AC Homopolar Generator Conundrum

[TinMan]

Time to get you thinking--

Over the last couple of years, i started messing around with the homopolar generator again.
But i decided to try an AC style generator, just to see if it worked, which it did, and quite well.
I then went one step further with the experiments.

I shared my results on another private group/forum, so i am asking the homopolar guru's a question-->
Below is a pick of my setup, motor sits behind the rotor.
The rotor is made up of two half copper disks, with two half's of a ring magnet that was cut in half, and attached to each half copper disk, so as to be of opposite magnetic polarity.
The two half copper disks are isolated from each other.
The circuit shown is electrically open.
The question for all those that think they have a handle on the homopolar generator, and electrical circuits, is-will a current flow
through R1 when the disk is spun-lets say at 1000rpm, even though the circuit is open ?
Rough drawing i know, but you get the idea.

Brad

[chief kolbacict]

The question for all those that think they have a handle on the homopolar generator, and electrical circuits, is-will a current flow
through R1 when the disk is spun-lets say at 1000rpm, even though the circuit is open ?

will not flow.

[Smudge]

A current will flow to charge the mutual capacitance between the two discs.  When the insulator passes between the brushes the current reverses to then discharge the capacitor and charge it to the opposite polarity.  That is my take on this interesting experiment.

Smudge

[CITFTA]

Hi Brad,

I haven't tried it, but I believe current will flow except during the time the brushes are contacting the insulator.  I expect you will get a square wave instead of a sine wave with the polarity switching with each half revolution.  Since the homopolar generator normally produces power between the shaft and the edge you might get more power if you had the two halves connected in the center to the shaft.  Then you could have one contact on the shaft and another one on the edge and you will still get AC with your setup. Just thinking out loud.

Carroll

[broli]

A current will flow to charge the mutual capacitance between the two discs.  When the insulator passes between the brushes the current reverses to then discharge the capacitor and charge it to the opposite polarity.  That is my take on this interesting experiment.

Smudge

I agree with Smudge, a current will flow due to the "homopolar effect" continuously reversing its induced voltage polarity and thus you end up having a capacitor. It will be less than if you had no insulator because of the very low capacitance but there will be a current present nonetheless.

[TinMan]

A current will flow to charge the mutual capacitance between the two discs.  When the insulator passes between the brushes the current reverses to then discharge the capacitor and charge it to the opposite polarity.  That is my take on this interesting experiment.

Smudge

So this capacitor would charge without the brushes connected as well ?
And as the magnetic fields are stationary in relation to the copper half disks (the conductors), this capacitor would charge without induction, and without the flow of current through a circuit ?


Brad

[broli]

So this capacitor would charge without the brushes connected as well ?
And as the magnetic fields are stationary in relation to the copper half disks (the conductors), this capacitor would charge without induction, and without the flow of current through a circuit ?


Brad

The external circuit is experiencing the induced voltage no the rotating copper plates. This circuit becomes a capacitor as the induced voltage is flipping due to the magnet influence flipping. Does this mean the rotating copper plates become irrelevant? Yes they add no value to the measured voltage.

[Cadman]

And as the magnetic fields are stationary in relation to the copper half disks (the conductors)...

Are they? Or are they stationary, for example, relative to the earth's center? If to the latter then induction will occur as the half disks rotate.

[TinMan]

Are they? Or are they stationary, for example, relative to the earth's center? If to the latter then induction will occur as the half disks rotate.

As stated in the opening description, each half magnet is fixed to each half copper disk, so there is no relative motion between the half copper disks and half magnets.

[TinMan]

The external circuit is experiencing the induced voltage no the rotating copper plates. This circuit becomes a capacitor as the induced voltage is flipping due to the magnet influence flipping. Does this mean the rotating copper plates become irrelevant? Yes they add no value to the measured voltage.

Are you sure about that ?

The diagram below is shown for clarity.
The circuit follows the circumference of the spinning rotor, and so no voltage can be induced, as the magnetic fields are now running along the wires, not cutting across the wires.
A twisted pair is used from the resistor to the scope probe some distance away, so as the scope probe it self is not within the magnetic field, and yet the same voltage is still seen across R1.


Brad

[Cadman]

As stated in the opening description, each half magnet is fixed to each half copper disk, so there is no relative motion between the half copper disks and half magnets.

