Help needed in HAWT design

[remcade]

Hi,

i was planning on following James Biggars 3kw double stator plans for my turbine build, but then i realized the price for the required materials and further read that doubling on rotors is less efficient/cost effective than just going bigger single stator setup, i decided not to go through with it and go a little bit smaller scale for the build.

Then i thought what if i just went single stator but otherwise just follow the plans as closely as i can.

So my question is, what kind of performance can i expect with the following:

32 50x25x10 N45 magnets (16 per rotor)
12 coils 80 turns of 1.6mm (14awg) copper wire
300mm diameter rotors
3.7m total blade diameter

Plan is to go 3phase of course and a 24v system, but i am unsure what can be achieved with just single stator that was designed for double stator setup and if the blade diameter is too big now?

I tried (and failed patheticly) to do my own calculations based on some formulas i found on research gate 

Thanks.

[MagnetJuice]

Hi remcade, welcome to Fieldlines.

A 300mm rotor is a bit small for 16 of those magnets. You should go with at least 350mm to avoid too much flux leakage from magnet to magnet, and to allow room for the coils.

You should also consider designing for 48 volts. That way you can use a thinner magnet wire for the coils.

This is what I calculated for a cut-in at 130 RPM.

The calculations are for 2 magnet rotors with 16 magnets each and a stator with 12 coils.

For 24 volts you need 43 turns per coil, and for 48 volts you need 84 turns.

For 24 volts, your wire gauge needs to be 2.5mm. That is very thick to wind into a coil. 3 parallel (in hand) wires of 1.4mm will give you the equivalent of 2.5mm.

For 48 volts your wire gauge should be 1.4mm.

Maximum power for that alternator would be about 1900 watts.

That would be a nice system.

Ed

[remcade]

Thanks for the reply.

I see..

I would like to keep the setup as 24V as it is much easier to find wind turbine charge controllers for it, at least where i am from, also they are much more affordable

The truth is i got really exited with this wind turbine project of mine and already ordered the previously mentioned magnets and enough copper wire for all the coils about a week ago, (haven't ordered anything else yet thankfully) so that's kinda what i have to work with now.

I could technically return the stuff i already ordered (since they haven't even arrived yet), but since i had to order them abroad (not available locally + much cheaper abroad) it will be a pain in the ass to return them, so i rather not deal with it honestly.

So any suggestions on how to make this build happen would be appreciated.

Also wanted to mention that I live inland and don't get that much wind here, according to wind atlas yearly average is just 3-5m/s, 5-7m during winter months), which is why i went a much bigger to get more output, ill be happy with 300-700Wh.

[remcade]

Learned new things on interwebs!

I now realize the 48 volt route is the way to go, and i will be increasing the rotor size to 350mm aswell and stator size will increase as well of course.

With larger diameter rotors i can even fit more turns to coils or make suggested 83 turns/coils even when using 1.6mm wire, to make my stator thinner (aiming under ~10mm) which in turn would give me lower cut-in RPM, and more performance at lower wind speeds, right?

I am basing my assumption on the fact that the build guide i am following could fit 80 turns of 1.6mm wire onto a stator that was sized for 300mm diameter rotors with a ~10mm wide stator.

[MagnetJuice]

With larger diameter rotors i can even fit more turns to coils or make suggested 83 turns/coils even when using 1.6mm wire, to make my stator thinner (aiming under ~10mm) which in turn would give me lower cut-in RPM, and more performance at lower wind speeds, right?

I am basing my assumption on the fact that the build guide i am following could fit 80 turns of 1.6mm wire onto a stator that was sized for 300mm diameter rotors with a ~10mm wide stator.

Yes, I think those assumptions are correct, to a point.

Since you already ordered the 1.6 wire, might as well use it. The thicker wire will give the coils a little extra headroom in high winds.

Hugh Piggott uses an alternator very similar to what you will be making for his 2 largest turbines; the 3.6m and the 4.2m. But your magnets are stronger than what Hugh uses. He uses the same alternator for those 2 large turbines. The only difference is that for the 4.2m, he uses more turns per coil to start charging at a lower RPM.

By the way, if you don’t have Hugh Piggott’s book, you should get it. Anyone building a wind turbine should have his book.

Also wanted to mention that I live inland and don't get that much wind here, according to wind atlas yearly average is just 3-5m/s, 5-7m during winter months, which is why i went a much bigger to get more output, ill be happy with 300-700Wh.

