DC Power Sources 230

This course introduces the various means by which DC power is created and used. It also discusses DC power generation and the limits of its applications. Includes an Interactive Lab.

Class Details

Class Name:
DC Power Sources 230
This course introduces the various means by which DC power is created and used. It also discusses DC power generation and the limits of its applications. Includes an Interactive Lab.
Number of Lessons:
Additional Language:
Related 2.0 Class:
DC Power Sources 271

Class Outline

  • Objectives
  • What Is Direct Current?
  • What Is a DC Power Source?
  • Batteries
  • Primary and Secondary Cells
  • Fuel Cell
  • Solar Cells
  • Magnetic Flux
  • Magnetic Induction
  • DC Generators
  • DC Generator Motion
  • Types of Armatures
  • Types of DC Generators
  • Generator Efficiency Losses
  • Generator Strength
  • DC Motors
  • Limitations of DC Power
  • Summary


  • Describe the behavior of DC.
  • Describe DC power sources.
  • Describe batteries.
  • Distinguish between primary and secondary cells.
  • Describe fuel cells.
  • Describe solar cells.
  • Describe magnetic flux.
  • Describe magnetic induction.
  • Describe the major components of DC generators.
  • Describe the basic operation of DC generators.
  • Identify the main types of armatures for DC generators.
  • Describe the main types of DC generators.
  • Describe the causes of efficiency loss in DC generators.
  • Describe the factors that affect generator strength.
  • Distinguish between generators and motors.
  • Describe the limitations of DC power.


