About Wind Generators

Wind power is fun to experiment with, and not that difficult or expensive. But you should first have realistic expectations of what kind of result you’ll be able to get with how much work and expense. Another important aspect of science projects (and required at science fairs) is demonstrating your use and understanding of the Scientific Method of observation, hypothesis, predictions, testing, and conclusion. Hopefully I’ll be able to give you some good background knowledge so you can decide how to proceed with your project.

First, it would be an excellent idea to familiarize yourself with how wind turbines extract energy from the wind, and their basic components and how they work together. Take a look at Part 1 of my “Small Wind Turbine Basics article in the ESSN for the math involved – it’s very simple. Familiarize yourself with Ohm’s Law – a Google search will fill you in. There are also excellent introductions to wind power and wind turbine components at Windpower.org – be sure to take all their “guided tours”, not just the one for kids.

The two most important design issues you’ll have to decide on are:

Can your wind turbine fly outside in real wind to test your design and gather data, or does it have to fly inside using wind from an electric fan, such as at a science fair inside a gymnasium?

Do you only need to show and measure power output on a meter, or does your wind turbine have to do something physical like power a small light bulb or LED, or make a small pump turn?

If fan power must be used, options for your turbine’s power output are more limited. But for younger students, fan power is the best way to go – a very safe, fast and easy way to demonstrate wind power. The safety precautions needed are minimal. Fan power may frequently be the only option if the turbine must be demonstrated indoors. However, it’s very difficult to do anything with fan power besides making a meter move and measuring the results. Powering light bulbs and LEDs with fan power takes lots of extra complexity and expense – but it can be done.

The “real wind” can be from mounting the turbine outside on a tower, or from mounting it on a vehicle and collecting data while an adult drives – slowly, on a rural road with little traffic

– and calls out the vehicle’s speed. If real wind can be used for power, more options for experiments are available, but everything must be built better and sturdier.

The problem is that a small, experimental turbine designed to fly and make power efficiently in real wind won’t even start to move with a fan, while a small turbine that can turn under fan power will quickly blow apart in real wind. Wind made by a fan is very slow and very turbulent, so it doesn’t have much power available in it.

As for choosing your load, whether it’s a light bulb, LED, charging a battery, or some other type of load, it’s simpler to first choose your generator and then decide on a load. Here’s an overview to get you started.

DC Hobby Motors

Many people decide to go this route, since a DC motor when driven acts as a generator, and it’s easy – put a rotor on a DC motor, mount it, and let ’er rip! It’s quite suitable for younger students who have not yet learned any more than the basics of electricity in class, and for classes that will not be studying electricity further.
However, the results are usually disappointing as far as what loads you can run. The problem is that most DC hobby motors are made to spin at very high RPMs, many being rated 5000-10000 RPM. To get the motor’s rated voltage as output, you’ll have to spin it about 20% faster than its rated RPM. Most small wind turbines never spin faster than 500 RPM, with 1000 RPM as an absolute maximum on smaller ones. Many of them, especially if bought as surplus, don’t have their ratings printed on them.

However, there are DC hobby motors that do work at low RPM. Computer fan motors may be the right kind, but some are brushless and won’t work for this application. To test a motor, you’ll need an inexpensive multimeter (available at Radio Shack). You’ll need a multimeter for ANY kind of electrical experiment, so it will get used throughout your school career! Note! If the motor has more than 2 leads coming out, it’s the wrong kind and can’t be used! Connect the multimeter to the 2 leads and set it for DC volts in the 2-12 volt range. Spin the motor by hand and record the reading, then try spinning it with a cordless drill set at low speed and record the reading.

The voltage you get using the cordless drill at low speed is probably the most you can ever expect from your project. The hand-spun voltage will be more typical. Compare your numbers to the following MINIMUM voltage requirements for some common loads: Red LED: 1.7v White LED: 3.6v Flashlight bulb: 3v to 6v Tiny water pump: 3v to 6v Battery charging: Voltage of battery, plus at least 1 volt, then another 1 volt for the diode.

If you can’t get to these levels with your motor, you’ll need to find another motor to test, try one of the other gearing or generator options below, or settle for just using a meter to measure your power output. The accuracy of your data won’t suffer, only the visual drama. Analog meters (the kind with the moving needle) are much more dramatic to watch than digital! There’s also more to it than just voltage – the amperage is also important in a real-world wind power application, because volts times amperes equal Watts – and Watts are what power output is measured in. Volts are only “potential” power –they don’t do any “work” until a complete circuit is formed (like from your wind turbine to an LED). But the typical loads listed above are very low power, and most hobby motors should have no problem running them.

Another option is to gear up the the hobby motor to make it spin faster. Michael Arquin of KidWind.org came up with a really clever geared hobby motor system that boosts the output in the 1.5v-3v range, enough for almost any application, including water pumps, charging batteries or tiny demonstration hydrogen fuel cells, and a large variety of lights.

