Small Wind Generator/Motor

[sr71p38]

I am definitely a Newbie to the wind generation community.  If this topic has been discussed I apologize I looked through a lot of the post but might have missed it.

I am working on building my first wind generator and just when I think I am making progress I run into a new brick wall.  I built a nacelle based on a Windstream Permanent Magnet DC Generator in a direct drive configuration.  I was running the blades at over 300 RPM and getting only milliamps of current, the voltage is 13.9 V or 24 V depending on the battery configuration I use.  Didn't realize I should look at the RPM vs Amp curves before I started this whole thing.  Seem this particular generator needs to run at over 1000 RPM to produce 1 amp at 12 volts.  So basically I am getting no real power out of this. 

I was wondering if anyone has any suggestion for a generator that is approximately 2.5" in diameter that will actually produce some power at 300 RPM?  I am not looking to produce a ton, I would be happy with 40 Watts, or even 10 Watts at this point.

I am also open to other suggestions, like having one custom build, adding an inline gearbox, or even a transformer if that might help.   I was hoping not to redo the Nacelle but if there is a generator at 3" that will do this, I guess I will do what makes sense.

[mab]

I seem to recall folks using Amtech motors - it's a few years back though - could try searching the old posts.

otherwise look  & see if you can find a small high voltage dc motor, but i don't know what's out there TBH.

[bigrockcandymountain]

1000 rpm might be a perfectly ok speed depending on the diameter of your rotor.  If you are only looking for 10w you might be ok with a pretty small diameter.  What did you have in mind? Sounds like maybe you have blades already.  How big are they?

[Bruce S]

sr71p38
Welcome to the forum.
Could you give us a little bit more info on your build? There may be a few items that can be tweaked to get you a bit more out of your current unit.
Could things we could use is wire dia imperial or Metric ( we speak both ) magnets use (i.e. Ceramic, Neo, cobalt, etc)
How you are getting the power readings, HAWT Blades 2,3 or ??, VAWT S-type, squirrel cage, etc or test bed driven , drill, drill press or??.
 
ON a side note your user name leads me to thing your are either a pilot, or aviation enthusiast?

Again Welcome aboard

Bruce S 

[SparWeb]

Hi
Welcome to Fieldlines!

You might want to stick with used DC motors to experiment with, but watch the specs carefully.
A very rough guide:

Diam.   Speed      Wind Power         Electric Output
2 feet 1400 RPM  Pwind=60 Watt   Pelectric = 30 Watt
3 feet  950 RPM  Pwind=130 Watt   Pelectric = 65 Watt
4 feet  700 RPM  Pwind=230 Watt   Pelectric = 115 Watt
5 feet  560 RPM  Pwind=350 Watt   Pelectric = 175 Watt

This is based on 20 mph wind and blades turning with TSR = 5.0 and blade efficiency 40% and electric efficiency 50%.

This should help you set expectations, because a small prop won't get the wind energy needed to run a large generator or a heavy electrical load.  You can use it the other way, too.  If you want to power a 120 Watt load in 20MPH wind, then you'll need a rotor 4 feet or bigger, or make what you have more efficient than what I've assumed them to be.

Thanks for joining, and you are welcome to share everything you do and all the fun it causes.

And.... the blackbird takes it every time.

[sr71p38]

Wow!  Thank you so much for all the responses.  This is some awesome information. 

I was going to reply to each but not sure how to do that just yet.  So I am able to get the 1000 rpm but I have to get upwards of a 26mph wind to do it, which seems really insane to me.  I did cheat and use a drill at one point to make sure the motors were doing what they said. 

It seems by some of what was said below this RPM might not be crazy.  I was reading that many of the wind generators on the market produced their rated power output at 90 RPM in 10 to 15 mph winds. Or is this complete rubbish? 

