Low wind DC motor HAWT

[CmeBREW]

Hello RE group,

    This is the progress so far on my Low wind genny using a Leeson DC motor I recently bought.  It is rated 180vdc / 1800rpm / 4.5 amp (weighs 40lbs).  The 12 volt cut-in is about 135rpm.  There was some discussion about here:

http://www.fieldlines.com/story/2007/12/19/35449/016

Of course we all know that homebrew brushless alternators are much better for many reasons, but this low rpm motor might be a good alternative to a high rpm small 4 foot diameter PM motor windmill. Of course I love ALL windmills they are ALL good!

These are the first PVC blades I have ever made. I made them like Ben's at Gotwind.org.  They are alittle different since the leading edge is actually the curved side of the blade instead of the straight side. So these blades turn Counter clockwise-- which is the correct direction for this particular DC brush motor.

Jigsaw goes thru it like hot butter. Very Quick and easy especially after you make the cardboard template. These blades are made from the 6" pvc pipe. I actually have enough from one 10 foot long pipe to make SIX SETS of pvc blades! So thats plenty extra for experimenting with different shapes. They are quick and easy and look very good, but I am suspecting they have more drag (slower) than a good set of wood blades.

The over-all diameter of the rotor blades is alittle less than 7 feet. It is 6 feet and 9 inches.

I had thought that 7' was probably too much , but now after seeing that each blade is only 1.5 lb and the weight of the entire blade rotor (including 3/4" treated plywood hub) is less than 6 lb, I thought it would be safe to go alittle bigger rotor, and then cut it down if I decided to later. I think it is fine for now as is.

Plus, I intend to probably furl early to limit the AMP output for this motor to less than 8 amps or so.  But as of yet, I havent seen it go this high yet. There has been no real big winds yet hit it.

I made it in only about 6 working hours, plus a couple more hours today since I trimmed about 3/4" of the top widest part of the blades to get alittle less drag and some more speed. It did helped. All the photos are before I made this change. The blades now look alittle thinner than in the photo below near the widest part of the blade.



It is at ground level ONLY for testing. As soon as I get things adaquate, I will put it up on a higher pole, hopefully with alittle less turbulance.

I do not have the furling system on it yet, but it absolutely will have FURLING soon. It is a MUST to have a good furling system with the extreme wind gusts now.

I may make a set of faster blades for this mill and furl very EARLY to keep it under control.  

I certainly have ALOT to learn about everything. Please keep that in mind-- I am not that experienced yet.  But I like experimenting and trying New and different things even though they may not work out so well sometimes.



I put silicon caulk on the back side to keep water out of the back bearing. And put some grease in the front 'soft' seal and the back.

Then I spray painted the motor white.

Heres an interesting experiment: I put some rubber band pieces behind the blade mounting bolts to see it the blades might all twist back alittle to a better angle for more speed once it gets going. You can twist the blade back fairly easy with your hand. I don't know if it helps any yet, but it isn't vibrating or anything, so who knows.




Heres a pretty good shot of the blade angles. When I first started, the angle at the tips was about 10 degrees and the max angle near the thickest part of the blade was probably about 25 degrees! (That is, from the upper part of the arc to the lower part of the arc)

In the photo though, the tips are about 8 degrees and with the newly trimmed blades the maximum thickness of the blade is probably about 20 degrees. Is that bad??

Yes, in the photo you can see why I had to trim some off the thicker part. I didn't need it to be such a steep angle. Even the thinner blades (not shown) still EASILY get over the cogging of the motor in a tiny 5mph breeze. It is almost always turning at least 60rpm.

The swept area of the blades is THREE TIMES that of a 4 foot mill. Of course it is more noticable since it is bigger and the motor is heavier, but all in all I am VERY pleased with the initial performance. It is MUCH better in lower winds than my 4' treadmill windmill at 23 ft up.  The small mill is not even turning at all when this bigger pvc hawt at ground level IS consistently charging my battery. (even a small amount adds up for my small 12v system)

I am using only 18ga wire for the testing though. Still need to get much bigger wire.

It usually is doing just 1-2 amps in fairly low winds. I have seen 4 and 5 amps in a better bigger wind a few times, but this is at GROUND level a few feet from the corner of my house. It is very turbulant location as I'm now learning. I've only begun testing the thinner blades a few hours ago. I will know better when I put it alittle higher in the air.  

From my ground testing so far, it seems to be at least TWICE as good as my 4' small mill in Watthours into my batterys.  Truthfully, I had hoped it was going to be even better than that.  I will know even better over a week of testing.  Anyway , I am very happy with it so far. It is much more CONSISTENT in lower winds. I live in a horribly LOW wind are (8mph average) AND I have a very small battery bank. So I need to try my best to re-charge what little I use each and EVERY DAY. (unlike folks with a serious batt bank)

I do have one basic question for the group about blade angles:

The tips of the blades are at 7 or 8 degree angle and so are obviously going to have some lift--- but does the middle part of the blades ever get any LIFT since thay are obviously at much steeper angles like 12, 15, and even 20 degree angles???