Understood.

I was talking about the magnetic fields, not the physical magnets. I once used a CRT to 'see' the field pattern of magnets. I put an axially magnetized disk magnet on the end of an iron rod and spun it with a drill with the flat side of the magnet parallel to the screen. The field pattern displayed around the magnet never changed, and it did not change when I moved the drill in a circle around the screen while it was spinning the magnet.

To me this indicated the magnetic field was not physically connected to the magnet material but was rather like the magnet altered the space around and through it.

Your copper half disks and magnets would be rotating relative to the field in your set up. The copper would be in one of the poles of the field and an emf would be induced. And since your half disks are opposite polarity a current should flow through R1.

[CITFTA]

Understood.

I was talking about the magnetic fields, not the physical magnets. I once used a CRT to 'see' the field pattern of magnets. I put an axially magnetized disk magnet on the end of an iron rod and spun it with a drill with the flat side of the magnet parallel to the screen. The field pattern displayed around the magnet never changed, and it did not change when I moved the drill in a circle around the screen while it was spinning the magnet.

To me this indicated the magnetic field was not physically connected to the magnet material but was rather like the magnet altered the space around and through it.

Your copper half disks and magnets would be rotating relative to the field in your set up. The copper would be in one of the poles of the field and an emf would be induced. And since your half disks are opposite polarity a current should flow through R1.

From my own experience with magnets I think the part I high-lighted might very well be true.

Carroll

[Smudge]

So this capacitor would charge without the brushes connected as well ?

No, current must flow for the capacitor to charge.

And as the magnetic fields are stationary in relation to the copper half disks (the conductors)

No, that is incorrect.  What we call field lines are a math construct that has limitations.  There are many examples of the Faraday homopolar system where the copper disc is fixed to the end of the magnet so the magnet rotates with the disc yet the homopolar voltage induction still occurs.  So the field lines do not rotate and it is correct to assume they are stationary.  This becomes evident when you consider the electron spins who's spin axes are parallel to the rotation axis.  The magnetic field effect is coming from those spins that have effective rotation far in excess of the trivial magnet rotation rates that we apply.  The conduction electrons in your Cu half discs are moving through a stationary bunch of field lines so you get the same typical radial induced E field that would occur if they were full discs.

Smudge   

[broli]

Are you sure about that ?

The diagram below is shown for clarity.
The circuit follows the circumference of the spinning rotor, and so no voltage can be induced, as the magnetic fields are now running along the wires, not cutting across the wires.
A twisted pair is used from the resistor to the scope probe some distance away, so as the scope probe it self is not within the magnetic field, and yet the same voltage is still seen across R1.


Brad

Using classical EM you would be right as longitudinal forces are taboo in classical EM (ironically they show up in the Maxwell stress tensor construct). However there is no such taboo with Webers electrodynamic force model which was lost due to the history of scientific egos. I have played a lot with these forces in my own written simulations using the Weber Electrodynamics force model which made things much more clearer and eliminated ambiguities in these homopolar motor designs. Oh and it predicts longitudinal forces quite readily as well. So your last example actually does not change the parameters of the experiment at all and again you will measure the same P2P voltages. I will go even further, the rotating copper plates are NOT needed at all. Essentially you can hold an antenna to the rotating magnets and you will measure an oscillating voltage of equal magnitude, consistent with your previous thought experiment, which also has a linear relationship with the RPM of the spinning magnets.

This is no OU though, as the induced current flow in this antenna would also apply a back torque on the rotating magnets. This is the ''homopolar motor'' effect showing its head. The funny part is that you can use the Lorentz force model in this case to measure the effect on the PMs. The beaty of Webers Electrodynamics though is that its a complete model (for non relativistic speeds) which Heaviside disagreed with due to it not being a conservative force model. After his critique Weber quickly and swiftly shut him down after he published analytical proof that his force model WAS in fact a conservative force model and thus conserved kinetic and potential energy. In other words using purely conservative electrical systems you cannot extract more energy than you put in.

Unless you start tapping into the source of the electron spin itself which requires a different design as you hint at in your previous threads.

