Storing Cookies (See : http://ec.europa.eu/ipg/basics/legal/cookies/index_en.htm ) help us to bring you our services at overunity.com . If you use this website and our services you declare yourself okay with using cookies .More Infos here:
https://overunity.com/5553/privacy-policy/
If you do not agree with storing cookies, please LEAVE this website now. From the 25th of May 2018, every existing user has to accept the GDPR agreement at first login. If a user is unwilling to accept the GDPR, he should email us and request to erase his account. Many thanks for your understanding

User Menu

Custom Search
« previous next »
Pages: 1 ... 99 100 101 102 103 [104] 105 106 107 108   Go Down

Author Topic: MH's ideal coil and voltage question  (Read 487953 times)

poynt99

  • TPU-Elite
  • Hero Member
  • *******
  • Posts: 3582
Re: MH's ideal coil and voltage question
« Reply #1545 on: July 04, 2016, 07:53:45 PM »
Quote from: picowatt on July 04, 2016, 06:19:34 PM
.99,

I added the following to my post you referenced:

If Partzman wants to attempt this, do you have any better or simpler suggestions as to how he might to go about it?

PW
These two references (I prefer the approach with the green schematics (pspice), last page):

Should not be difficult.
Logged

partzman

  • Sr. Member
  • ****
  • Posts: 379
Re: MH's ideal coil and voltage question
« Reply #1546 on: July 04, 2016, 07:56:51 PM »
Quote from: tinman on July 04, 2016, 04:44:37 PM
Pm

Do you have a scope,or access to one?


Brad

I have a very well equipped bench including a Tek MDO3034 scope with math and FFT capability. What do you have in mind?

pm
Logged

partzman

  • Sr. Member
  • ****
  • Posts: 379
Re: MH's ideal coil and voltage question
« Reply #1547 on: July 04, 2016, 08:05:37 PM »
PW and Poynt,

I still have family visiting so I have glanced thru the posts quickly and will have to follow up later as time permits. I am willing to give the sim a go.

pm
Logged

picowatt

  • Hero Member
  • *****
  • Posts: 2039
Re: MH's ideal coil and voltage question
« Reply #1548 on: July 04, 2016, 09:18:52 PM »
Quote from: poynt99 on July 04, 2016, 07:53:45 PM
These two references (I prefer the approach with the green schematics (pspice), last page):

Should not be difficult.

Do you seriously believe that many will accept, or even recognize, those models as being similar to the model being discussed?

I was looking for something much simpler and easily recognized as the actual model at hand.  How about this:

A fixed Vsource set to 4V is used for the applied EMF and a voltage controlled Vsource is used for for the CEMF.  The CEMF Vsource is selected so that 1 volt on the control input equals 1 volt on the CEMF Vsource output.

For a di reference current, Iref, an ideal 5H inductor is simultaneously connected to a second fixed Vsource of 4 volts and the current measured thru that inductor is used as Iref.  The current flowing thru the model is detected, Idet, and a comparator function is used to generate an error voltage to control the CEMF's Vsource.

I think most people would be able to recognize this as being similar to the inductor model and the CEMF voltage can be measured directly, or by proxy, via the 1V:1V CV input.

I would be most concerned with how to control damping/ stabilizing the loop.  Your thoughts regarding that, and this concept in general, would be most appreciated.

PW
Logged

poynt99

  • TPU-Elite
  • Hero Member
  • *******
  • Posts: 3582
Re: MH's ideal coil and voltage question
« Reply #1549 on: July 04, 2016, 11:03:55 PM »
Quote from: picowatt on July 04, 2016, 09:18:52 PM
Do you seriously believe that many will accept, or even recognize, those models as being similar to the model being discussed?
No, I do not. That is why I changed my mind about doing it, as I mentioned. But with all due respect what you are proposing is pointless as well, in my opinion, because it won't be accepted, especially since you are proposing to use an ideal inductor as part of the model (this in itself is part of the contention).
Logged

picowatt

  • Hero Member
  • *****
  • Posts: 2039
Re: MH's ideal coil and voltage question
« Reply #1550 on: July 05, 2016, 12:14:04 AM »
Quote from: poynt99 on July 04, 2016, 11:03:55 PM
No, I do not. That is why I changed my mind about doing it, as I mentioned. But with all due respect what you are proposing is pointless as well, in my opinion, because it won't be accepted, especially since you are proposing to use an ideal inductor as part of the model (this in itself is part of the contention).

