My small wind generator build

[jwxr7]

I did some driving tests with a 3 blade rotor. Conditions weren't perfect, but I really wanted to see some power #s. There were light winds out of the NE between 2-6mph and my elevation is a bit over 900ft above sea level. Most of the testing was done driving north, but I tried to adjust the speeds to compensate for the light headwinds.

I was able to get 500 watts out of it at around 30mph using a 4 ohm load. I didn't go over 30 mph, that would be pushing the test rig more than I'd like. My load bank was maxed out anyway and those blades were really going! At speeds 20 mph and less, I had to lighten the generator load to 32 ohms to get the best power.

Here is a summary of max power vs wind speed I recorded;
12mph ~ 20w into 32 ohms
15mph ~ 70w into 32 ohms
20mph ~ 125w into 32 ohms
22.5mph ~ 231w into 8 ohms
25mph ~ 352w into 4 ohms
30mph ~ 506w into 4 ohms

Observations I had;
The low speed numbers probably aren't very accurate and should be redone on a windless day. Actually, don't put too much into any of the numbers since I was going by vehicle speed on a less than calm day.
This blade set really has a sweet spot for loading where it runs best at.
Too much load and it never gets into it's power band, too little and the generator doesn't put out enough. I suspect that with all 6 blades, low speed power will improve and high speed will probably come down some.

[jwxr7]

I'm not sure it would be useful to compare these 2 tests since the 1st one had poor conditions.

I was able to test the wind turbine with 6 blades last evening. Conditions were much better, so I trust these numbers pretty well. There was no headwind and the slightest breeze, if any, was perpendicular to my test runs. I still used the speed as read from my scangageII as before. I was able to obtain meaningful data down to 10 mph on all load resistances. With the 3 blades I only tested down to 12 mph and that was only with the lightest load because it wasn't producing enough torque to do much.
Here's some 6 blade data showing the max powers;

10mph~8-10w into 8-32 ohms
12mph~18w into 8 ohms
15mph~36w into 4-8 ohms
20mph~110w into 16 ohms or 100w into 4 ohms
25mph~361w into 4 ohms
30mph~552w into 4 ohms

I didn't test with a 2 ohm load since it didn't work well on the 3 blade test. Afterwards I wished I did a 2 ohm test because the 6 blades probably would have done a better job. I may do a retest at 2 ohms if I get a chance.

Right now I need to go over the data and figure out which grid tie inverter matches the voltage and power curve best. Then I need to decide on a furling speed that will help protect things. That speed will most likely be around 30 mph.

[Xringer]

Is it just me? Or does the power look better at low wind speeds with 3 blades??
I know you had some error factor in the 3 blade tests, but looking at 15 mph
results, just seems like too much difference to be error caused by a light wind.

[jwxr7]

Originally Posted by Xringer

Is it just me? Or does the power look better at low wind speeds with 3 blades??
I know you had some error factor in the 3 blade tests, but looking at 15 mph
results, just seems like too much difference to be error caused by a light wind.

Yeah, I noticed that too. It was tough on the 1st test to get a good steady state reading due to the varying headwind. A 5mph gust can easily double the output reading at that speed though. I may redo the 3 blade test on a good day. I'm getting better at testing anyway. My wife is just not interested in helping, so I have to do everything solo .

[jwxr7]

I did a little graphing with the 6 blade data.

Sorry, I like using a paper and pencil still .

I compared mine to a manufactured wind turbine that is built specifically for low wind areas. Lite Breeze Complete Low Wind Generator Kit
Their power curve seems trustworthy. There are some in this rotor size that seem questionable.

They have me beat under 15mph, but mine shure takes off after that. Unfortunately, mine will probably be running under 15mph much of the time.

[jwxr7]

I put a tail on and unlocked the yaw bearing. I have a lightweight tail on right now and did a driving test. It seems to furl around 23-24 mph, so I need to add some weight and get that up to a speed where it makes around 400 or 500 watts.
The furling system worked pretty well . It would hit about 200 watts (into 8 ohms) then it would begin furling, it would then hold that power level even if under increasing speeds. I only went up to 35 mph though.

I noticed today that my hub is bent . It is turned a bit convex when viewed from the front. I think it may have happened during the 6 blade testing. I took everything down so I could figure out what I'm going to do about that.

[Xringer]

Is the convex shape symmetrical? There must have been a lot of wind loading
to bend a disc shape like that..
I can understand bending an aluminum bar, but not convexing a flat disc..

If you put a steel backing disc under the hub disc, you will need to replace
the bolts with longer ones.

My experience with most aluminum alloys tells me that you can't bent it back into shape too many times,
because of the small fractures produced during bending just weaken the heck out it..

Might be better to just replace it with steel.. Maybe some steel that will spring back if bent.

[jwxr7]

It's a steel hub, and it is pretty symetrically bent. If the company that sold me the hub and blades won't send me a free new one, I'll probably try turning it around so the wind will bend it back. First I think I'm going to modify the shaft adapter I made so i can add a large washer to beef up where the middle of the blade hub mounts. That should hopefully prevent it from bending as easily.

[Xringer]

That's steel! Wow, then maybe there is something wrong with it?


Now that I look at it, those three big holes can't be doing nothing but adding flexibility to the hub..

What are those holes for??

[jwxr7]

What are those holes for??

I believe they are for ventilating the automotive type alternators that these set-ups usually go on.