STEORN DEMO LIVE & STREAM in Dublin, December 15th, 10 AM

[captainpecan]

Paul, could you please indulge me with a test?  I appreciate using specs, but personally I need to have experience or seen evidence of the experiments that confirm those spec to solidify my understand sometimes.  All I want to know is if you can pull a PM off the Metglas cores more easily than any steel object.  I understand that test is completely subjective and geometries of the core vs. steel are important, but with such radically different "permeabilities" you should be able to confirm for me if the attraction "feels" the same, greater, or less.

I guess I just have trouble with the idea that a PM can attract anything with more force than steel.

Thanks,

M.

Well, in Pauls defense here, I don't think he will be able to feel a difference.  I know I have tried feeling the difference already with harddrive magnets attracting to MUMetal and regular steel.  I could not tell a difference at all.  I am just not sure that test can be done without more equipment.  One you hit a spot where the magnet is very attracted, it is hard to tell anymore when it is more attracted.  It is possible if he used a pull scale and saw the force needed to pull the magnet free of the materials.  But overall, I think we're stuck with the graphs on this one.  There may not be any way to tell for sure with what he has.  I agree with Paul on that one though, there should be a stronger attraction.  But I don't understand enough about it yet to say whether it is just mostly due to the quickness the domains are able to change state or other stuff.

[PaulLowrance]

Looking at these cores are very difficult to make any determination, but with such a tiny hole in the middle of their coils, they either started with an overly fat toroid with barely any hole in the middle, or they added layers and layers of turns.

You have me thinking about this. Now IMO there's no way they have 27 *layers* @ 37 turns per layer, which is what it would take to get close to 1 Henry with a normal ferrite core, but lets say they can fit maybe 3 layers in their core. BTW, I've looked at various photos of their toroid, and I don't see a tiny hole. Anyhow, even at 3 winding layers it would require something with ultra high permeability.

[mondrasek]

I believe that I said steel will have the greatest pulling force if were talking about fields over 0.57T, but again what's important here is that it requires ~ 10000 times less energy for the coil to saturate a Metglas MAGAMP core than a steel toroid core of the same size.

And a PM has a FINITE amount of energy.  Attraction of a PM to another object requires that the PM orient (or SATURATE) the magnetic domains of that other object so they become (in effect) an equal and oppositely polarity magnet.  If the other object saturates too easily, I do not think your magnet can achieve the maximum attractive force and therefor cannot achieve the maximum rotor torque.

But I understand that those cores are yours to do with what you will.  It was only a request.  I'd just hate to see a bunch of people order these cores and then find a PM is not as attracted to them compared to one with slightly less permeability.

I believe the correct permeability to PM strength ratio is very important.  Maximizing permeability may not maximize performance.

[PaulLowrance]

I'd just hate to see a bunch of people order these cores and then find a PM is not as attracted to them compared to one with slightly less permeability.

Hi,

The cores are only $2.65 each, and so far it appears to be the best matching core to Steorn's. I would think people would want to be encouraging to buy these Metglas MAGAMP cores, not discouraged, right?

[lumen]

I believe it is a requirement that at least part of the core is saturated by the magnets.
This is what lowers the inductance of the core at the start of the pulse. As the magnets move further away from the core the full inductance of the coil will return to normal.

The distance from the magnets will determine at what point the core saturates for any particular material.