If its TOO complex a matter to explain then don't bother-- I will understand it one fine day like everyone else.

Any comments, knowledge, questions, pvc suggestions, or concerns, greatly appreciated friends!!

We all learn.

[FishbonzWV]

Nice job BREW,

Here's a couple things I have learned about these motor mills.

The motor should have vent holes drilled into the bottom of the case. I tried to seal up a brushed motor and some Zubbly conversions. After about a month I opened them up and they had rust on everything that would oxidize. My recommendation is to disassemble it, tape up the commutator and spray everything with clear enamel. Drill a couple 1/8" weep holes in the very bottom to let it breathe. One near the front and back.

The good part with using the PVC blades (like you have already found) is they are easy to modify and if you go overboard with the changes just trash them and start over. I've been through about 6 different configurations with my plastic sets so far and still experimenting. The fastest set I cut was only about 1" across at the tips and they were screamin' demons in high winds. The root angle will cause a lot of drag also and can self regulate the speed.

If you have a router put a round over bit in it and it makes a nice leading edge. You can then trim off a little at a time until you get it where you are pleased will the performance.

Fishbonz

[CmeBREW]

Thanks FishBonz,

     That is good advice about drilling the holes and painting the inside. I will do so. Thats what I had done to my small mill.

You also convinced me to trim these blades down even more. It was quite windy today, and I realized that the blades never did fly out of control. There was still too much drag on those wide blades. So I took a chance and trimmed another inch all the way down to the tip. Now they are about 3" wide at the widest part , down to alittle less that 2" wide at the tip. The length is the same. They USE to be an inch wider all the way down the blade. The blade rotor still starts up in a very low breeze-- probably about 6-7 mph. (which is good)

One thing I was worriied about though, is the blades bent inward somewhat down the length. I hope they don't bend anymore. At the tips, it is difficult to see any angle now at all. They look straight up and down. Difficult to tell.

I can see now how AWESOME fast WOODEN blades would be with 4 degrees at the tips.

       




This was a GREAT improvement!! It goes MUCH faster now, even in Lower winds!

It is doing 1 to 3 amps even more consistently now. I love it.

Early today, when the blades were much wider, It did upto 6 amps briefly in a pretty big turbulent wind gust. Thats when I knew it was being held back alot. The blades didn't even make any noise.

The winds are not that strong right now-- but it is doing alot of 1-3 amps even at this disgustingly turbulant ground location. I can't wait 'till I get my mounting pole/pipe soon and put it higher. I am quite certain it will  fly out of control in a big wind now.

So I must put the furling system on it very soon.

I expect I will at least see 8 amps now!  We'll see.  I am very happy with it so far.

It is doing what I had hoped it would do. I just have to LIMIT the amps now.        

-Thanks.

[TomW]

BREW;

If you are concerned with blade tips striking the tower, shim the front of the motor up that will give some clearance.

Just an idea others have used.

Cheers.

TomW

[ghurd]

How far from the blade tip to the tower?  16"?

Wondering how far they'll bend before they break.

G-

[hvirtane]

I have never had any PVC blades. But I've seen many people posting here about experimenting with them and so thought about improvements.

Besides machining the leading edge and the trailing edge, maybe some filling with fiberglass resin or other plastic the thickest point of the airfoil would make the airfoil to look perfectly like the K2 airfoil?

Maybe good paint would make them to last in the sunshine?

- Hannu

[Capt Slog]

Nice job and a good write up.

I like PVC blades too, for much the same reasons as you, you can make quick changes to them.

I've also found that they have a natural curve to them after they have been cut.  Mine tend to curl so that if the rotor was lying on its back (leeward side) the tips would be higher that the centre.  I've always considered this to be an advantage, because it appears that they are sort of pre-stressed and will straighten out in the wind.

I can't see any shaping on your blades.  The trailing edges of mine are usually like knife edges,

a bit like this

http://www.velacreations.com/chispito.html

I take off a lot of plastic to try to acheive an aerofoil section.  If you want to go down this route, and for shaping in general, I'd recommend a 'flap wheel'

http://www.lawson-his.co.uk/scripts/products.php?cat=Flap%20Wheels%2040-50mm

I start off using a surform blade and finish with the flapwheel in a drill.

[CmeBREW]

Right now clearance is 14" from the pole. It is very windy today and the gusts are hitting it and the blades are not bending that much anyway with it spinning very fast. The blades are still not making much noise yet. I',ve only had a minute to watch the ammeter, but was hit 6 amps often.

I believe I can make these blades even more aerodynamic. The only thing I have done so far with the edges it sand the leading edge down a bit with my finish sander. I will sand it some more. I may, as suggested, sand down the trailing edge to. So far I have done nothing to the trailing edge.

