Trace: pitch

PEN wiki

Alternator (for Savonius Wind Turbine)

What is this lesson?

This lesson teaches basic electricity and magnetism, and gives students experience building a device that converts rotational motion into electricity. The ability to build a device such as this will allow the student to generate power from a wide range of items they encounter/design that undergo mechanical work. Moreover, it is practice in making one’s own component if that item is unavailable (ie you can’t find an extra DC motor lying around). For this lesson, the alternator was being used for a Savonius wind turbine

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What this lesson teaches

Science/Engineering principles

Basic electricity and magnetism

Single versus 3 phase voltage

AC to DC conversion

Technical skills

Casting (not mandatory)

Rectification circuit design

Design skills

Calculating required component sizes to obtain desired output voltage

Other skills

Teamwork, as it is unlikely that this project will not be carried out by an individual student for the first time.

Deliverables

Students build their own alternator, rectification circuit

Students demonstrate voltage storage in a battery

How this lesson fits into the curriculum

PEN lessons that meet the requirement are noted in brackets.

Curricular knowledge and skills

Basic circuits [dynamo lesson]

Wind turbine design (mechanical components) [Savonius wind turbine lesson]

Extracurricular skills

Can cast materials (not required)

Soldering

Follow-up lessons

Charge Controller Design

Practical Work

Demonstrations

(Note: these are similar/identical to what would happen in the dynamo lesson) Teacher has a mini wind turbine model (made out of water bottle halves, for ex), blow on it, and says “let’s learn how to get power out of this!” Relate that to something the students have seen before, but perhaps don’t fully understand: Show them a small DC motor, plug it up to a battery and note the axle turning. Explain that the reverse can also happen – mechanical to electrical energy conversion.

Experiments

(Note: these are similar/identical to what would happen in the dynamo lesson) Pass around the DC motor, and have the students look in the small opening to see that there are a bunch of coils inside. Also pass around a magnet and note that it sticks to the motor. Explain that coils and magnets are key to the mechanical/electrical conversion.

Design/Build Work

Optional design exercise can be done afterwards to optimize number of coils/magnets used to generate a specific voltage.

Logistics/Resources

Building materials

Coils/magnets:

Large spool of copper wire (thicker wire can carry more current), magnets (preferably something strong like neodymium), steel/iron plate to mount the magnets, two plates of arbitrary material to mount the coils, resin for casting, wood or other material to make a mold in which to cast the resin (to hold the magnets and coils in place), glue (if you decide not to cast the items in resin), long bolts to fix the stator to something rigid, long bolts to hold the two rotor plates together

Retification circuit: fuse, zener diodes, capacitors, resistors, circuit board/breadboard

DC Battery (car battery, for ex)

Demonstration materials

small DC motor, magnet

Other materials/equipment

whiteboard to sketch the whole assembly, draw magnetic field lines to explain magnet/coil interaction

Classroom logistics

Ideal class size 10-20 students. For building work, students split off into teams of 2-4, with one teacher/teaching assistant helping with each team.

Optional Questions

Why should students want to participate in this lesson?

They’ll learn how to get electricity out of many mechanical components they encounter. They’ll have something built at the end.

Why should teachers want to teach it?

It’s a chance to show kids the science behind something that they’ve seen but probably not thought much about before. The students will likely enjoy getting to build something they can show off later.

If this lesson (and its prerequisites) were the only PEN lessons someone took, what should they be able to do?

Describe how rotational motion can be converted to electrical energy. Explain the difference between single and 3 phase voltage. Make their own alternator. Build a simple rectification circuit.

If you had to teach this lesson tomorrow morning, what would you spend tonight working on? (assuming that materials were not an issue)

Reviewing magnetism theory….. Coming up with any useful analogies. Practice sketching diagrams that explain the path of the magnetic field.

If you hadn’t taught this lesson before, what questions would you have for someone who had taught a very similar lesson?

Do you have a good rule of thumb for selecting number of coils/magnets based on wind turbine size/type? Do people ever use 2 phase voltage for wind turbine alternators?

If the only materials available were broken radios, TVs, and computers, could you do all the electronics in this lesson? (assuming you had solder, soldering irons, etc.) If not, what would be missing?

The magnets, metal plates, and circuit components are probably salvageable from there (in fact I think we are going to use the outer shell of an old computer….) You need quite a long stretch of wire to make the coils though.

If the only structural materials available were dish-cloths, cardboard, and plastic bags, could you make the mechanical bits of this lesson? (assume equipment as above) If not, what would be missing?

You want to firmly mount the magnets onto the rotor plates, as they’ll be spinning around fast, so you’ll need glue/resin casting to hold them on. Everything else would be fine.

Thanks for reading!

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