  • MSSC Maintenance Awareness


Vocabulary Term Definition
adapter A device that converts AC to DC. Adapters take the AC from a wall outlet and convert it to the DC that recharges secondary cells.
alternating current Current that regularly reverses the direction of its flow.
armature The rotating portion of a DC generator.
battery A device that converts chemical energy into electrical energy. Batteries are a source of direct current.
bidirectional Moving in two different directions. Alternating current is bidirectional.
brushes Sliding electrical contacts used to provide a connection between the armature and the external circuit.
byproduct A secondary product in addition to the primary effect, as a result of a chemical reaction. Some byproducts can be harmful to the environment.
cell A single unit of a battery.
charging cycle The process of restoring the chemical reactivity of a secondary cell battery. The charging cycle involves forcing DC back through the system.
coil The loop of conducting wire wrapped around the armature. Each additional armature coil will be on a different axis, to produce smoother output voltage.
commutator The rotating switch attached to the brushes of a DC generator. The commutator maintains DC when the rotation of the armature switches the polarity of the conductor.
compound generator A method of connecting field windings to the armature both in series and in parallel. The compound generator combines the positive qualities of the other two methods.
Conventional Flow Theory The belief that electricity flows out from a positive source seeking a negative conclusion. This theory is no longer accepted.
Copper loss A power loss due to current flowing through wire. Copper loss is proportional to the resistance of the wire and the square of the current.
corrode To deteriorate the useful properties in a material due to oxidation.
direct current Current that travels in one direction. It does not reverse the direction of flow.
discharge cycle The chemical reaction process of a battery. The discharge cycle is complete when a battery can no longer react to produce voltage.
Eddy current loss A phenomenon caused when a rotating conductor intersects a magnetic field. The relative motion causes a circulating flow of electrons or current within the conductor, leading to efficiency loss.
efficient Having an energy output that is close to the total energy supplied. An efficient system has very little resistance loss.
electromotive force Electrical pressure, abbreviated emf. It is the force that pushes electrons through a conductor, measured in volts.
electromotive series A list of metals in order of most reactive, or most likely to give up electrons, to least reactive. These metals are used in batteries.
Electron Flow Theory The belief that electricity flows out from a negative source seeking a positive conclusion. This theory is currently accepted.
Faraday's Law A law that states an electric field is induced in any system in which a magnetic field is changing with time.
field windings The conducting wire connected to the armature that energize the pole pieces. Field windings are connected in series or parallel.
fossil fuel Any naturally occurring organic fuel formed in the Earth’s crust, such as petroleum, coal and natural gas, that can be burned to release stored energy.
Frogleg wound armature Term used to describe a series-parallel combination armature winding. Froglegs are the most commonly used winding.
fuel cell A potentially very efficient DC power source where hydrogen is oxidized, with water the only byproduct.
generator A device that converts mechanical energy into electrical energy by magnetic induction.
hydrogen A colorless, odorless gas, and the most abundant element on the planet. While it is so common, the pure hydrogen needed for fuel cells still must be manufactured with fossil fuels.
Hysteresis loss The power loss in a conductive material caused by molecular friction. As an armature rotates, the molecules rub against each other, leading to effciency loss.
ion A charged atom. Ions react because they are not neutral.
Lap wound armature Term used to describe a parallel armature winding. Lap connections are used for high current, low voltage loads.
left-hand flux rule An easy method to remember the direction flux moves around a conductor.
left-hand generator rule A method to determine the relationship of the motion of the conductor in a magnetic field to the direction of the induced current. The current flow is opposite in motors.
magnetic flux A measure of the strength of the field formed around a magnet. Flux is expressed in webers (Wb).
magnetic induction The use of magnets to cause voltage in a conductor. Magnetic induction occurs whenever a conductor passes through magnetic lines of flux.
magneto A type of small DC generator that uses permanent magnets instead of electromagnets to cause magnetic induction.
motor A machine that converts one form of energy, such as electricity, into mechanical energy or motion.
oxidize To remove electrons from an atom, an ion, or a molecule.
photon A particle of light energy produced by the sun. A photovoltaic cell converts photons into DC voltage.
photovoltaic cell Another name for a solar cell. The photovoltaic cell converts light energy into DC voltage by using semiconductors.
PN diode A diode that has one positively charged side and one negatively charged side.
polarity Having two oppositely charged poles, one positive and one negative. Polarity determines the direction in which current tends to flow.
pole piece Devices mounted on the inside of a generator armature. When connected to field windings, the pole pieces form the electromagnets that create lines of flux.
primary cell A type of cell that cannot be recharged. Primary cell batteries are usually thrown away once their charge is spent.
pure semiconductor A semiconductor that contains no added impurities.
right-hand motor rule The relationship between the factors involved in determining the movement of a conductor in a magnetic field. The current flow is opposite in generators.
ripple Characterized by a varying value. Unlike the constant values of DC, the average value of an AC output constantly ripples.
secondary cell A type of cell that can be recharged. Running current through a secondary cell restores the chemical potential.
self-excited The residual magnetism of the pole pieces produce the initial generator voltage that permits current to flow through the field.
semiconductor A material with a conductive ability that lies between that of a conductor and an insulator. At high temperatures, semiconductors act like a conductor.
separately excited The fields are connected to an external source of DC to provide the initial generator voltage.
series generator A method of connecting field windings in series with the armature. This system is not very efficient.
series-parallel A compound connection that uses both series and parallel connections.
shunt A low-resistance connection between two points in an electric circuit that forms an alternative path for a portion of the current.
shunt generator A method of connecting field windings in parallel with the armature. The shunt generator is commonly used.
sine wave The most common type of AC waveform. A sine wave consists of 360 electrical degrees and is produced by rotating machines.
solar panel A circuit of linked photovoltaic cells. Currently solar panels are not a very efficient source of DC.
stepped down In electricity, a phrase used to describe voltage adjustment. To step down voltage means to decrease voltage.
transformed Having voltage stepped up or down in a circuit. There is no known way to transform DC.
turn The number of times a coil is wrapped around the same armature axis. Each additional turn increases generator output voltage.
unidirectional Moving in only one direction. Direct current is unidirectional.
valence The outermost orbit of electrons in an atom.
voltage drop The amount of voltage needed to push a given amount of current through a given amount of resistance.
Wave wound armature Term used to describe a series armature winding. Wave windings are used for high voltage, low current loads.
weber A unit used to express flux density. One weber (Wb) is equal to 100 million lines of flux.
windage A force created on an object by friction when there is relative movement between air and the object. Windage loss is the heat as a byproduct of the friction.
winding The conducting coils that are wound around the armature in which voltage is induced if moved within a magnetic field. The way in which coils are wound influences the characteristics of the system.