Author Topic: Low RPM generator - good or bad idea? (Read 15289 times)

claude · « **on:** August 29, 2006, 11:37:02 AM »

Hello fine people,

My name is Claude, I'm from Romania and I recently signed up to this board. I'm passionate about wind energy. I want to build my windmill using regular items. Neo's here in Romania are a bit hard to find and/or very expensive. So I thought of using speaker magnets. The idea I have should work (by the way, I'm a designer, I don't have any technical background so have mercy..) I'll try to post a drawing of what I have in mind. Please share your opinion on this. I need to find out several things:

1. Do you think it will work at all?

2. How many magnets and coils should I use and what kind of wiring?

3. There will be small coils used so please advice what size of wire should I use and how many turns.

I will answer any question will arise, on a daily basis.

claude · « **Reply #1 on:** August 29, 2006, 05:40:26 AM »

drdongle · « **Reply #2 on:** August 29, 2006, 06:45:13 AM »

The problem with your design is that the poles (N&S) are on the faces of the magnets not on the inside and outside.

May I suggest that you define how much power you need (with reserve capacity) and then you can design a system to provide what you need.

I also further recommend that you read through the archive of articles here for more in depth info.

Flux · « **Reply #3 on:** August 29, 2006, 06:57:39 AM »

As it stands you will have very poor use of your magnets. You could probably make the idea work by reversing alternate magnets and using laminated iron flux concentrators between magnets. You may even get reasonable results without laminating the concentrators at the expense of some iron loss.

The core the coils are wound on will need to be well laminated.

I am fairy sure it is a workable idea but will be costly and heavy to produce.

It seems to be a modification of a Holmes alternator and generally falls into the category of torus. It will have a reasonably high specific output for a machine using ceramic magnets.

I can see some challenges in building it but will be interested in the results.

Flux

pepa · « **Reply #4 on:** August 29, 2006, 07:00:28 AM »

hi claud, this is a unproven desigh that i have been playing with. it works on the same principle of a horseshoe magnet with the poles facing each other. it should work for you if you use stainless steel bolts and use a non magnetic base for the rotor. having the outer part of the horseshoe detachable you can install a regular stater in place and reinstall the outer magnets safely, with out the use of jacking screws and still get the full magnet flux with iron backing. just a thought pepa

electrondady1 · « **Reply #5 on:** August 29, 2006, 07:28:34 AM »

greetings claude,

this is a unique design.!!

i don't have the experise to anser your questions.

the tube shaped coils will be exposed to both poles as they go through the center of the mags. very much like the voice coil of a speaker.

it is difficult to know if this is a good way to generate power.

i will caution you in using ceramic magnets in this way.

the magnets are very brittle and may break during the cutting processor and when they are secured in place.

i have found it difficult to obtain similar size speaker magnets.in order to build a precise machine.

i ended up cutting the magnets into small pieces and using them in a conventional dual rotor.a lot of work for the power you get.ceramic magnets will generate power but you need a lot of them and you need to spim them quickly.

a source of neo magnets is in broken computor harddrives . try computor repair places.

pepa · « **Reply #6 on:** August 29, 2006, 07:30:40 AM »

sorry claud, i posted a early design, this should give more clearence for the magnet flux.

pepa

ghurd · « **Reply #7 on:** August 29, 2006, 08:21:48 AM »

Hello Claude,

I thought about something like that for a long time.

It takes a lot of magnets.

It will be big, heavy and bulky. Some parts would be difficult for me to make.

Is the plan to use existing coils? The resistance is quite high for the coils I found, and many coils will need to be paralleled. The laminations will need to be left in the coils.

The last plan I thought about was to cut the magnets in half, turn them radial, stack them very deep.

And then use transformer coils, that are on plastic forms. They slide off the laminate core.

This would look and be much like a standard single rotor design.

I did not proceed because it seemed like a poor use of resources.

Ed made a nice windmill from microwave magnets and microwave wire.

I believe something like this is probably best.

Microwave magnets are smaller than most automotive speakers.

