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self excited homopolar generator (no PMM!!!)

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Salvador

Fri Apr 03 2015, 10:40AM

Registered Member #54402 Joined: Mon Feb 02 2015, 11:09PM
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Posts: 86

I;m sorry folks but this is getting me confused , is there a definite answer so can a loop of wire or a faraday disc continue to generate its own current from the magnetic field of that current if there is rotational energy supplied to the disc?

Also I thought about what some responders told here earlier and yes if the load would rotate at the same speed at which the disc then there would be no current generated through the load no matter whether using permanent magnets or he field from the disc itself, and that would be because there would be no torque exerted , but since the disc spins ad the brushes and the load attached via the brushes that completes the cirucit is stationary with respect to the spinning disc I think there should be current generated both in the case of separate permanent magnets or the very current through the disc that creates the field , what do you think?

I am not concerned about the efficiency of the single disc because as others pointed out that is more a matter of geometry etc I am more concerned about the very principle of whether this works the way i think or not.
I guess if I will not be able to understand this here I will haev no other option but to try it out by building a physical test setup , sadly my maths are not that good either so I can't make complicated calculations before I test something.

Dr. Slack

Fri Apr 03 2015, 03:24PM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

Salvador wrote ...

I;m sorry folks but this is getting me confused , is there a definite answer so can a loop of wire or a faraday disc continue to generate its own current from the magnetic field of that current if there is rotational energy supplied to the disc?

A homopolar generator works by the disc motion and the magnetic field being at right angles. So ...

Yes, if the external loop of wire is arranged to make a magnetic field perpendicular to the disc, for instance the Barlow Wheel arrangement, where the current flows lie in the plane of the disc

No, if the external loop of wire is arranged so that its field does not have a component at right angles to the disc, for instance the brush being supplied by a wire parallel to the shaft so that the external current flows are perpendicular to the disc motion, producing a field parallel to the disc.

Salvador

Fri Apr 03 2015, 05:02PM

Registered Member #54402 Joined: Mon Feb 02 2015, 11:09PM
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well in that case it is pretty much a self excited dc generator , as those also have some small winding with thinner wire in series with the main load windings to provide the field for the generator , except here the current induction process is via Lenz law.

Maybe then just have two disc paralel and close to each other but one goes one way and the other goes the opposite way this would be even better than a stationary field coil next to a spinnign disc as it would make the drag on the electrons twice as strong because of the adding of the speeds but each in the other direction.

I guess the question then becomes , if a single disc cannot be its field source and current source without a separate field coil or magnet , then could two discs be their own field sources for each other and also current generators at the same time given that they spin at different speeds with respect to each other or in opposite directions?

Wastrel

Fri Apr 03 2015, 05:29PM

Registered Member #4095 Joined: Thu Sept 15 2011, 03:19PM
Location: England.
Posts: 122

"except here the current induction process is via Lenz law."

I don't see a difference.

If your generating disc has radial current evenly distributed then the field it creates will be flat circles.

radiotech

Fri Apr 03 2015, 06:52PM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
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Posts: 1546

Lenz' law describes an effect of damping seen in Faraday's law.

Some light may be shed on your query by the Wilson Experiment .

Uspring

Sat Apr 04 2015, 10:10AM

Registered Member #3988 Joined: Thu Jul 07 2011, 03:25PM
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Posts: 711

Salvador wrote:

I guess the question then becomes , if a single disc cannot be its field source and current source without a separate field coil or magnet , then could two discs be their own field sources for each other and also current generators at the same time given that they spin at different speeds with respect to each other or in opposite directions?

That could take care of the angular momentum and energy conservation problem. But think of the magnetic field a radial current from the axis to the brush creates. It will circle around the direction of the current, i.e. go down through the disk at one side of the current and up on the other side. When the disk rotates, the emf will be radial and pointed in opposite directions for the sides. That doesn't really add up to a voltage at the place the brush is located.

radiotech

Sat Apr 04 2015, 03:47PM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
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Do you really need a disk ? Think about a microwave oven. I has spinning charges
between the poles of a powerful magnet and has no difficulty in transferring energy.

Then consider the origin of the signal that came from the Starfish Prime shot. Again,
spinning in a magnetic field.

Salvador

Sat Apr 04 2015, 04:46PM

Registered Member #54402 Joined: Mon Feb 02 2015, 11:09PM
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Posts: 86

the disc was used here for simplicity as I was more interested in the very physics behind it than the geometry as I can figure out the geomtry later,

radioteach could you please elaborate on your last post I did not understood it fully.

Salvador

Sat Apr 04 2015, 09:58PM

Registered Member #54402 Joined: Mon Feb 02 2015, 11:09PM
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Posts: 86

oh , one more follow up question here while we're at it.

In a faraday disc when you spin just the magnet and keep the disc stationary no current is produced , but heres a situation , what about if I spin a magnet that has a time, amplitude and/or polarity varying field and still keep the copper disc stationary , can a changing magnetic field have the same lenz effect on a homopolar generator if the field source rotates , would the electrons in the disc be dragged from rim to center and vice versa with the frequency of the field and the power of the source that rotates the field ?

I know a changing/varying magnetic field can induce current in stationary wires as that is how most generators work, but I am interested can in also make the " drag" effect on electrons , as we normally get when there is a static field and a rotating disc , assuming the coil ormagnet or whatever produces the alternating field physically rotates.

As far as I see it should do that because a time varying field is a so called " action at a distance " thing and the since it changes and also physically moves in this case theoretically the changes should be dragged along with the field and should then present themselves as radial current , what do you think?

radiotech

Sun Apr 05 2015, 09:26AM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546

The electric current is movement of charges. In your description, electrons aren't
dragged. It can be shown that there is drift, very slowly.

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