Author Topic: Steel disc question (Read 2715 times)

Devo · « **on:** July 30, 2005, 11:19:40 PM »

I am working out a few ideas in my head before firing up the welder & stuff.

If the steel disc used to "complete" the magnetic path is only a ring of say 2 inches & totally hollow in the centre will it still have the same improvement?

Or say if each mag is on a steel pad in a circle & all pads joined by 1/2" rod would the output improvement still be there?

I am still toying with making a small mill with the mags & coils near the tips of the prop just to see the outcome, I think I have the coil ring & spacer bearings to stop the mags from hitting the coils under blade flex figured out just working out the outer ring of magnets

Thanks

Devo

kitno455 · « **Reply #1 on:** July 30, 2005, 07:29:56 PM »

steel ring is fine, flux wants to form shortest path to next mag, basically no flux really passes across the center. the 1/2 inch rod does not seem like such a good idea. not enough contact, and the flux path gets longer because of the thickness of the pads, and the circuitous path thru the rods.

i myself have been considering a small genny with small mags on a big circle. unfortunately, the last couple inches of the blades are the ones doing the most work. you will likely cause a great deal of airflow problems if you put the mags there. plus the linear bearing speeds at the outer edges of anything bigger than a few inches become a real problem. i am interested in your solution...

allan

phil b · « **Reply #2 on:** July 30, 2005, 07:56:13 PM »

I remember a few years ago, someone posted a pic on this site of a modern wind generator that had a ring or hoop around the tips of the blades. I presume the ring was to help with blade stability. It might be a good place to put magnets. Keep in mind the blades will have to be extra strong if you embed magnets. This might work. Keep us posted.

Victor · « **Reply #3 on:** July 30, 2005, 07:58:37 PM »

Hi Devo and Alan,

As crazy of an idea as I think this is I still have a few comments.

If I understand what you want to do correctly I would look at a radial flux alternator as this both solves some of the blade flex problems and acts as a ducted turbine.

How many magnets and at what diameter are you thinking? or in other words just how long is the flux path to the adjacent pole? Flux goes though iron roughly 1000 times easier than air so your air gap (thats the gap from the magnet face to the backing iron on the other side of the coil) will still dominate the circut reluctance. Figuring that you will have a flux density though the coil of .6 -.7 tesla and steel saturates arount 1.8 tesla if the cross section of the flux path to each adjacent pole is 20% of the cross section of the magnets you will be well below saturation.

Of course if the backing iron is to be stationary it will need to be laminated.

Writing this makes me realize how unclear my understanding of what you are trying to do is. Anyway I'm sure we will all love reading about how it comes off.

Good luck

Victor

rotornuts · « **Reply #4 on:** July 30, 2005, 09:16:46 PM »

I had a similar idea last year and experimented with attaching magnets to a tireless bike rim and placed a cluster of coils in a linear fashion in one location rather than all around the rim. I had a cad drawing of the idea but I've missplaced it and I must have deleted it from my user files. Electric ed had the idea of using transformers cut in half and rewound with heavier gauge wire. The output of my little experiment wasn't impressive but it was a hack job. I think the tranformer halves place in a linear fashion in a cluster covering just a portion of the diameter(perhaps five big coils with ten poles?) would be the way to go so you don't have to worry about supporting coils all the way around the rotor. If you had a rim around the blades for the magnets then you'd only need pillow blocks or equivelent roller bearings to guide the rim through the coil cluster.

Here's a link to the post from last year.

http://www.fieldlines.com/story/2004/11/25/43923/481

I thought at the time it was a pretty good idea but I'm not so sure now as I'm thinking theses days there is probably better ways to increase output and regardless of confiquration there is still only so much power available in the wind.

Mike

ghurd · « **Reply #5 on:** July 30, 2005, 10:50:29 PM »

OK. This was silly.

Looked really great at the time. Still does.

But I took a shaded pole motor from a 12-16" fan or something.

Left the windings intact. 120VAC, and I don't recall but maybe 300ma?

Put 2 hard drive neos on the rotor.