You can order his kit from the KidWind Store. The gearing makes it harder to get the blades spinning but, once they are moving, the power output is excellent.

There are plenty of sources for hobby motors in addition to KidWind. You can find them at local Radio Shack stores, online retailers like All Electronics, C&H Sales, and MECI – and even by disassembling your little brother’s motorized toys!

Keep in mind that if you want to charge batteries with your experiment, you’ll need to put a diode in the line to keep the batteries from just spinning the motor—and the diode will drop your output voltage by about a volt.

Homebuilt Alternators

Michael from KidWind has already successfully tried this. The rectifier diodes to convert the 3-phase AC output to DC are included in the kit, and I recommend it highly.

Another kit option is the PicoTurbine, with both a kit and freeon-line plans available. It’s also a vertical axis machine, though it would be harder to convert to horizontal than the Windstuffnow design. If you are interested in designing and building your own small alternator from scratch, a good place to start is reading through my Hamster-Pow- ered Alternator pages for a design that can light LEDs at only 40 RPM – it was originally powered by Skippy the Hamster, but could be easily converted to wind power instead of rodent power.

Tape Drive Motors

Some larger tape-drive motors are powerful enough to get you into the realm of real wind turbines, with rotor sizes ranging from 3 to 5 feet in diameter and generating significant power. Such designs must be extremely sturdy, and can be quite dangerous in higher winds. So, this scale of project is best suited for a teacher and entire class to undertake, or an older, advanced student with experienced help. Some of these designs can produce up to 100 Watts in output at 12 volts! Perfect for charging a deep cycle marine battery.

UPDATE03/18/06—- Kit, plans and parts now available for a 4-foot, 100 Watt turbine.

It looks really slick, and uses a treadmill motor as a generator, with blades cut from PVC pipe. You can buy all the hard-to-find parts, or an entire kit, from the designer—click the photo above, or go HERE to velacreations.com. The plans are free and published on their website, if you want to scrounge up the materials yourself.

To us, this looks like a great way for a high-school or junior-high student (who maybe caught the wind power bug building a tiny, science fair turbine in elementary school) to step up to making some real power that can charge a 12V marine deep cycle battery. And of course a great, inexpensive introduction to home-brewed wind power for any curious adult!

More On Fan Power

For fan power, you’ll need large, wide blades to get enough torque out of the limited wind to start things spinning. Blades salvaged from a table fan or homemade balsa wood blades, such as these shown here at a KidWind Seminar, are a good place to start experimenting. KidWind also sells machined plastic hubs so students can experiment with different numbers of blades easily. With fan power, the blades won’t get spinning fast enough for lift to help performance, so airfoils and twist won’t make any difference in performance—though you might want to include these elements for demonstration purposes.

Blades
Here we come back to the issue of fan versus real wind power. In a good, efficient wind turbine design, the blades will be matched in size to the generator’s output in lower, more normal wind speeds. If the blades are too small for the generator, it will be difficult to start and will stall in higher winds. If the blades are too large, the generator won’t be able to extract enough energy, and the turbine may fall apart in higher winds!

None of this is an issue with fan power, but the problem then is that there’s very little power available, and a good design for real wind would most likely not even spin under a fan.

A good design for real winds would resemble the blades in this photo – skinny and thin at the tips with only a small pitch, and thicker and fatter at the root with as much pitch as the wood thickness allows, plus an airfoil carved on the back for lift. These blades were made with a CAD machining system by a friend, contact me at My Email address if you are interested in trying a set.

Wide, multi-bladed designs, while great for fan power, will often break in real winds – however, testing different blade designs in real winds makes for an excellent experiment.

In my experience, computer fan blades are too small to work well in either real wind or fan power—they don’t sweep enough area to get spinning rapidly enough. Model airplane props are also marginal—they must be reversed (the curved side faces back in a wind turbine blade) and that also reverses the airfoil. They are also difficult to get started spinning. Instead, I recommend carving your own blades or trying a set of the wooden ones similar to those shown above. We have some information available about blade design and carving for our big 10-foot wind turbines that can be scaled down for sceince fair blades. It's located HERE. Another good source of free blade information is at Scoraigwind.com.

Measurements and Meters
Once you have something working, whether from fan power or wind power, you’ll need to take measurements. In many experiments, only the output voltage is measured. This gives a direct correlation to how fast the blades are spinning, but is only part of the story. Watts (volts x amps) are the important figure, and measurement requires a load. The amperes will be determined by how large a load you attach – how many LEDs or light bulbs, for example. If you built a system good enough to charge batteries, your load will change with how full the batteries are.

What you measure and how are dependent on the goals of your project. A digital or analog multimeter (for volts and amps) might be all you need. For an advanced project, you could even get a computer-interfaced multimeter (available at Radio Shack) that connects to a PC for data logging!

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