First build. Savonius style VAWT

[Ungrounded Lightning Rod]

so often in windmill discussions the idea of wind mill efficiency of different designs  comes up.
the way i like to think of drag mills is, they may only capture 15% of the energy of that swept area,
 but it is 15% of an infinite resource .
they are easy to duplicate and easy to make larger

The argument actually applies to all types of energy-harvesters where there isn't a substantial downside to harvesting more.

They way I usually phrase it is variants on:

When the fuel is free, the relevent measure of efficiency is not the ratio of energy delivered vs. energy collected.  It is the ratio of energy delivered vs. resources spent to build and maintain the collector.

[Adriaan Kragten]

Adriaan, the link that you have on report KD 599 doesn't work any longer.


I have checked the link on my website to report KD 599 and that link works. So I think that you mean that one of the links given in KD 599 to reports about Savonius rotors which I found on the Internet is no longer working. This might be true as KD 599 is a rather old report. But which link isn't working?

www.vawt.om2cm.sk/sites/default/files/2or3savonius.pdf

Ed

[Adriaan Kragten]

When the fuel is free, the relevent measure of efficiency is not the ratio of energy delivered vs. energy collected.  It is the ratio of energy delivered vs. resources spent to build and maintain the collector.

When we compare a well designed Savonius rotor with a well designed HAWT, we see that the Savonius rotor can have a maximum Cp of about 0.2 and that a HAWT can have a maximum Cp of about 0.4. So for the same power at a certain wind speed, the swept area of a Savonius rotor must be about a factor 2 higher. A Savonius rotor has a solidity of more than 1 and the amount of material needed to make such a Savonius rotor will be about a factor five higher than for a HAWT with the same power at a certain wind speed.

A Savonius rotor has an optimum tip speed ratio of about one and a well designed HAWT has an optimum tip speed ratio of about five. The diameter of the Savonius rotor depends on the ratio H / D but it will be equal or larger than that of the HAWT. The rotational speed at a certain wind speed of the HAWT will therefore be in between a factor 5 and 8 higher than for the Savonius rotor of the same power. This means that the average torque level of the Savonius rotor will be a factor 5 to 8 higher than for the HAWT of the same power. If both wind turbines generate electricity with a direct drive transmission, it means that the torque level of the generator of the Savonius rotor will be a factor 5 to 8 higher. So not only the rotor is much more expensive but also the generator is much more expensive. If we don't take a wel designed Savonius rotor but a pure drag machine, the picture becomes even worse.

Another problem of a Savonius rotor is that the rotor thrust at high wind speeds can't be limited by turning the rotor out of the wind as this is an option for a HAWT. So a Savonius rotor and its tower must be made very strong and this is another reason why a lot of material will be needed.

[JW]

Lets not forget about Elemental madness topic. I believe it was the inspiration for the other topic. On these VAWT machines.

[Adriaan Kragten]

This discussion about Savonious rotors was transferred to another new topic because it deviated from the original post. But I no longer can find the new topic. All other recent topics about VAWT's deal with Darrieus rotors. What has happened?

[JW]

Adriaan,

The other topic is still intact but has been moved to the back side of the forum. I can work with you on this.

If you would like I can restore the topic so that you can glean the areas that you want. But we will have to move the topic back after were done.

Let me know if you want to do that.

[Adriaan Kragten]

What is the back side of the forum, why it is moved to the back side and how can I find the back side? I am not especially interested in Savonious rotors. It is just the opposite, I will always discourage people to start with Savonious rotors and other VAWT's. But I don't see it as a subject which should be removed from the front side of the discussion.

[JW]

Follow this link  https://www.fieldlines.com/index.php/topic,149874.0.html

[Elemental madness]

Hi all, I apologise for my absence, I have been a bit tied up finishing some other projects. Thank you to everyone for their input and involvement I have learned quite a bit and gotten some grea ideas from everyone.


I'll definitely be following the Savonious discussion on the other thread.

I have been experimenting with building a radial flux generator for the turbine before I start making changes to the turbine design. This is not the final design for the turbine or the generator, all still just experimenting and learning as I go.

I used ferrite magnets to experiment with as they are a lot cheaper to play around with and learn the basics.

Due to the lower flux of the ferrite magnets I decided to go single phase instead of 3 phase to get the volts up at lower RPM.

The generator has 18 stacks of 5 magnets. Arranged in alrernating polarity.

The magnets are 3x25 mm

There are 9 coils wired in series. Each coil has 200 turns of 0.5mm wire. 

