Aluminum

[artv]

Hi All,..I used AL shields to hold magnets on my rotor,.....it didn't seem to effect the flux, since AL is non-magnetic
but now I want to use aluminum to hold my coils in between the magnet rotor ,and the blank spinning disk...
Will the aluminum fork cause problems?............thanks artv

[rossw]

Hi All,..I used AL shields to hold magnets on my rotor,.....it didn't seem to effect the flux, since AL is non-magnetic

True, under certain circumstances.

I want to use aluminum to hold my coils in between the magnet rotor ,and the blank spinning disk...
Will the aluminum fork cause problems?

1. Aluminium conducts electricity.
2. If you use aluminium to hold the coils, it'll be in the changing magnetic field
3. It *WILL* cause you problems.

Suggest you research "eddy current brakes" for detailed explanation of why.

[TomW]

If you have a spare magnet around try this:

Place the magnet on an aluminum pie plate or cake pan. Now try to shake the plate or pan side to side. Note how the magnet "sticks" to the aluminum when it tries to slide.

To compare try it on glass or plastic.

Afterwards you will know about eddy currents.

Tom

[JW]

Also,

You need steel rotors to complete the magnetic circuit. I know if you wave a magnet over a piece of aluminum it will warp and get hot near the magnets proximity.

-edit- even though it may be said that the aluminum is moving with the magnets, the law of "mutual induction" still applies since the coils are saturated with magnetic flux, and the magnetic field "must" colapse, the back EMF will warp the aluminum rotors.-

-edit2- the diode bridge causes the "back EMF" it could be possible that if the alternator voltage was"un-rectified" (AC output) the warping could (atleast in therory) be minimized, this does satisfy the need for completing the "magnetic circuit", so you could expect substantially less output compared to an alternator that has a complete magnetic circuit. For example there would be no advantage to the dual rotor arrangement, since the rotors would not need to be indexed N-S vertically per pole or coil.-
JW

[madlabs]

For another fun experiment, get a piece of 1/2" copper pipe and a NIB magnet that fits inside the pipe. Drop the magnet through the pipe and see what happens. Very cool. This works with aluminum pipe too, just harder to get your hands on.

Jonathan

[fabricator]

Wow!...........What the heck have you got going there? Are those broken up chunks of magnet? Is the white stuff some kind of epoxy putty?

[artv]

Thanks for the replies....I have done those testes with the copper tube and the pie plate...not really sure if the magnet is creating magnets of opposite polarity (around the magnet itself)...,but weaker(so they are attracting,... slowing the descent)??.....or if it creates magnets of the same polarity( ahead of the falling magnet)... ,but weaker(so they are repelling ,...slowing the descent)??
The idea for the fork was to have each half of the fork insulated from itself ,..then use the two halves to be the coil connections ,since AL is a conductor......not sure if that's clear..
JW ...the rotors are steel ,..the AL cut-out were placed over top of the magnet stacks(on my first build) just to hold them in place..
I'm still trying to understand your edit#2...?
Fab...I screwed up the pole spacing on that rotor...I just use spray foam that way it is easy to take apart...it works well for holding the magnets in place...lot less work than the aluminum retainers.....
I tested the twelve poles with one of my coils, with the blank metal spinning with the rotor,..the output was only half of my open pole idea....but I don't think it's an accurate test because of the pole spacing.........artv