Cut the laminations so the flux could not get shorted around the coil. Removed the 'shade' to reduce eddie currents.

Nothing. Volts or amps.

I couldn't even tell if made enough to accuratly register on the meter.

I was expecting a LOT of volts and very little amps.

Knowing much more now, the coil could have been bad.

Still looks like a do-able urban VAWT for AA powered LED landscape lights to me!!!

somehow

G-

41south · « **Reply #6 on:** July 30, 2005, 11:19:31 PM »

For a small experimental VAWT I was going to use these steel rings.

They are disk brakes off a Honda motorcycle and are 24 cm,or about 10 inches in diameter.

ghurd · « **Reply #7 on:** July 30, 2005, 11:21:53 PM »

Dang !!!

Now I'm thinking about it again!

Probably been 2 or 3 years!

Nothing.

As fast as I could turn it.

The lam cuts (removed sections) were larger than the mags.

The mags were N-S. Facing out.

The air gap was so small, rotating took some epoxy(?) coating off the mags.

Bushings, Al ends, 1,000,000 turns of 100ga coil, ...

coil must be bad.

Flux · « **Reply #8 on:** July 31, 2005, 01:10:01 AM »

41south Those Honda discs look great, but check that they are not stainless, many motorcycle discs never rust and I suspect that they may be stainless.

If they are a magnetic grade of stainless they may still be ok.

For Devo I tend to agree with Victor about going radial. I seem to remember a German firm tried this many years ago but can't remember who it was.

Flux

tecker · « **Reply #9 on:** July 31, 2005, 02:44:29 AM »

There is improvements in out put with a nonmetallic hub the flux is isolated to the adjacent magnets and not to the hub assembly( I am assuming ) . The improvement is most noticeable at running speeds but I've made no calculations at lower speeds .

stevesteve · « **Reply #10 on:** July 31, 2005, 03:29:13 AM »

I seem to remember seeing rust on motorbike disks when they have been left out for a while. They may just stay shiny as the brake pads polish them each time they are used.

I wondered about using them before, those disks look great as they are solid and not the perforated type(through the disk from face to face not just vented within the thickness), which I suspect would interfere with the flux path.

Still at the 'must wind coils stage' for my small machine based on steel rings.

Experimental · « **Reply #11 on:** July 31, 2005, 09:32:10 AM »

Tried this many years ago -- thinking that the faster the mags pass the coils, the more current made , and a fellow by the name of "Smokey Yunic", made a very large one, many years ago -- it was featured in Popular Mechanics magazine..

Mine worked pretty well -- but, because the mags are so far out on the blades -- it took a twenty knot wind to get it going, and about the same to keep it going !!!

Many of us have experienced problems with "cogging", preventing our mills from operating in light and even moderate winds -- thus, the farther out you put the mags, the greater the effect at startup..

This is not to say, it won,t work, I,m just pointing out, a major problem with this type of mill...

Keep thinking and experimenting, you might succeed, where others have failed, Bill H.....

Ungrounded Lightning Rod · « **Reply #12 on:** July 31, 2005, 12:53:46 PM »

The ring turns the prop into a "ducted fan" - in addition to strengthening the structure it keeps the wind from running around the end of the blade, increasing the amount that passes through the blades.

You can build a ducted fan with the duct stationary or rotating with the blades, or just use little airfoil-shaped pieces of it at the tip of each blade. (Search for "wing keel" to see the same thing done to greatly reduce the depth of sailboat keels.)

If you have built a duct structure it seems like a good place for the genny - lots of relative speed for the magnets and coils means more efficient use of the magnets. Downside is that you have to keep the rotor and stator close but not striking each other under varying wind speeds and yaw action, which could be very difficult. The rotor will experience huge gyroscopic forces under yaw trying to tip it, the stator will not.

Ungrounded Lightning Rod · « **Reply #13 on:** July 31, 2005, 01:03:23 PM »

If the steel disc used to "complete" the magnetic path is only a ring of say 2 inches & totally hollow in the centre will it still have the same improvement?

The return flux from each magnet is split in half and goes to the two adjoing magnets. So a donut is fine. The middle part is only structural.