I’m not sure if a 3.7 meter blade rotor would be the best match for that alternator, considering your lower winds.

What I know is that your alternator can start charging the battery at around 130 RPM (or lower with more turns) and with good winds can produce close to 2kW. To start charging at a lower RPM you have to increase the number of turns per coil.

There are other users here that have turbines up in the air and are better able to help you match the prop to the alternator.

Hopefully one of the wind PRO’s will jump in. 

Ed

[SparWeb]

I'm not sure if I'm the pro you're looking for...   I'll try.

I think MJ's gut feel is a good one: the blades could be too small for a low-wind area that you describe.

Before changing the design, however, you should get more information about your location and the wind that will be available at your site, on your tower.  The specifics affect the performance a lot.  If the wind isn't as good, you would see better performance with bigger blades - but not too much bigger.  When you have a larger rotor, you also need a more robust furling mechanism to keep things under control.  The tail in the Biggars video looks undersized, both from a weather-vane sense (keeping into the wind when it counts) and at the hinge point (absorbing the punishment of slamming up and down).

I took a similar approach to my Zubbly project and it's a good performer in my moderate wind situation.

[remcade]

Hello again!

I have updated my plan during past couple months.

I am increasing Blade diameter to 4.2 meters from Hugh's book and rotor size also to either 400mm or 450mm.

I sourced some free 1.6mm diameter electrical wire to mock-up coil shapes/sizes for given rotor size and based on results did some maths.

I can fit 114 turns into a rectangular shaped coil when using 400mm rotor disk which according to my calculations would output 50volts DC @ 95 RPM according to this formula (A x B x n x rpm x 2,7/30)-1,4.
I also tried to calculate at what m/s wind speed the turbine would reach 95 RPM, by using this formula > ((2xPIxradius)/60)*RPM which gave me ~2m/s, but that doesn't seem right...

I also spun a triangular shaped coil, 120 turns, with room for at least another 10-15 turns. So lets say 130 turns for triangular coils: 57,2872, but there would be losses due to not all flux linking, but i dont know how to calculate those losses.

Now obviously i could fit quite a bit more copper into coils if i used the 450mm rotors, but should i? At which points is the cut-in rpm too low that will cause stalling issues?

Heres a few pics of my mockup coils:

114 turns square coil on 400mm rotor:

114 turns square coil on 450mm rotor:( ignore incorrect amonut of magnets on the 450mm diameter, i did an oopsie in Fusion 360, didnt want to reprint  )

120 turns triangle coil on 400mm rotor:

120 turns triangle coil on 450mm rotor:

[bigrockcandymountain]

Figure 20.8m/s tip speed divided by whatever tsr you are planning.  (4.2m x 3.14 x 95rpm x 60)

So 4.16m/s wind speed at tsr 5.
2.6m/s wind speed at tsr 8
Mine is almost the same diameter and cuts in about 160rpm.  I wish it was a bit lower so you are right in the ballpark at 95 rpm. 

[MagnetJuice]

I think that the 1.6mm magnet wire is going to make for a larger coil size than the electrical wire coil. The stiffer wire won’t bend as easy, so there will be more air pockets within the coil.

It would be nice if you can get 120 turns, but the coil legs could be too fat. That increases your rotor diameter and add weight to the turbine.  Also adds expense for a stronger and heavier tower. You might have to increase the coil thickness to at least 12mm to keep the diameter at a reasonable size.

I think that anything over 420mm for rotor size will increase weight and cost without much benefit. There is only so much flux, and area in those magnets. Voltage is only generated when the wire is under the magnet. Having coil legs that are too fat wastes copper and add unnecessary resistance to the stator.

At which points is the cut-in rpm too low that will cause stalling issues?

If you build the alternator in a way that you can adjust the air gap, you can decrease the efficiency by opening the air gap. That way you can ‘tune’ your cut-in RPM, so make it as efficient as possible for your low winds. You can also add a bit of resistance to the line coming from the tower to keep it from stalling.

You can wind a coil with the 1.6mm magnet wire and get some measurements.

That would be a good start.

When you make the form to wind the coil, the inside of the coil should be about 80% of the width of the magnet. In your case, about 20mm.

I did some mods with the dimensions and got something like this image.



Ed