Author Topic: DC instead of AC Generator (Read 2800 times)

apollospeed · « **on:** July 27, 2006, 10:27:50 PM »

Hello, I just had a couple questions if you don't mind.

I currently working on an "experiment" (just an experiment, it will not be a windmill) that is simularly built like otherpower's windmill volvo rotor altenators/generators are..... But my problem is that I can't use alternating poles on my generator....long story.

Anyways, my question is that If I use the same poles across the coils, will I get DC current ?

And should I use the 3 phase setup on those coils, or single phase ?

And last but not least....I'm looking at faster rpms (around 800-2500) Should I use smaller wire and more turns for the coils??

thanks a bunch,

Drew

willib · « **Reply #1 on:** July 27, 2006, 04:43:39 PM »

long story ??

if you want an answer you should explain what the problem is

apollospeed · « **Reply #2 on:** July 27, 2006, 04:58:19 PM »

basically, I got this experiment where I need all the same poles up, because I'm an electromagnet as well, so I need all poles up.

So, there for, I'm wondering If I can still make generator electricity from the same poles running across coils as apposed to alternating poles.

Can I not make electricity from same poles across coils?

willib · « **Reply #3 on:** July 27, 2006, 05:21:50 PM »

ok i'm going to give you one more chance , so please choose you words wisely.

use the preview several times , ok?

"I got this experiment where I need all the same poles up"

why?

Slingshot · « **Reply #4 on:** July 27, 2006, 05:42:47 PM »

Are you asking whether you will get electricity if you orient the magnets all north on one disk and all south on the other, rather than alternating them?

The answer is yes, you will, but the voltage will be much lower and it will still be AC.

The voltage generated depends upon the rate of change of magnetic flux through the coils.

Consider the normal case where the flux starts out (a) north-to-south, then becomes (b) south-to-north, then goes back to (a) north-to-south, etc. Let's arbitrarily all changing from (a) to (b) "decreasing" and (b) to (a) "increasing". Let's further say that when flux is decreasing you get a negative voltage across a coil, and increasing gives a positive voltage. Obviously you have AC because the voltage periodically varies from positive to negative and back.

Now consider the case where all the magnets point the same way, for example, (a) north-to-south. As this pair of magnets moves out of the coil, flux will decrease, though it never becomes zero. Then, as the next (a) north-to-south pair approaches alignment with the coil, flux increases back to the original level. So you still get both a negative and a positive voltage across the coil, because flux went down and then back up again. It doesn't matter that it never reached, or went beyond, the zero point.

What does matter is that the change was now smaller, in the same amount of time, so all you have done is made an alternator with a lower output voltage. It is still going to be AC.

powerbuoy · « **Reply #5 on:** July 27, 2006, 05:53:13 PM »

apollo ...scan a quick drawing ...that'll help us a lot

apollospeed · « **Reply #6 on:** July 27, 2006, 06:38:55 PM »

http://www.myplasticfriends.com/drawing1.gif

there is a rough Windows Paint sketch that I did.

The south magnets are all face up on the smaller Diameter.....and the north are all up on the to bigger Diameter(may only do one large diameter, not decided yet).

I gotta have all poles the same on each corrisponding wheel..... I will explain more on this later ( it is sorta putting together the principles of a windmill alternator and a electromagnetic motor).

So, should I got for the single phase (1 coil per magnet pole)

or 3-phase (3 coils per 4 poles) ?

willib · « **Reply #7 on:** July 27, 2006, 07:04:20 PM »

My opinion is , it will not work well

the idea of the axial flux generator is to have one north pole passing over one leg of a coil while a south pole is passing over the other leg.

or a north south pair , over one leg and a south north pair passing over the other leg , in a dual rotor design

Ungrounded Lightning Rod · « **Reply #8 on:** July 27, 2006, 07:06:13 PM »

Getting DC (long-term) from moving a conductor in a magnetic field ALWAYS involves a sliding contact.

