Doris B - Carpentry and Computing

The design is slowly moving forward. I’ve messed with small wind turbines before, but Doris B is an attempt to create some design rules. The objective is to get an output of 2.5 Watts in a 5 m/s wind. The current rotor is 0.7 metre in diameter with six buckets and s of the drag type. It’s had a couple of runs without instrumentation, but eyeballing the rotor suggests that its operating speeds are between 50 and 150 rpm. The current activity is figuring out the electrics and creating a functional data logger.

Almost any design of turbine will turn in a 10 m/s wind, but at 5 m/s the available energy is about 70 Watts/m2, which is not a lot, thus small things become important. The first attempt at creating a power box used a basic silicon bridge rectifier, smoothing capacitor and a voltage regulator. The voltage drop across the diodes in the rectifier was approx. 0.7 – 0.8 volts which is about 10 – 15% of the voltage of the generator, the rectifier will shortly be replaced with four Schottky diodes which hopefully will have a voltage drop of around 0.3 volts. The voltage regulator did nothing useful, three partially discharged Ni-Mh cells drew around 300 mA without the voltage regulator which is roughly a charge rate of 0.15 abd a reasonable working level. Removing the regulator cleaned up the power curve, which currently looks like this:

Part of the design is to match the power drawn by the generator to that generated by the rotor. With no load, the generator turns freely in a light wind. place a 10 ohm resistor across the terminals and it seems likely that it will cease to do so. Experiments with pulse width modulation of the load suggest that this is a potentially efficient way of optimising the relationship between the rotor and generator.

My love of the Arduino is growing steadily. Over my professional life, computing power has increased dramatically, CPU speeds are now measured in GHz, RAM in GB and storage (which is not necessarily local) in TB. The Arduino Nano was originally purchased as an analogue to digital converter for a Raspberry Pi, however, with experience, I’m realising the capability of the Nano. This should not be be surprising, my first programming experience was on an ICL 1900 which if I remember correctly had 16 Kb of magnetic core storage, static data lived on punched cards and if that was not enough the only option was a tape drive which required serious negotiating skills to access. Those machines were a great opportunity and so are the Arduinos. If you are used to working with GB databases, 1 Kb of EEPROM does not seem a lot, but it’s enough and there is the potential of IoT to explore.

Footnote – A month ago, my laptop died, it was expedient to hook up a Raspberry Pi. At some point I will have to replace the laptop, but the Raspberry Pi is doing fine, I have not done any serious analysis, but the energy I use whilst messing with computers might have dropped by 0.5 kwh/week (a guess)