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Author Topic: Advanced and Delayed magnetic field's.  (Read 51770 times)

tinman

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Advanced and Delayed magnetic field's.
« on: December 27, 2014, 11:03:57 AM »
This thread is about advanced and delayed magnetic field's-no lenz delay PLEASE
Below is a video of a generator that uses two ferrite C core's to form the complete ferrite core assembly. As you will see in the video,the secondary coil recieves most(about99%)of it's magnetic flux from the primary coil(once the primary is loaded).How ever,there seems to be a bit of a mystery here,as the current in the secondary is leading in phase when the load is reduced. This brings the question-->how can it be recieving the magnetic field from the primary before the primary starts to produce current?.

It should also be noted that the secondary(regardless of load) in no way reflects a CEMF to the rotor. So enjoy the video,and post your thoughts.

https://www.youtube.com/watch?v=FFwIF4B7BP4

Pirate88179

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Re: Advanced and Delayed magnetic field's.
« Reply #1 on: December 27, 2014, 11:06:25 AM »
Tinman:

Very nice.  This will be an interesting topic I am sure.  You are off to a good start.

Bill

tinman

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Re: Advanced and Delayed magnetic field's.
« Reply #2 on: December 27, 2014, 11:35:49 AM »
Tinman:

Very nice.  This will be an interesting topic I am sure.  You are off to a good start.

Bill
Cheers Bill.

The next step is to make it solid state,and use an electromagnet insted of the rotor. In saying that,dose anyone have a simple DC to AC converter that is triggered by an SG-so as to be able to raise and lower frequency. Im not looking for any space shuttle schematic's,but more a very simple and robust one. I was thinking along the lines of a push/pull circuit,unless some one has even a simpler one?.

Cheers
Brad.

dieter

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Re: Advanced and Delayed magnetic field's.
« Reply #3 on: December 27, 2014, 12:36:32 PM »
Interesting.

TinselKoala

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Re: Advanced and Delayed magnetic field's.
« Reply #4 on: December 27, 2014, 04:01:21 PM »
HI Brad
I see you answered MarkE's question about having the dots mixed up in the video, so that _probably_ takes care of that issue. Could you take a look at my sketch below, and tell me if it accurately represents your circuit and the measurement points?

As far as the DC-to-AC circuit you are asking about, there are several ways to do it, but the easiest way requires a bipolar DC power supply that will supply -V to 0 to +V. Most dual-output DC supplies can be configured to do this, if you can put the two outputs in series. You use the negative of one output for -V, the common (+ of one connected to - of the other) for 0 and the positive of the other output for +V. Also very easy to do with two batteries in series. The circuit that I used for the MescalMotor driver is an example that you could easily adapt for your purpose, subbing the SG for the photosensors or potentiometer in that circuit.
The 741 op-amp is easy to use, common as dirt,  the standard supply voltage is -15_0_+15 for the op-amp but it will work on quite a bit less and your FG will have no trouble driving it. Give it a sine wave input and the output will be a sine wave, square wave input, output square wave, etc. The feedback connection cleans up the pulse shape on the output. You can have the power pushpull stage switching as much as the transistors can handle (careful about that feedback connection though). See below for the basic circuit. Op-amps are mega-cool!

http://www.youtube.com/watch?v=-hNEpCwRX_k

Cheers--
--TK

ETA: Oh, I see that I may have one of the rotormagnet polarities wrong. I think you are using alternating polarities rather than all one polarity up, right?

TinselKoala

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Re: Advanced and Delayed magnetic field's.
« Reply #5 on: December 27, 2014, 04:30:54 PM »
Hi Brad
A point I forgot to mention: Could you please test the current draw of the rotor motor with and without a slight mechanical load? That is, let it run freely as in your video, show the draw, then put a slight drag on the rotor with a fingertip or suchlike, and show the current draw in that condition?
Thanks--
--TK

MarkE

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Re: Advanced and Delayed magnetic field's.
« Reply #6 on: December 27, 2014, 06:54:34 PM »
This thread is about advanced and delayed magnetic field's-no lenz delay PLEASE
Below is a video of a generator that uses two ferrite C core's to form the complete ferrite core assembly. As you will see in the video,the secondary coil recieves most(about99%)of it's magnetic flux from the primary coil(once the primary is loaded).How ever,there seems to be a bit of a mystery here,as the current in the secondary is leading in phase when the load is reduced. This brings the question-->how can it be recieving the magnetic field from the primary before the primary starts to produce current?.

