect take place simultaneously, or in sequence?"

bemf is a simultaneous phenomenon, whereas the IK effect takes place in a certain sequence of events. In a motor, the instant you apply power there is very little if any bemf generated, so the input current is high, but once the motor is running at speed, the applied emf, and bemf are in opposition simultaneously. When you are switching inductors, there is a definite sequence of events; i.e. you energize a coil, then remove the applied emf, then the coil tries to continue the current flow and as such reverses its output voltage, most often in a short high voltage spike. But that is determined by the load seen by the IK spike. THAT is IK.

So generally speaking, if you are switching/pulsing inductors, you are generating/collecting IK. If you are powering motors, the bemf effect is taking place, limiting the current into the motor. Without bemf, motors would draw huge amounts of current all the time.

Hope that clears things up a bit
.

So it seems that Poynt99 agree's with me,or to be more correct,i agree with Poynt.


Brad


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