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Forum Index : Windmills : 10 kw - Blade balancing
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| Abhinav India Newbie  Joined: 26/07/2006 Location: IndiaPosts: 8 |
Hi, I am making the 10KW machine (see earlier post) and have made 3 Blades of 5.5m lenght each. But they vary in weight by 1 to 3 Kgs. I have two questions: 1) How does the diffrence in weight affect the turbine? 2) What should I do to correct it. I wonder if the prob is similar to car wheel balancing. Abhinav Wind is Free, wind energy is Freedom |
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Yes you will have to balance them. I once made a set of blades , and thought they were "close enough" and didn't need to be balanced. At certain wind speeds the whole windmill and tower would shake so much it was scary. Next day I took them down and balanced them as well as I could, and that fixed the problem. You need to add weight or remove weight to balance your blades. Some info here and here. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| Abhinav India Newbie Joined: 26/07/2006 Location: IndiaPosts: 8 |
Hi Glenn, Thnaks for the info. Now that we are sure that unbalanced blades will harm the turbine. As you said we need to add balancing weights to the Blades. Please give some details on this like 1) How do I measure at what lenght the balancing weight should be added? 2) What is the material for balancing weights? I have a Electronic weighing machine, similar to the one used in Shopping centers, it can weigh upto 30 Kgs. How can I use it to find where to add weights Abhinav Wind is Free, wind energy is Freedom |
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| KiwiJohn Guru  Joined: 01/12/2005 Location: New ZealandPosts: 691 |
I think for best results the entire blades and hub should be balanced as one. Although I have never tried this I suggest putting some sort of cap on the hub so that you can balance the entire assembly horizontally on a sharp point. I mean with the blades horizontal and the axis vertical. You will quickly see where the gross unbalances are and you can address these by adding weights to the tips or removing material from the heavier blades. Maybe someone has a better idea? John |
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Bryan1 Guru Joined: 22/02/2006 Location: AustraliaPosts: 1344 |
The way I balanced my 8' blades was firstly I put 2-12" disks to help support the blades one on each side of the blade. Then I bored the hub that attached to the genny shaft to 1" lubed it up and put some 1" diameter brass rod thru. Then I secured the brass rod so the blades could run freely off the ground and spun the blades, when the blades stopped I marked the highest point and repeated this 3 times. Now with the 3 pockets after screwing in some tek screws to help retain the lead I poured motlen lead into the pocket that was at the bottom meaning the heavy end. It took about 5 pours to get the blades 95% balanced then I sealed the lead with some wood putty. Lucky for me the wood putty worked a treat and after a gentle spin with a slight breeze going it took 10 minutes for the blades to stop. Then I took the blades in the shed and did a final balance check with my laser level to check the blade tips for alignment and found my first blades were balanced pretty well. Cheers Bryan |
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| Abhinav India Newbie Joined: 26/07/2006 Location: IndiaPosts: 8 |
Hi Bryan, Sound convincing way of doing the task. But I could make the complete picture of the things you did. If you can upload some photogrpahs that would be great. Or send them on mail toabhi78@yahoo.com cheers Abhinav Wind is Free, wind energy is Freedom |
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| Bryan1 Guru Joined: 22/02/2006 Location: AustraliaPosts: 1344 |
Allo Abhinav, Unfortunately I didn't take any pic's of the process and now the blades are fully painted it won't show. Anyway to explain abit further, I made a 3 blade setup and cut the blade ends on an angle so they all meshed together then I cut some slots in the sides and placed some 20x5 mild steel to key them together before glueing. Then with the 12" disc's I glued one on each side to form the 3 pockets. What I didn't mention when I was balancing before adding the lead I screwed weights of a known weight to the heavy spot to give me an idea of how mucch lead to melt and allowed another 100 grams for loss when heating. Now the tek screws I put in were the countersunk variety and I left them about 1/2" proud. One thing I found when I needed to pour a second batch of lead into the same pocket the first batch melted as the second one was poured so it formed a single mass. The wood did burn abit but the wood filler soon fixed any deforms from the burning. I set the blades up for a test over 2 weeks on a dummy shaft to see if the lead would hold and after some strong winds with the blades a virtual blurr the lead stayed put with no signs of the putty or paint cracking. So I think this is a good method to use if the blades you make are way out of balance and you don't want to carve more wood off. Hope This Helps Cheers Bryan  |
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