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Version complète : A dynohub wind turbine built to last.
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This project started when I found some aluminium section on something that had been washed up on the shore. I could see a possible aerofoil shape hiding within it if I cut sections out of it, see photo. It didn’t make a perfect aerofoil but the finished section is very strong. The blades could definitely be used underwater if I ever felt like making a tidal turbine.

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The next challenge was how to attach the blades to a hub. I wanted to rivet aluminium brackets to them such that they were bent to blend in to the blade shape. These could then have been screwed on to a wooden disc. I decided that bending the metal would have been a bit too complicated and I didn’t have the right thickness. I instead choose to use bolts pushed and rived into the blade. This is never an ideal method because stresses are concentrated at the blade roots and reducing the size at this area to that of a bolt creates a weak point. However an M10 bolt supporting a 30cm blade should be fine. The big advantage of doing this is that the blade pitch can be made adjustable. The hub is made out of thick plywood and the bolt holes are threaded so that tightening the nuts will lock the blade pitch.

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As I had 6 blades the finished rotor would be a slow turning one and of a small diameter of just 0.8m. It was therefore good for coupling to a dynohub. Something to be aware of with dynohubs is that they are very affective at limiting their current output. Therefore if the battery voltage is 12 volts the power output will be at most about 5 watts. Which means it’s easy to under load the rotor in windy conditions resulting in over speeding. This brings me to the other reason my blades are suitable and that is that they are untwisted. Untwisted blades are inefficient and that’s ideal because in this situation as it greatly reduces the risk of over speeding. Even with its low efficiency the rotor is capable of producing without much wind the few watts needed by the dynamo.

I have made turbines with dynohubs before but they were never built for long term use. There were a few issues with them.
My previous turbines had the blades built around the hub which made weather proofing very difficult. In the west coast of Scotland climate and the winter sea spray a hub would not last very long. That would be a shame because these old dynohubs are well made but surviving our weather is asking a bit much.
The other issue with mounting the blades on the hub is that any unbalanced forces on the blades will apply bending forces to the axle which can only be supported on one side. The weight of the rotor adds to the problem. The rotor may do many millions of revolutions and over time the axle could fail from fatigue.

What I decided to do, which will also reduce the wear on the hub, was to use a separate bearing to support the rotor. This means the dynohub can be completely protected within a nacelle made of thick aluminium sheet. Also because the axle can be the rotating part the bearing is also within the nacelle giving it protection from the weather. The challenging bit and I had to remake was the connection between the bearing and hub.
It was a compromise between spending days making an elaborate part and just making something that will work. The coupling rattled a bit and did the job but it wore out much faster than I had expected.

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Most of the wear that can be seen in the photo below occurred in just a month although it was a windy one. It has now been replaced by rubber coupling made out of strips of old tyre. This is smoother running, much quieter, should last longer and didn’t take that long to make. The other thing I found was a fatigue crack in one of the tower attachment brackets which I fixed and reinforced. This will have been due to vibration from the rotor which is not quite balanced, something I still need to fix.

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The tail is the most basic form of furling tail and simply hangs on a hinge. The nacelle is attached off centre to the tower which means that any thrust forces from the rotor will try to rotate the turbine away from the wind. The tail will try to counteract this but if the wind is strong the tail will lift allowing the turbine to rotate out of the wind. If the weight of the tail is right the power output of the turbine can be limited. It’s a rather crude way of doing it and there are better types of furling tail design. A furling tail is not really necessary on a rotor of such a small diameter but I was recycling it from another turbine.

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So what do I use the turbine for, well it trickle charges a leisure battery that I use as a backup power supply during power cuts. If it’s windy I use some of the surplus to provide lighting or charge a mobile phone via an inverter or to charge my bicycle light directly.

A short video of the turbine in its location.
You are again... amazing!

5 watts is verry little though! Enough to keep a spair battery charged, but I doupt it can be used to recharge....
What do you use as a voltage/charge regulator?
BTW, the coupling is verry ingenious!
Thanks Normand
I know is not much 5 watts but it is so often windy here in the winter the energy it produces adds up. I don’t intend to power the house with it.
Lead acid batteries as a backup power supply are not ideal due to the requirement to keep them fully charged but the wind turbine does this job very well as long as I don’t use the battery too much. It’s an interest question though, what would happen if I fully discharged the battery and assuming the wind blow for weeks afterwards would the battery recharge? In theory I don’t see why if given long enough it shouldn’t but I also know that fully discharged lead acid batteries are supposed to be charged with a large current. What I do know is that I can have a 24 watt bulb on for maybe 4 – 5 hours and the battery seems to get recharged, although it may take most of the next day. However this is only discharging the battery by about 10 – 15%.

I do have a charge controller details on Hugh Piggott’s (homemade wind turbine expert) website. For a wind turbine of this power output it is totally unnecessary, it was from when I had a larger car alternator turbine. At full output of 5 watts and a fully charged battery the voltage levels off at 13 volts, perfect for long term trickle charging of a large lead acid battery. The charge controller won’t cut in until about 14 – 15 volts.
To keep a lead acid battery topped... it takes just a few milliamps at 14.4v

To recharge without sulfurisation of the anodes, I have always been told that it takes 2 amps or more. High current heats up the solution in the battery helping dissolve the crystals that form when it discharges.

Those numbers are of course "things I always herd" so maybe they are not accurate !