holes in coils waste space?

[artv]

why do we need the holes in the coils,?everything I read says get as much copper in there as you can..3/4" wide magnet every 3/4"of wire change connections ,whether its 20 strands of wire/3/4"thick, or 200 stands of wire/3/4"(very thin wire)..3/4 being the overall width of the conductor seeing the magnetic flux

[bob g]

Art:

you seem like a very nice guy, and sharp enough to formulate some good questions, however
i wonder why you don't go at least find and check out some books on the subject.

the answer to you question comes down to the need to have this space, because if you didn't you would have
both legs of the coil under the magnetic field at pretty much the same time, so what power is induced in one leg
of the winding would be mostly offset by the power induced in the opposing leg.

there are some benefits to partial pitch, but under about 2/3 pitch whatever benefits you will get will be offset by the
cancellation factor.

when i mention benefits, i mean waveshape formation and not efficiency (generally)

bob g

[artv]

bob g.....I appreciate the reply...I've been searching the internet ,(I don't have time to go to a libraury,or the means).So what your saying is the voltage  produced in a single coil,goes in one direcetion in one leg opposite direction in the other leg of same coil,you need that hole for the reversing affect?Without the hole the two would overlap causing cancelation??So basically what your saying is you want the flux linkage to produce on the first leg of the coil ,then stop , then produce on the second leg ,but in the opposite direction,thus AC...........Is this an accurate understanding???..........believe me I've been reading all that I can find but they all seem to say the same thing...........artv

[wpowokal]

http://www.6pie.com/coilsandmagneticflux.php

[artv]

thanks for the link ....best explanation I've read so far ...theres probably more out there just have'nt found them yet.They all say the same thing though,as the flux cuts across the conductor it creates current flow, which inturn creates its' own magnetic field which opposes the original flow of flux...........artv

[ghurd]

"as the flux cuts across the conductor it creates current flow, which inturn creates its' own magnetic field which opposes the original flow of flux"

If it do not create an opposing field, then the PMA would spin freely.
Meaning a 10,000RPM weed whacker motor could spin a PMA making a gazzillion watts.
Meaning it could make more power than it used.  Meaning OU, which does not exist.

Make a PMA or get a decent DC motor.  Short it.  Turn it.  The theoretical opposing force becomes very real at that exact moment.

What I think you are missing:  All this stuff is interconnected.  Completely intertwined with everything else.  You don't seem to be applying one topic's relative information to the next.

[wpowokal]

G so say all of us!!!!!!!!!
Cleaver questions, my money i on this guy is pulling our pislar.
allan

[artv]

ghurd and allan ....I appreciate the replies ,I'm not trying to fool anybody or anything like that .I need to understand exactly what takes place when you start the rotor turning .The way I see it now is as the mags approach coil leg, flux induces current flow,lets say clockwise,hits hole stops,hits other leg induces current flow in the other direction(counter clockwise)but at the same time current flow in the coil creates its' own magnetic field opposite of the mags themselves .Do I understand this correctly ,if not where am I wrong??..............artv 

[ghurd]

Yes.  It is that simple.

A moving magnetic field creates a current flow in a conductor,
and a current flow creates a magnetic field.

The strength of the field, or the voltage, or whatever, is all related to each other.
Can not have one without the other.

[artv]

so let's get rid of the holes, more room for more wire, more power..............stair step the coils, and could'nt you just do a 360 degree phase,.......instead of 3 phase.........artv

[ghurd]

Yes and No.

You understand how a 3 phase can have 6 coils (2 per phase)?  As long as the coils in a phase are "in phase".
Then a 6-phase is really a 3-phase.
And 360 coils, one every degree, is really a 3-phase.

A 4-phase is really a 2-phase.  Etc.

Pretty much limited to 3, 5 and 7 phases.  (one of Hugh's books has plans for a 5-phase {non overlapping coils} PMA)

"get rid of the holes" means overlapping coils.
2 main problems with that.

First, there is not a 'hole'  ( ) lot of space in there to get rid of.  Look at Ed's Alt From Scratch.  The stator is pretty full, and thats only a 3-phase.
http://www.windstuffnow.com/main/alt_from_scratch.htm

Second is the ID and OD of the coil area.  That's a lot of wire to stack on top of each other.  The stator becomes very thick, and the air gap becomes too large.

5 phase could be a bit more efficient than 3.  7 phases could be a bit more efficient than 5, but the change is less.
Every time another phase is added, the gain becomes considerably less than it was for adding the last phase.
And every phase makes the stator thicker too, so eventually the extra copper will actually reduce the output.

Somewhere in there, it becomes futile chasing the gain, and you realize it would make more sense to just use 3 (or 5) phases with a single layer of coils and just use a bit larger magnets to make up the difference.

Back to 360 phase.  Must have an even number of magnets.  Pretty much need to have a prime number of phases (I think).
So 359 phase.  The next step below 359 phase is 353 phase.  And the difference between them is completely negligible.

Going from 3 phase with a single layer of coils to a 3 phase with overlapping coils is probably the biggest gain to be had,
but most people who try it for a dual rotor find the gain is not worth the pain.
G-