Ideal Alternator Construction

[wind4Reg]

Hi I am looking to pick a few brains on here. If you had the financial resources to build an alternator rated for 15KW - 20KW using the Axial flux type style are there some general calculations that can be used to determine what materials would be selected and the required numbers of components?

For instance, number of coils, number of magnets, etc.

I was looking at Sintered NdFeB N52 for the magnets, the N52 seems to have the maximum energy of the Neodymium magnets. What shape is best to use: rectangular, disc, wedge, tegular, ring, etc?

What gauge coil wire should be used?

Should you build the alternator as several stacked units, so that it would be like having more than one Axial flux alternator stacked on top of each other and is there any reason not to do this?

I saw that the 3KW Axial flux alternator on otherpower.com used steel discs that the magnets were affixed to. Is steel the best material to use for this or would aluminum be better?

If there is a website link that answers these types of questions please respond with it.

Reg.

[Jon Miller]

Please do an advanced search on this board there is a link on the top right to the Google search.  Before you posted this comment it asked you to do a search so pleas do one.  If that fails to help you then ask some more directed questions that are more specific then general questions then we can all help you more and quicker.  Also read other questions for a week, two maybe three.

.

[MountainMan]

Jon,

Just an opinion from somebody who has been a member of many forums over the years and who has moderated a forum with thousands of participants...

The surest way for a forum like this one to dry up and blow away is to attempt to have ONLY brand new information every day.  Trying to get people to search first,  while perhaps logical on the surface, simply doesn't work.  It ticks off the new people and leaves those that have been around for awhile with nothing to do.  It quite simply chokes the life out of any forum where it is attempted.  Saying something like "you will find lots of interesting info on this topic if you search for 'green glurples'" is often useful and polite.  Saying something like "how dare you post this tired old question yet again" does a lot more harm than good.

These forums will obviously be moderated as the owners see fit.  I'm not trying to tell you that you can't do it, just telling you what the result will be if you try really hard to enforce the "search first or else" flavor of that last posting.  As somebody who really enjoys this forum and doesn't want to see it dry up and blow away, I merely offer this as advice.  I hope you will take it that way.

As a corallary, just imagine a bunch of old buddies getting together to drink beer...but the host is contemptuously enforcing a "no previously told jokes or stories" policy.  That would be one dull party for sure, and not many would bother to attend the next one.

best,

jp

[drdongle]

 In this instance I have to agree as this was a pretty specific question.

[niffa]

Thanks mountainMan,

   Every time a topic is explored something new be drawn from the participants. I for one enjoy the stimulation of veiwing an old "argument" from a new perspective.

Phil

[steak2k1]

Reg:

I'm not an expert by any little minute stretch....however as for aluminum backing ..nada.

I believe it has to do with the steel intensifying the magnetic flux...if using two mag rotors, then the steel intensifies the attraction of the flux across the air gap/stator...(an expert can correct this if need be). That is also relative to using one mag plate and steel laminations on the other side of the stator. There is also a problem with eddy currents in aluminum...what/why/how...I am not all that sure.

As for Magnets, my vote would be for the wedge type. Seems they are a natural fit for axial flow and I would think, allow the flux to cover more of the coil area. Mind you, that is on a 12-14" mag rotor plate. If one where to go with a much larger diameter mag rotor, then rectangular may do just as well.

N52 eh.? wow and I thought that N42 was about the highest...interesting and good to know.

15 to 20 Kw is gonna be a fair sized unit. I assume a grid tie/community unit.?

Just a thought,  Hugh Piggots book Windpower Handbook is a pretty good investment..lots of formulae and the like..great read.. excellent info if you don't already have it.

rgds and best of luck,  We all would like to see how you progress.

there will be lots of comments on your question for sure.

stk

[Flux]

You would need to tread carefully here. Most things evolve by scaling up something smaller. There often comes a time where a big leap lands you in trouble.

I don't know whether you are after 20kW sustained power or 20kW peak in high winds, but either way it is a big leap from anything proven to work here.

Battery charging is just about out of the question so it seems likely it will be heating or grid tie, which makes it a more reasonable prospect. I am not sure how easy it would be to get permission to grid tie.

The axial designs are easy to build with little facilities as you don't need machining facilities to control the air gap, but given those facilities I wouldn't use an axial design for that sort of power. You will not be concerned by a bit of iron loss so it would seem wise to use some sort of iron core and a radial design would eliminate the considerable problems of instability of large discs with enormous magnetic forces acting on them. It could of course be done but not the easiest way.

You would also need to keep the efficiency very high and match the prop by other means than using resistance. Dissipating 20kW in a stator at low speed is not an option.

At this power level everything becomes a considerable engineering project and not something to be undertaken lightly on a bit of advice, however well intended, from a discussion board.

Flux

[Ungrounded Lightning Rod]

Let me second that.

Sometimes I come up with something new for an argument that's beyond the horizon.  If I were to add it to the ancient thread it would only get seen by searchers - which probably means not at all.  So if it's not some major breakthrough worthy of an item of its own I'll usually just wait for the subject to come up again and post it in the discussion then.  Thus an occasional newby-inspired recap is useful.

Also:  Searches can resurrect old stuff that was wrong or obsoleted, making the filtering problem difficult and resurrecting old myths.

Nevertheless, constant rehashes of old stuff can get tiresome, and a newbie can find a LOT of useful stuff by searching, a lot faster than by posting again and waiting for people to come back with new writeups of old stuff or pointers to it.

Seems to me that a balance is good idea.  I'd recommend to newbies that they do a search, then make a post summarizing what they THOUGHT they learned for the board to correct and expand on.  That will get two iterations of learning done in the time of one, keep the board fresh and active, and keep stakes in the hearts of old myths and misinformation.

[hvirtane]

I don't think that there

is one single ideal solution.

If you'll have a look at

the 'otherpower's' 17 feet

generator and its axial

flux alternator... You'll

see that doubling the diameter

and doubling the magnets you

would get about 15 kW. But

you might have some difficulties

with the disks... Maybe you would

do it easier by scaling it up only

by the factor 1,5 and then stacking

two of them on the same axle?

If you would start with a reasonable

induction motor and convert that

into radial flux PMG, the job

might become easier, because

most of the jobs have been

already done in the factory,

which made the motor.

I've witnessed a project in India

to convert an 8 kW induction engine

into radial flux PMG with the power

output in the range of 10 kW.

We didn't have much big problems.      

- Hannu

[sven]

Not related to the alternator, but I was wondering how one would go about safety for high winds for such a large unit.  I would imagine that the stresses to the blades that come from furling would add a great deal of problems.

I have seen on this board (a long time ago) someone who rotated the blades in higher winds (like the huge ones do) but I forgot the exact term with which it was described (and since English is not my first language, I can't make a guess).

I'm sorry to add more questions, and not solving any.

Sven