[dbcollen]

I have never made any pvc blades, but I had the thought of covering them with large heat shrink tubing to make an airfoil shape. several long thin plastic water bottles could also be used for the heat shrink, (and free) they shrink nicely with a heat gun.

Dustin

[ghurd]

That a crazy idea.  I love it!

A heat gun and a lot of care could shape the blades a hair more "goodlier" before the bottles were added.

Still, 7' PVC scares me here in town.

G-

[CmeBREW]

Thanks all for the ideas.

I was surprised these PVC blades did this good. I will round over the edges better to get even more out of them.

The dimensions of these (6" pipe) PVC blades are: 40" long / 3.25" wide at the widest part of the blade / 1.8" wide at the tips / and 2" wide at the 'root' end where the mount holes are.

The weight of each blade is now exactly 1 lb. So the whole rotor is only 4.5 lbs.(Very light)

Today was windy and so I found out the limits for these blades as they are right now.

7 amps is where the blades start to make the 'wirling' noise. That just happens to be the maximum rpm of my drill testing earlier which was 500-550rpm.  So I will set the furling for 7 amps. This is about 100watts.

I knew this was not going to be a big AMP producing motor/generator for the rare high wind gusts.  I do hope to get alittle more amps when I round over the edges of the blades better. Of course, a proper made brushless alternator is going to be more efficient and get the big amps in the big wind gusts.

But I wanted something QUICK and EASY to make that does good in low wind-- and I think I got it.

By the way, I took off those little rubber pieces from behind the blades. Did not need them.

I am VERY satisfied with the results. It is exactly what I wanted. In low winds (so-called 5-10mph wind days) it  does mostly 1-3 amps for numerous accumulated hours each day. My 4' mill did nothing or almost nothing in low winds like that.

Even though it does much more watthours than my 4' mill, it certainly is much more noticable visually.

I'm going to paint the blades with that Krylon 'fusion' white spray paint for plastics you can get at Wallymart.

It sticks very well to PVC and should protect some from UV sun. It would just take a minute to recoat every year. Or I might make fast tsr WOOD blades. We'll see.

When I get it higher and the furling on it, and test the Watthours more extensively, I will keep you posted on progress. I see I will need to buy more batteries now.

-Thanks.

[ghurd]

PVC might be just the ticket for that one.

Just what I think...

PVC does better in low winds for low RPM windmills that have any cogging.  Many of my little ones make amps into a battery with PVC Zub-Woofer pattern blades before 5.5 TSR wood blades are turning.

The PVC blades hit a almost-max RPM (might be my fault, or from the pressure deforming the shape) below the RPM of wood blades, but about when the/my generator is maxed out anyway.

PVC blades make noise when they are near maxed out on RPMs.  After that, they start to bend back, twist, and deform as wind speed increases, making more noise at a similar RPM.

While typing this, I wonder if a 5-foot 5-blade PVC blade would be just as good, or better?  More torque and RPM in lower winds?  More rigid. Less noise. Guessing less tower/bearing pressures and more efficient.

"I am serious. And stop calling me Shirley."

G-

[Capt Slog]

I liked that idea too.

It's close to another that I'd considered......

  Wrap the blades with something like cling film, and then fill the hollow thus created with expanding polyurathane foam (the stuff that comes in a can).  When it's set, take off the clingfilm and sand the foam to how you want it.  Finally, cover the foam with sheets of glass fibre tissue and resin, lapping over the original PVC to make a foam filled, double sided plastic blade.

.

[ghurd]

People talked about that a few years ago.

The general consensus was it was too much effort compared to normal methods. Weaker too, IIRC.

And 'normal' wood blades have a far better airfoil.

Covering the cups(?) could lose the low wind and high torque properties I like in PVC blades. Not sure I would put that much effort into it until the hollow type worked out well.

G-

[CmeBREW]

Thanks again Ghurd.

Yes, I like the PVC blades for now. Seem to be doing very well. I sanded them better with my finish sander and painted the whole thing brownish color  to blend in better with the background. (less noticable)

I raised the testing pole to 8 feet now and it is doing very good even where it is.

I am still getting the tilt back furling better and testing Watthours.

I did notice that these flexible blades DO bend back some when spinning fast. Insodoing, the blades are only about 6 inches from the pole now that I changed things.

Today was a so-called 5-15mph wind day, according to my calculations, and If I had ALOT more battery storage, it looks like it would have done at least 1200 watthours today. (1.2 KWH in 24 hours)

I certainly have improved it again. It generates in very low breezes day and night.

I will soon show the progress in my DIARY.

P.S. Sorry, I didnt mean to call you Shirley.  I was just hoping a drop-dead gorgeous blonde female named Shirley would answer me and say: "Tell me about it stud".

Oh well...