In message , Craig Carmichael
craig@saers.com> writes
>
>There's a big difference between ferrite and iron... I quit using
>laminations when I found commercially made iron powder cores. Inside
>are actual iron particles, so it is an actual iron core, not ferrite,
>and magnets clamp on strongly.
>
>For my axial flux "Electric Hubcap" motors (36V, 4.6KW 0-2000 RPM...)
>I use a separate 2" O.D. x 1" thick iron powder toroidal core for
>each coil. (Unlike typical usage, my coil is wound as a doughnut
>around the outside, the wires epoxied with heat conductive epoxy.)
>These donut coils are individually attached in a ring to non-metallic
>(molded PP-epoxy) body parts with no electromagnetic drag. At 2000
>RPM the frequency is just 100Hz, so high frequency losses don't come
>into play. It's almost lossless. Iron losses at 1200 RPM (60Hz)
>calculate as 1W per coil, total 9 watts. No eddy currents because
>every powder particle is insulated from all the others.
>http://www.micrometals.com/ makes them.
>
>To further improve motor efficiency I paint the coils with ilmenite
>in sodium silicate, a para- ferro-magnetic skin that bends magnetic
>lines of force that are headed for open air around and into the
>cores. It's also something of an internal completion of the magnetic
>circuit. AFAIK no one else has ever done that. Motor idle currents at
>various speeds on two motors dropped 25-35% when painted. Peak
>efficiency of the motors is probably about 95%, but has never been
>properly measured.
>
>I would have inclined to solid cores, but toroids with no center is
>what there is, and it actually is better - 40% less iron to have
>losses in, and the field is more concentrated at the edges where it's
>more useful. After all, the coil is turned off whenever a magnet pole
>is over its center.
>
>I've done it all without computer modelling or even a proper study of
>magnetic circuits and materials. More just recognizing and coming to
>understand problems with the early ones and trying out promising
>solutions whenever I come across them, even to the point of pretty
>radical construction changes. I have no doubt that simulations could
>help find the optimum magnet spacing and flux gap for smoothest
>torque ripple or other desired characteristics. I will however say
>that the motors run great and take a fraction of the power of my
>earlier ones to spin them.
>
>(A mild steel plate rotor backs 12 supermagnets to complete the
>magnetic circuits of the rotor.)
>
>BTW: My previous implementation of "laminates" for the coil cores
>were strips of nail gun finishing nails broken to length and spray
>painted - rather thick but the metal was good.
>
>BTW 2: I'm working on a 24V, 3KW, 0-3000 RPM version with 6 coils
>instead of 9, the "Mini Electric Hubcap" motor.
>
>>A switched reluctance motor having no permanent magnets is desirable, as
>>a PM motor always has a strong magnetic field in the gap between the
>>stator and rotor, even when not running.
>
>With an axial flux motor, the flux gap is around 1/2 an inch. I put a
>PP-epoxy plastic wall between the rotor compartment and the stator so
>the coils are entirely out of harm's way in any event.
>
>>The canal silt has a lot of
>>ferrous material in it which will quickly get trapped in this field on
>>the sort of rim-drive motor I envisage (outer stator, ring rotor, with a
>>4-blade prop fitting inside the ring). An S-R motor has no residual
>>field, but has the problem that the gap between the salient poles of the
>>rotor and stator has to be narrower than with a PM type to ensure a high
>>efficiency. Hence my interest in the simulation software.
>>
>>Anyone else here have any working knowledge of rim-drive ring thrusters?
>
>Not me. Would a prop with a ring around the outside, driven from the
>center axle, accomplish about the same thing? I'd rather keep my
>motors out of the water.
>
>Craig
>http://www.TurquoiseEnergy.com/
>http://www.saers.com/recorder/craig/TurquoiseEnergyNews/
>
>=====
Hi Craig, thanks for the interesting ideas here.
I hadn't thought of using dust-iron toroids as cores for the stator
field coils, but it makes a great deal of sense. Plenty of choice of
sizes and a confusing choice in the different dust-core materials!
For conventional craft, a ducted propellor on the end of a normal
prop-shaft gives most of the efficiency improvements. My interest in
integrated ring thrusters for the canal trip boat is:
1. The canal is very shallow, and a conventional prop under the boat
(even if ducted) will cause scouring of the canal bed. The stretch of
the canal that the boat will work contains endangered aquatic flora and
fauna. To be allowed to operate the trip boat, we have to show that we
have minimal impact on this.
2. Following from the above, we need to operate the prop fairly close
to the canal surface, so an integrated ducted unit is ideal.
3. Being able to remove the thruster assembly to allow traditional
horse drawn operation on certain 'Heritage days' is an added advantage.
--
Chris Morriss
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