You can also use a thicker steel strap to connect pairs of adjacent magnets, so they exchange all their return flux with a single neighbor. (Downside is you don't get the structural strength of the steel disk or donut and have to provide it some other way.)

Or say if each mag is on a steel pad in a circle & all pads joined by 1/2" rod would the output improvement still be there?

Compared to no steel rod, yes. But a wide steel plate is much better than trying to squeeze the flux down a narrow channel.

41south · « **Reply #14 on:** July 31, 2005, 02:30:35 PM »

Thanks for the info Flux, I see some rust on these already, would this indicate that they are not stainless?

Devo · « **Reply #15 on:** July 31, 2005, 05:07:22 PM »

Thanks for all the input , I may try a small version first & work up , I am going to lay the coils right under a baearing that will run against the steel ring outside of the magnets a fair ways to reduce eddy currents as the bearings will be stationary .

I would set it up so the air gap was a little wide for easy start up & under heavy wind the blades would bend into the coils , The bearing holding the mag ring so as to just clear the coil. Hopefully the stronger the wind the smaller the airgap until max is reached.

I have been thinking about this for a few years , that's how I found this site -looking into wind energy (Glad I looked as this place is great).

I think it would be less proned to stalling as the space between the coils could be enormous with the same "pulse" or rpm , or one could run way less turns & use more coils or coils & mags to make a super smooth output.(I think)

One other question I have is can I carve the blades so the tips go to no angle & attach the ring or would this hamper performance? Also if I was to add an airfoil would it be to direct air in towards the blades from the front or to "pull" it out & away on the aft side if you catch what I mean?

a fella could through a quick test rig together with some pvc,a hoola hoop & some small neos, no iron though...

Thanks

Devo

rotornuts · « **Reply #16 on:** July 31, 2005, 11:45:42 PM »

I tried a mountain bike rim still spoked to the hub. I used black tape and taped it around the spokes to create "blades". It actually caught the wind not bad but it really smacked as the magnets passed the coils. You could hear the thumping of the magnets passing the coils from a good distance. The magnets held themselves to the steel rim with no tire on it in a radial fashion rather than axial. I didn't go any farther with it.

It occurred to me that I may be chasing a dead horse with this one when it dawned on me that a windmill is a form of a lever and putting the "load" outside the "applied force" changes it from a second class lever into a third class lever. In other words you go from multiplying the force generated by the rotor to multiplying load placed on the rotor. The averaged applied force is between the fulcrum and the load and I'm not sure that's desirable even if it amounts to increased speed because it's at a lower level of available torque.

Mike

Devo · « **Reply #17 on:** August 01, 2005, 03:13:09 AM »

Mike I agree that it may not be a good idea but I always have to prove this to myself before I can let it go...., sometimes this is a good thing & sometimes it isn't:-)

I will work away at this little side project & if I ever make any headway I will of course post it at the board.

My wifes grandpa (no longer with us) used to have bike rims on end 3 deep with little coloured scoops that would turn the rims. It always caught my attention when we visited,even now my little mill has only put out 15 amps but it always brings a smile to my face when the wind blows.

Quite addicting

Devo

electrondady1 · « **Reply #18 on:** August 01, 2005, 05:57:03 AM »

smokey ynic is a famus engine builder, didn't know he made genies

Experimental · « **Reply #19 on:** August 01, 2005, 11:12:36 AM »

Your right Electrondady -- Smokey was involved in raceing, and was quite an inventer -- that wind gin, as I remember was very large, 12 or 16', like a farm type and if I remember correctly, it was on top of his shop -- seems to me, it was in Florida...

I still have a bunch of old Popular mechanics books -- i might see if I still have it !! Bill H....

rotornuts · « **Reply #20 on:** August 01, 2005, 12:16:26 PM »

I'm in agreement with you and I don't mean to discurage you from trying it. It's fun, fun, fun doing this stuff and seeing for oneself is a fantastic route to better understanding and innovation.

Mike

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Author Topic: Steel disc question (Read 2715 times)