23in vs 29in airfoil blades

[nb wind]

Hello again

Well another windy day in Northern New Brunswick today we are getting substained winds of 40kph with gusts of 65kph no need to say that my windgenerator is spinning like a bat out of hell, All day blades have bein reaching up to 2200rpm wich is good because output voltage has bein around 42vdc not bad for an old threadmill motor.Around Christmas and new year I had taken it down for repair I have bought a second hand metal lathe wich works prety well for the sum of $300.00.Wich is prety cheap.I was having problems with a hub I ad bought of ebay.Wich by the way was not defective in any way my mistake when I ordered it I gave wrong shaft dimentions and so I got a perfectly machined hub but with the wrong size arbour it was only off by a tiny bit but that was enough to give me a slight vibration. So I decided to make my own,luckely I still hade the pulley that was on the threadmill motor that I'm using in my windgenerator so I took the motor appart removed the shaft instaled the pulley on the shaft put eaverything on the lathe and machined my own hub,Wich is working great with no vibration at all,The blades I was using before were also bought on ebay they are 23in long airfoil blades air x knock off's and seemed to work great but I had bought an extra set of 6 airfoil blades mesuring 29in wich I had figured would work even better for my next project, So I decided to replace my 3-23in blades wich were verry silent with 3 of my new 29in blades wich to my suprise were extremely noisy.

Now when I say noisy I mean when the blades reached about 1800rpm I turn around to see if the love boat whas coming up the driveway there was that extreamely loud fog horn like sound comming from the blades???

So I took the mill back down replaced the blades with the 23in ones put the mill back up and now It's working like a charm with no noise or vibration still geting all those high rpm's with no noise at all.

So with all that said my question is

Why all the noise from diferent blade lenght??

I know these 29in blades will be useless to me unless I cut them down a bit to try to reduce the noise what do you think??

Have a nice windy day.

[SparWeb]

Hard to say without more information.  If one is quiet and the other is noisy, at roughly the same RPM, then I can't say that the tips are travelling too fast, though 2200 RPM is darn fast on any windmill.  do the two sets of blades have different airfoil?  Different angle of attack?  If you look at each of the 29 inch blades, do they have different angles of attack?  Is the trailing edge sharp?  Are the tips flat, tapered, bevelled, etc.?  Have you weighed each blade?

[Airstream]

Voltage is not really where it's at, its current at voltage that does the work.

Sounds like you may need larger conductor wires down the tower? If very small and high resistance there will be low current no matter the voltage so there will not be enough work effort to slow the turbine blades down...

My calculations put tip speed (60-inch disc at 1800rpm) at 325 MPH so what you hear is flutter...

[dynaman]

The tip speed on the 29" blades is about 25% faster than the 23" blades and can make quite a differance in the sound levels. I myself would not want the blades running that fast.

[nb wind]

Neither do I but I think I found the problem on last post I put up someone told me to conect wires from windgenerator directly to battery bank and battery should regulate it keeping it under 14.5v or so, And should slow down windgenerator but it was not working ,But I think I found the problem I had a loose conection so I fixed it and now windgenerator seems stalled when voltage hits about 14v.Wind is still houling out there but generator seems to have calmed down.

[Flux]

For any wind system an ammeter is virtually essential and I can't imagine anyone not having one. Having one would have shown that you were getting nothing.

I am not surprised it was howling running on no load in a gale, at least you know your blades are tough.

Now that you have got it on load you need that ammeter to see what you are producing. Most likely the larger blades will do far better and you may still be on the small side.

You need to monitor the current in lower winds and find your cut in wind speed ( point at which it makes current). Then you can choose the blades that suit your generator best for average winds.

If things are working voltage tells you nothing except the battery voltage, you can't see the generator open circuit voltage when running normally.

Flux

[Electron Pump]

  What is the rating on that treadmill motor? I'm in a similiar situation. I fixing to order a set of the six blade ones like your talking about tring to get up to the charging level. The most I've seen from my treadmill motor is 10.1v in a 25, G35 wind with my homemade PVC blades.

  I'm worried that my motor is no good. Both my motors. I've got 2 very similar motors. But you are talking RPMs that would put me into the "+" zone. My motor is 130v rated at 7099 RPM. The other is 120v rated at 7000 RPM.

  Have you ever played with the 260v 5100 RPM motors likes on E-Bay? Do you think the six blade set could get this motor up to power producing range or should I plan on a different motor at this point also.