>This alternator   http://others.servebeer.com/misc/alternator.jpg has NO
discernible cogging

Looks very inefficient to me; like it has a lot of magnetic 'short circuit'!


>The real benefit to the brake drum (disk) windmill is just that it costs
perhaps $150 to build, more or less ..

good luck!


On Wed, May 21, 2008 at 5:26 PM, Apptech <apptech@paradise.net.nz> wrote:

> > The Axial Flux in this very descriptive
> > http://www.windstuffnow.com/turbine%20kit.pdf has 12
> > magnet pairs for 6 pole
> > changes per turn,
> > It puts out 3 phase current from 3 coil sets of 3 each (9
> > coils)
>
> > It has problem that some consider a solution, namely to
> > minimum startup wind
> > speed, it doesn't use cores in the coils to better close
> > the magnetic
> > circuits...
> >
> > The result is that the maximum achievable magnetic flux is
> > limited by the
> > width of the air gap...
> > No professional made motor or generator allows itself such
> > a 'fo pa'!
>
> Arguable.
> Engineering is about both optimisation and compromises.
> If low wind speed startup and generation is adequately
> important to you and you can achieve the requisite power
> levels at an acceptable $ cost by eg using more expensive
> magnetics then if that is an acceptable tradeoff for you
> then it is an acceptable solution. Adding ferromagnetic
> material (iron, ferrite, ...) to the magnetic path can help
> you maximise the utilisation of both magnetics and
> conductors (copper, aluminum, ...) at the expense of
> increased weight and new complicating factors such as
> saliency (aka cogging), 'iron' saturation etc.
>
> > We recently started this group
> > http://tech.groups.yahoo.com/group/Performance_Axial_Flux/
> > to develop
> > functional improved Axial Flux Motors and Alternators!
>
> I'll look at that with interest, but
>
> > We know that cogging as produced by only 3 phases closing
> > magnetic circuits
> > over the paramagnetic cores of only 3 phases is an enemy
> > to low wind speed
> > wind generator startup...
>
> While many 3 phase machines exhibit 'cogging', it is
> possible to produce three phase and even one phase designs
> that have essentially zero 'cogging', even though most
> commercial designs that use ferromagnetic material don't
> manage. One reason for this is that the target application
> is usually more sensitive to other factors where the cogging
> is less important than other factors such as maximum
> material and/or spatial utilisation.
>
> This alternator
>
>        http://others.servebeer.com/misc/alternator.jpg
>
> has NO discernible cogging. It, and others like it, will
> turn with the slightest of input. Note that the numbers on
> the magnets are meaningless (even though the person who
> wrote them didn't realise this) and the magnets are
> magnetised en situ after insertion so the magnetic field
> pattern is not aligned with the physical magnets.
>
> This alternator is capable of about 300 Watts at 1800 RPM
> but the person who designed this is about to produce a 1 kW
> or better unit at the same or lower RPM. He is not willing
> to be directly contacted by email as the world beats a very
> well worn rut to his doorstep whenever they discover him due
> to his genetal expertise in this area BUT if people are
> strongly interested I would pass on well framed queries.
>
> Note that most alternators are NOT operated with sinusoidal
> waveforms but trapezoidal (quite close to square waves),
> with the voltages rapidly transiting in polarity at the zero
> crossings. This has major implications for how power is
> extracted.
>
> As a generalisation, cogging/saliency is minimised when the
> net magnetic forces are balanced between all poles in a
> system as the rotor turns so that as a metal/magnet gap
> decreases at one point and equivalent gape is opening
> elsewhere. It is not overly difficult [tm] to arrange things
> so that net force is notionally zero. It's then a simple
> matter of engineering [tm][again] to try and make practice
> match notionality as well as possible.
>
> Things like magnetic pole skewing can help. Gargoyle
> probably knows.
>
>
>        Russell McMahon
>
>
>
>
>
>
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>



-- 
Tobias Gogolin
Tel. Movistar (646) 124 32 82
Tel. Telcel (646) 160 58 99
skype: moontogo
messenger: usertogo@hotmail.com

You develop an open source motor controller at
http://groups.yahoo.com/group/GoBox
and an open source electric motor/alternator at
http://groups.yahoo.com/group/Performance_Axial_Flux
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