You are probably correct.  What I proposed would, however, allow the voltage of the CEMF to be investigated when di=.8A/s.

Even if the 5H inductor used as an Iref source were replaced with a programmed current source as I originally suggested, there would likely be those that would not accept that either.

Even with all the electronic design examples in use by everyone everyday, it often seems as if some believe the field of electronics to be just another conspiracy theory...

PW
Logged

tinman

  • Hero Member
  • *****
  • Posts: 5365
Re: MH's ideal coil and voltage question
« Reply #1551 on: July 05, 2016, 01:14:04 AM »
Quote from: poynt99 on July 04, 2016, 04:55:26 PM
No, the sim is indicating the results it should be. I did clearly specify that these results are for an inductor that is free from parasitic capacitance. I guess you missed that.

I guess i must have,as i have taken the 1 ohm resistor as the circuit model that represents the winding resistance,and as such,assumed we were now dealing with a non ideal inductor in one of your two examples.

As we have been talking about the CEMF difference between ideal and non ideal being the same at T=0,i thought i would point out that it is not the same,for the very reason you just listed-the ideal coil will have no parasitic capacitance,and the non ideal one will.

So this relates to what i said,that the CEMF with reference to a non ideal coil,is not equal to the EMF,due to the capacitance of the windings.
When a coil is hit with a pulse,and then the circuit becomes open,and the coil ring's down--is this not showing that there is capacitance within the coil?--it's own tank circuit?.

I only ask so as to work out how this would make things different in regards to the ideal coil that has no capacitance.

Brad
Logged

tinman

  • Hero Member
  • *****
  • Posts: 5365
Re: MH's ideal coil and voltage question
« Reply #1552 on: July 05, 2016, 01:17:35 AM »
Quote from: partzman on July 04, 2016, 07:56:51 PM
I have a very well equipped bench including a Tek MDO3034 scope with math and FFT capability. What do you have in mind?

pm

I am just wanting to confirm what i am seeing on my bench.
Do you have a large value inductor ?--or ,what is the largest value one you have,as the larger the value,the easier it will be to see what i am seeing.

I will get some scope shot's and a circuit up tonight after work,as it was a tad cold over here last night,and the work shop is too far away from the heater :D


Brad
Logged

Magluvin

  • Hero Member
  • *****
  • Posts: 5884
Re: MH's ideal coil and voltage question
« Reply #1553 on: July 05, 2016, 02:40:27 AM »
If anyone has a series connected bifi coil, the initial input current charging the capacitance will be more visible as the capacitance is greater.

Mags
Logged

poynt99

  • TPU-Elite
  • Hero Member
  • *******
  • Posts: 3582
Re: MH's ideal coil and voltage question
« Reply #1554 on: July 05, 2016, 03:51:13 AM »
Brad,

What you are describing might be core saturation. With parasitic capacitance you will have a short sharp spike of current right at connection, then the current rise will resume as per normal from a low value.

What type of inductor are you using? Voltage? DC resistance? Resistor value? Inductance?
Logged

poynt99

  • TPU-Elite
  • Hero Member
  • *******
  • Posts: 3582
Re: MH's ideal coil and voltage question
« Reply #1555 on: July 05, 2016, 04:51:17 AM »
Quote from: tinman on July 05, 2016, 01:14:04 AM
I guess i must have,as i have taken the 1 ohm resistor as the circuit model that represents the winding resistance,and as such,assumed we were now dealing with a non ideal inductor in one of your two examples.
Yes, that is the non-ideal inductor without any capacitance, just like we've been discussing the last couple of weeks.

Quote
As we have been talking about the CEMF difference between ideal and non ideal being the same at T=0,i thought i would point out that it is not the same,for the very reason you just listed-the ideal coil will have no parasitic capacitance,and the non ideal one will.
As up until now we have not discussed parasitic capacitance (or at least I don't recall it), the point being made was that the two are equivalent at t=0. Now that your real-world inductor measurement is indicating some artifact, this may not be the case with your inductor. If you tell me what you used, I may be able to try it myself.

Logged

tinman

  • Hero Member
  • *****
  • Posts: 5365
Re: MH's ideal coil and voltage question
« Reply #1556 on: July 05, 2016, 06:30:23 AM »
Quote from: poynt99 on July 05, 2016, 03:51:13 AM
Brad,

What you are describing might be core saturation. With parasitic capacitance you will have a short sharp spike of current right at connection, then the current rise will resume as per normal from a low value.

