Double permanent Magnet Generator

[gijsvm]

Hello,

I have a question and maybe someone can help me.
At the moment i have a homemade windmill 4,3M with a asynchrone generator.
It produce power wenn the blades rotate 170 rpm.
I thinking about to build a pmg what could work with this windmill configuration.
My question is; would it be possible to build 2 pmg build in-line with each 12 magnet and 10 coils, so i have a pmg with 24 magnets and 20 coils.
I wil do this, so i can build it in the place where now the asynchrone generator is located.

Best Regards,

Gijs

[fabricator]

It's been done many times, do a search on Chris Olsons posts he's built several.

[tecker]

May be some pics of the generator setting

[gijsvm]

Thanks for your reply.
Did search and found really a lot of info.
But so mutch info, that it`s hard where to begin.

Here a picture from my windmill 2 years ago

[gijsvm]

And here as he make me happy...

[SparWeb]

Welcome to the forum, Gijs!

Your turbine looks good already!  I venture a guess that it may develop up to 4 or 5 kW.

I think the difficulties you will have, changing from the asynchronous generator to the axial-flux generator, are the space in your turbine's nacelle and the dissipation of heat.

The first issue you seem to have identified in your original question, because an axial-flux generator with the same diameter as the generator shown in your photo will be too small.  Not enough magnets and not enough wire...  Hence the need for a dual (or a triple!) axial generator.

Stacking axial-flux generators has been done before by amateurs, and there were products on the market from Korea like that, too.  I do not know if they have the capacity to match a 4.3 meter rotor, however! 

The heat issue may or may not be difficult.  At high load the heat dissipated by the stator becomes very large.  In common amateur building technique, the stator and magnet rotor are fully exposed to the air flow.  Your system needs the nacelle but that dramatically reduces the cooling airflow on the stator.  Ducting, temperature sensors, cautious selection of materials...  many things you may need for it to work safely.

Should not be hard for someone with your abilities!

May I ask, why you need to change away from the generator you already have?

[tecker]

You can build 8" multi rotor if you need . Several stators and rotors on a one inch haft sounds good .

[gijsvm]

Welcome to the forum, Gijs!

Your turbine looks good already!  I venture a guess that it may develop up to 4 or 5 kW.

I think the difficulties you will have, changing from the asynchronous generator to the axial-flux generator, are the space in your turbine's nacelle and the dissipation of heat.

The first issue you seem to have identified in your original question, because an axial-flux generator with the same diameter as the generator shown in your photo will be too small.  Not enough magnets and not enough wire...  Hence the need for a dual (or a triple!) axial generator.

Stacking axial-flux generators has been done before by amateurs, and there were products on the market from Korea like that, too.  I do not know if they have the capacity to match a 4.3 meter rotor, however! 

The heat issue may or may not be difficult.  At high load the heat dissipated by the stator becomes very large.  In common amateur building technique, the stator and magnet rotor are fully exposed to the air flow.  Your system needs the nacelle but that dramatically reduces the cooling airflow on the stator.  Ducting, temperature sensors, cautious selection of materials...  many things you may need for it to work safely.

Should not be hard for someone with your abilities!

May I ask, why you need to change away from the generator you already have?

Thanks for your information.
The reason wy i will build a axial generator is that, where i live the wind is mostly not enough to let my windmill generated.
I need at least 1500rpm on my generator to let it produce power, and a lot of time it stocked by 1200-1400 rpm because the wind is not enough. It`s verry frustrated to see there is wind, but not enough to produce energy.
Think it`s better to get a long time little power, than to wait for a day mutch power from your windmil.

First must do some more research and find out what way i must go.
I have thinking about to build 2 identical pmg (10 coils and 12 magnets) as discribe in the map from Hugh Piggot.
But maybe i must build a other nacelle so i get more space.

[gijsvm]

You can build 8" multi rotor if you need . Several stators and rotors on a one inch haft sounds good .

Can you explain, or do you have picture ?

[jlt]

   Are you prepared to go from a grid tie set up . to a battery set up. There is a lot of equipment you will need.

To name a few battery's, charge controllers , dump load. inverter, The battery's alone could cost a lot

 Maybe a gear box change to a higher ratio would. get you making some power at a slower wind speed.

 there is no substitute for not enough wind. May be solar would be a better option.
                                                        JLT

[opo]

What kind of blades do you have?, You may be able to fab a new set, maybe shorter, higher torque that could reach cut in speed more often in your location. This is not  an ideal solution because I bet those blades are correctly matched to the generator, but you may still be able to grasp a little bit more power, who knows. If you are still planning on making an investment then, as somebody stated, maybe solar is a better solution in the long run for your area.

Very nice turbine, by the way.

Cheers,

Octavio

[SparWeb]

Thanks for your information.
The reason wy i will build a axial generator is that, where i live the wind is mostly not enough to let my windmill generated.
I need at least 1500rpm on my generator to let it produce power, and a lot of time it stocked by 1200-1400 rpm because the wind is not enough. It`s verry frustrated to see there is wind, but not enough to produce energy.
Think it`s better to get a long time little power, than to wait for a day much power from your windmil.
First must do some more research and find out what way i must go.
I have thinking about to build 2 identical pmg (10 coils and 12 magnets) as discribe in the map from Hugh Piggot.
But maybe i must build a other nacelle so i get more space.

Gijs,
I had assumed that you have a gearbox, and that it is the large blue component on the left of your nacelle photograph.  Then I assumed that the generator is out of the field of view, but you did mention an asynchronous generator (to my vocabulary an induction generator).
If I am wrong, please correct me.

