Blade Help

[need bb]

I recently did some testing of my tape drive motor wind turbine.  The motor is 1/3 bigger than an Ametek 30v and has very good low RPM performance.  Just slowly turning it produces a couple of volts.  I hooked up a drill and it produces 12V at around 300RPMs and 45V at 1200RPMs.  I tested the turbine in 12-20MPH winds, but was disappointed in the performance.  Most of the time it was producing between 9-10V, but a couple of times it made it to 14v.  I am wondering if my blades are the issue.  I had some PVC blade, but they didn't perform well and snapped in high winds.  I replaced them with a pair of aluminum blades that I bought from eBay.  The eBay blades have a diameter 70 inches and weigh around 10lbs.  I am thinking that they have too much surface area for my tape drive motor and that is why I am not reaching cut in.  The hub can support two blades, so does it make sense to try it with two blades?

Thanks

[DanB]

If your cutin speed is 300 rpm then I should think your blades are quite a bit too large.  4' diameter blades would be better.  Those are also rather wide which will also make them slow and  - I am not a fan of aluminum blades like that, I expect they are far from ideal.  I would also be surprised if they lasted very long before they snap off at the root where they're bolted on.

There's a lot of crap on ebay - lots of people selling blades and motors and you cannot just take any set of blades and bolt it on to any old motor - it's a roll of the dice and the odds are very much against good performance.  It's critical that the blades and the generator/alternator and the load all be matched well to one another.

I used to mess with ametek tape drive motors and made lots and lots of blades before I got something that worked reasonably.  (that was before ebay or the internet existed so I didn't have any feedback from anyone else and I really didn't understand at all what I was getting into - in many ways, I probably still dont... lots of trial and error)

[ZooT]

You could try two blades......but boy, are those aluminum blades going to flex when it yaws.......

What I think I'd try first from looking at your bladeset is relocating the blades themselves from those extension arms to the holes in the hub itself......that should shorten it up by a foot or more in diameter.....and maybe make it useful even if it does steal some from the blade roots....

Are both sets of holes spaced the same?....if they are try it and see if it helps

[Flux]

Yes those blades look very similar to what you would get with pvc. They also look similar to the LVM blades. They probably work quite well with a high torque low speed alternator.

At near 6ft diameter you need fast blades for a cut in of 300 rpm. The Freelite and small Winco machines used 2 blades running in this speed range with good results but your blades would probably need to cut in at just over 100 rpm.

You may get what you want if you have the ability to do a 2:1 speed increase with a chain drive ( weather conditions permitting). Otherwise you are looking to build a decent low speed alternator or blades to match your generator.

I am not impressed by the long term prospects of aluminium either, but they should perform in lower winds if you match them right.

I back everything Dan said about pot luck projects. Don't buy ebay special bargains unless you have seen someone else's results and you know what's coming.

Flux

[CG]

If your pvc blades were as wide as the one in the picture, I am not surprised they snapped. My pvc blades are narrower and have only snapped at the root because I didn't reinforce them there enough. I can see the tips of my blades flexing backwards in high winds, and they curve slightly forward when they are at rest. Also if you are cutting you pvc blades from soil pipe they will probably have a thicker wall than my gutter blades.

[tecker]

 Re bolt those blades closer to the center that give more support and also increase your speed somewhat and cut some pvc blades to match your motor to get an idea of the size start a little large so you can cut them in .

[TheCasualTraveler]

What these guys said,

ZooT:
 What I think I'd try first from looking at your bladeset is relocating the blades themselves from those extension arms to the holes in the hub itself......that should shorten it up by a foot or more in diameter.....and maybe make it useful even if it does steal some from the blade roots....

tecker:
Re bolt those blades closer to the center that give more support and also increase your speed somewhat

But leave the extension arms on behind the blades. Looks like the 3 bolts line up the same on the arms as on the hubs so you should be able to move the blades in like they said but leave the arm behind for support. Is that what you guys meant?

[tecker]

400 rpm is a tall order really . mabe bb dosen't want to hack on those blades and a set of pvc blades to test is a better idea.

[MattM]

Those are not extruded aluminum, they are milled, which means they are high quality material.  People have seen the stories of aluminum blades failing and assume all aluminum is bad.  But this is far from the truth, it all has to do with the grade of aluminum and the forming process.

The simple solution for the OP is to get some simpler sheet metal blades to mount.  A simple 4" wide piece of 24 gauge rolled steel bent with a 1/4" leading edge perpendicular to the hub and 1" trailing edge to mount with the main part of the blade on a 45 degree angle to both edges.  Here's the side view somewhat:

|

.\

..\

...\

....\

.....___

It's simple, its easily reproducible, its silent, and it works.

[MattM]

This may sound stupid, but this is the front of the blades facing the camera, correct?

They don't look terribly inefficient as they are right now.  But I can see problems with catching wind if that was the backside.

[need bb]

Well today the wind was between 10-20Mph and I did some more testing.  As for the concern regarding the aluminum blade, they are thick and very strong.  So far they haven't had any issues and have survived 50Mph winds.  They seem to be very similar to the Boast Buster blades from TLG.  I tried the turbine without the blades extenders since they would reduce the diameter by 1 foot to 5 feet.  With the 3 blades, the performance was better than before with an open voltage hovering between 10-12v.  I also measured the shorted amps which was between 3-5A.  I imagine my motor is much more powerful than the 30V Ametek's because what I have read they produce around 2A at 300 RPMs.  I estimate that my blades were spinning around 200 RPM's for the 5A, thus at 300RPM's would be much higher.  I then tried with 2 blades and they performed a bit better than the 3 blade setup.  The turbine's open voltage hovered between 11-14v, but I didn't test the shorted amperage.  

[MattM]

Thanks for keeping us up to date on it.

Interesting that 2 blades was better than 1 for you.

[finnsawyer]

Judging by the visible bolt he may have been mounting them backwards.  The convex side should be toward the alternator, the concave side toward the wind.  You want a component of the lift in the direction of rotation.

[Aqueel U Siddiqui]

I think you are right! same case with me