My PBL Project - Hand Crank Generator

1. INTRODUCTION;

How do generators work?

I will try to explain the following concepts in my page.

• One simple way to think about a generator is to imagine it acting like a pump pushing water through a pipe. Only instead of pushing water, a generator uses a magnet to push electrons along. This is a slight oversimplification, but it paints a helpful picture of the properties at work in a generator. A water pump moves a certain number of water molecules and applies a certain amount of pressure to them. In the same way, the magnet in a generator pushes(attracts or repels them) a certain number of electrons along and applies a certain amount of force to the electrons.

Faraday`s Law

• Michael Faraday explained this as follows. Any change in the magnetic environment of a coil of wire will cause a voltage (emf) to be "induced" in the coil. No matter how the change is produced, the voltage will be generated. The change could be produced by changing the magnetic field strength, moving a magnet toward or away from the coil, moving the coil into or out of the magnetic field, rotating the coil relative to the magnet, etc.

Generator or Motor

• A generator converts mechanical energy into electricity. A motor works on the same principles, but in the opposite direction (Conservation of Energy) -- it converts electrical energy into mechanical energy. To do this, a motor needs a special kind of magnet known as an electromagnet. In its simplest form, this consists of an iron bar wrapped in a coil of wire. If you pass an electric current through the wire, a magnetic field is formed in the iron bar, and it becomes a magnet, with definite north and south poles. Turn off the current, and the magnetic properties disappear.

Parts of a Motor

In the above diagram, you can see two magnets in the motor: The armature (or rotor) is an electromagnet, while the field magnet is a permanent magnet (the field magnet could be an electromagnet as well, but in most small motors it isn't in order to save power).The armature is an electromagnet made by coiling thin wire around two or more poles of a metal core.The armature has an axle, and the commutator is attached to the axle. You can see that the commutator is simply a pair of plates attached to the axle. These plates provide the two connections for the coil of the electromagnet.

The "flipping the electric field" part of an electric motor is accomplished by two parts: the commutator and the brushes. The contacts of the commutator are attached to the axle of the electromagnet, so they spin with the magnet. The brushes are just two pieces of springy metal or carbon that make contact with the contacts of the commutator.

• • If you ever have the chance to take apart a small electric motor, you will find that it contains the same pieces described above: two small permanent magnets, a commutator, two brushes, and an electromagnet made by winding wire around a piece of metal. Almost always, however, the rotor will have three poles rather than the two poles as shown in this article. There are two good reasons for a motor to have three poles:

    • • It causes the motor to have better dynamics. In a two-pole motor which is shown below, if the electromagnet is at the balance point, perfectly horizontal between the two poles of the field magnet when the motor starts, you can imagine the armature getting "stuck" there. Therefore I had to give a push to start the motor below. That never happens in a three-pole motor.

• • • Each time the commutator hits the point where it flips the field in a two-pole motor, the commutator shorts out the battery (directly connects the positive and negative terminals) for a moment. This shorting wastes energy and drains the battery needlessly. A three-pole motor solves this problem as well.

    • It is possible to have any number of poles, depending on the size of the motor and the specific application it is being used in.

5. SAFETY REGULATIONS & MAINTENANCE

Pay attention to the following maintenance recommendations, and add these important safety precautions to your normal laboratory procedures:

¨ Be cautious with magnets. Strong magnets can disrupt electronic devices and severely pinch any skin that comes between them.

¨ Use caution when working with sharp objects.

¨ Use caution when operating the hand-cranked generator connected to the sensor, so as not to overload the sensor. Note that the PASCO Voltage–Current (VI) sensor has a range of (+/-) 1 A, while the hand-cranked generator has a maximum output of 25 watts, 12 volts. The sensor's overload protection shuts down the sensor when the current is too high. The sensor automatically resets after the overload is removed.