www.SunAndWindy.bitz.me.uk

A site for some of my micro generation projects!

I should add, this site is not complete, and will be added to on an ad hock basis as and when I have time

Wind generator blades from CMS

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  • Complete change in direction for my Blades

    Having started off making some fibre glass blades from some 6" fibre glass pipe, I've now taken a new direction as detailed below.

    Due to the present economic situation where the American dollar is so weak against the British pound, makes the purchasing of stuff from America very attractive. Following a forum post on http://www.thebackshed.com/Windmill/FORUM1 about a chap selling fibre glass wind turbine blades, I took a look at them on eBay and was surprised how cheap they had become. The guy selling them (eBay name -magnet_master) has an eBay shop called China Magnet Source has various sizes. I choose a set he describes as having a diameter of 110" with a starting bid of US$49.99 and shipping to the UK as US$96.90 so after bidding etc. with postal insurance, came to a total of US$149.29. After PayPal had done their bit, the total price was 73.92. The delivery arrived via Royal Mail Parcel Force in about 10 days.

    Below is the original text from the eBay advert.


    PowerMax+ 092

    The Powerful High Efficiency Fiber Glass Wind Turbine Blades

    Diameter = 9.2'=110"=2.8 M

    Offered by CMS Magnetics,

    The Pioneer of the Small Fiber Glass Blades

    Used on Commercial Wind Generators 

    600 W at 17.9 mph

    Balanced

    Hub NOT Included 

    Description:

    Our fiber glass wind turbine blades are mass produced and based on aerodynamic theory. The efficiency of the blades are among the best----0.49. 

    In the addition, the exact same products are applied to thousands of 600 watt wind generators and produce electricity for thousands of customers. If you need a set of blades to build your own wind turbine, this is the best choice for you!

    Note: We have been selling commercial wind generator blades for over a year now. Our customers require quality, durability, and efficiency. This is why CMS Magnetics is at the top of the small wind generator industry. We provide renewable energy to last. You will be happy knowing you made the right decision when you choose CMS Magnetics!

    Features:

    • Light Weight: 5.85 lb / blade
    • High Efficiency: 4.9. Airfoil was made to pick up the wind power efficiently. 600 W at 17 mph and 3,319 W at 27 mph. 
    • Heavy Duty: Very strong and can withstand the weight of a fully grown man. (see picture below). The blades will last you for years to come.  
    • Efficiency: 4.9. The ideal value is 0.50. Home brewed blades typically range from 0.25-0.35. 
    • Start-Up Wind Speed: 3 m/s = 6.7 mph
    • TSR:  1:6 at heavy load, 1:8 at light load and 1:10 with no load.
    • Cut off Wind Speed: 20 m/s=44.7mph=38.9knots

    Applications: 

    • Power: 600 W system. From an engineering point of view, this set of blades is perfect to drive a 600 W system if your average wind speed is about 17 mph.

    Q & A

    Q. Do more blades equate to more power?

    A:(From Hugh's Book, P 11)

    More blade will produce more torque, but that does not equate to more power. Mechanical power is speed multiplied by torque. For electricity production you need speed more than you need torque. Extra blades help the machine to start to turn slowly, but as the speed increases the extra drag of all those blades will limit how much power it can produce.

    Q. What factors decide the blade power?

    A: In theory, blade power is as following:

    Blade Power = 0.5 X E X RotorDiameter**2 X WindSpeed**3

    Based on this fomula, the blade power is decided by rotor diameter, wind speed and efficiency E. The range of efficiency is from 0.25-0.5. Ideally, you want blades with the highest E rating possible. The E value of home brewed blades typically ranges from 0.25-0.35. Most blades sold by individuals and small companies are in this range.

    The E value of our blades is 0.49. This means they are very efficient in transferring wind power to mechanical power. Based on this value, if we assume wind speed to be 12m/s, this set of blades can produce 3,319 W of mechanical power.



    Reading through the text above, and having weighed the blades, I'm not so sure the blades are 'balanced' as when I weighed them, they came out as 2.29Kg, 2.304Kg and 2.306 Kg. I'll weigh them again to see where the weight difference is, as the edges do need a bit of work to tidy them up. The actual overall length is about 54" and about 7" (I only roughly measured them) at the widest bit.

    There was no dimensional drawings with the blades, so I had to measure the predrilled holes as close as possible, then using AutoCAD work out the appropriate angles to use on the dividing table.
    Below I've bolted the blade hub to a dividing table and centred it to within 4thou. I suppose with a bit more time I could have got it closer, but I think there's going to be far more than 4thou error in the blades, plus the fact there is quite a bit of difference in the weights of the blade, so a lot of balancing is required.
    So much for the accuracy on the above exercise, after tidying the blades up with a belt sander and getting them all the same weight (well, within 2 grams), I assembled the blades on the hub, only to find the assembled hub and blades were miles out of balance! Although the blades are basically the same weights, the weight distribution within the blades must be different. After playing around a bit with different sized 'G' clamps on the hub, I could get the balancing somewhere near correct. Trouble is with needing such a large balancing weight, I had no where to fix it. So I disassembled the whole lot again to drill some weight fixing holes as shown below.

    Not easily seen in the above photo is the letters stamped in to the hub disc and all the fixing plates. The reason for this is, so that I can reassemble everything in exactly the same place.

    Close up of stamped letters

    Blades assembled on to the hub (prior to drilling the extra fixing holes)

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