If you have a coil and don't reconnect it to the external circuit in different ways at different parts of the cycle of motion, by the time the moving parts get back to the starting position you'll have had both positive and negative voltages across its output terminals, and the time integral of the voltage induced during the cycle will have been zero.

apollospeed · « **Reply #9 on:** July 27, 2006, 07:11:31 PM »

SO yall are saying that, no matter what the arrangement of coils......my design will not provide any electricity? Even though there is a N-S-N between all the diameters?

kitno455 · « **Reply #10 on:** July 27, 2006, 07:22:45 PM »

you have drawn the coils flat on both views of the device. that is impossible, unless it has two sets of coils, of course. which one of those you choose changes the way the magnets must face.

if you build the coils and stator flat like the usual axial-flux genny so popular here, then you must alternate mags NSNS on each plate, and the plates must have opposing mags so they are attracted to one another. in this design, your radial S pole mags would be completely useless, as they dont cut across any turns in the coils, but rather, move along them. you could build it with only N poles, but then what happens is the gaps between the mags actually build up enough field to act like S poles, so you might as well put mags there, and make it stronger.
if you build your stator like a toroid machine with an iron core, you want alternating NSNS on each plate, but you likely want the plates to have the same pole opposite one another. in that case, your S poles would need to alternate the same as the plates.
if you build your stator like a toroid without the iron core, your airgap will be too big, unless the stator is quite thin. but with like poles across from each other, it does not matter how tight you get the air gap, most of the flux will turn away from your coils!

#2 is reasonably workable if you alternate your mags, i built something like it myself. with non-alternating mags? sorry dude, either you have left something very important out of your description/drawings, or your idea is going to disappoint you.

allan

kitno455 · « **Reply #11 on:** July 27, 2006, 07:23:57 PM »

no, we said it would provide very little, much more could be had from the same amount of mags and wire with a traditional design.

allan

kitno455 · « **Reply #12 on:** July 27, 2006, 07:29:07 PM »

let me re-phrase that:

depending on the stator configuration (axial vs toroid, iron vs air) you will either get less output than a traditional system, or none at all.

allan

apollospeed · « **Reply #13 on:** July 27, 2006, 07:38:37 PM »

it will be axial.....and Iron backing the magnets on the large diameter, and aluminum on the smaller.

But, should I got for Single Phase Config on the coils, or 3 phase config ?

Countryboy · « **Reply #14 on:** July 27, 2006, 07:40:54 PM »

How about explaining what your goal is. You're babbling incoherent nonsense thus far.

Be articulate. Write it out so that an 8th grade student with no knowledge of electric generation will be able to understand what you are asking, even if they won't be able to provide you the correct answer.

My opinion - if you want DC current, either use a DC motor to generate DC, or rectify the AC into DC current.

powerbuoy · « **Reply #15 on:** July 27, 2006, 07:59:59 PM »

kitno is correct ...must have read spooners paper :-))

I can see what you are doing, trying to route as much flux through the coil as possible ...I guess nobody has tried that wild arrangement yet ... surely quite a difficult genny to built. Sometimes simpler is better ...

Is my drawing correct? Powerbuoy

apollospeed · « **Reply #16 on:** July 27, 2006, 08:28:42 PM »

Ok, PowerBuoy's drawing is pretty close to what I'm trying to explain.

Sorry for the confusion guys.

So going off that, should I have 1 coil per magnet (single phase style) or 3 coils per 4 (3 phase style) ?

Nando · « **Reply #17 on:** July 27, 2006, 10:07:09 PM »

DREW:

I have read all the posts for your message and still you do not give an intelligent question nor inform what are you trying to do and STILL the only thing you ask is 3 phase setup or single phase.

SIMPLE:

To produce electricity the wires need to cut the lines of Flux, also since the coils or wires are finite, they need to have a FLUX change for properly generate the voltage.

If you are planning a generator, the coil or coils need alternating magnetic FLUX .

DO inform in detail if you want to receive a practical suggestion NOBODY can read your mind.

