Electrical Fundamentals

Voltage drop

• Common causes of voltage drop are: too small of wire, broken wire, broken wire strands, dirty connections and defective contact switches or controls. All of these cause increase resistance and therefore reduce the flow of free electrons.

Resistance Heating• When electrical current flows through a conductor

the presence of resistance produces heat. The greater the current and/or the greater the resistance, the greater the heat produced.

• However if the wire is too small for the amount of current flowing, considerable heating will result.

• A light bulb uses resistance heating to produce light.

Temperature effect on resistance

• The higher the temperature of a metallic conductor, the rapid the internal vibration of the atoms in the material.

• It is difficult for free electrons to move from one valence to the next creating electricity.

Direct and Alternating current AC/DC

• In A/C current the electrons flow in one direction, then in the opposite direction. One complete change from one direction to the opposite direction and back again in one second is called a Hertz.

• Example a 60 HZ AC cycle means that, the current goes through a complete cycle 60 times in one second.

DC Current

• In DC current the electrons flow in one direction only. In the automobile battery the electrons flow from the negative post of the battery through the circuit and return to the battery through the positive post.

• All vehicles run on DC current, also all batteries operate on the principle of DC current.

Rectifier bridge Diode

• This can be used to rectify or (convert) AC current to DC current. This principle allows the Alternator to be used on modern vehicles to generate current. Without diodes the alternator would produce unusable current to run the electrical system.

Permanent Magnets• Magnetic material (ferrous), such as iron, nickel, steel has the

property of magnifying or concentrating a magnetic field. • Magnetic lines of force penetrate all substances and are deflected

only by magnetic materials or by another magnetic field.• There is no insulator for magnetism or lines of force, but an object

can be shield from magnetic lines of force by distance. • Magnetic lines of force converge around the poles where the

magnetic field is the strongest. All magnets have both a North and South Pole.

Electric Motor

• You can see two magnets in the motor: The armature (or rotor) is an electromagnet, while the field magnet is a permanent magnet

Electromagnetism• An electric motor is all about magnets and magnetism: A motor uses

magnets to create motion. • The north end of one magnet will attract the south end of the other.• On the other hand, the north end of one magnet will repel the north

end of the other (and similarly, south will repel south).• Inside an electric motor, these attracting and repelling forces create

rotational motion.

Faraday's law (Induction)• A changing magnetic field

(oscillating)produces a changing electric field. That is, you can produce electricity by moving a magnet in and out a close circuit (loop or coil)

• The flux of the magnetic field through the coil will change over time and produce a circulation of charges in the coil.

• Electromagnetic induction is the production of voltage across a conductor moving through a magnetic field. It underlies the operation of generators , all electric motors, transformers .

• Moving a conductor in a magnetic field (or by moving the magnet field near a stationary conductor) creates a voltage.

• The wire must be part of an electrical circuit. Otherwise the electrons have no place to go.

Induction Principle

Permanent Magnet Generator (P.M. Generator)

• The speed of moving components on an automobile can be monitored with a permanent magnet generator.

• As the reluctor wheel rotates, the magnetic field strength will increase and decrease with each passing tooth.  The fluctuating magnetic field induces AC voltage/current into the coil of wire.  The faster the rotational speed of the reluctor wheel, the higher the AC output voltage. 

Wiring Diagrams• Electrical devices are shown in wiring diagrams as

symbols. A wiring diagram is a drawing that shows the wires, connectors, and load devices in an electrical circuit.

• A wiring diagram sometimes called schematic, shows where the components are connected in the circuit.

Electrical symbols • They are much like the icons used on your personal

computer displays. The symbols represent components. The different symbols used by manufactures are similar but not always identical.

• The vehicles service manual will explain each symbol.

Electrical test equipment

• This equipment is used to isolate the causes of electrical problems. D.V.O.M (digital volt, ohm meter) measures volts, current, and ohms. The voltmeter on a D.V.O.M. has very high impedance (resistance).

• High impedance meters protect the circuit components and ensure accurate readings while measurements are being made.

• Use only digital meters on electronic equipment and circuits.

Test Lights

• Test lights are powered by the circuit being tested. They have two; one lead connects to ground, and the other has a probe tip. A 12 volt bulb is connected between the ground lead and the probe tip.

• It the probe tip contacts a 12 volt source the light bulb will illuminate.

Jumper Wire• This is a short piece of wire used as a temporary

connection between two points in a circuit. It may have alligator clips or other connectors on each end of the wire. Jumper wires should have a fuse located between the connectors, no more then 10 amps.

Solid-state Device• Solid state electronics are those circuits or devices built entirely

from solid materials and in which the electrons, or other charge carriers, are confined entirely within the solid material.

• There are no mechanical moving parts in a solid-state component, the current is confined to solid elements and compounds engineered specifically to switch and amplify it.

• To create PN material the silicon layers are doped. Doping creates a positive (P) and a negative (N) layer on the silicon chip. The two layers are known as a “PN junction”.

Transistors• Transistors are constructed from layers of P and N

material. They have three terminal connections instead of two. A transistor is often used as a electronic switch or relay.

• The transistor can be used as a high speed switching device turning a circuit on and off thousands of times per second, with no moving parts.

Handling Solid State Components

• High temperature, impact, high voltage, reverse polarity, and static electricity may damage solid state components.

• Heat sinks are used to protect solid state components from damage when they are mounted in a location that is subjected to heat.