Re: Permanent magnet Tesla coil

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Harvey Norris <harvich@xxxxxxxxx>



--- Tesla list <tesla@xxxxxxxxxx> wrote:

> Original poster: William Beaty <billb@xxxxxxxxxx>
>
> On Fri, 19 Aug 2005, Tesla list wrote:
>
>   > Read about the Alexanderson alternator for a way
> of
>   > generating high frequencies with relatively sane
> RPMs.
>   > Tesla owned some alternators like these and used
> them
>   > to drive his coils, so it's not a new idea.
>
> Who invented "Alexanderson" alternators?  I thought
> Tesla built and used
> these before the wireless age, and only much later
> did they become known
> as Alexanderson alternators.
Fessenden worked with production of high frequency
alternators, where apparently Alexanderson may have
been the primary engineering influence in their
production. An ordinary alternator has a field
that moves in rotation by slip ring contacts, via DC
delivery for a rotating (magnetic) field. The
receiving coils, or stator winds are stable and
mounted in the housing. In the high frequency
alternator both windings are designed to rotate
against the other. It is said that Fessenden once
insisted in a wooden commutator, which caused
Alexanderson to shake his head and mutter comments of
derision.

Actually the concept of using non- ferrous materials
may not be that rediculous. After so high a frequency,
probably past 500 hz, use of iron to aid or amplify
the changing polarity magnetic field becomes less
effective, and heat losses undoubtably are greater.
The use of special ferrites comes to mind which were
not available at the centuries turn.

>  > Thinking about the original idea some more I
> figured that one might be
>  > able to work such a system by using a ring of
> magnets inside the inner
>  > diameter of a toroid wrapped with wire that
> switches direction every
>  > turn.
The spinning DC field  of a car alternator uses a pole
face rotor where the DC current is usually introduced
on the spinning part by slip rings. However the so
called reluctance alternator does not have a
"spinning" energized DC field, rather there is a set
of spinning pole faces mounted around a cup shaped
electromagnet, where the spinning ferrous pole face
metal actually grabs the magnetism from the field by
being the path of least reluctance, however an extra
air gap is introduced on the dc field itself, where
with normal alternators the only air gap is the one
between the spinning field and the stationary stator
coils. I have some larger bus alternators that use
this principle. The pole face rotor looks like a set
of  separated hands with the fingers spead apart to
allow alternating fingers and air gaps in a circle. On
one hands fingers are all south poles and vice versa
the other hands fingers are north poles. In between
the fingers are flux leakage of magnetic field. The
air gaps between these pole face projections allow for
a path of stator metal to react between the air gaps,
introducing changing magnetic flux on their stator
cores.

An alternator in rotation will produce both amperage
and voltage WITHOUT the field being energized, however
this is usually only about 10% of what would be
available if the field were actually energized to its
optimum performance. Some folks explain this as
remanent magnetism of the pole face rotor, but I do
not accept that explanation. The macroscopic rotation
itself of the ferromagnetic domains, when applied as
gyroscopic reactions of electron orbital spins may
cause this magnetism, which is why there is a
"correct" polarity designation for sending current
through the rotating field. In order to make the
rotating alternator output zero power one must
actually send in a current that makes a magnetic field
in the opposite direction to the prexistant rotational
one.
    This facet of a pre-existant magnetic field on the
pole face rotors due to rotation alone allows for some
unusual manipulations of the alternator, essentially
applying the principle of controlled feedback currents
to the field to achieve any desired mode of operation.
In the alternators ordinary operation it is the flux
leakage of the pole faces that circularly rotates
through space that introduces the changing magnetic
field on the stator cores. However if the fields
energized current is obtained from one particular
phases pre-existant or what is also called a
parametric stator output, if the energized field
current is instead taken as a DC rectified pulse, that
pulse means that DC field is now also expanding in
space via the use of a field that varies in time. And
one of the three output phases will record a higher
flux change and voltage from this internally timed
self energized field effect.
    The effect however is not so easily controlled. If
one merely rectifies an parametric output phase to be
introduced as a recycled field current, this quickly
leads to a magnetic  field -stator chain reaction
leading to overload operation. Special circuits need
to be used to control the amount of field amperage
that gets recycled. In this situation since only
motive power input is needed for the self energized
field method, it is almost as efficient to the
conventional method when  both  conventional and self
energized field outputs are compared to the normal
method of using extra input electrical energy to serve
the fields demands.

> Instead you could base it on this idea:  If you
> stick a "C" shaped piece
> of iron across a bar magnet, you short it out.
This is essentially what happens when the pole faces
air gap sweeps by the stator metal cores of those
windings, and indeed we only need to make a very large
pole face assembly with many teeth to make a higher
frequency alternator. But one may need to change the
stator core material if frequencies are excessive. The
normal car alternator may have 7 pole face projections
on each side, making 7 cycles per rotation. This is
practical for making frequencies in the 500 hz range.
HDN