Fundamentals Of Motor
Before we can examine the function of a drive, we must understand the basic operation of the motor. It is used to convert the electrical energy, supplied by the controller, to mechanical energy to move the load. There are really two types of motors, AC and DC. The basic principles are alike for both. Magnetism is the basis for all electric motor operation. It produces the force required to run the motor. There are two types of magnets the permanent magnet and the electro magnet. Electro magnets have the advantage over permanent magnet in that the magnetic field can be made stronger. Also the polarity of the electro magnet can easily be reversed. The construction of an electro magnet is simple. When a current passes through a coil of wire, a magnetic field is produced.
This magnetic field can be made stronger by winding the coil of wire on an iron core.
- One end of the electro magnet is a north pole and the other end is a south pole The poles can be reversed by reversing the direction of the current in the coil of wire. Likewise, if you pass a coil of wire through a magnetic field, a voltage will be induced into the coil And, if the coil is in a closed circuit, a current will flow.
- When a current passes through a conductor, lines of magnetic force (flux) are generated around the conductor. The direction of the flux is dependent on the direction of the current flow. If you are thinking in terms of conventional current flow (positive to negative) then, using your right hand point your thumb in the direction of the current flow and your fingers will wrap around the conductor in the same direction of the flux lines.
- If you are thinking in terms of electron current flow (negative to positive) then you must use your left hand. If we look at the air gap between two magnets that have their opposite poles facing each other, we would see magnetic lines of force (flux) from the N to S poles.
Now, if we place a current carrying conductor in the air gap of two magnets, the lines of flux in the air gap will be affected.
- On the side of the conductor where the lines of flux oppose each other, the magnetic field will be made weaker. On the side of the conductor where the lines of flux are not opposing each other, the magnetic field will be made stronger. Because of the strong field on one side of the conductor and a weak field or, the other side, the conductor will be pushed into the weaker field.
- Now, lets apply this principle to the operation of the DC motor. The armature of the motor is a loop of wire (current carrying conductor) which is free to rotate. The field magnets are permanent or electro magnets with their N and S poles facing each other to set up the lines of flux in the air gap.
- The armature is connected to the commutator which rides along the brushes which are connected to a DC power source. The current from the DC power source flows from the positive lead, through the brush labeled A1 through one commutator section, through the armature coil, through the other commutator section, through the brush labeled A2 and back to the negative lead.
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