Critical pulse motor core info

[aether22]

>But laminations actually work pretty well.

They can't possibly if the magnetic field leaks out and with it the induced voltage.
They work just find in closed magnetic systems but if you think about it do not in open ones.

>By Faraday's law, the voltage driving an eddy current around it's loop is proportional to the rate of change of flux through the loop.  If you divide a solid core into 20 laminations longitudinally (so that the laminations are parallel to the flux lines), then the largest possible eddy current loops will have 1/20th the area and will be driven by 1/20th the voltage.


And there are 20 of them!
20 = 20
1 x 20 = 20

Here is another image which will hopefully make it clearer.
note: I made an error and fixed it, also i have made 2 versions, one saved as jpg2000 and the other as orig jpg, both are the same size (the max I was allowed to upload) and of the same content.
no, the .jp2 was not allowed either.

[hoptoad]

@aether
The purpose of laminations (and some other methods) is not to prevent eddy currents, because you can not prevent them. The purpose is to diminish the ability of eddy currents to produce localised non aligned magnetic fields which are mostly counterproductive to the main induced field. The laminations do this because each lamination has an area between it and another, where the electric field produced as a result of induction from the magnet is in the opposite direction to its neighbour. This causes the electric fields to cancel each other out by vector addition +/-, thus inhibiting localised resultant magnetic fields from those eddy currents. Eddy currents would not necessarily be a problem at all if they only followed the direction we wanted them to, but alas, they tend  to follow muliple complex paths.

In the coil, the same cancellation between windings occurs and is called interwinding capacitive loss. But the current induced into the coil which has an iron core is not generated by the eddy current effects of the core, it is generated by the changing main induced magnetic field which is at right angles to each winding along the core. In most of Tesla's high voltage experiments, he specifically left a small air gap between each winding to minimise interwinding capacitance.  You are correct that losses will be incurred using laminations, but they are less than the losses incurred without using them. (compared to solid iron that is)

Cheers

[aether22]

>The purpose of laminations (and any other method) is not to prevent eddy currents, because you can not prevent them.


I disagree, in a closed magnetic system they are prevented from any real presence because the magnetic and hence inductive force in the laminate core in illustration 1 would be to the left at the top, bottom and middle at the same intensity since almost all the flux stays in, it would be like shorting 2 parallel secondary coils in a transformer, the voltages are equal and opposite so no current will flow.

I also take issue with your claim that there is no way to entirely eliminate eddy currents, it is possible to make a core from a conductive magnetic metal in a non conductive matrix.

>The purpose is to diminish the ability of eddy currents to produce localised non aligned magnetic fields which are mostly counterproductive to the main induced field.

All induction is counterproductive as all of it opposes change. (except in Thane and your designs)

>The laminations do this because each lamination has an area between it and another, where the electric field produced as a result of induction from the magnet is in the opposite direction to its neighbor. This causes the electric fields to cancel each other out by vector addition +/-, thus inhibiting localised resultant magnetic fields from those eddy currents. Eddy currents would not necessarily be a problem at all if they only followed the direction we wanted them to, but alas, they tend  to follow muliple complex paths.

I disagree with the last (an eddy current is induction of electrical energy wasted as heat, therefore always bad)
I will formulate a response to the cancellation argument when I have time, but even IF it is a valid point (and I don't understand it yet) it is still far far better to have less wasted energy induced into the core and the different levels of success of lamination in open and closed magnetic paths IS huge regardless.

>In the coil, the same cancellation between windings occurs and is called interwinding capacitive loss. But the current induced into the coil which has an iron core is not generated by the eddy current effects of the core, it is generated by the changing main induced magnetic field

er, no of course not, how did you ever get the impression I said it was? (if you did)
Although the eddy currents in the core oppose the change in the magnetic field and do reduce the induction into the coil.

>which is at right angles to each winding along the core. In most of Tesla's high voltage experiments, he specifically left a small air gap between each winding to minimise interwinding capacitance.  You are correct that losses will be incurred using laminations, but they are less than the losses incurred without using them. (compared to solid iron that is)

Of course laminations are better than solid core, though IMO for open paths not hugely so. (at least for eddy currents)
And it is possible to do so much better.

What I am saying is that while not perfect in closed and near closed flux paths they work far far better there than in open circuits where voltage is induced unevenly in a lamination and the induced voltages can happy short through a less induced reigon of the same lamination, laminations are designed to stop current flow from one lamination to another but when induction supports a current to circulate in a single lamination it breaks down and become drastically less useful and in such cases better possibilities exist and are mentioned above.

[Groundloop]

@aether22,

An air core coil has no eddy current loss. Use thicker magnet wire and more turns to compensate for the weaker magnetic field produced.

Another idea is to use insulated soft Iron wire and make a coil core. Then wind normal magnet wire on the outside of the Iron coil. The
eddy currents produced in the iron coil can then be brought back into your circuit. (Have not tried this method yet.)

Groundloop.

[hoptoad]

All induction is counterproductive as all of it opposes change. (except in Thane and your designs)

If all induction was counterproductive, then Teslas AC "induction" motor would not have become a standard industrial tool worldwide. Without induction, no motor would run. Without induction you could put as much current through a wire coil as you liked, but it would not "induce" an aligned magnetic field into the metal core.

P.S There is no perfect system, so you will always have losses, be it from heat produced by eddy and load currents, or just plain old rotor windage and bearing friction. There will always be the possibility that better methods for reducing losses exist. Thats what R&D is for.