200 Watt Turbine

The design and construction of a larger 200 Watt Wind Turbine

200 Watt Turbine Home Page

Introduction

Having learned a lot from building the 12Watt machine, I now set-out to build a larger machine that would be able to produce some more usable power. I had noted many of the shortcomings of the 12 Watt design and set about correcting them the second time around.

Incidentally, just by changing all the bulbs in the house to use high efficiency light bulbs saves you more energy than all this windturbine/solar power marlarky ever will. So if you are feeling green and don't want to turn your wife into a welding widow, try changing the light-bulbs instead!

With a suitable rectifier and inverter, it should be possible to get some usable mains power out of this machine, not exactly enough to power a house, but certainly enough to illuminate a couple of household light-bulbs. Allowing for inverter inefficiency, if I could get 150Watts at 240 Vac, that would be enough to light two 60W light bulbs, or ten 15W, high efficiency bulbs. Although I realize it is more practical to run a higher voltage turbine (24V, 36V or 48V) to get useful power, a 12 Volt machine will be more useful to me. A lower voltage means higher current, so to generate 200 Watts of power at 12 volts means 200/12 = 16.7 Amps. This requires high current wiring and beefing everything up in my rectification/regulation system. 100 watts is the about the maximum my existing regulation system can cope with and also the maximum charge rate I can safely push into my batteries without beefing up the battery bank. Therefore, I believe 12V, 5 - 8 Amps seems a more realistic goal to aim for. I can make the generator so that it can produce higher power, but I am limited by the size of the turbine blades I can use in suburbia and the wind will need to be able to turn the generator. I may experiment with using more blades which rotate at a lower speed but produce more torque. The maximum turbine diameter I can realistically go for is about 2 metres so we will have to see if I can extract enough power from the wind to turn the turbine to produce usable power.

I still have all the environmental caveats that will severely limit the power I can generate (namely, very little wind and living in suburbia) so although I suspect I could generate much more power if the turbine was mounted in a suitable location with suitably large blades, I needed a goal and so set myself one:

Raw Materials

The aim was to more-or-less scale up the existing design. Although I'm sure a 10mm shaft and bearings may be ok, I decided to move up to 12mm as everything starts becoming rather more robust. The steel frame could still be made from 25mm box-section although its dimensions may be larger. The rotors on the 12Watt machine were made from 100mm angle-grinding disks. I managed to buy two 230mm 'diamond' angle-grinding disks at a market for £10 and these looked like they will do nicely. I found a suitable sprocket that I could use to mount the disks with and worked out I could use much larger magnets now as there was much more room on the disk to play with. The smaller turbine used 12 x 19mm diameter magnets that were 5mm thick. I found that with the new disks, I could mount twelve 25x50x10mm rectangular magnets which have a very powerful magnetic force. Having more disk real estate to play with also meant I could increase both the size and number of coils on the machine. The current generated by the coils can be much larger in this design (due to larger magnets and a larger diameter rotor). I decided to opt for 18SWG wire which could deliver 20 Amps and as I can have more coils in this design, a three-phase alternator was a distinct possibility

It should be noted that as the size of everything scales up, so does the cost. The 12 watt machine cost about £40 to build whereas, the 200 Watt machine will be in the order of £250, the majority of that going on magnets.

The Frame

The frame used on the 12 Watt turbine worked very well so I decided to use a similar structure for this design. The rotors are 230mm in diameter, so I decided to make the stator 300mm in diameter, as this would give enough space for the coils, the stand-off bolts and the electrical connections. Then mean making the frame slightly larger than the that for the 12 Watt design and I also made the arms that are used to support the tail part of the frame rather than having to weld them on separately (as in the 12 Watt design).

I pre-drilled most of the holes while the steel was still in pieces before starting to weld it. Rather than using a wooden disk as the stator mount, I decided to use steel strip and would make this only when the stator had been completed. Here is the layout of the frame prior to welding it together

After welding, the main part of the frame was still a two-dimensional structure, prior to adding any vertical mounting bars. The frame was temporarily mounted between two wooden boards to enable some testing to be done conveniently as shown below

Having such an arrangement meant I could use the actual frame as a test jig now and could mount rotors and test coils when they had been produced. However, first it was necessary to make some more parts so the frame was put aside for a while.