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Cut Into How Many Pieces 12 or 14
By ghurd, Section Homebrewed Electricity Posted on Tue Oct 17th, 2006 at 01:52:03 PM MST
From a Big Donut Magnet

I have a big speaker mostly apart.
It has a big Strontium magnet measuring 5.3 OD x 2.5 ID x 0.8" (135 x 63 x 22mm)
Not as impressive as it sounds.
I intend to...
Use a speaker plate for the magnet disk, so the magnets can not be spread out.
Single rotor, `probably' no laminations, 12 magnets 9 coils.
Should the magnet be cut into 12 pieces that will nearly touch? About 2mm.
Or should the magnet be cut into 14 pieces, discard 2 pieces, allowing for more distance between the smaller magnets?
Laminations?
It looks like about 100 turns of #20 (0.81mm). (Yes, I know)
Would there be any advantage to using laminations with such long magnets, short coils, and small blades?
G-

Cut Into How Many Pieces 12 or 14 | 16 comments (16 topical, 0 editorial)

Re: Cut Into How Many Pieces 12 or 14 (3.00 / 0) (#1)
by Flux on Tue Oct 17th, 2006 at 08:39:55 AM MST
(User Info)

Without increasing the disc diameter and without a flux return path I doubt that it would be worth the effort of cutting that thing.

The only way to get useful power from it would be to cut it and spread it out on a 8" or so disc and use another spinning disc for the return path.

You would get far more from a few hd magnets placed on the speaker pole pieces.
Flux

Re: Cut Into How Many Pieces 12 or 14 (3.00 / 0) (#2)
by ghurd on Tue Oct 17th, 2006 at 09:36:50 AM MST
(User Info)

That's certainly not what I wanted to hear, after a month of work getting it seperated without breaking the darn magnet. I knew better too.
Thanks Flux,
G-

[ Parent ]

Re: Cut Into How Many Pieces 12 or 14 (3.00 / 0) (#3)
by willib (willibur at comcast dot net) on Tue Oct 17th, 2006 at 09:45:46 AM MST
(User Info) http://www.njwind.com/webcam.html#

well you still have a nice rotor plate
is the dia of the plate the same as the Magnet
or a little smaller?
Carpe Ventum (seize the wind)
[ Parent ]

Re: Cut Into How Many Pieces 12 or 14 (3.00 / 0) (#4)
by ghurd on Tue Oct 17th, 2006 at 10:14:57 AM MST
(User Info)

What do you have in mind?

A little bigger, both about 5.7" with a small lip at the edge, and a gap between the lip and magnet.

"a nice rotor plate" Nope!
The one with the 'hat' has a too big ~13/16" hole, and is sort of conical where the magnet was. A bit of lathe time may get 3/4" of flat surface for magnets, on the same side as the 'hat'.

The flat one has a center hole about 2-3/16".

I'll probably do it anyway, if the magnet cuts easy. Would not be the first time I made something that I knew would not work. The only money will be $4 in epoxy.
G-

[ Parent ]

Re: Cut Into How Many Pieces 12 or 14 (3.00 / 0) (#7)
by willib (willibur at comcast dot net) on Tue Oct 17th, 2006 at 10:49:42 AM MST
(User Info) http://www.njwind.com/webcam.html#

well ,how thick are they?
5.7" dia would make a nice little wind mill
the one with the small hole can go next to the bearing
the larger hole one can be supported by allthread to make a dual rotor machine

Carpe Ventum (seize the wind)
[ Parent ]

Re: Cut Into How Many Pieces 12 or 14 (3.00 / 0) (#15)
by ghurd on Wed Oct 18th, 2006 at 09:18:57 AM MST
(User Info)

It seems that way. :-/
All-thread uses up outside space, outer dead area of the coils, move the magnets in, remove some magnets so they fit, allow for inner dead area of the coils, allow for most of how I plan goes out the window (fudge factor), add more turns for less magnet- meaning more inside and outside area wasted, and I'm out of space. LOL.

But I have a plan. If bike bearings cooperate this time.

[ Parent ]

Re: Cut Into How Many Pieces 12 or 14 (3.00 / 0) (#5)
by bj (jackbp996@msn.com) on Tue Oct 17th, 2006 at 10:28:25 AM MST
(User Info)

Ghurd--don't know if this will help in the future, but I have
had good luck separating those magnets with a bit of heat. Just a
bit though, as they are a somewhat heat sensitive. I use a hair
dryer, and a knife. When the epoxy has softened somewhat, they
can be pried apart with a subsstantial knife.
Hope it helps
bj
thanks all bj
[ Parent ]

Re: Cut Into How Many Pieces 12 or 14 (3.00 / 0) (#8)
by ghurd on Tue Oct 17th, 2006 at 11:08:52 AM MST
(User Info)

Normal speakers, I crack them with a hammer from the inside. No problem. The magnets usually come out OK, but I usually only want the plate with the 'hat'.

This one is a monster. 48oz magnet. The plate lips would not allow any kind of sharp edge to reach in.
An assortment of automotive chems, soaking choke & carb cleaner seemed best, and the lip held the liquid. Then I gave up on saving the magnet and beat it (again) with a pick ax. Really.
Once the magnet was unglued, the pick ax was used to pry up one side enough to get 1/4" plywood in, repeat with thicker plywood... Quite a job. It DID take a month, and it's not yet seperated from the front plate.

