Progress (and more to learn and some bugs to find). The Arduino captured a one minute time series of the voltage across a 22 ohm resistor attached to the generator’s output terminals whilst it was hand cranked. The load on the crank varies during a rotation so there are constant variations in speed and this can be seen in the time-series, the flywheel effect of the wind turbine’s rotor will probably have a smoothing effect. The circuity between generator and the ADC needs to include a zenor diode to provide some protection for the chip, once that’s in place, the DC biasing can be setup sensibly. However, the time series was good enough to passed through a Fourier Transform routine which allowed the rotational speed to be estimated.
The speed and voltage data can then be combined into a power curve, the variations in power are due to uneven cranking. The 22 ohm resistor was chosen because I had one in a box somewhere. To get peak performance from the generator will require matching the impedance of the load to the impedance of the generator. The planned load is a USB power pack.
Whilst messing with electronics and Fourier transforms has been instructive, so too has hand cranking the generator, clearly the torque required varies with the value of the resistor, with a 10 ohm resistor the torque required almost pulls the generator of its mounting.
So on the next trip to the beach, I’ll take a bag of resistors and see how they effect the ability of wind to turn the rotor.
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