Nando

Nando · « **Reply #18 on:** July 27, 2006, 10:12:46 PM »

Powerbuoy:

PLEASE EXPLAIN what is : must have read spooners paper :-))

In detail

Nando

apollospeed · « **Reply #19 on:** July 28, 2006, 12:12:44 AM »

I'm just experimenting with electromagnets and the axial generator designs. That is why I need all the same poles on the large diameter plates. And all opposite of those on the smaller inside diameter wheel.

I just wanted to know the best why to wire up the coils when not actually using the standard alternating pole design.

I'm thinking that, between both opposite north poles and the inner south pole magnets create a fair amount of flux to make electricity across a coil?

Flux · « **Reply #20 on:** July 28, 2006, 12:27:09 AM »

What you seem to be proposing is a unipolar version of the torus.

Unipolar machines of this type produce ac. You need gaps between the N poles equal to the S poles that you have eliminated and the winding needs to be as if all the poles were present.

Although it will work it will not be as good as a conventional torus. What you gain by adding flux on the 3rd side will be more than offset by the removal of the intermediate poles. You have thrown away the main virtue of the torus by making the coil turns longer and increasing the resistance.

Flux is limited by core saturation so you will see no more flux.

Just an awkward and expensive construction to make something that was rejected 120 years ago.

As always for any ac machine the 3 phase version is far better than single phase.

Have fun, should be a good learning curve.

Flux

dinges · « **Reply #21 on:** July 28, 2006, 02:29:29 AM »

Whatever you like. Single phase, three phase, 5 phases. It's your party, after all.

Haven't you read other people's responses?

powerbuoy · « **Reply #22 on:** July 28, 2006, 05:21:24 AM »

Apollo, I like the way you are trying new things. Once in a while you have to leave the box. Nobody has built this animal yet, therefore you'll be left with our assumptions. Personally, I believe that this might work to some degree, but that the complexity will outway the performance and potential benefits.

Keep in mind ...that's what they probably told Bill Gates as well when he started in his garage :-))

If you have the time and some cash to spare then built it and let us know how it went.

Powerbuoy

powerbuoy · « **Reply #23 on:** July 28, 2006, 05:25:44 AM »

Oh ... and I forgot ... start a simple design with single coils first ... don't even go three phase at this point. Meaning one magnet -> one coil. Keep it simple.

kitno455 · « **Reply #24 on:** July 28, 2006, 06:12:55 AM »

ok drew- this thing is not axial, its a torus. there is no reason at all from your drawing that this thing needs to be unipolar. if you alternate NSNS on the rotors, and SNSN on the center section, it should work. i think it will make less power than an equivalent dual rotor, due to the huge airgap, but should be a fun experiment.

lots of narrow magnets will enable lots of narrow coils per phase, which can be good. you will need larger mags on the small diameter to complete the circuit for the other two, but unfortunately, you have less space at the center. turn it inside out, and put the S mag on the inside of a drum at the outer diameter...

one other point- dont make anything backing the magnets out of aluminum, including the center section. you have to have an iron path for the return flux.

allan

Flux · « **Reply #25 on:** July 28, 2006, 09:33:31 AM »

What he is proposing is a torus adaption of Mordey's alternator.

With a wound field there is less leakage flux from a unipolar alternator and in the early days some people got better results with the unipolar design. The loss from not reversing the flux was compensated to some extent by the reduction in leakage flux.

If you insist on using wound fields rather than magnets the same may still be true to some extent.

As a wind generator design it would be virtually useless, but you did specifically say it was not for a wind generator so it wouldn't be fair to comment.

As I said previously the coils for unipolar designs are conventional. You treat the magnet rotors as though the opposite pole is missing so you need wide gaps between adjacent like poles.

Try to search for Mordey, but it was so long ago that everyone will have forgotten and likely not put it on the internet.

The Mordey design was single phase ( I think it was pre Tesla).

Much time is spent re-inventing the wheel, let's be honest, the axial air gap design is descended directly from Ferranti and Siemens. The torus, unipolar and hetropolar, has been around from the same period or a bit earlier (DeMeritens) and was adapted to dc by Gramme.

Good fun .