The diameter is small about 15" with 6 blades, which are all custom designed, which are direct drive to the permanent magnet motor.  They are using two high-energy saturated C8 ceramic magnets. The system is set up as a traditional horizontal axis system.  I am using a bayite DC 6.5-100V 0-100A LCD Display Digital Current Voltage Power Energy Meter Multimeter Ammeter Voltmeter with 100A Current Shunt which is right before the 12volt batteries. 

Maybe it needs to be geared, as motors this small seems to need to run at these higher RPMs.  It sounds like even a custom-built motor wouldn't work. 


To answer one of the questions, yes I am a pilot and very much an aviation enthusiast.  Yes, the SR-71 takes it every time.  I got to see it fly once.  The P-38 is a really underrated bird and was a workhorse of its time! The link was they were both designed by Kelly Johnson.   

[bigrockcandymountain]

I like the Hawker Hurricane for the same reasons you like the P38.  You'll find lots of aviation enthusiasm here. It seems to be a common interest with wind turbine people.

90rpm in a 15mph wind is quite normal also, depending on diameter and tsr (tip speed ratio).
A normal tsr is between 4 and 8 for a horizontal axis turbine with airfoil blades.  A 6 blade might be the lower side of that si lets use tsr 4 for your turbine.

In a 25 mph wind at tsr 4 your blade tips would be doing 100mph.  (4×25) This is 147 fps.

At 15" diameter your circumference is 3.9'

147' ÷ 3.9 = 37.7 rev/second or 2261 rpm

So if you do half the wind speed it should be half the rpm or 1130 rpm at 12.5mph.

That isn't what you are seeing though correct?

Maybe your blades are 15" so your diameter is 30" or maybe they are just the wrong angle of attack. Wind turbine blades stall, just like airplane wings.  If they are set too flat to the wind with not enough downhill, they stay stalled and won't make power.

Welcome to fieldlines.  I'm glad you joined.  Hopefully we can get you making some power.  It gets really fun when the watts start to flow.

Cheers
Derek

Ps I fly an antique Aeronca Chief off of a dirt strip. 

[sr71p38]

Derek,

No, I am not seeing what you have calculated below at all.  I have been using Digital Photo Sensor Tachometer that I got from Harbor Freight to check the RPM.  When there is no load or no batteries attached I can get 500 to 600 Rpm with an 11mph wind, I use a handled wind gauge to measure this speed.  Once a load is applied it goes down to about 300 rpm.  I am measuring on the blade hub, so not tip speed, which might be one issue. 

I doubled checked the diameter and it is 16", in a 25mph wind I should get 2,100 rpm, I am not even close.  The blades are 3d printed with a 48-degree pitch. 

It seems what I am seeing is a little more than half of everything theoretical.  if I do a 25 to 30 mph I get the 1000 rpm but should see a lot higher. Or with an 11mph I should be at 1000 rpm and I see 300rpm with a load and 500rpm without.


Regards
David

PS.  a taildragger on a dirt field that is impressive.     

[bigrockcandymountain]

48 degree pitch is your problem.  Most turbine blades are around 4 degrees.  Really high speed ones are even flatter. 

[bigrockcandymountain]

Oops, missed your ps. Yes, it is a different skill set than nosewheel on pavement that's for sure.  The soft surface makes the taildragger easier to control actually. 

What segment of aviation are you part of?

Can you heat and twist your blades flatter on your turbine?

[SparWeb]

Hi again SR71P38,

That's one heck of a cruise prop you got on there.  Like BRCM says, usually about 5 degrees.  Although for your scale of machine, maybe I'd go for 10 degrees at the tip.
And just to be clear, that's the angle to the plane of rotation.  Looking at the front you see pretty much the whole blade almost face-on, not edge-on.

The Fieldlines forum has a "Pub" section if you scroll down the list of sections...  Just guessing, but I have a feeling that there are a few pilots out there who like to tell stories over a beer... 

[Bruce S]

The Fieldlines forum has a "Pub" section if you scroll down the list of sections...  Just guessing, but I have a feeling that there are a few pilots out there who like to tell stories over a beer...