What type of inductor are you using? Voltage? DC resistance? Resistor value? Inductance?

Yes,that is what i see-a sharp rise in current ,where the current traces the voltages virtical rise across the inductor.-both current and voltage trace track virtical on scope,unless i narrow the time devisions right down,at which point the voltage trace is not vertical,but starts to slope--so even the voltage takes some time to rise across the inductor,but we are now looking at Pico seconds in time with a 480 mH inductor.

I am using the primary side of a large MOT,as that is the largest in L value i have-short of pulling my welder apart.
The circuit is just the circuit model for an inductor, where the R is being used as the CVR.
Value of the CVR dosnt seem to make any difference,other than a reduction in voltage across it of course,as we decrease the R value of the CVR.

I must say,it is getting hard to know what we are discussing at anyone point in time here now.
I must have missed the bit on looking at a real coil that has no parasitic  capacitance,which of course means it is not a real coil.

So ATM, i am looking at a real coil-with it's  parasitic capacitance,so as to see what we have ,that we would not have in an ideal coil.
To me,this makes sense,and from there we can work out if the ideal coil would act the same as a real coil at T=0. So far,it would seem not,because at T=0 with an ideal coil,there would be no insthant current to charge the parasitic capacitance,such as we have with a real coil. I would also suspect that the parasitic capacitance  value would increase with the increase of windings-such as that guitar  picup you were talking about some time back.

I will try and get those scope shots up tonight.
P.S-the coil/inductor has a resistance value of 1.7 ohms,and is being pulsed with a square wave from my FG,with 10% duty cycle. I also have a diode on the positive input,and the CVR is on the negative side of the inductor,due to my common ground issue between scope and FG.

Brad
Logged

tinman

  • Hero Member
  • *****
  • Posts: 5365
Re: MH's ideal coil and voltage question
« Reply #1557 on: July 05, 2016, 02:20:43 PM »
OK,the scope shots below.

In the first picture,we have the 470mH inductor,and circuit attached.
In the top scope shot,we see the current trace as expected.
In the bottom scope shot of that same picture,we have decreased the time base P/D,and we now see at T=0,the current trace track the voltage trace,and then settle back down to a 0 value. After a short time,it then starts to show the current trace seen in top pic.
At T=0,the winding capacitance seems to charge first.

In the second pic,i have swapped over to a 540mH inductor,but with a much higher winding resistance value--> lots more turns of smaller gauge wire. Looking at the two scope shot's,it would seem that although the inductance value is greater,so is the winding capacitance,and so at T=0,once again we see the current trace track the voltage trace,and for a short time,the current actually leads the voltage. This would mean a clear indication of capacitance being charged.
And once again,we see the current value return to 0,once the capacitance is charged.

My point is this.
At T=0,with regard to a real world inductor,the CEMF is not equal to the EMF,due to capacitance charging. This means that the ideal coil will react differently to that of a real world coil that has parasitic capacitance.
At higher frequencies,this parasitic capacitance would greatly alter the CEMF to EMF ratio

The frequency used in these tests was 10 Hz,with a 10% duty cycle.


Brad
Logged

poynt99

  • TPU-Elite
  • Hero Member
  • *******
  • Posts: 3582
Re: MH's ideal coil and voltage question
« Reply #1558 on: July 05, 2016, 02:49:57 PM »
So what do you suppose your traces would look like if we could somehow first remove the capacitance, then the resistance?
Logged

tinman

  • Hero Member
  • *****
  • Posts: 5365
Re: MH's ideal coil and voltage question
« Reply #1559 on: July 05, 2016, 02:58:35 PM »
Quote from: poynt99 on July 05, 2016, 02:49:57 PM
So what do you suppose your traces would look like if we could somehow first remove the capacitance, then the resistance?

I do not know,nor do i have the means to find out.

My point is this--
We would assume that we would not see this with an ideal coil,and we know we do have this situation with a non ideal coil,and so the two will not act in the same manor.
As far as i can see from bench tests,the CEMF dose not equal the EMF at T=0 ,with real world inductors--am i incorrect in saying that?,and if so,what is the initial current spike at T=0,if it is not the charging of coil capacitance ?.


Brad
Logged
Pages: 1 ... 99 100 101 102 103 [104] 105 106 107 108   Go Up
« previous next »