Air gap between magnet and inside steel ring is about 18mm. About 6mm to top of coils

Turned by hand it easily makes up to 13.8 volt. Only about 0.6 amp, it gets very tough to spin the shaft by hand when measuring amps.

I'll likely add another magnet to all the stacks to close the gap.

Anyway here are some photos.

[CraigM]

Elemental madness,

Nice to see your build coming along. Don't see too many people that take on a radial design... I like the rotor drum you made.

What are your coils attached to? Is that a motor core?

Also looks like you could fit additional coils if you wanted so you have the same number of coils as magnet poles. This would give you a bit higher output as well.

Keep sharing, would like to hear more about this and help determine why your current is a bit low. How are you measuring amps? Can you provide a rough idea of what rpm you have when measuring?

Thanks,
CM

[electrondady1]

interesting alternator.

[hiker]

Nice alt,,three phase would work,,more turns per coil and two strands of wire=more volts and amps,,endless combos you could use use..😜.

[hiker]

[SparWeb]

EM,
Very interesting!
It must have a fair bit of inertia.  Not trying to be a downer, but we will have to remember that while considering the self-start of the VAWT you want to put together.
I agree with Craig, that you could stack in more magnets and wire coils if you wanted.

[Elemental madness]

I added an extra layer of magnets making the total 6 per stack and also making the air gap smaller. The voltage has gone up to 18 volt and around 1 amp.

I'll definitely try some coils with more windings and two wires.

It does have bit of inertia to get going, hopefully it won't be too much of an issue if I can get it to generate enough voltage without needing a gear ratio or at least not a very high one.

Would it be worth while to replace the top magnet on each stack with a 3x25mm neodymium?

Hiker that is a really nice alternator you have there, I did not even think of putting the coils on the outside.

[Elemental madness]

Elemental madness,

Nice to see your build coming along. Don't see too many people that take on a radial design... I like the rotor drum you made.

What are your coils attached to? Is that a motor core?

Also looks like you could fit additional coils if you wanted so you have the same number of coils as magnet poles. This would give you a bit higher output as well.

Keep sharing, would like to hear more about this and help determine why your current is a bit low. How are you measuring amps? Can you provide a rough idea of what rpm you have when measuring?

Thanks,
CM

The coils are currently attached to a steel ring made from 3x30mm flat bar around a piece of high density foam to hold it in place.
I do plan to cast the stator when I'm satisfied with the performance, this is a temporary solution for testing.
 The space between the coils are a bit small to fit additional coils of the same size.

If I had to guess I would say that voltage is at about 180 RPM and when measuring current it is slightly lower.  I don't currently have a means to measure both at the same time and my meter is not a clamp type so it does restrict current at least to some extent.

[hiker]

For a little more power out..fill the  coil holes with metal as well..I just hacked sawed up a bunch of flat metal ,,glued those togeather then installed in each coil,,,😜

[oneirondreamer]

For a little more power out..fill the  coil holes with metal as well..I just hacked sawed up a bunch of flat metal ,,glued those togeather then installed in each coil,,,😜

I agree this should get you more watts, probably higher Volts, but it might also make it cog, so that startup might be limited to higher winds.   

Your next issue sounds like a controller.    If your alternator is too strong for your turbine, which I'd guess yours is, then you can use a controller to help it match.

In general terms when the wind speed doubles, you have 8 times as much power available at your turbine, but your turbine speed only doubles, it's output isn't linear but cubic.  As your alternator speed doubles, generally it's output only doubles.   You can wind your alt for higher speeds, or lower speeds (and maybe risk burning out, though there are experts here who can help you to calculate best your winding design, I'm not one).   

Fancy controllers (MPPT and low voltage boost) can be used to maximize performance over the whole turbine speed range, as well, many can as overload it to slow it down in very high winds, and pull it down below it's efficient range so it doesn't overspeed.  Generally fancy controllers have cost a lot of money in the past, but there's some cheap stuff coming out of China that might be OK.   There's some very cheap stuff, that is probably pretty bad.

[electrondady1]

very few people have built radial alternators on this site . mostly dual rotor axial flux. with ferrite  mags i have built quite a few using old 10" dia. table say blades for magnet rotors.
with  a dual rotor you can double the amount of magnetic flux going though your coil and there is no need to get iron involved in the coils. so there is no cogging and your mill will still rotate freely .

the radial alternators i  have  seen place the coils over a narrow spool of mild steel wire that transfers the flux smoothly and continuously .
there is a type of radial flux alternator that is made from a washing machine motor . very popular in Australia . they are experts at rewiring them .you can check "the back shed" forum.

the alternators i build now use  two single phases overlapping. keep posting