Then there are those of us who like to jump out of those perfectly good planes and have a few beers too  .
Except the crop dusting bi-planes, they're just too much fun to ride in.

Bruce S 

PS>> I too did a double take on the degree of pitch.

sr71p38;
 Perhaps you could send a few pics to the forums' email address , we can then post them to help other aide in the blades pitch?

[DamonHD]

I have jumped out of one plane (13,000ft), but NOT with beers.

Rgds

Damon

[Bruce S]

I have jumped out of one plane (13,000ft), but NOT with beers.

Rgds

Damon

The beers are when you're back returning the used chute , not before or during , both are usually a waste of good beer. 

Cheers
Bruce S

[sr71p38]

I had the blades 3d printed so I can have them reprinted at a lot lower pitch angle, and it was measured on the angle to the plane of rotation.  Is there a NACA airfoil profile that most folks use or a place I can find one?  I didn't see one when I was searching so I just did a symmetrical profile since I used a high pitch angle.  The blade is 1.75" wide and 1/8" thick for reference. 

David

I fly a 172 G1000 off a very long runway. Always wanted to jump but run into the why would I jump out of a perfectly good airplane.   

[bigrockcandymountain]

Cool.  I trained in a 172 and think they are awesome.  It was no G1000 though.  I hand prop my chief because it has no electrics. 

The blades sound a touch thin at 1.75" x 1/8"

An average airfoil would be about 12% thickness vs chord.  It is probably ok though.  I'll let others tell you which airfoil.  It will be whichever is best for super low reynolds numbers.  Model airplane forums might have some stuff.

 Lots of people use flat bottom airfoils resembling a clark y with good results. 

[SparWeb]

Agree - the scale of the prop lets you get away with stuff you wouldn't do on a larger scale.  NACA airfoils are great for this, so is Clark Y.  You can make it fancy but you can't measure the difference.  If you're re-printing, then doing it a bit thicker will be good.  Wind turbines have a low Reynold's number (scale factor) so they're sensitive to stall in a way that aircraft props aren't, meaning a generous round leading edge is helpful. 

[sr71p38]

Thanks.  I did some research yesterday and found a paper NREL Airfoil Families for HAWTs and figured I would use that as a starting point.  I designing them and working to have the 3d printed.

thanks for the help!!

[Bruce S]

It'll be interesting to see what those numbers show and what the printer builds.

Cheers
Bruce S

[SparWeb]

Let us know when you're up for posting pictures and we'll help you out if you need any.

[sr71p38]

I printed new blades at the 10-degree angle that you all suggested and I am getting slow rotational speeds.  I am using an industrial fan to test the rotation speed and I did it on a freewheel, so no motor to just see the speeds.  I attached images of both the original and  new blades attached ot the hub for suggestions. 

[bigrockcandymountain]

It is hard to tell from the pictures but do you have the airfoil bottom side facing the oncoming wind?

It is also hard to tell how many mph an industrial fan would make and how turbulent that flow would be. 

[sr71p38]

here are some additional pictures of the two different blades.  I took them from the top angle since as you can see they have a root base that is attached.  they are facing the plane that the wind would be coming from. 

Also if you say an industrial fan may not be a way to test, do you have suggestions for something that can be used? Right now I don't get much wind and I don't want to be taking up and down off a tower with all the changes.

[bigrockcandymountain]

https://images.app.goo.gl/yG1zqokk8eSqUXz4A

Not saying it is a good idea

Your blades look good. 

[SparWeb]

I'm trying to sort out the blade direction too.
The red one is a a good shape.
In the lower pair of pictures, the view is from the front.  Wind comes from the camera to the blade in that direction.  On the hub, it will turn to the left.
To many people, this is counterintuitive.  One reason is that the curve is opposite to the blade of an aircraft propeller.  I think you might have it right, though.

