How does rotor edge flux leakage effect performance?

[esc]

I'm working on a small axial PMA.  There is no noticeable flux leakage on the back of the rotor when testing with a paper clip, but there is a lot on the edge.  The magnets (3/4" x 1/4" N42) are currently 1/4" from the edge of the rotor.

Should I be concerned?
If so, what steps can be taken to remedy the situation?

Add lots of extra diameter to the rotors?  That seems like a waste of good steel.  My guess is that the flux retained would cause less of a power increase than moving the magnets father out.

Any thoughts?

Thanks,

Eric

[Flux]

I am not sure if this is single rotor or dual rotor. if it is single rotor it is pointless worrying much about leakage the whole thing is a joke magnetically.

If it is dual rotor then if you have no really serious flux loss on the back of the discs all will be well. you will be testing within the active magnet region and there is bound to be flux there.

Flux

[esc]

It is a dual rotor and there is no obvious/measurable flux on the back side, so 1/4" of rotor radius outside of the magnets is probably fine?

Do I need ANY additional steel rotor radius outside of the magnets?
To rephrase, is the 1/4" I have outside the magnets now (other than helping to secure the magnets) a waste?

Thanks,

[Flux]

Any steel outside the magnet radius only serves mechanical use, magnetically it will have negligible effect.

Flux

[esc]

That is the answer I was looking for.

Thank you Flux.

[artv]

Flux ....does'nt the magnetic field radiate out from any magnet in a 3d pattern ,like that of the earth,thats why maximum flux linkage occurs when magnet pair are centered in hole of coil,but no generation until they move forward , producing flow in the legs but none in the tops and bottoms of the coils?Could you not use this edge flux leakage by putting the whole assembely inside a steel pipe slightly larger than the stator, thus changing the direction of flux 90 degrees ,that way producing in the tops and bottoms as well............just a thought ........artv 

[Watt]

How about building a magnetic rotor with proper magnets and use iron power and paper to test theory. 

[electronbaby]

Are you testing for this "flux leakage" with the two rotors assembled? properly aligned and facing / attracting each other?? or are you testing with them apart? because if they are apart, there will be flux all over the edge. Try it again with them assembled, and the air gap set to a reasonable distance for the thickness magnet you are using. Ill bet that most noticeable leakage goes away and it becomes a non-issue.

Not sure if you stated if rotors were together or apart?

[esc]

They were apart.  I will retest and report.

[chazsql]

Flux,  Out of curiosity, you said the single rotor turbine is a joke?  Why do you think Hugh Piggott includes that build in his information?  I know you can't read his mind.  Would the 1 magnet rotor with a plain steel rotor opposite it work?

[electrondady1]

back when i was experimenting with ceramic mags ,
 i bagged a completed mag rotor in plastic and sprinkled a lot of iron filings on it to see the magnetic flux pattern.
the flux all went sideways to the magnets next to each other  or back  into the iron disk
and it didn't project out very far from the surface
then i put  the second rotor in place the flux all moved to form a bridge between rotors
and because the distance between rotors was less than the distance between mags on the same rotor
the iron filings  could not be drawn sideways to the joining magnets.
by using a dual rotor layout you are shaping and controlling the path of the magnetic flux.
forcing it to travel through the coils at 90 degrees. which is ideal.

[esc]

I tested the flux leakage on the edge of the rotors of the assembled PMA.   It fell just short of passing the "paper clip" test.  Before the PMA was assembled, testing an individual rotor, the edge leakage would easily support a big screwdriver.

Assembling the PMA rerouted almost all of the flux, causing a dramatic reduction in rotor edge flux leakage.
Flux, you were right.  Electronbaby, you proved it to me.  I thank you both.

It seems that the answer to my question is, I have nothing to worry about because there is no significant rotor edge flux leakage.
I like that kind of answer!