Magnetics and Motors

Physics 12 Direct Current Motors

Joke of the day:An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

Direct Current Electric MotorAn electric motor converts electrical energy into mechanical energyAn electromagnet is the basis of an electric motor A motor uses magnets to create motion. Opposites attract and likes repel. Inside an electric motor, these attracting and repelling forces create rotational motion. Direct current (DC) means the electrical current is flowing in only one direction in a circuit. Batteries are a good source of direct current (DC).

The basics:STATORROTORAn electric motor has two basic parts:The stationary part (external magnets, power source, brushes)The rotating part of the electric motor is called the rotor.Parts (and function) of a DC motor:DC power supplyRotor (armature) Commutator Brushes External magnets

1. DC Power SupplyAka batteryTo provide the current

2. Rotor (Armature)the revolving structure wound with the coils that carry the currentmoves under the influence of a magnetic field

Diagram: Spinning Armature

3/4. Commutator and brushesCommutator is simply a pair of plates attached to the end of the rotor These plates provide the two connections for the coil The brushes are attached to the leads from the power supply Commutator and brushes work together to let current flow from the power supply to the electromagnetic coil when they make contact with each other

Brushes attached to batteryCommutator attached to rotor5. MagnetsProvides the external magnetic fieldUsed to create a net rotational movement

A key component of motors: TorqueTorque is a measure of how much a force acting on an object causes that object to rotate. The object rotates about an axis or pivot point

TorqueTorque is the cross product of radius and forceThe units are Nm The direction is positive for ccw and negative for cw

Torque on a Current Carrying LoopIn a motor.

Video clip:http://www.youtube.com/watch?v=Ue6S8L4On-Y

Build some simple motors!

While both A.C. and D.C. motors serve the same function of converting electrical energy into mechanical energy, they are powered, constructed and controlled differently. 1 The most basic difference is the power source. A.C. motors are powered from alternating current (A.C.) while D.C. motors are powered from direct current (D.C.), such as batteries, D.C. power supplies or an AC-to-DC power converter. D.C wound field motors are constructed with brushes and a commutator, which add to the maintenance, limit the speed and usually reduce the life expectancy of brushed D.C. motors. A.C. induction motors do not use brushes; they are very rugged and have long life expectancies. The final basic difference is speed control. The speed of a D.C. motor is controlled by varying the armature windings current while the speed of an A.C. motor is controlled by varying the frequency, which is commonly done with an adjustable frequency drive control. 2

Published by Ohio Electric Motors: http://www.ohioelectricmotors.com/what-is-the-difference-between-an-ac-motor-and-a-dc-motor-673#ixzz2PFxVRFMG