Update (03/26/14): The Wind Turbine was deployed down in Curacao two weeks ago. The actual data from the Turbine matched this article quite well. About 60-90ma at 15 MPH. Not much (and not nearly enough to run the box – takes about 300ma) but it did provide a trickle charge at night. A windstorm took out the turbine about a week later. See the blog posting about Project Curacao Operational.
You can find this $80 50W Wind Turbine on Amazon here.
You can find this $80 50W Wind Turbine on Amazon here.
We have now completed the 50W Wind Turbine characterization. During the test of three weeks ago, we blew out the DC/DC voltage regulator with an over voltage condition. The damage was limited to the regulator.
Why did this happen?
The open loop voltage measurement on the 50W Turbine gives us a clue. The regulator is specified as a maximum 19V input. When the turbine hits more than about 25MPH, we started to generate more than 22V, even loaded. This eventually fried the regulator.
What did we miss in our test setup?
The 50W Wind Turbine very minimal specifications say in perfect conditions we can get 2A at 25V which is 50W. However, if we aren’t taking 2A (which is 2X to 4X our maximum), the voltage goes up. Eventually, it killed our regulator. We did not think that one through.
How to fix it?
We added an over voltage circuit on the Wind Turbine side of the DC/DC regulator. The wind turbine is rated at 50W, but we aren’t going to trust the number. We built one using TVS diodes and made sure we sized it for about 4A@25V (100W) to cover hurricanes (although in a hurricane, that will be the least of our problems – We would expect the Turbine to be halfway to Aruba by then). We did this by getting a 50W 5 Ohm resistor and putting 10-5W TVS diodes in parallel. TVS diodes operate by shunting excess current when the induced voltage exceeds the avalanche breakdown potential. It is a clamping device, suppressing all over voltages above its breakdown voltage. Like all diodes of this type, it automatically resets when the over voltage goes away.
We set the over voltage protection at 20V to avoid this problem in the future.
A good link for a diode based over voltage protection circuit is https://www.electronics-tutorials.ws/diode/diode_7.html
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| Completed Overvoltage Circuit |
We ran another set of loaded tests for the 50W Turbine after the over voltage circuit was added and got the following curve (without generating any smoke).
Conclusion
We are going to go with the 50W wind turbine for this project down in the Caribbean. Our curve shows some power generation at 15 MPH and it gets really good at about 25 MPH. When we get the box down to Curacao, we are going to further characterize both the 50W and 15W wind turbines (UPDATE: Before we went to Curacao, we determined that the performance of the 15W wind turbines was so poor that it wasn’t worth bringing them to Curacao).
Our control system takes the weather into account on cloudy days (low luminosity and solar voltage) and turn the wind turbine on. Of course, we will turn the wind turbine on at night all the time. As our curves show, generating even 10W on an ongoing basis from the wind poses a set of special problems. Our next wind powered system will use better (and more expensive) turbines but as this is a secondary source of energy, the chosen 50W turbine will work for Project Curacao.
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