The 'hat' on the rear plate makes the magnet seem stronger that it is. The material does not seem much better or different than a microwave magnet.

Jerry has some 9" x 1". Those must have been a bugger to get out whole!
G-

[ Parent ]

Re: Cut Into How Many Pieces 12 or 14 (3.00 / 0) (#6)
by Flux on Tue Oct 17th, 2006 at 10:44:48 AM MST
(User Info)

Just to give you an idea, I cut 2 of those sized things into 6 pieces and made a 6 pole dual rotor with them on about 8" discs. It made a reasonable 80W alternator for a 3' 6" fast 2 blade prop.

With one magnet, no increase in diameter and no flux return path you may get about 20W from a 3 ft very fast prop if you have enough wind.

Ferrites have such low remenant values that you must work them in effective magnetic circuits. This strange desire for single rotor axials and their radial equivalent with no flux path is only viable with neo.

If you have the technology to do it, you loose very little if you don't cut the ring and magnetise it with a multipolar pattern. This is not easy but is what marlec do with their machines. It is much more cost effective than cutting them.

You may be able to make a fairly effective unipolar claw rotor design with these ring magnets, but now that neo is comparatively cheap, ferrites seem a waste of time.

Try it by all means, just don't expect too much.
Flux

[ Parent ]

Re: Cut Into How Many Pieces 12 or 14 (3.00 / 0) (#9)
by ghurd on Tue Oct 17th, 2006 at 12:15:54 PM MST
(User Info)

I did expect more than 20W, with a slower prop, and I certainly do not have enough wind.
Reality always interferes with my hopes and dreams.
I will start thinking about how to use those HD neos on the speaker plate.
Thanks!

But,
Now that you mention claw rotors, and I am not 100% sure what a unipolar claw rotor is.
I have a crazy idea, where the coils are fixed to the donut magnet, and the claw rotates in front of the coils, with the claw's center reaching inside the donut hole.
The field would change because the flux is sometime shorted around the coils.
Very simple to build, if it has any chance of working. I do not expect much.
Crappy sketch (40K) of how I was thinking... King Tut probably had one just like it.
http://www.otherpower.com/images/scimages/2050/RotClaw.jpg

[ Parent ]

Re: Cut Into How Many Pieces 12 or 14 (3.00 / 0) (#10)
by Flux on Tue Oct 17th, 2006 at 12:29:36 PM MST
(User Info)

That is not the way I was thinking of doing it, but it is the same idea. In that simple form it would not be very efficient but it would work.

I was thinking about mounting the inductors on either side of the magnet ring with teeth on the outside with the coils in a small gap. You could perhaps use 12 inductors to make a 12 pole. The coils could be as a disc with claws facing or as a cylinder with claws overlapping.

Not an easy construction without a lathe and mill.
Flux

[ Parent ]

Re: Cut Into How Many Pieces 12 or 14 (3.00 / 0) (#11)
by Flux on Tue Oct 17th, 2006 at 12:31:01 PM MST
(User Info)

Sorry 12 inductors to make 24 pole.

[ Parent ]

Re: Cut Into How Many Pieces 12 or 14 (3.00 / 0) (#12)
by ghurd on Tue Oct 17th, 2006 at 01:54:17 PM MST
(User Info)

Thank you! Understood.
G-

[ Parent ]

Re: Cut Into How Many Pieces 12 or 14 (3.00 / 0) (#13)
by willib (willibur at comcast dot net) on Tue Oct 17th, 2006 at 03:35:44 PM MST
(User Info) http://www.njwind.com/webcam.html#

just had a thought about using a cast iron skillet as a magnet rotor , would just need a little grinding, ok a lot of grinding
but it would work
one would have to cut the lip off and leave the flat round part
Sears is having a sale on three different size skillets all for $13.59 !!
if i buy two sets then i could have three different size rotors to play/work with..
Carpe Ventum (seize the wind)

Re: Cut Into How Many Pieces 12 or 14 (3.00 / 0) (#14)
by electrondady1 on Wed Oct 18th, 2006 at 08:08:47 AM MST
(User Info)

gurd,
i've got the same magnet.
well maybe i sould say i had the same magnet .
i initialy cut it into 8 pieces and cast the pieces into a plastic disk to make a dual stator single rotor gen.
i used that rig for my little erma windmill.
then i discovered this site.
so after two years the geni stopped .
i just pulled it apart and cut the mags in half, 16 pieces.
they all fit nicely on a ten inch saw blade with 50/50 spaceing.
i will use it as one half of a dual rotor with hard drive neos on the other rotor(saw blade).

[ Parent ]

Re: Cut Into How Many Pieces 12 or 14 (3.00 / 0) (#16)
by willib (willibur at comcast dot net) on Wed Oct 18th, 2006 at 10:38:20 AM MST
(User Info) http://www.njwind.com/webcam.html#

neos really stick well to the two i bought, i didnt go for the sets ,but i got two individual ones (8" skillets)
and cast iron cuts real easy with a hacksaw
the brand is Lodge made in USA they seem flatter than the imported ones
Carpe Ventum (seize the wind)
[ Parent ]

Cut Into How Many Pieces 12 or 14 | 16 comments (16 topical, 0 editorial)

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