[TinMan]

Using classical EM you would be right as longitudinal forces are taboo. However there is no such taboo with Webers electrodynamic force model which was lost due to the history of scientific egos. I have played a lot with these kind of setups using that force model which made things quite clear. Oh and it predicts longitudinal forces quite readily too. So your last example actually does not change the parameters and again you will measure the same voltage. I will stress again, the rotating copper plates are NOT needed. Essentially you can hold an antenna to a rotating magnets which such split poles and you will measure a field consistent and which has a linear relationship with the RPM of the spinning magnets.

This is no OU though, as the induced current flow in this antenna would also apply a back torque on the rotating magnets. The beaty of Webers Electrodynamics is that Heaviside was even proven wrong after his critique of it back in the time which Weber shortly after analytically proved to be conservative. In other words using purely conservative electrical systems you cannot extract more energy unless you start tapping into the source of the electron spin which requires a different design as you hint at in your previous threads.

And do you believe this is the same for the standard homopolar generator ?
If so, i assume you can show a voltage being produced with the brushes disconnected from the disk, as you state the disk is not even needed.

I would also like to see you produce a voltage across the resistor in the ac setup i last depicted, as i tried this very experiment, and got absolutely zero across the resistor, which to me makes sense, as not only is it an open circuit without the disk, the magnetic field is also not cutting the conductors. But once the conductor/wire is sat back on the disk, a voltage appears across the resistor.
The diagram depicts brushes at right angles to the magnetic field, but that is only for clarity. In reality, the wire is just sitting on the disk, so there is no conductor at right angles to the magnetic fields.

The homopolar generator can produce hundreds of amps, which is not going to come from stray magnetic fields cutting through a single conductor, such as the circuit wires.

Copper disks work well, due to having a low resistance, and a lot of free electrons.
When the disk is spun in the presence of a magnetic field, you get electron separation through the disk, where as the electrons, having mass, are either forced to the outside of the disk via centrifugal forces !against the spinning magnetic field!, or toward the center of the disk, depending on field orientation  through the disk, and/or direction of rotation.

The copper disk is an exact replication of the impellor of a centrifugal water pump.
If you put a loop line on the water pump, you can continually pump water out of one end, and into the other.
If we reverse the direction of the pump motor, we reverse the flow of water.
Now, flipping the magnetic pole on the disk would be exactly the same as curving the pump blades to the right, or to the left, which also would determine the waters flow direction.

A PMs magnetic field has spin. Although the spin is relatively slow, it is not motionless.
It is this spin that allows electrons to flow freely through the copper disk in one direction, and encounters great resistance in the other direction.
When you flip the magnet over, the electrons are now free to travel in the opposite direction through the disk, because the spin has reversed.
Reversing the rotation of the motor will also reverse the spin of the magnetic field through the disk.
We once again can use our water pump to explain more clearly.
For example, lets say that the impellor is spinning at 500rpm, and water is flowing in one direction.
We then spin the pump motor at 1000rpm in the opposite direction, which results in the impellor spinning at 500rpm in the opposite direction, now pumping water in the opposite direction.
This is why spinning a homopolar generators disk in one direction at say 1000rpm, will always result in a slightly higher power that spinning it at the same rpm in the opposite direction.
The direction of rotation that gets the higher voltage x current (power) across the disk, is determined by the orientation of the magnetic field, and rotation direction of the disk.


Brad

[TinMan]

author=Cadman link=topic=4611.msg110896#msg110896 date=1710847070

To me this indicated the magnetic field was not physically connected to the magnet material but was rather like the magnet altered the space around and through it.

There you go.
Finally.

Now, what is it that is altering the space around the PM, and how does it do it ?

I take it you also agree that there is no such thing as magnetic field lines ?, but where this distortion of space could be seen as a cloud.

Brad

[TinMan]

No, that is incorrect.  What we call field lines are a math construct that has limitations.    The conduction electrons in your Cu half discs are moving through a stationary bunch of field lines so you get the same typical radial induced E field that would occur if they were full discs.

Smudge

No, current must flow for the capacitor to charge.

And this current comes from where ?

There are many examples of the Faraday homopolar system where the copper disc is fixed to the end of the magnet so the magnet rotates with the disc yet the homopolar voltage induction still occurs.  So the field lines do not rotate and it is correct to assume they are stationary.  This becomes evident when you consider the electron spins who's spin axes are parallel to the rotation axis.  The magnetic field effect is coming from those spins that have effective rotation far in excess of the trivial magnet rotation rates that we apply.