It should also be noted that the secondary(regardless of load) in no way reflects a CEMF to the rotor. So enjoy the video,and post your thoughts.

https://www.youtube.com/watch?v=FFwIF4B7BP4
Tinman here is what is going on:  The windings have a very low coupling factor.  So what the secondary sees is effectively a 10mA p-p current source applied across a roughly 70mH inductor that is in parallel with the potentiometer and 100 Ohm resistor.  Driving at 102Hz:  When the pot is turned down to 2 Ohms the p-p amplitude is 40mV as on your scope, and when the pot is cranked to 1K so that you have 90 Ohms, the p-p amplitude is 800mV as seen on your scope and the phase is advanced ~58 degrees relative to the 2 Ohm case as seen on your scope.

What makes the source look like a current source is a low coupling factor.  (I used a coupling factor of 0.01 in my simulations. ) We know the coupling factor is low from other parts of your demonstrations:  Changing the load on the "secondary" has very little effect on the primary and doesn't affect the current reading on your DMM at all.

So, I think this is a case of mystery solved.

gyulasun

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Re: Advanced and Delayed magnetic field's.
« Reply #7 on: December 27, 2014, 08:23:34 PM »
Hi Brad,

When you have a few minutes, would you check the inductances of the coils with an L meter, please. I know you included the number of turns for the primary and the secondary coils, still knowing the inductances can further help to understand the operation.
First remove the resistors and check the L values and then attach the 2 Ohm to the secondary and see the how the primary coil may change, this is also an info for the coupling between the two coils.

One more question: did you use some glue to fix the two C cores to each other? If yes, can you tell the gap between the cores, I assume it is a fraction of a millimeter?  I can see the rubber band over the cores lengthwise, so maybe there is no glue layer between the touching surfaces.

Thanks,
Gyula

TinselKoala

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Re: Advanced and Delayed magnetic field's.
« Reply #8 on: December 27, 2014, 09:37:42 PM »
There is bound to be a little gap in there, or at least not full contact across the core diameter, which is why I drew my diagram the way I did.
It would be interesting to sandwich a tiny ratiometric Hall effect sensor in there somewhere, wouldn't it?


tinman

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Re: Advanced and Delayed magnetic field's.
« Reply #9 on: December 28, 2014, 01:37:54 AM »
Hi Brad,

When you have a few minutes, would you check the inductances of the coils with an L meter, please. I know you included the number of turns for the primary and the secondary coils, still knowing the inductances can further help to understand the operation.
First remove the resistors and check the L values and then attach the 2 Ohm to the secondary and see the how the primary coil may change, this is also an info for the coupling between the two coils.

One more question: did you use some glue to fix the two C cores to each other? If yes, can you tell the gap between the cores, I assume it is a fraction of a millimeter?  I can see the rubber band over the cores lengthwise, so maybe there is no glue layer between the touching surfaces.

Thanks,
Gyula
Hi Gyula

I would be more than happy to do so,but i dont have an L meter-must get one one day.
The two core's are just being held together with the rubber band-- not glue'd together.

picowatt

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Re: Advanced and Delayed magnetic field's.
« Reply #10 on: December 28, 2014, 02:02:30 AM »
Hi Gyula

I would be more than happy to do so,but i dont have an L meter-must get one one day.
The two core's are just being held together with the rubber band-- not glue'd together.

Tinman,

Consider making a scope shot with your external trigger coil positioned right next to the leading edge of your pole pieces so that the trigger pulse is generated from the same magnet passing thru the pole pieces and just prior in time to the pri/sec outputs.

Keep the trigger coil and pri/sec polarities all the same for convenience.  You can temporarily use a channel to view the trigger to ensure this.  Trigger on rising edge.

Thanks...

PW

tinman

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Re: Advanced and Delayed magnetic field's.
« Reply #11 on: December 28, 2014, 02:20:45 AM »
Tinman here is what is going on:  The windings have a very low coupling factor.  So what the secondary sees is effectively a 10mA p-p current source applied across a roughly 70mH inductor that is in parallel with the potentiometer and 100 Ohm resistor.  Driving at 102Hz:  When the pot is turned down to 2 Ohms the p-p amplitude is 40mV as on your scope, and when the pot is cranked to 1K so that you have 90 Ohms, the p-p amplitude is 800mV as seen on your scope and the phase is advanced ~58 degrees relative to the 2 Ohm case as seen on your scope.

