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​General procedure (details to follow)

1. Acquire a bicycle and build a stand to make it stationary

OR

1. Acquire a stationary bicycle.

2. Connect the rotating bike wheel to the rotating portion of an alternator or motor.

3. Construct a circuit that yields some useful electrical output from the bike pedalling input.

Materials and tools:

​The Circuit

​​

  • 12V DC motor or car alternator with 12VDC output
  • hookup wire 
  • ​wire cutters
  • 2 metal aligator clips
  • 12V rechargeable battery
  • inverter (input is 12V DC, output is 120V AC at 100W)
  • soldering iron and solder

​Stand Building Procedure:

Procedural note: for every wood to wood connection, always drill a pilot hole in the piece that the wood screw will go through first.  A pilot hole is drilled with a drill bit (lip and spur bit or twist bit are recommended).  Drilling a pilot hole helps stop the wood from splitting during the screw driving process.  The drill bit should be slightly smaller in diameter than the wood screw that will be used.  The wood screw should extend at least half an inch into the second piece of wood.  When screwing two pieces together that are not parallel or perpendicular, but are at an angle, keep the screw perpendicular to the first piece of wood it will go through.

​

1. Measure and mark the 2x4s according to the measurements shown in the figure.  As good woodworkers say, "measure twice and cut once."  In a or b, measure where the chain of the bicycle will hit and cut out a groove in the inner side of one of these pieces.  Shown in the figure on the right.

2. Using a table saw and appropriate safety precautions (safety glasses, covering saw when not in use), cut the 2x4s to the required dimensions.

3. First, screw together pieces a, c, d, and h.  Then screw together the same pieces that are for the opposite side of the stand: b, e, f, and i.

4. Place the back wheel of your bike in the two triangle supports that you've just made.  Measure what distance should be between them to allow the back wheel to spin freely.

5. Screw in pieces k and m to the front and back (respectively) of the two triangle support pieces.

6. This will be a sufficient support for most riders.  However additional supports may be added.

7. Screw together the alternator stand.  Only attach the alternator board once the circuit is properly connected and soldered.  It will be easier to solder before the stand is on.

8. Remove the rear wheel (use wrenches to loosen).

9. Use the bike tool to remove the tire and inner tube from the rear wheel.  Fit the v-belt around the wheel and reattach the wheel to the bike.

10. Fit the bike into the stand and measure where to place the alternator (based on the length of the v-belt).  The v-belt must be taut.

Instructions:

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image courtesy of: http://www.geeknewscentral.com/2009/05/06/quantum-dots-and-the-quality-of-light/lightbulb/

​Circuit Building Notes:

 

The basic nature of the circuit is that the mechanical input from spinning the alternator or motor induces a DC voltage signal which is then input to a basic car inverter.  The inverter converts the signal to 120V AC so that most household devices can be plugged in.  The inverter requires a certain range of input voltages.  The one used in the example requires 11V-15V DC as input.  If the input is outside of this range, the inverter will shut itself off.

 

There is a bit of freedom involved in choosing the circuit.  The following options are possible:

  • Use a 12V DC motor and use the mechanical energy from bicycle pedalling to turn the shaft and get voltage out.  In other words, run a motor in reverse.  There are two main obstacles to overcome with this method.  First, the motor may have a diode built in in order to make sure that it goes from electrical input to mechanical output (and not the other way around).  Either look for a motor which does not have a diode built in, or take the motor apart to remove the diode.  Second, because the pedalling may not be at a consistent speed, this setup will require a voltage regulator circuit to make sure that the inverter is getting a constant voltage.  This option has the advantage of having simpler circuitry than the other.  The reason for this is that a motor has a permanent magnet, not an electromagnet, so it does not need an additional electrical power source.
  • Use a car alternator.  An alternator uses an electromagnet.  This means that an inductor coil must be "turned on" by a voltage source in order for it to be a functional magnet.  This makes for some more involved circuitry than with the motor, however, most alternators have a voltage regulator built in, so that the output voltage is easier to deal with.
  • If this will be your first time soldering, check out this instructional video.  Only solder the connections once you have tested the circuit's functionality and it behaves the way it should.  Aligator clips are recommended for electrical connections during testing.
  • Remember that positive connects to positive and negative connects to negative.
  • Rechargeable batteries MUST be used (rather than non-rechargeable batteries).  When the motor/alternator is in action, this circuit charges the battery and this is dangerous to do with a non-rechargeable battery.
  • Mount the alternator and its circuit onto a flat piece of wood.
  • The alternator and its baseboard will sit a distance away from the bicycle frame such that the v-belt is taut.
  • Note that on the circuit diagram given in the "understanding the alternator" link, the vehicle load is where the inverter should be connected.

Electromagnetic Induction Explained

In the apparatus, the alternator or the motor acts as a generator.  The basic explanation of how a generator works draws on some basics of electricity and magnetism.  

A magnetic field, in this case, is a region under the influence of a magnet.

The magnetic flux through a surface is the "amount" of magnetic field that passes perpendicularly through the surface.

Current is the flow of electric charges.

 

 

Inside the generator, there is a magnet inside a closed loop of wire.  When the alternator's/motor's shaft spins, the magnet spins and so the magnetic field changes.  When the magnetic field changes, the magnetic flux through the loop changes.  This causes a current to flow in the wire and this phenomenon is known as Faraday's Law of Induction.

Constructing the Circuit

Construct the circuit as shown in the photos.  Remember to test all functions before soldering.  Here are some additional resources for understanding the alternator:

Above left: a groove has been cut in one of the a or b pieces of wood.  This groove allows the chain of the bicycle to pass easily on the under side.  

Above right: another piece of this leg has been removed to allow the chain to pass easily on the upper side.

​The Stand/Bike

 

  • electric drill with bits for drilling pilot holes and bits for screw driving
  • wood screws (2 inch)
  • hammer
  • nails (2 inch)
  • 2x4 wood
  • tape measure
  • sandpaper
  • pencil
  • ​protractor
  • table saw
  • clamp
  • v-belt (long enough to fit around bicycle wheel and alternator axle)
  • bicycle
  • bike tool

Right: the final product.  2x4s are used to space the alternator and bike to make the belt taut.  A bungee cord is used to hold everything in place.

Above: wood pieces to measure and cut.

Above: side view schematic diagram of the stand.  Below: top view schematic diagram of the stand.

Above: schematic diagram of electromagnetic induction. Below: alternator terminals and their electrical connections.

Above: photo of the finished circuit.

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