If this is the case, then why does the polarity and direction of current flow change when the rotation of the disk is changed, if-as you said-->(This becomes evident when you consider the electron spins who's spin axes are parallel to the rotation axis.  The magnetic field effect is coming from those spins that have effective rotation far in excess of the trivial magnet rotation rates)

That to me says that the rotation speed and direction should have little effect on the electrons spin speed.
But as we know, the faster you rotate the disk, the more voltage you get across the center to outer edge of the disc, and more current flowing through the disk.

BTW, there is no such thing as field lines, and this only adds confusion when dealing with magnetic fields.

Brad

[poynt99]

When the disk is spun in the presence of a magnetic field, you get electron separation through the disk, where as the electrons, having mass, are either forced to the outside of the disk via centrifugal forces !against the spinning magnetic field!, or toward the center of the disk, depending on field orientation  through the disk, and/or direction of rotation.

If I understand correctly, I'm not sure I agree that electrons are flung about within a conductor due to centrifugal forces within the spinning disc. Why do you say electron separation is caused by that, vs. being caused by conventional electromagnetic induction?

[TinMan]

author=poynt99 link=topic=4611.msg110907#msg110907 date=1710891955]
If I understand correctly, I'm not sure I agree that electrons are flung about within a conductor due to centrifugal forces within the spinning disc. Why do you say electron separation is caused by that, vs. being caused by conventional electromagnetic induction?

Because there is no changing magnetic field to cause !standard! induction.

The magnetic field is stationary, regardless of whether the magnet spins with the disk or not. This is why it does not matter if the magnet rotates with the disk, or is stationary when the disk rotates.
This is because the magnetic field around a PM is not fixed to the PM, but more so like a cloud of gas (so to speak) around the PM, and where there are no !magnetic field lines! pinned to the PM it self. In saying that, the magnetic field can exert a force on the PM body itself-as we all know. But if you spin a PM on it's axis, the field will not spin with it.

If it were induction, the copper disk would increase in temperature when spinning without a load placed across it, as it is a shorted turn it self. But as we all know, the copper disk does not heat up when it is spun, when no load is placed across the disk, even though a voltage appears across the disk.

If in the case of my AC model, then the magnet halves must rotate with the disk halves.
If the magnet halves were stationary, and the half disks rotated around the stationary magnets, then  !standard! induction would occur, and the half copper disks would indeed get hot without a load placed across them.

With the homopolar generator, which ever part is moving (except the magnet itself) relative to the stationary magnetic field, is what will produce the emf across it.
So if it is the disk that is rotating, and the circuit is stationary, then it is the disk that produces the emf across it. If the disk is stationary, and the circuit is rotating, then it is the circuit that is producing the emf across it, and the disk just becomes a conductor in the circuit.

I have watch for many years people making the same mistake over and over again, and where different people carry out testing, and just confirm the results of those that made the mistakes.
Real science is not about making confirming experiments--it is going about trying to debunk previous findings.

Mistake 1--Take for example the test pictured below.
They (the experimenters) rotate the disk, while the voltage meter remains stationary, and they get a voltage across the meter.
They then rotate the voltage meter with the disk, and they get no voltage.
They then come to the conclusion that it is these magic magnetic field lines cutting through the voltage meters circuit conductors that is creating the emf.
So they just happily confirm others mistakes, and are blind as to why they get these results. This is not science. This is the same mistake being made over and over again.
Why no one can stand back and see this obvious mistake is beyond me.

So in summery-
1- No changing magnetic field, and no generated heat across the shorted turn disk, means no !standard! induction is taking place, regardless of the fact that a voltage still appears across the disk form the center to the outer rim of the disk.
2- Disregarding the magnet, what ever is rotating in the stationary magnetic field, is what produces the emf across it.
If the disk is rotating, and the circuit stationary, then it is the disk that produces the emf.
If the disk is stationary, and the circuit is rotating, then it is the circuit that is producing the emf.


