Advice on making a simple wind-powered generator in a high-school.
October 6, 2010 12:16 PM   Subscribe

Advice on making a simple wind-powered generator with high-school students.

I'd like to make a simple wind powered electricity generator with a small group of students in a high school. The idea I had was to get some bicycle dynamos and attach fan-blades to cause the dynamo-core to spin and illuminate a light.

Do you think this exercise is useful and illustrative? Do you have any examples of people doing this before? What problems should I anticipate?

My other challenge is getting the parts to do this. I'm in the Boston area, and have a small budget to get parts, so I planned on getting a sidewall-dynamo and letting the students make the blades (I would ensure that there is some easy way to connect the two).

I'm not certain about the gearing issue, due to wheel-speed/wind-speed but I imagine I can figure out this aspect.<>
posted by a womble is an active kind of sloth to Education (14 answers total) 1 user marked this as a favorite
If you want to show the science of how electricity comes from motion, make them wind the coils and arrange the magnets themselves -- adding a fan to a sealed thing to produce electricity doesn't teach them where the electricity comes from.

The good thing is this: An electric motor and an electric generator are functionally the same thing. If your school has some "build an electric motor" kits lying around, put a light bulb where the battery is and spin the shaft, and you'll be generating electricity.
posted by AzraelBrown at 12:23 PM on October 6, 2010 [1 favorite]

I thought about winding the coils, and wondered if that would take too long (but I agree with your point). We don't have any electric motor kits - do you have any recommendations where to get some?
posted by a womble is an active kind of sloth at 12:26 PM on October 6, 2010

Take a look at the Chispito Wind Generator, which uses a re-purposed treadmill motor for the generator and a cut-up piece of PVC pipe for the vanes. It's designed to be made of salvageable parts and is apparently pretty good.
posted by jquinby at 12:38 PM on October 6, 2010 [1 favorite]

Otherpower is a nutty couple of Dans in the foothills west of Fort Collins, CO who shape their own props and wind their own generators. I'm pretty sure you'll find some interesting content on their (frustratingly designed) site. Or get their book "Homebrew Wind Power" instead.
posted by richyoung at 1:13 PM on October 6, 2010 [1 favorite]

Oh, and you might try a Savonius rotor instead, as detailed in the book Wind and Windspinners. They're super-simple because of the vertical axis of rotation, though they're not the most efficient design.

You could build a Savonius rotor out of cardboard barrels, attach it to a bike sidewall dynamo directly, and see if it turns. My experience with sidewall dynamos is that they require a lot of force to turn 'em, probably more force than you're likely to produce by putting a bunch of fan blades on a bike wheel.

For bonus science points, do it both ways and see which one works better.
posted by richyoung at 1:25 PM on October 6, 2010 [1 favorite]

This sounds like a great project with the potential to teach a lot of different things.

If you have them wind the coils/position the magnets themselves then they could also see how changes to the system will (or won't) change the electrical output.

Your students could also experiment with fan blade designs/materials to see which work best.

Hook up a battery to the system and your windmill becomes a fan.

If you scrap the wind angle and just hook up a bicycle to the system then you can measure the energy output of your more energetic students as well.
posted by any portmanteau in a storm at 1:31 PM on October 6, 2010 [1 favorite]

You might want to see what KidWind has to offer. Not merely do they sell the bits, but the entire set of curriculum materials is free to download. All the material has been checked by people like AWEA and NREL, so it makes sense. Having Michael Arquin - KidWind's founder - come to your school might be a bit pricey, but his stuff's good.

(Actually, if you're interested, I've got an early Kidwind generator from the AWEA conference in 2006. Memail me if so. Their new AlTurbine looks much more fun.)
posted by scruss at 1:40 PM on October 6, 2010 [3 favorites]

Like others have said, you can use a motor as the generator. Be aware that bicycle dynamism take a fair amount of force to turn and are inherently geared down by the bike gearing. You will probably need to gear it down.

To solve the angle problem, consider using a differential. If you don't want to cut up the rear axle of a rear wheel drive car for lantern and spider gears, you can model it in lego.
posted by plinth at 3:00 PM on October 6, 2010

Use a small light bulb... not a 120V 100W AC bulb, and use a DC motor for your generator. This will allow you to use smaller blades and lower wind speeds for the wind.

Both of these are important.

If you want a simple method of vane construction, use the fan assembly from a fan. You can also use a fan to provide the wind, when the time comes to demonstrate it.

