Testing and Tuning

Test Flights

I monitored the new PVC blades for some weeks, brought the machine down to check for cracks and concluded they were physically strong enough for the job. They also seemed to turn the machine easily enough although the spped of rotation was relatively low until the wind picked up. The machine still furles early but that is fine with me, I would rather produce less power rather than risk things falling apart at high speed.

In a light wind, the rotors will turn at less than 30 rpm which unfortunately produces no useable power. In a light to moderate wind, the rotors turn at 100-200 rpm. The output is about 8v (rms) between phases which is not quite enough to start charging. As the wind gets stronger, the blades spin at > 200 rpm and I see 10 Amps or more being generated. The autofurl and electric brake kick in at that speed so it tends to be quite spikey. So the machine is capable of producing lots of power as the wind increases.

Conclusions

The PVC blades have been in operation for several months and their performance is vastly superior than their wooden predicesors. They are light, well balanced and turn easily, even in relatively light winds.

I have tried running the machine in 3-phase star and also in single phase. When the wind picks up, the amount of power produced is well over 150W and I have seen in excess of 10A. However, although the blades turn easily in low winds, the amount of power produced is not usable as it lies in 9-12V range. I believe this is a limitation of the alternator/blade length. I get lots of torque with the larger blades so when they are turning, they keep running, but in ight winds they do not rotate fast enough to produce the voltage required. This is part buy design as I did not want a rapidly rotating object that close to civilization! The machine is also much heavier than the 12W design so requires more wind to to turn it to the wind. Since my battery bank is kept charged up quite well with solar, when the turbine does produce lots of current, the regulator kicks in and brakes the turbine. It would be more beneficial to have a lower charge current at lower wind speeds so I think that this 200W design would be ideal for good wind, high power requirements but it is not pushing the right buttons in my urban environment.

Although it is possible to further tweak parameters, I believe that I have hit the limits for the wind available to me. This larger turbine is perhaps too large for my environment. I am also staring to look at grid tie inverters and these require a much higher output voltage (> 40Vdc) at the expense of some current.

This has been an interesting experiment and I've learned so much on the way but I feel it is time to move onto other things as I'm quite keen to spend some time working on larger-scale solar generation. I do have a few ideas about a multi-stator high voltage, low current turbine but that will have to go onto the back-boiler for a while. It is time to find another playground for a while :-)