Brad

[poynt99]

The magnetic field may not be increasing or decreasing, but there is relative movement between the electrons in the discs and the field produced by the magnets. Therefore, you have conventional induction.

btw, the depictions of your disc do not show a brush at the axis, but two brushes opposite each other at the periphery. Very ingenious, and why you get an alternating voltage and no heating of the discs.

[Allcanadian]

The magnetic field may not be increasing or decreasing, but there is relative movement between the electrons in the discs and the field produced by the magnets. Therefore, you have conventional induction.

I agree and it's not that difficult to figure out.

In Fig 1 we see the force produced on a moving electron by the Lorentz force. The magnetic field (North Pole) is coming out of the page. As the electron moves to the right it experiences a force causing it to curl upward.

In Fig 2 we see a homopolar generator with the magnetic field North pole also coming out of page through a conductive disk. As the disk spins CCW to the right  it carries free electrons to the right with it. Since the free electrons are moving in a magnetic field just like Fig 1 they experience a force upward. Hence the reason the disk perimeter is (-) and the disk center (+).

Fig 3 is just a side view showing a better view of the electron curl towards the disk perimeter.

It would seem to me the Lorentz force explains the phenomena perfectly and I'm not sure what the problem is. If we understand a permanent magnetic field is stationary with respect to it's source everything works.

AC

[TinMan]

I agree and it's not that difficult to figure out.

In Fig 1 we see the force produced on a moving electron by the Lorentz force. The magnetic field (North Pole) is coming out of the page. As the electron moves to the right it experiences a force causing it to curl upward.

In Fig 2 we see a homopolar generator with the magnetic field North pole also coming out of page through a conductive disk. As the disk spins CCW to the right  it carries free electrons to the right with it. Since the free electrons are moving in a magnetic field just like Fig 1 they experience a force upward. Hence the reason the disk perimeter is (-) and the disk center (+).

Fig 3 is just a side view showing a better view of the electron curl towards the disk perimeter.

It would seem to me the Lorentz force explains the phenomena perfectly and I'm not sure what the problem is. If we understand a permanent magnetic field is stationary with respect to it's source everything works.

AC

So we have standard induction, and we have a potential between the center of the disk, and the outer edge.
If the copper disk is say 5mm thick, and has a radius of say 50mm, what would the resistance value be from the center of the disk, to the outer edge ?
Lets say that resistance is 0.001 ohms, and the voltage potential is 100mV. Ohms law states that a current of 100 amps should be flowing through the disk.
So why doesn't the disk get hot if it is standard induction ?, as the disk is a shorted turn.

Also, with my AC example, the magnetic fields are moving with the disk halves in this circumstance, as each field is pulled around by the opposite field as the disk and magnets rotate together.
So there is no relative motion between the magnetic fields and the copper disk halves, and yet a voltage still exists across the 2 half disks.
In fact, with the AC version, the disk does not have to be in two halves. It can be a solid disk, and will still produce a voltage across the opposite outer edges, creating an AC waveform across a resistor.
How can this be standard induction, when the magnets are moving with the disk, and there is no relative motion between the magnetic field and the disk ?
If however, the two half magnets are stationary, and only the disk is spun, we then do get normal induction, where will still get a voltage across the disk, but heat is also generated by the disk.


Brad

[unimmortal]

Okay, let's turn this conversation on it's head - sorry if this sidetracks a little Brad, but I think it is pertinent.

Question:
If I get my precision gyroscope (2" diameter), and spin it to 8,000-9,000 using the supplied starting motor ... what does a voltmeter measuring between the axle and the perimeter of the rotor see? (and why)

[TinMan]

Okay, let's turn this conversation on it's head - sorry if this sidetracks a little Brad, but I think it is pertinent.

Question:
If I get my precision gyroscope (2" diameter), and spin it to 8,000-9,000 using the supplied starting motor ... what does a voltmeter measuring between the axle and the perimeter of the rotor see? (and why)

It will see nothing unless your rotor is in the presence of a magnetic field.

[unimmortal]

It will see nothing unless your rotor is in the presence of a magnetic field.

Incorrect. The rotor will actually induce its own magnetic field, and then pass through it generating potential. I saw around 80mV. I also saw a little (10%) weight loss when running the rotor vertically and placing a N/S magnet either side of the rotor  .

It's been suggested to me that I look into spinning bronze alloy discs (C93200) at high speed... but this will require a lot more learning.