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More on laminations
By monte350c, Section Homebrewed Electricity Posted on Sun May 30, 2004 at 12:44:35 PM MST
Slots vs. Slotless - FEMM simulations

Hi All,
I've been trying to wrap my few brain cells around the slotted vs. slotless laminated designs for disk alternators lately. So I ran a couple of simple simulations with two configurations. I tried to keep the main parameters the same for both.
In the first simulation (slotless), the stuff in the screen shot from the top - 1st, a steel disk with 1" by .25" magnets (NdFeB40), then a .25" gap where the coils would lie, then a .75" lamination stack.

In the second sim (slotted), from the top; the same steel disk and magnets, then a .015" gap to the tops of the slots, then the same lamination stack, but with .25 x .25" slots in it.

Measurements in the slotless design in the simulation, pretty much .6 T anywhere in the .25" gap where the coils would be.
Measurements in the slotted design, taken in the middle of the slots, .5 T at the top of the slot (nearest to the magnet), .2 T mid slot, and .1 T near the bottom of the slot.
Now, I need some help with this! Is there something else going on with the slots, or would the slotless design look pretty good providing a good way to hold the coils can be worked out?? Help!
Ted.

More on laminations | 10 comments (10 topical)

Re: More on laminations (none / 0) (#1)
by DanB on Sun May 30, 2004 at 01:36:07 PM MST

I think holding the coils is not a problem with slotless laminates. But I think the .25" airgap you figured might be optimistic... depends I guess.

The field density you need to be worried about I dont think is whats in the slot.. but rather whats in the teeth passing through, and around the coil. The slotted design is much more powerful at any given rpm assuming the magnet rotor is the same.

Re: More on laminations (none / 0) (#2)
by Norm on Sun May 30, 2004 at 02:17:44 PM MST

What a coincidence...I was just reviewing your posting....
http://www.fieldlines.com/story/2004/4/10/182742/367
and you were talking about running the wires thru holes instead of slots, remember? okay now if I can make a small sketch

now if you were to make two coils of laminate of narrower strips as in B clamp them together drill your holes for your coils place your coils in the slots of the bottom strip, put the top strip over the bottom strip with the half-holes aligned and as far as the coils and magnetic flux is concerned the coils are running thru holes.
(These two strips where the holes are will actually be touching the gap in the sketch is just for clarification)
Should be very little cogging (magnetic drag instead) very small air gap(between laminates and magnets)
What do you think?
( :>) Norm

( :>) Norm

Re: More on laminations (none / 0) (#3)
by Victor on Sun May 30, 2004 at 02:30:38 PM MST

Hi Norm,

What you described will work very poorly if at all, since most if not all of the flux will be shunted before it passes the coils.

Victor

[ Parent ]

Re: More on laminations (none / 0) (#5)
by Norm on Sun May 30, 2004 at 02:44:34 PM MST

Victor, Yeah you're probably right just a passing thought about something similar in the design of transformers and how they put the laminates over the coils...
( :>) Norm.
( :>) Norm
[ Parent ]

Re: More on laminations (none / 0) (#4)
by Victor on Sun May 30, 2004 at 02:41:20 PM MST

Hi Ted,

The flux needn't go through the actual copper. The iron routes the flux around the copper which is the whole idea. Note that the slots can be very deep (limited by the physical strength of the teeth) containing lots of copper without increasing the gap at all.

Think about transformers. Virtually all of the flux is in the core, yet fully coupled to the windings.

Victor

Re: More on laminations (none / 0) (#6)
by windstuffnow on Mon May 31, 2004 at 11:24:07 AM MST

Ted,
Can you represent the flux path of a N to S magnet arragement and also a N to N magnet arrangement?

I'll follow up with the point relating to why the laminants work much better.

Have Fun
Windstuff Ed

Have Fun! Windstuff Ed

Re: More on laminations (none / 0) (#7)
by monte350c on Mon May 31, 2004 at 01:20:28 PM MST

Hi Ed,

The pics above have alternating magnetic direction, ie the center magnet has North pointing up and the outer two magnets have South pointing up.

Here are the same simulations with all magnets pointing in the same direction:

Slotted -

and unslotted:

I've been doing a bit of reading about slotless designs in both motors and alternators.

http://www.motion.org/9802bark.htm

http://www.thingap.com/advantage.htm

I'm not too sure if this avenue will have any decent results or not, but I do know it's a lot easier to put together a unit without punching, milling, or drilling the laminations for slots, if there's an alternative...

I'm working on just such a laminated machine without slots at the moment, involving use of some pieces of large sewer pipe (PCV or ABS I'm not too sure - it's big, and blue, and free)

If it works out I'll post some pictures. The innovation is a way to hold the coils without fiberglass or epoxy etc. And the coils can be made quite thin ( .25" or even less) and quite strong.

Looking forward to your input on the slot thing!

Ted.

[ Parent ]

Re: More on laminations (none / 0) (#8)
by windstuffnow on Mon May 31, 2004 at 03:07:04 PM MST

Hi Ted,
That wasn't really what I was looking for, I was thinking in terms of the magnetic flux between 2 magnets, one set in attraction and the other in repulsion.

Anyway, If you take a N and N or S and S and press them together the field extends, or in other words you'll get a larger field. In the case of laminants all the plates become repelling forces. You can see this by taking a few short pieces of steel and put them together like a laminant would be, dont glue them - simply hold them between your fingers and place them on a magnet. Slowly remove the pressure on the pieces between your fingers and you'll find that all the pieces repell each other, If you try to bring them together the center ones will try to escape or get spit out because of these forces. It sort of focus's the field into the wires. If you measure the gauss on the end of each plate you'll find the difference between the magnet and the edge is fairly close to the same reading.

Aren't magnets fun...

Windstuff Ed

Have Fun! Windstuff Ed
[ Parent ]

Re: More on laminations (none / 0) (#10)
by monte350c on Mon May 31, 2004 at 06:23:34 PM MST

Hi Ed,

Beginning to see what you're talking about. So the slotted design will cause more of the field concentrating on the legs of the coils passing through - and there will be more action for less magnet.

Two magnets in attract:

and the same two in repel:

Looks like slots!

Thanks -

Ted.

[ Parent ]

Re: More on laminations (none / 0) (#9)
by RobC on Mon May 31, 2004 at 05:54:25 PM MST

The coils on my machine are fastened to the laminate with thin cotton string and then the whole assembly is coated with Minwax Urethane varnish. So far so good. Gap is .25 or less. RobC

[ Parent ]

More on laminations | 10 comments (10 topical)

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