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Wind Turbine and Power Generation

  1. Apr 14, 2016 #1
    Working on a wind turbine for a class project and making an attempt to add a brake. The idea is that the turbine will generate power at a certain wind speed and if the wind speed is increased, we would slow the turbine with a mechanical brake.

    We're using a 10V low-torque motor and have created the fan blades and gearing system. While running the turbine in a wind stream, we see 9-10V on a multimeter connected directly to the motor.

    We then purchased a linear 10V solenoid that appears to have 8-9ohms of resistance. The goal is that it would be in parallel with whatever it is we're using the turbine to power up. When we tested the solenoid on a power source, it appears to activate around 3.3V and .36A. We had hoped to just put a potentiometer in front of the solenoid so that a voltage drop would occur and we could "dial" it in to activate once the turbine was generating around 9V from the motor. As the voltage from the turbine increased, the solenoid would press against the back of one of the gears covered in rubber adding friction to the system. More voltage, more friction.

    In an effort to test our design, we connected the solenoid in series with the motor assuming it would work fine (considering we generated 9-10V and the resistance of the solenoid was low). As soon as I connect the solenoid, the turbine slows down despite no change to wind velocity and doesn't seem anywhere close to activating the solenoid. We have not yet put the solenoid in parallel with the object to be powered as we do not have it yet (that will happen when we demonstrate the turbine to the class).

    Overall, my electronics knowledge is novice at best. Why is this happening? How can we set it up to work without adding a separate power supply for the brake? How would we set it up with a separate power supply if that's what we have to resort to?

    I do not have the measurements of current or voltage running through the circuit while the solenoid is attached...yet. Let me know if that is necessary to help diagnose the problem.

    I'm not an electronic engineer so statements such as "add an amplifier or a capacitor" still leave me scratching my head and would need to know how to set it up.
  2. jcsd
  3. Apr 14, 2016 #2


    Staff: Mentor

    Welcome to PF.

    Since your electronics skills are low, I think that you should consider a micro switch that would be triggered by centrifugal force of the speed gets too high. That approach is more direct because overspend is what you are trying to protect against.

    In fact you could make an all mechanical brake.

    You did not say how big your wind turbine is. Depending on the size, this simple fishing reel centrifugal brake might work.

    Excellent Fishing Line Spool Spare Parts for Casting Reel Centrifugal Brake S7K0

    Good luck.
    Last edited: Apr 14, 2016
  4. Apr 14, 2016 #3
    Is there any way of doing it with the solenoid?

    Incorporating that would require a bit of work to our axles (which currently work) and too close to the deadline in the case something doesn't go well
  5. Apr 14, 2016 #4


    Staff: Mentor

    We need more information before we can help with the solenoid. You said that you can make 10V on a multimeter. Good for you. But you did not say how much power your wind turbine makes. A solenoid requires nonzero power, and it is possible that is a significant fraction of the power your turbine makes, which is why it slows down. You already hinted at that, 3.3V at 0.36A is 1.18 watts.

    You should run an experiment with a variable resistor (a potentiometer) connected across the output. Power ##P=V^2/R##. Using that, you could measure P versus speed in RPM. If one watt slows it down appreciably, then the solenoid draws too much power for your project.

    A zener diode and a resistor may provide all the braking you'll need. Post again, after making your P versus RPM measurements, and we can help.
    Last edited: Apr 14, 2016
  6. Apr 15, 2016 #5


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    Before working on the brake I suggest you connect a variable load to your turbine. Pick a constant wind speed and while changing the load plot a graph of the power output. For example with no load (open circuit) the output current will be zero so the output power will also be zero. With a high load (eg short circuit) the output voltage would be zero so the output power would also be zero. Somewhere in between the power output will be a maximum.

    It sounds like you are planning to use the generator voltage to control the brake. I'm not sure that is a very good idea. For example when the brake is ON the turbine will slow down causing the voltage to drop which will release the brake. You may find the brake switches itself on and off a lot causing it to wear out? I believe the brake needs to be latching, either electrically or mechanically?
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