Is there a reason one dose not use aluminum?
Aaron
From: Craig Carmichael <craig@saers.com>
To: electricboats@yahoogroups.com
Sent: Thursday, January 3, 2013 8:05 PM
Subject: Re: [Electric Boats] Magnetic Circuits & The Prototype Motors
To: electricboats@yahoogroups.com
Sent: Thursday, January 3, 2013 8:05 PM
Subject: Re: [Electric Boats] Magnetic Circuits & The Prototype Motors
>...you need thin laminations of electrical
>steel, either stamped or (for small quantities) cut by NC water-jet
>machines.
...
>Sadly, dust-iron or ferrite materials can't take the high field strength
>of NiFeB magnets (or don't have a high enough permeability), so although
>an interesting idea, I'm not sure any type of printed magnetic core
>materials are likely to be suitable for these type of motors (not in the
>foreseeable future, though I could be wrong...)
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/
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