Turn A Ceiling Fan Into A Wind Turbine… Almost

It’s not uncommon to drive around the neighborhood on trash day and see one or two ceiling fans haphazardly strewn onto a pile of garbage bags, ready to be carted off to the town dump. It’s a shame to see something like this go to waste, and [Giesbert Nijhuis] decided he would see what he could do with one. After some painstaking work, he was able to turn a ceiling fan into a wind turbine (of sorts).

While it’s true that some generators and motors can be used interchangeably by reversing the flow of electricity (motors can be used as generators and vice-versa) this isn’t true of ceiling fans. These motors are a type called induction motors which, as a cost saving measure, have no permanent magnets and therefore can’t simply be used as a generator. If you make some modifications to them, though, like rewiring some of the windings and adding permanent magnets around them, you can get around this downside of induction motors.

[Giesbert] does note that this project isn’t a great way to build a generator. Even after making all of the changes needed to get it working, the motor just isn’t as efficient as one that was built with its own set of magnets. For all the work that went into it, it’s not that great of a time investment for a low-quality generator. However, it’s interesting to see the theory behind something like this work at all, even if the end result wasn’t a complete wind turbine. Perhaps if you have an old ceiling fan lying around, you can put it to better use.

9 thoughts on “Turn A Ceiling Fan Into A Wind Turbine… Almost

  1. I think the original motor with the staggered coils was actually designed to work as a shaded pole motor. Otherwise, with just one phase going into the motor you couldn’t choose which direction it turns – but as the video claims the fan had a switch for direction.

    Suppose that either the inner coils or the outer coils are connected through a capacitor to cause a phase shift. That makes the magnetic field sweep with a preferred direction just like in a shaded pole motor. Otherwise the field would just alternate between S and N, and the motor would start in whichever direction happens to be closest – or neither.
    By choosing the polarity of the inner and outer coils, you can make the coils work with or against each other, which gives you a speed selection switch.

    Obviously this type of a motor would work poorly as a generator because the magnetic paths are needlessly long. That’s another thing he could improve since he’s not using the inner coil slots at all. He should fill up the gaps in the iron to make the magnetic loop path as short as possible.

    Anyhow, not all is lost. Even with all these un-optimal features, he can have a decent power output by finding the optimum load. He simply needs to up the intermediate voltage to a higher level in order to reduce the current draw from the generator – and spin the generator faster. It may not be optimal for the wind turbine since the cut-in speed will be higher, but that depends on the turbine. The biggest issue is that anything above 50 VAC will put him above the safety voltage regulations and may need licensing or some sort of certification process to be legal for use.

    1. That said, while you can press just about any motor to service as a wind generator, there’s some serious optimization questions you need to solve.

      For example, the available power increases in the cube of wind velocity, while the power output into a constant load (resistor, battery) increases in the square of voltage. This means the turbine tends to overspeed and it runs above the optimum tip speed ratio, which is the ratio between the wing tip speed relative to wind speed. This results in low efficiency and can damage the turbine in gusts. You need a smarter load controller, or a mechanical governor to keep the turbine speed correct regardless of the load.

      This is why induction generators were commonly used before the DC inverter. It can’t overspeed because it hits a “wall” as it tries to overtake the excitation frequency. That however meant that the generator would only turn at one speed, so they needed elaborate gearboxes and blade pitch control to keep up with the wind. These systems then froze up in the winter and became sluggish and the turbines would break every so often.

  2. MOST of the fans I have seen vary the capacitors value for speed control, with the larger values giving more speed. Reverse just switches the one set of coils.

  3. I never considered induction moors “cheaper” because they do not use permanent magnets. They are simply another type of motor. I have seen very large and expensive induction motors.

    As far as efficiency or suitability goes, a lot has to do with what you want it to do. Years ago I built a spiral pump to move water from the creek to dribble on my mushroom logs. Much easier than moving the logs into a tub to soak or into the creek. One of my engineer friends looked at the spiral pump and started worrying about it’s efficiency. I had him schlep down to the creek a few times and bring back a couple 5 gallon jugs of water each time, and all of the sudden the true efficiency of the spiral pump hit him. So if you are using this for some light duty electric, it might be a good bet.

  4. As far as I know you need to embed a small permanent magnet on an induction motor if you want to use it as a generator. to get it started. The magnet induces a bit of current in he coils, which then further induce a bigger magnetic field in the squirrel cage etc.

    If there is no permanent magnet, then it’s just a lump of iron rotating in (or around in this case) some copper coils. Sometimes the remanent magnetism of the rotor is enough to an induction motor going, but it’s not a good idea to rely on that.

    When an induction motor is used as a motor, this is not a problem, because you start generating magnetic fields as soon as you push current through the coils.

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