Flux

kitno455 · « **Reply #26 on:** July 28, 2006, 10:00:58 AM »

"With a wound field there is less leakage flux from a unipolar alternator"

Flux- is this because the poles of a wound field have to be so long/tall?

allan

Flux · « **Reply #27 on:** July 28, 2006, 10:49:01 AM »

Yes. The extreme shortness of neo for the same flux has drastically changed a lot of things for the better. It is this that has made the air gap alternator a practical proposition.

Every so often we should look at old ideas, things may become reality with changes in materials.

Flux

dinges · « **Reply #28 on:** July 28, 2006, 11:12:27 AM »

Your flux lines won't run the way you have drawn them; why have you drawn them as if they are 'attracted' by the coil? That's not how flux lines go, no matter how much you would want them to.

For the real magnetic field:

first, draw a straight line between N and S; then, draw lines next to them, but a bit elliptical; getting more elliptical as you get further from the shortest line between center of N & S. Now, you'll see that flux will, at best, go through the bottom corners of your coil. Virtually nothing goes to the top half of the coil.

Also, the two magnetic fields (left N&S vs. right N&S) will influence eachother a bit, complicating the drawing of the correct fluxlines.

Remember: for induction electricity generation, you need maximum flux change in as short a time as possible. Which mean a STRONG magnetic field should go to zero (or even, reverse field, as in axial flux gennies) as quickly as possible. If you manage to do that, you will generate the most energy the best.

Whether you're Edison, Tesla, or whomever; the same physics laws apply. Remember, Edison had a big lab, practically unlimited funds and a lot of employees & junk parts. I think it was he who said that invention is '1% inspiration, and 99% transpiration' (which is why engineers sometimes smell really bad). Most of his inventions were not a succes; we only read about the ones that made it.

Succes.

Ungrounded Lightning Rod · « **Reply #29 on:** July 28, 2006, 12:28:16 PM »

In addition to dinges' critique about the field shape, I'd like to point out something more significant.

Notice that you have an equal number of field lines going through the coil turns in both directions (since they're the same lines).

As your magnets rotate, the places where the lines cross from outside to inside induce a voltage in one direction, and the places where they cross from inside to outside induce an equal voltage in the other direction.

The result is you get NO voltage AT ALL at your coil terminals.

You have a big flywheel, not a generator.

apollospeed · « **Reply #30 on:** July 28, 2006, 01:13:39 PM »

Ok guys, thanks for all the help. I will experiment with this, and other suggestions that where said here.

Here is another rough draft I did in SolidWorks.....

I have the coils arranged in 3 phase, but I think I will start with Single Phase and go from there. Also my design invisioned a Steel larger diameter wheel, Aluminium smaller center wheel, and Lexan coil stator.

thanks much,

Drew

Flux · « **Reply #31 on:** July 28, 2006, 02:19:07 PM »

That looks to have missed the boat completely. you seem to have abandoned the torus.

Those centre magnets will do nothing with those coils, they probably wouldn't do much anyway on aluminium. The magnet spacing is wrong for a unipolar design.

I can't work out where your field coil is going if it is an electromagnet.

You seem to have no basic idea of what is needed. This arrangement bears no resemblence to the torus that you showed in an earlier drawing.

Flux

dinges · « **Reply #32 on:** July 28, 2006, 02:25:16 PM »

This is my last comment on the subject, since your mind seems to be made up anyway.

-Make the center wheel steel too, as another poster has explained.

-make a drawing of the flux lines. Are your coils in the maximum of field density? Do they see a rapidly & completely changing flux?

-single phase is always less efficient as three phase.

To me it seems a waste of magnets, copper, material, machining time & your time. But if you really are determined, I'd say, give it a go, but don't be ashamed to report back later to this board that it didn't work, and why you think it didn't work.

Of course, I'd really love to be surprized and read a story from you that explains that you've just invented the ultimate wind generator and that it works much better than axial flux gennies. I'd probably swallow my pride and start building one too. But, remember, before you can think outside of the box, you must be able to think inside the box...

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Author Topic: DC instead of AC Generator (Read 2800 times)