Stacking magnets 2 or 3 deep and using 2 rotors (no laminations) could make a decent dual rotor machine.

http://www.windstuffnow.com/main/microwave_wind_generator.htm

G-

claude · « **Reply #8 on:** August 29, 2006, 09:06:31 AM »

Hy electrodandy,

I know about the HD magnets. I have a few but are fairly unusable because of their double poles. Thank you for your appreciations. I too thought it will be nearly impossible to find so many similar magnets and cut them to shape. I know ceramics, i was playing with them as a little boy. I admit my design poses so many technical challenges that i'll never be able to do it. Nevertheless I still needed "expert's approval" .. :-)

Claude

claude · « **Reply #9 on:** August 29, 2006, 09:15:43 AM »

Thank you dr. Dongle,

I now realize I would have great field losses like this. Wasn't paying enough attention on Phisics classes...

The power i'm expecting would be something like 16V, 2A. I think I'll stick to finding bigger steppers or DC motors. For now, living in a downtown apartment doesn't leave too much space for projects like the generator I posted. And believe me, I read the forum cover to cover. Neodynium magnets everywhere...

Thanks, Claude.

willib · « **Reply #10 on:** August 29, 2006, 09:18:49 AM »

This isnt directly related to the O.P. question, but i've been thinking about it on and off for some time.

Has anyone ever thought of using the ferrite material that comes with almost any TV (right behind the deflection coils ), for an additive to a stator ,or for a core in a toroid alternator?

it is very brittle and can be crushed and ground into a powder , and then cast into a core on a toroid ? or cast into a stator with the wire?

claude · « **Reply #11 on:** August 29, 2006, 09:21:59 AM »

"I am fairy sure it is a workable idea but will be costly and heavy to produce."

Yes, you're right, for now it's impossible for me to build it. Laminations and magnet cutting to shape, especially. Not speaking about finding that many of them at the same size.

"I can see some challenges in building it but will be interested in the results."

Tell me about it. If someone builds it, (by the way, it's free, no patents pending, no copyright or stuff) I think I'll be on the first plane out there to see it... :-)

Claude

claude · « **Reply #12 on:** August 29, 2006, 09:31:12 AM »

Thanks for the info ghurd!

I saw Ed's project a while ago. Nice. My coils were intended to be new, no other used parts involved. Microwave magnets...well, let's say that microwave ovens are not something you'll find at the scrapyard here. We're still repairing them :-). But hey, we've got neodynium's around here (imported & prohibitive as prices) so it's not so bad!

Claude

finnsawyer · « **Reply #13 on:** August 29, 2006, 09:38:51 AM »

The problem with this design is that the coils will always be in a region of low magnetic field. The magnetic field (and flux) will go from a north pole of one magnet to the south pole of the next magnet, through that magnet (not the air) to the north pole of the magnet and on to the next magnet. There will never be any subtantial flux passing through the coils, nor will the wires of the coils be crossing the magnetic field at right angles. Faraday's law says this will not work. You would be better off using the 3:4 design or my 3:2 (unproven, see my diary) design. If you're looking for a low rpm alternator you might get better results with my design, but it's going to take a lot of copper wire. With 24 magnets you will need 36 coils and a very large rotor. But it's those aspects that should make it a better low rpm alternator.

powerbuoy · « **Reply #14 on:** August 29, 2006, 11:05:12 AM »

Claude:

I believe that this drawing shows how the flux would cut the coils.

In this screnario, no current is generated because each coil sides tries to push the current into the same directions, result is cancellation. This assumes that the coils have air cores.

Powerbuoy

Flux · « **Reply #15 on:** August 29, 2006, 12:47:02 PM »

It can't work with air cored coils, flux must pass circumferentially through an iron core, output would be tiny without an iron core. It is only a slightly modified form of torus with flux entering 3 sides rather than 2.

Chalmers and Spooner have done a fair bit of work on this type of machine. It's nothing new, just more attractive with modern magnets.

Proven have used it for years. Like all iron cored machines it is difficult to get decent core material in small quantities and if you use crap iron you spoil the machine.

RogerAS · « **Reply #16 on:** August 29, 2006, 01:52:50 PM »

Claude,

Just get two pairs of pliers and snap the hard drive magnets in half.Actually very easy to do. If you eliminate the center section, about 1/5 the overall length, the poles will be quite strong and well defined. That middle is a "no mans land" that can be either N or S. Wear eye protection and give it a try, it's really easy to do.

powerbuoy · « **Reply #17 on:** August 29, 2006, 02:29:36 PM »

How actually is Provens generator designed? Does anyone know?

