Vertical Magnet Alternator Setup Questions

[memphis66]

Hi all,

Great forum!

Wondering if someone can answer some questions I have.

I want to create an alternator with maximum charge output at a minimum weight.

Looking at a commercial wind turbine alternator (see picture below), it has the magnets on the rotor placed vertically and the stator has the windings vertically as well but with layered metal placed behind it.

Is this construction more or less efficient than an air core solution with the stator horizontally wedged between two magnets like most of the designs discussed here?

With a solution like this, would the stator winding setup be very different to an air core solution?

Realizing it would be quite disastrous using aluminium on an air core alternator, but would it create too many Eddie currents in a solution like this?

Thanks

Memphis66

[Flux]

Depends on what you mean by efficient.

If your concern is the maximum output for the lightest weight then an air gap alternator is not likely to be your best option. Whether you use a radial design as in your sketch or an axial as commonly used here is another issue. It would need a lot of investigating to determine which would win out.

I have a feeling that a dual rotor with laminated iron core slotted on both sides may win out but it would be a pig to build. You would get close with a conventional radial as in your sketch.

Much has been claimed for the power density of transverse flux machines, but power density is difficult to directly relate to weight, besides that they have a serious problem with leakage reactance and will not do as claimed with a normal rectifier.

Flux

[DanB]

Looks familiar...

I think for mass production it's much easier to build that way and they have their own set of pros and cons.  Overall - power per pound per given rpm I'm not sure they're any better.  They do require a lot less magnetic material and perhaps less copper (much of the weight is iron) so they certainly cost less to mass produce.  Not easy to build at home though....

What you've shown above is similar to some of the motor conversions you'll see here and they work quite well.  The particular machien you showed is also trying to save in manufacturing by using pre-existing alternator parts (I believe the stator laminates are straight out of a Delco alternator).  I think better (and what you see on most wind turbines) is to have the magnets on the inside of a 'drum' rotating outside the steel laminates.

[memphis66]

Thanks for the quick replies.

Looks identical...

The problem I have is that the OD (outer diameter) of the alternator can only be 250mm diameter, while the height is not as crucial.
Hence the transverse flux machine would be more appropriate size wise but what was mentioned regarding manufacturability as well as complications with the rectifier doesn't sound promising.

I am aiming at building a small vertical turbine with h=750mm (+ the height of the alternator), diam=300mm; charging a bank of two - four 12v batteries.

Any suggestions what would be an appropriate setup bearing in mind your previous statements, remembering weight is a major factor?

Memphis66

[memphis66]

Any thoughts on the above questions?

Sorry not very good with inches.. from Australia...

Cheers

[oztules]

memphis66

I think all went quiet when you mentioned that you were on the way to build a monster vawt. The real problem here is that from your dimenions, unless you dropped it  down a mine shaft you will be scratching to get the blades to develop  enough power to drive any iron core turbines. A small axial flux turbine will be the best to build in this instance, as cogging will kill this little mill. Dual axial flux or single  will allow you to make the most of a very limited power source. Any iron core device will rob you of early startup, and use up valuble energy in core losses.

.........oztules

[memphis66]

Hi Oztules, thanks for that.

Ok, well the sizes for the unit hasn't been worked out yet other than the size of the alternator can be no bigger than 250mm... If its an air core to remove the cogging that would be fine as long as it fits inside the predetermined size.

The main aim is to try to cover as much as I can of the average 90 amp hours per day drawn. Hence I need the most efficient design for the smalles possible size both for the foils as well as the alternator design.

The height of the installation is to be no lower than 13 meters of the ground.

Its going to be installed in a tower and it would be to hazourdus (for maitenance) to have a horizontal unit due to the design of the tower. A vawt would be somewhat more contained (hopefully).

Hope that helps...

Cheers

M

 

[oztules]

hi memphis66

go to this address. There is a power calculator for vawts, sav, and hawts. This will give you a better idea of what you need to do to get near the 90ah / day you require.

http://www.fieldlines.com/story/2006/1/17/19211/5079

As you will appreciate, the mean wind speed would be good to know, or guess at.

What voltage are you using you say 4x12v are they in parallel or series. ie 48v or 12 v or two banks of 24v.

If you multiply the volts by the ah, you get w/h use this in the formula for that calculator.

if that is 48v then you are using close to 5kw/day I figure about 4sq/m of swept area may get close for smallest. Thats 4meters high, by 1meter wide.  with 22km wind continuous.

not quite what you had in mind I feel.

..........oztules

[memphis66]

Thanks, thats brilliant! Will go through it..

I will be using 12v (parallell).

Cheers

[memphis66]

Sorry if it sounded as if it was going to be big.. "build a monster vawt" as mentioned was not really what I wanted it to come across like...

I need a very compact unit. i.e. as small and as light as possible...

Need to cover as much as possible of 90amp hours usage per day from two parallel connected 12v batteries.

Had a look at the calculator (is great, thanks oztules) and as long as I can cover at least half of the power requirement it is useful to me.

Has anybody built a "small" radial flux generator compared to the horizontal (ala Hugh's) ones built by many in this group?

Hope I am not making a total ass of myself... Just getting started with this...

Cheers

[oztules]

Go to windstuffnow

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

Ed seems to be the pre-eminant small vawt man, and very very adept at trying different generator types. He has also got kits of various sizes. Some I think were around the 250mm mark (10 inch alternator) Also check his posts and comments here.

And no ,-by Monster Vawt, i mean a vawt that generates 90ah into a 12v batt pack per day is no tiddler. Thats why I directed you to the calculator page, to give you an idea of what size you are asking about.

 The size you mentioned i think has about 1/4 sq meter exposure....cannot do much with that at all unless a hurricane is present..... or a long mine shaft nearby to get some speed up.

there's always a way though, compromise is the key.....it may need to be bigger than you hoped, or maybe stack a few together.

.........oztules

[memphis66]

Thanks,

Will look in to it.

Cheers

M