A wind turbine powered weather station displaying temperature, humidity and wind speed by persistence of vision using 8 white LEDs along a wing tip. The turbine blades were cut from a length of 4 inch PVC pipe.
A 12v stepper motor salvaged from a floppy drive is used as the generator. The stepper body is mounted to the turbine, the shaft is held stationary. This allows the for the omission of slip rings to transfer power to the persistence of vision display. The controller, sensors and display system is mounted to the motor and rotates along with the turbine blades.
The 4 phase AC from the stepper is rectified with 8 schottky diodes and shunted to 36 volts by three 1 watt 12 volt zener diodes in series. The shunt serves two purposes, to prevent the DC input voltage from exceeding the switch mode buck regulator maximum input, and to provide electrical braking to the turbine in the event of high wind speeds. The resulting input voltage is switched down to 3.5 volts by way of a TPS5420 buck converter.
The MCU controlling the common anode POV display is an AtMega88, chosen for it’s ability to operate at up to 10Mhz from 3.5 volts. The temperature and humidity are sensed with an SHT21 via I2C and absolute position by a hall sensor salvaged from a floppy drive. The hall sensor allows for positioning the POV display as well as calculating rotational speed. A resistive divider was added to sense the voltage generated by the stepper.
The cut in speed appears to be around 100 RPM as the SMPS requires at least 5.5 volts to start up. At 1500 RPM the open circuit voltage of the stepper is just over 60 volts.
1) Schematic 2) Board 3) PCB 4) Turbine 5) Testing Video (below)