What is a DC Motor?
DC stands for "direct
current". A DC motor is an electric motor that uses electricity and
a magnetic field to produce torque, which turns the DC motor.
A DC motor consists of two magnets
of opposite polarity and an electric coil. When a power supply is added to the
coil electric current flows through in a circuit and generates a small magnetic
field. The repellent and attractive electromagnetic forces of the magnets
provide the torque that causes the armature to turn.
DC MOTOR THEORY
A DC motor works by converting
electric power into mechanical work. This is accomplished by forcing current
through a coil and producing a magnetic field that spins the motor. The
simplest DC motor is a single coil apparatus, used here to discuss the DC motor
theory
How it Works ???
Magnets are polarized, with a positive and a negative side.
A DC motor uses the attraction between opposite poles and
the repulsion of like poles to convert electric energy into kinetic energy.
As the magnets within the DC motor attract and repel one
another, the motor turns. The magnetic force on the armature works
perpendicular to both wire and magnetic field.
If an electric current goes through the coil, the motor will
act like a generator and produce an electric motive force (EMF). When the motor
spins it produces a voltage called the back EMF because it opposes the applied
voltage on the motor. Therefore, the voltage drop across the motor consists of
the voltage drop from the back EMF and the voltage drop from the internal resistance of the rotation of the armature
The current through the motor is given by:
I = (Vapplied Vbackemf) / Rarmature
Main component of DC motor
A DC Motor usually consists of: An armature core, an air
gap, poles, and a yoke which form the magnetic circuit; an armature winding, a
field winding, brushes and a commutator which form the electric circuit; and a
frame, end bells, bearings, brush supports and a shaft which provide the mechanical support
The basic testing equipment you
will need to trouble- shoot DC motors in the field includes..
- Megohmmeter
- AC
voltmeter
- DC
clamp-on ammeter
- Ohmmeter
- DC
voltmeter
- Tachometer