Box fan, meh.  Take it outside on a windy day.

[sr71p38]

I think if I strapped this to my car in my neighborhood I might get arrested.  But that idea has crossed my mind.  Going outside on a windy day is often done but waiting for such a time, I am just not that patient. 

As for the blades, the wind would be coming from the camera direction, so they are positioned as if they are on the hub.  The red one has 10 degrees and the gray one has a lot higher angle, at 48 degrees.  The interesting part is the new design, the Red ones, at least when testing with a fan doesn't move even close to the speed that the gray one does.  This might be the turbulent nature of the fan's wind.  I am up around 15mph on the wind meter.  I put a label to show the wind direction. 

[MattM]

The startup of the gray will definitely come sooner, but the top speed of the red under sustained wind shouldn't even be close.  The fan kind of pulsates a concentrated spiral of movement.  Mother nature will be much different.  I fell for the same trap doing sheet metal blades.  In front of a box fan was far different than natural wind and a proper shape keeps accelerating well beyond the rotational rate of a scoop.  The lesser angle of your flat blade will be much better.  I liked more of an ogee shape like a reflex camber wing.

I really like your jet turbine inspired locking hub.  I am surprised you went with a full in-fill rather than a more hollow blade to shave off weight.  You'd save considerable material.  You also could taper as you print the blade to put a proper twist in the blade.  Your design can literally go from the gray shape at the root to the red shape at the tips.

I see your nick is inspired by a plane.  I  loved seeing that plane visit the local SAC airbase as a kid.  Such a rare treat.  Someday I'd like to try a blade with a reflex curve inspired by the B-2A Spirit. 

[sr71p38]

Happy Holidays to all!!

I wanted to give an update and get some more opinions.  I took your advice and I went outside, actually took the wind generator and attached it to the car, and drove at different speeds to see what I could get.  Hoping the neighbors aren't calling the cops on the crazy man. 

The first thing I did was gear the motor, since it seemed to be to slow with the direct drive, I put a 2.25 gear ratio.  I put the grey blades on and got 200mA at 15mph and it got 463mA at 25mph (5.86Watts on a 12.6volt battery).  So in order to get 1A, I would need to be going about 50mph.  The red blades or the 10degree pitch ones started to spin at 20mph but it was too low even register any amps. 

Does this seem correct from what you have all seen?  To me, it just seems very low from a theory perspective. 

David

[MattM]

It sounds like you cut in the motor too soon for the grey set to get up to an efficient RPM.

[sr71p38]

Matt, what does that mean?  Cut in the motor too soon?  The blades are direct onto the motor and the batteries are wired on the back.  I know that when there are no batteries or I do 24v I get a larger RPM, much larger.  but once the blades are spinning if I plug the batteries in after it does slow the blades right down to the 12V or 24V spin, if that is what you are saying. 

[MattM]

I meant your generator basically is a bad mismatch to the blades.  It's not overcoming the generator losses as well as the other set to be useful.  They should have potential to spin faster but can never get fast enough to overcome the generator.

You might try taking out the gearing for the grey set to see if that allows it to spin up to an RPM more suited to it's generator.  Are you starting with batteries at the same charge in your experiment? 

[sr71p38]

Matt - Ah I think I understand.  I actually just recently added the gears in.   When I originally didn't have them in I was not getting near the 1000rpm that was needed to generate the 1amp.  When no batter is connected they seem to spin past the 1000rpm.  When I change the battery to 24v they do move faster and I get much closer to the 1amp but then I am on a different generator curve.  So it seems that the generator regulates the blades.  I have tried to put a load on the battery as well and even used battery in the 8 volts charged.  I can get it to 1amp but like I said I have to have a very high wind. 

I have thought about changing out the generator but not sure what to use instead. 

[MattM]

How hard would it be to print a short extension to increase cumulative blade length?

Bonus if that extension is 2-3 times as wide and has an aggressive pitch near the root.