LaFonte Group can turn off permanent magnet without work

[mscoffman]

@butch;

My view is that the particle domains of ferrites are to magnetic fields,
sort of like antennas are to emf. The smaller the domain the less amenable
they become to having lenz induced eddy currents. In my view the adhesive
binding agent plays an important role by creating resistivity between
metal particle domains. The more you compress them the higher the
ferrite density, but also the higher the leakage conductivity can become.
You can use the old stamped iron "layers" if the frequency is low and
the magnetic field always comes in from the same angle because of
the right hand rule. But when frequencies become RF and magnetic fields
can come in from different angles that is when the domain isolated
ferrites are required. While ferrite's all probably reduce eddy currents
the ferrite magnetic parameters of inductance, historysis, and remnance
probably vary all over the place in various metallic compositions. Don't
forget that many applications of ferrites have RF frequency ranges in
the megahertz or gigahertz regions and I don't think this application is
in those frequency ranges yet. For the frequencies you are dealing with
standard stamped armature iron probably has near optimal characteristics
but would be difficult to make for an experimental version. There is the
open question of what happens in the "mixer" ring as the rotational
frequency increases. It could be that reaction forces act inside this
ring material.

:S:MarkSCoffman

[Low-Q]

I did some research on the web and called one guy who sold iron powder and he told me that any powder had high resistance even copper powder if it is just in a lose pile. He said to think of it as large copper spheres in a pile and only the area where the spheres touch each other is the place where current could flow. But he also said that the more you compress the powder toward resembling a solid the electrical resistance drops. What do you guys think about his comments? It seems to me that the ideal material is soft ferrite in powder form, but I have not been able to find it yet. The Switcher needs as close to zero eddy current in the stator as possible. I would really appreciate it if you guys that are making the different powder based stators could take some resistance readings after the resin has cured and is in solid form. I'm very concerned that builders are going to get rotor drag from eddy currents in the stator and get discouraged because they think it is the Lenz effect doing it when it reality it is eddy current drag.
Thanks guys,
Butch

It is true what you have been told regarding compressed DRY powder. However, if you put resin in there, there will allways be a given space between each metal sphere, so they dont touch. Because it is litterally impossible to make a resin-powder mixtrure that has a mixdure ratio that make each metal particle collide and make a conductive path all the way through. Yes, some of the particles will make small chains of conductivity, but it will be litterally impossible to make the piece of compressed powder-resin mixdure to be conductive all the way.

Vidar

[LarryC]

@Bruce, thanks for the build info.
@All,
Lots of interesting posting. But, I liked Mark's comment 'For the frequencies you are dealing with standard stamped armature iron probably has near optimal characteristics but would be difficult to make for an experimental version'. That is what I am currently using but it is limited to certain configuration where the lamination's can be edge to edge.

The other day when I was testing a request from Gyula, I noticed a rotor speed up in switching from the 10 ohm load to unloaded. I was using a different magnet configuration from my original and had to go back to the original to get rid of the speed up. I retried the new configuration test today, which has four 1" diameter magnets instead of the two that I showed in my last pictures.  So 2 N poles and 2 S poles and because of the predrilled holes they are 3/8" apart. Not the best setup as this causes more peaks in the waveform and got the following results:

                    AC input
Ohm              Watts          RMS     
100               37              17.4
50                 35              11.3
10                 28                2.78
unloaded        24               31.9

I use a variac to adjust the input voltage to the AC induction motor, so that a speed of ~2950 rpm is maintained, so that is why the Watts varies.
@Gyula, LC meter is in and the primary coil is 172 MH.

Not sure what is causing this speed difference, but I am ordering 2" X 1" X 1/2" magnets to eliminate the 3/8" gap. Those results should be more conclusive, if there is a problem.

Regards, Larry   

[Bruce_TPU]

It is true what you have been told regarding compressed DRY powder. However, if you put resin in there, there will allways be a given space between each metal sphere, so they dont touch. Because it is litterally impossible to make a resin-powder mixtrure that has a mixdure ratio that make each metal particle collide and make a conductive path all the way through. Yes, some of the particles will make small chains of conductivity, but it will be litterally impossible to make the piece of compressed powder-resin mixdure to be conductive all the way.

Vidar

That is correct!  There is zero conductive path through these homemade black Iron powder bars.

[Butch LaFonte]

[A author=Bruce_TPU link=topic=8852.msg237266#msg237266 date=1271027221]
That is correct!  There is zero conductive path through these homemade black Iron powder bars.
[/quote]
I can not emphasize enough the importance of eliminating all eddy current drag in the switcher stator.
Does anyone have an idea for a simple test fixture that a sample of a material could be placed in and the sample be free floating and rotate a field across the sample and try to find a material that would not move due to eddy current drag. The problem here is the fixture design would need to be designed so the pull of the magnet did not move the sample, but at the same time the filed lines would be cutting through the sample.
Any ideas? Mark could build it I believe and we could test everyones samples. Mark has a motor that rotates at 20,000 RPM. We could come up with a standard size and shape for the samples. Just think, we could find a truly eddy current free, cheap to make, home made magnetic material not in theory, but practice.
Thanks,
Butch