Powerbuoy

ghurd · « **Reply #18 on:** August 29, 2006, 02:50:17 PM »

Not sure how relative it is, but I think it could add some insight to the concept.

http://www.fieldlines.com/story/2005/9/2/15582/32487

G-

claude · « **Reply #19 on:** August 29, 2006, 03:44:52 PM »

Hello Flux,

First of all, I do not pretend to be the first to think about this. And believe me, I never heard of torus. I just wanted to put those round speaker magnets to work. This was just one idea I had last night before falling asleep. Sounds creepy, isn't it? My wife would kill me to find this out ...

Here's one for you: If you smash a ceramic magnet to tiny pieces (sand-like size), mix it with epoxy and cast it in some shape, how many poles will it have? And where?

Thanks for your input.

Claude

finnsawyer · « **Reply #20 on:** August 30, 2006, 08:17:20 AM »

You will get two poles. Why? The epoxy is a liquid medium at first. This allows the little sand like magnets to rotate relative to each other to form a larger magnet. They will tend to line up with the Earth's magnetic field just like the tiny magnetic crystals in cooling magma. So, to find where the poles are, find the direction of the Earth's magnetic field relative to the casting at that point on the Earth.

finnsawyer · « **Reply #21 on:** August 30, 2006, 08:56:33 AM »

After I posted this comment, the thought occurred to me that you may want to grind up the ceramic magnets and reconfigure them to some special shaped composite magnets. This is doable, but don't rely on the Earth's magnetic field. Construct electromagnets such that you can put the mold between the poles of the electromagnet before the epoxy has set. You could even cause the casting to have more than two poles by using this technique. But be careful when grinding the magnets. Ceramic dust in the lungs can cause long term health effects. Extreme care must be taken.

wooferhound · « **Reply #22 on:** August 30, 2006, 09:11:46 AM »

A speaker is a generator

just as it is from the factory

http://www.fieldlines.com/story/2003/10/11/204029/79

Flux · « **Reply #23 on:** August 30, 2006, 10:24:26 AM »

Considering how poor bonded ferrites are I think that even if you could overcome the problem of mincing up the magnets, it would end up with poor results.

There are ideal particle sizes for magnet material before sintering but I doubt that you could achieve sensible results after the material has been fires.

It is perfectly possible to remagnetise ferrite magnets with different pole patterns as long as you keep the same axis for isotropic materials.

Almost certainly your best bet is to cut up larger speaker magnets into segments or use small ones complete like the microwave alternator.

With larger rings it is possible to use the magnets with claw type rotors for motor conversions. Elektro produced wind turbine alternators by this method, stacking several stages of claw rotors on one shaft. You will never achieve high flux densities but you will have lower iron loss.

Flux

Stonebrain · « **Reply #24 on:** August 30, 2006, 01:11:43 PM »

cool,woofer

I'm sure a very big speaker would make some significant

power if you take it to some techno-happening(don't forget the earprotection!)

and even better if you place a giant exponentious horn

in front of it.

cheers,

stonebrain

claude · « **Reply #25 on:** August 31, 2006, 12:47:50 AM »

Basically, my idea here moves the coil in a similar manner it moves in a speaker, isn't it? So why wouldn't it generate the same readings you got from moving your speaker? Assuming I leave the coils with their iron core intact and place - say 20 of them on this rotor along with their magnets then one coil passes through 20 magnets at one complete revolution. Multiply this by 20 coils per rotor and... well you do the math, i'm a grahic designer here...

Just in case, i'm won't quit my dayjob yet.

Claude

finnsawyer · « **Reply #26 on:** August 31, 2006, 08:02:57 AM »

I don't believe speakers place the coils in a hole inside the magnets. Anyway, in a speaker the coils will alternate their magnetic polarity, being attracted alternately to the north and south poles, since the magnet has a magnetic field outside it that bends back from the north pole to the south pole. The flux flows from the north pole to the south pole through the air and some passes through the coil. In your design you have channeled all the flux through that part of the air that is directly between the magnets. Very little flux will appear in the center holes.

claude · « **Reply #27 on:** August 31, 2006, 10:54:23 PM »

I don't believe speakers place the coils in a hole inside the magnets.

I don't know about you but all the speakers I opened up had their coils in that center hole of the magnet, with one iron core inside. And I do understand now why my idea won't work. I'm just daydreaming right now :-)

Claude

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Author Topic: Low RPM generator - good or bad idea? (Read 15289 times)