What makes the source look like a current source is a low coupling factor.  (I used a coupling factor of 0.01 in my simulations. ) We know the coupling factor is low from other parts of your demonstrations:  Changing the load on the "secondary" has very little effect on the primary and doesn't affect the current reading on your DMM at all.

So, I think this is a case of mystery solved.
Problem not solved Mark. I think you may be asumeing that more power is being disipated through the secondary coil and resistor when the resistance is turned down to 2 ohm's--> but this is not the case. Im sure you can get an estimation of power disipation from the P/P values over the 90 and 2 ohm resistive load's. The secondary is disipating more power when the resistive load is 90 ohm's,and this is when it is around 58* advanced to that of the primary.

Now,all fancy word's aside,the fact is that a changing magnetic field must be present through the inductor before a current is produced. So how is it that this changing magnetic field appears in the secondary before it dose in the primary?-we are starting from the zero volt line here.

I will also ask you if you know what position the PM's on the rotor will be at relative to the core when the voltage from the inductors is at it's peak?.

tinman

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Re: Advanced and Delayed magnetic field's.
« Reply #12 on: December 28, 2014, 02:26:23 AM »
Tinman,

Consider making a scope shot with your external trigger coil positioned right next to the leading edge of your pole pieces so that the trigger pulse is generated from the same magnet passing thru the pole pieces and just prior in time to the pri/sec outputs.

Keep the trigger coil and pri/sec polarities all the same for convenience.  You can temporarily use a channel to view the trigger to ensure this.  Trigger on rising edge.

Thanks...

PW
Will do PW.

@TK
I will show a drag test on the rotor in my next video.I am also going to wind some small coils on the top horizontal parts of the two cores-one closest to the rotor will be use as the trigger source,but we can also look at the magnetic field that is traveling across the top of the two coils as well.

MarkE

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Re: Advanced and Delayed magnetic field's.
« Reply #13 on: December 28, 2014, 02:42:29 AM »
Problem not solved Mark. I think you may be asumeing that more power is being disipated through the secondary coil and resistor when the resistance is turned down to 2 ohm's--> but this is not the case. Im sure you can get an estimation of power disipation from the P/P values over the 90 and 2 ohm resistive load's. The secondary is disipating more power when the resistive load is 90 ohm's,and this is when it is around 58* advanced to that of the primary.

Now,all fancy word's aside,the fact is that a changing magnetic field must be present through the inductor before a current is produced. So how is it that this changing magnetic field appears in the secondary before it dose in the primary?-we are starting from the zero volt line here.

I will also ask you if you know what position the PM's on the rotor will be at relative to the core when the voltage from the inductors is at it's peak?.
As described I have reproduced the relative phase shift and amplitudes in the secondary for the 2 Ohm and 90 Ohm load conditions you demonstrated.  We can divert into the power if you like, but:  It is a new issue and as long as the waveforms in simulation and measurement match for the same component values, then the power matches as well.  I am not sure why you are surprised that the power increases with higher resistance loads.  All that means is that the series impedance is much higher than any of the loads you have tested with so far.  You are on the low load side of the maximum power point.  This is consistent with your other observations that all point to weak coupling.

This is a recurrent intuition problem with AC systems.  It is the rate at which current changes in the primary that induces voltage across the secondary.  As you lighten up the load, it appears more resistive and therefore more in phase with the induced EMF.  The induced EMF is following the derivative of the primary current.  The derivative leads the current.  If the transformer were tightly coupled, the secondary phase lead would shrink and the amplitude would come up. 

The position of the PMs at the secondary peak changes with the load.  Relative to the primary where the relationship is more or less fixed, it will be where the rate of change of flux is highest, so that should be close to when the ferrite gap is half way between two adjacent magnets.


tinman

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Re: Advanced and Delayed magnetic field's.
« Reply #14 on: December 28, 2014, 06:53:20 AM »
Here is the drag test TK requested,and also the difference between the darg of steel laminated cores and ferrite cores.

https://www.youtube.com/watch?v=uAXtB_7RkEg