If you use a variable speed fan, you can demo the relationship of airflow (mass flow) to generator output. A cheap wind speed meter is available from Omega Engineering.

The motor you choose will have a motor constant, stated in KRPM/Volt. As a generator, it works the opposite way.... Volts per thousand RPM. You can measure the voltage somewhat directly if you put a small resistor across the motor. A 1000 Ohm resistor will do as a starting point.

Have fun!
posted by FauxScot at 4:34 PM on October 6, 2010

Have a look into permanent-magnet DC generators for a simple start. A common approach is to build one by starting with a disc-brake assembly (ditch the pads and hydraulics) from a car, glue a ring of serious permanent magnets to the face of the disc (circular helmholtz array) and have a stationary set of flat windings facing the magnets. Attach the propeller to the wheel nuts.

For better efficiency, consider adapting a car alternator. It needs some source of power (e.g. battery) to bootstrap it by providing field current, but they are quite efficient and can be carefully regulated to provide whatever voltage you need, regardless of the actual windspeed. That approach is simpler (mechanically) to build since you don't have to do your own magnets and windings and much more flexible in terms of power outputs, but you need to have a bit more trickiness with the electronics because it is actively regulated.

Googling for off-grid power will get you a lot of DIY wind generators and endless instructions on how to build them.
posted by polyglot at 7:56 PM on October 6, 2010

Can you tell us what is "small" when it comes to budget? Blades are actually a really difficult thing to get right - the amount of maths and applied science that goes into making them work with a range of windspeeds (or even at all) is astounding. And you can buy a set off eBay for well under $100 that are good for about 600W (a few feet in diameter) and mount them to the hub of your choice. Don't use fan blades, they're designed to run at a constant speed and push air, not be pushed by air.

Don't do gearing. It's just difficult, pointless and lossy. Mount the blades directly to the rotor of your generator and (assuming permanent magnets) choose the number of windings on your coils so that you get the voltage that you want at some typical wind-speed. That will probably require a bit of experimentation, but it's all good - you can teach a whole bunch of electromagnetics right there with the relationship between voltage and rate of change of flux, which in turn depends on rotor speed and magnet strength, etc.

If you want to go for smallish, pre-built generators, look for three-phase PMDC motor kits used in remote-control vehicles: for example. Those are very small ones and you can buy them off the shelf rated for up to 3kW (expensive) and/or as kits that you do your own windings for. Google for "LRK motor". Those will give you a pretty low output voltage by default (coarse windings, designed to run at very high speed off an 11V supply) but if you rewind them with much finer wire and more turns, you should be able to get the voltage you want.

As for a sidewall generator, they're designed to produce maybe 6V at 20km/h, which is about 5000rpm assuming they have a 2cm rotor. You won't get anywhere near that kind of speed with a small wind generator, so the voltage you get out will be so low as to be useless.

Do you have a machining and/or welding class at your school?
posted by polyglot at 3:09 PM on October 7, 2010 [1 favorite]

Some possibly useful resources:

Building A Windmill in High School

Kid in Malawi Homebrews a Windmill Generator
posted by bq at 4:24 PM on October 7, 2010 [1 favorite]

Hi polyglot, I have around $400 for equipment. We don't have access to a machine shop or welding in the school (but I do) so I can do that if need be. Based on some of the earlier responses, what we are going to do is make some very simple motors using cheap kits from here to explore the basic electromagnetic principles; use some of KindWind's kits (from Kidwind directly, and scruss is kindly giving is one also).

I'll take a look at LRK motors - it's useful to know the term. Point taken about the sidewall generator, I think I will shelve that idea.

Thanks everyone for all of your suggestions - it's been extremely helpful to get this input.
posted by a womble is an active kind of sloth at 6:08 AM on October 10, 2010

Doing it without machining or welding gear is going to be hard unless you work with kits for everything, however $400 for parts should be plenty to do something pretty interesting.

Motors have the same science behind them as generators do, not to mention that you have more-reliable sources of electricity than you do wind. You can still teach all about the voltage/speed and current/torque relationships as a function of winding count, magnetic flux, conservation of power, etc, etc.

You should be able to get a few small LRK kits, build them with differing windings and power them using cheap controllers from taiwan and a benchtop DC supply like the 12V rail from a PC power supply. Make one high-speed, low-torque and one low-speed, high-torque. Put a bigger propeller on the latter. Measuring speed can be pretty easy but torque is a lot harder.
posted by polyglot at 11:18 PM on October 13, 2010

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