Motors and Generators

This lesson explains how coils and magnets are used to create Motors and Generators / Alternators. We will be looking at how wires and magnets interact to create power, both mechanical and electrical. It is the interaction between these two forces that needs an over hall to counter the effects of global warming and pollution. With the higher cost of energy, the efficiency of these devices needs to be tuned. We need to get closer to 100 % efficiency so as not to waist so much natural resources to create the power we need to run the things that give us pleasure.

Relationship of coil and magnet

Now we get to the meat of my problem. I've got the magnets, I've got the coils now what do I do? It's like making bread. You can have everything needed, the water, the flower, the yeast; But to make a good tasting bread that doesn't come out like a brick? I've yet to be able to do it. This is where one has to do a bit of reading and learning. A painful process for us "no brains scientists".

Here's the problem I was having. Take a look at these photos below. Do you see anything that causes you concern?

Coil setup on alternatorMagnet setup on alternator

The coils in the photo above on the left are going to be fixed and placed on top of the magnets in the photo on the right which will rotate.

Here is a larger photo of the coils.

Wired coils.

Now the magnets are placed with alternating north and south poles facing up which will create alternating current in the output of the alternator.

Sounds great, but I intuitively felt there was a problem. And this is where I had to do some learning about magnets and coils. And what I found out was that when the magnet passes over the coil, as it first approaches the coil the current in the coil begins to flow in one particular direction. As the magnet begins to pass over the coil, half of the coil's current is trying to move in one direction and in the other half of the coil, current is trying to move in the other direction. Nothings going no ware. Now as the magnet exist the coil, current begins to move in the opposite direction of when the magnet approached the coil.

Current flow in a coil.

This means you only have current flow, and only a little at that, when the magnet is entering or exiting the coil. As it passes directly over the coil, when max output would be expected, close to zero output would be realized.

Many of the more popular alternative energy sites on the net are using this particular design. The reason I suppose is that the magnets are rotating rather then the coils. If the coils were rotating then you would need some kind of a commutator. Which for the home brewer would be difficult to manufacture. But don't take my word for it, lets look at how magnets and coil relate to each other.

Lets start from the beginning. Check out the photo below.

Direction of magnetic field as current flows through a wire.

The photo above describes a wire with a current flowing through it. The wire develops a rotating non polar magnetic field that has direction. Doesn't seem too important now but later you'll find out that this magnetic field is what keeps us all in chains.

Now lets look at the magnet. Check out photos below.

Magnetic field line of a bar magnet.

This is how the so important magnetic flux is in relation to the magnet.

Now to create electrical power we need that wire or coil to cut threw those lines of flux. But we also need to understand what happens when it does.

The first thing we need to understand is that depending on how the magnetic flux is cut will depend on how much power is developed and in what direction current will flow. The way the coils above were cutting the magnetic flux you had current attempting to flow in both directions at once. Not a good design because you don't get much net power.

Bycyle Dynamo

Above is an example of what I'm talking about. Here the magnet is inside the coil with the north pole effecting one half of the coil and the south pole effecting the other half of the coil.

Here, in the photos below, is an example of coils rotating inside a magnetic field. This is a great design because the magnetic flux is drown from the north pole threw the coil to the south pole. Normally the coil would have a core
of some kind which would further draw the magnetic flux threw the coil, which would cause magnetic cogging
between the magnets and the core, which would require greater torque to turn the alternator.

Graph of current produced in an alternator.

Now lets look at the interaction between the wire and the magnetic flux a little closer. Below is a photo that shows what's going on in a motor. This is called the left hand rule. This is for a motor where a voltage is applied to the wire. For a generator, the current flow created would flow in the opposite direction. So if you were attempting to create current flow you would move the wire in an upward fashion(for this example) which would cause current to flow counter to the direction of your middle finger.

Left hand rule for current flow.Direction of current flow in a wire with a magnetics field.

As a motor, a voltage is applied to the wire, which is in side the magnetic flux of the permanent magnet as in figure 9, as current begins to flow, the wire is forced up by the interaction between the magnetic field created by the current flow in the wire and the magnetic field of the permanent magnets. As it is forced up a counter current is created which opposes the current flow in the wire.

This is why if you stop a motor from turning while current is flowing, the motor get hot and begins to smoke. With out the rotation of the magnetic fields in the motor there is no counter force to the current flow and current flows freely and heats up the windings in the motor. So the more efficient the motor, the greater the opposing force and the greater the torque for less power used.

This is the problem with the generation of electricity, as the generator turns it creates current flow in the wire, which in turn creates a magnetic field in the wire that opposes the movement of the wire. If you had a 100% efficient generator and attempted to draw 100% of the current created by the generator the shaft would not turn because an equal and opposite force would be created. This is why you cannot get over unity. More torque would always be required then you are applying to turn the shaft to turn the generator.

I use the TI-89 Graphing Calculator for all my calculations
which has symbolic manipulation ability.

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