Wind & Wet

Arduino data logger (data acquisition system)

The data logger, or data acquisition system, was made to try to get more information about the performance of the wind turbines I have been making. While the wind speed and output power could be read from meters it was nearly impossible to store the constantly changing data.

The information I was hoping to collect would allow me to determine the efficiency of a wind turbine and compare different designs. The turbines were being used to directly charge a battery so the information I was interested in is:

  1. The output voltage. This would be approximately the voltage of the battery being charged.
  2. The charging current. This combined with the voltage gives the power output of the turbine and generator combination. If the resistance of the generator coils and wiring is known it can also be used to estimate the input power of the wind turbine.
  3. The wind speed. This gives the power available to a wind turbine if the swept area is known. Combining this with the output and input power of the generator from the current and voltage measurements the efficiency of the turbine, and overall efficiency can be found.
  4. The rotational speed of the turbine. This can be found from the frequency of the AC current from the generator and then adjusted to take into account the number of magnets in the generator. From this the tip speed ratio of the turbine can be calculated.

The diagram illustrates the measurement points.

Arduino data logger measurement points

This was my first attempt at designing electronic circuits and started with a lot of research on the web. The Arduino open source processor board has been used by people doing similar projects and with its multiple ADC and digital inputs and a USB connection to a PC seemed a good starting point. A new Arduino Mega 2560 from ebay cost £25.00(UK) and proved to be quite easy to programme with good documentation. The Arduino board does not contain any permanent data storage, although it is possible to connect an SD card with suitable adapters, so I intended to use the board connected to a laptop and stream the data into a file on the laptop hard drive.

The Arduino's ADC and digital ports are based on a 0 to 5V input range. The next problem was to take the measurement points in the diagram above and turn them into a signal suitable to be read by the Arduino. I don't claim any great experience of electronics so there may be better ways of doing this but the route taken seems to work.

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