The speed ratios that you describe, when you say that blades cut-in at 170 RPM and a cut-in speed of 1500 RPM for the generator, implies that you use a 8:1 gearbox.  Would it be simpler to find a gearbox with a 10:1 or 12:1 ratio?

Another question:  If you are over-driving an induction generator to produce power, then presumably you need 5% to 10% above the synchronous speed to do so.  Then why isn't your generator's cut-in speed 1600-1650 RPM?  That makes a difference in selecting the right gearbox ratio, too.

This isn't to discourage you from building an axial-flux alternator.  I only want to understand the problem thoroughly, before discussing the solution.

[gijsvm]

What kind of blades do you have?, You may be able to fab a new set, maybe shorter, higher torque that could reach cut in speed more often in your location. This is not  an ideal solution because I bet those blades are correctly matched to the generator, but you may still be able to grasp a little bit more power, who knows. If you are still planning on making an investment then, as somebody stated, maybe solar is a better solution in the long run for your area.

Very nice turbine, by the way.

Cheers,

Octavio

The blades on the photo are not the blades i used now, these where damaged with a storm and -15 degrees 1,5 year ago.
Have now a other set but i`m not so happy with them, so i think about to build new one in future.

[gijsvm]

Gijs,
I had assumed that you have a gearbox, and that it is the large blue component on the left of your nacelle photograph.  Then I assumed that the generator is out of the field of view, but you did mention an asynchronous generator (to my vocabulary an induction generator).
If I am wrong, please correct me.

The speed ratios that you describe, when you say that blades cut-in at 170 RPM and a cut-in speed of 1500 RPM for the generator, implies that you use a 8:1 gearbox.  Would it be simpler to find a gearbox with a 10:1 or 12:1 ratio?

Another question:  If you are over-driving an induction generator to produce power, then presumably you need 5% to 10% above the synchronous speed to do so.  Then why isn't your generator's cut-in speed 1600-1650 RPM?  That makes a difference in selecting the right gearbox ratio, too.

This isn't to discourage you from building an axial-flux alternator.  I only want to understand the problem thoroughly, before discussing the solution.
[/quote]

Yes you are right, it is a induction generator.
I have do a lot of test with different gearboxes but the problems stays, a other gearbox wil not give a real better result, for a induction generator the wind must be enough to let the generator go at least 1600rpm(without connected to the grid), because wenn you connected to the grid the generator goes back in rpm the first vew seconds. But wenn the windpower is enough he generated up to 3,5kw.
Wenn the generator make 1500rpm you get 50hz and it is synchronyse with the grid, wenn you connected at 1600rpm, your generator rpm should always go down, the wind will let the generator turn faster and make more hz and the generated power goes up.
So the grid will try to turn the rpm to 50hz, and the wind will try to make more rpm and more hz, and the result is power.

Is a little difficult to explain because my english isn`t so good 

[tecker]

I Know there are One or multi stator posts I don't remember right off there is one in the User section . Search for the others
The main challenge is stator alignment but you should be able to seris the Phases to take advantage of the wire length to get your Grid voltage

 here is one  a little non standard but the the main focus was to get Cutin voltage with more stators .
http://www.fieldlines.com/index.php/topic,143852.0.html

[SparWeb]

Ja, mijn spreken Duits slecht

The point I am trying to reach is that a change to the gearbox, in conjunction with a change to the blade pitch regulation, should (theoretically) make the blades and the generator match better.  This is what your problem seems to be.  The information you have provided so far have helped, and still confirm my theory.

What gearbox speed ratios have you tried?
Have you adjusted the centrifugal weights on the blades?

[midwoud1]

I see Gijs has an active pitchcontrol system.
There is a sleeve on the mainshaft , a keyhole and hollow shaft .
Looks a bit more complex as I have it.
With linkrods and an actuator .
Like to see the spider system on the hub.
Wonder how he made an electric or electronic sensor command  of rpm versus blade pitch.

Rgds - Frans -

 

 

[SparWeb]

Wonder how he made an electric or electronic sensor command  of rpm versus blade pitch.
Rgds - Frans -

Frans, we are all eager to see more!

Gijs, I hope you can come back with more information!

[fabricator]

I hang on Frans's every post, what he is doing is cutting edge for home built turbines.

[gijsvm]

The main thing is that for producing power with mine configuration is that there should always be enough wind to let the generator run for at least 1500 rpm otherwise the generator is not a generator but a motor.
Wenn changing the gearbox (now is i 8,5) you always wil keep this problem only change the value of the blades to cut in.
Wenn you cut in the generator in ( by 1520 Rpm) you will loose some energy, because that use the generator by making a magnetic field (make not by himself). The result is that the rpm goes done a little. Wenn it goes done to under the 1500 rpm, then the generator is not a generator anymore, but a motor that needs energy...
Wenn the wind power is enough, then there is no problem and the rpm can goes up to max. 1650 rpm.
Changing the pitch has maybe a little effect to make a better torque but the problem i describe will always be there.

Today there is wind and now it generated with my 1,5 Kw generator around 1000W and blade rpm is around 180 rpm.
Yesterday the wind was a little less and generated nothing because it didn`t reach the 170 rpm.

[fabricator]

Yes you need to look into a good axial, possibly geared turbine and you will far out perform that machine, at 1500 rpms a geared axial will have been making a LOT of power already. I think my geared machine at 4:1 is about the highest ratio I've heard of on here, are you saying your machine is 8.5 to 1 gear ratio?