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Automotive Electricity

Basic Electrical Systems

The electrical system is considered the most important support system of a car or truck. If the electrical system did not exist, gasoline engines would not run. Electricity provides the needed spark for combustion, and the power needed for starting, lighting, signaling, instrumentation, safety devices, and many other accessories. There is often confusion concerning the terms electrical and electronic.

Electrical and electrical systems refer to wiring and electrical parts, such as lights.

Electronics means computers and other items used to control engine and vehicle systems.

FLOW OF ELECTRICITY

Electricity is the flow of electrons from one atom to another.

To have a continuous flow of electricity, three things must be present.
- An excess of electrons in one place.
- A lack of electrons in another place.
- A path between the two places.
The automoblile uses two sources of power or energy.
- A car's battery.
- - A sourse of chemical energy.
- The car's alternator.
- - A sourse of magnetic energy.

ELECTRICAL TERMS

Voltage

Electrical Pressure
- Measured in volts
- Voltage is the force that cause electricity to flow

Current

Current flow
- The flow or movement of electricity along a given path of electricity
- Measured in amperes or amps

Resistance

Resistance to electrical flow
- Any thing that acts as an obstruction to the electrical flow
- Measured in ohms

CIRCUIT TERMINOLOGY

Closed Circuit
- A completed circuit.

Closed Circuit

Open Circuit
- This is not a completed circuit.

Continuity
- When the circuit is complete (closed) there is continuity.
- Electricity can and will flow though the circuit.

CONDUCTORS AND INSULATORS

Conductors
- Conductors are materials with a low resistance to the flow of current
- The number of electrons in the outer shell or ring of an atom is less than four, the force holding them in place is weak.
- The voltage needed to move these electrons and create current flow is relatively small.
- Most metals, such as copper, silver and aluminum are excellent conductors.
Insulators
- Insulators are materials with a high resistance to the flow of current.
- They can resist heat, moisture, and corrosion without breaking down.
- Thermal plastics are the most common electrical insulator used today.

Caution!

Your body is a good conductor of electricity. Remember this when working on a an electrical system. Always observe all electrical safety rules.

TYPES OF CIRCUITS

Series Circuit

A series circuit consists of one or more resistor connected to a voltage source with only one path for electron flow.
- In a series circuit, the same amount of current flows through the entire circuit. A series circuit is characterized by the following facts:
- - The circuit's current is determined by the total of resistance in the circuit; it is constant throughout the circuit.
  - The voltage drops across each resistor are different if the resistance values are different.
  - The sum of the voltage drops equals the source voltage.
  - The total resistance is equal to the sum of all resistances in the circuit.

Parallel Circuit

A parallel circuits provides two or more different paths for the current to flow through.
- Each path has separate resistors (Loads) and can operate independently of the other paths. A parallel circuit is characterized by the following facts:
- - Total circuit resistance is always lower than the resistance of the leg with the lowest total resistance.
  - The current through each leg will be different if the resistance values are different.
  - The sum of the current on each leg equals the total circuit current.
  - The voltage applied to each leg of the circuit will be dropped across the legs if there are no loads in series with the parallel circuit.

Series-Parallel Circuit

In a series-parallel circuit, both series and parallel combinations exist in the same circuit.

A parallel circuit is characterized by the following facts:

The total current in this circuit to the voltage divided by the resistance.

To find the current through each of the resistors in parallel, find the
voltage across those resistors first.

GROUNDING THE LOAD

In the illustrations above use to explain series, parallel and series-parallel circuits, the return wire from the load connect directly to the negative terminal of the battery. If this were the case in your vehicle, there would be literally hundreds of wires connected to the negative terminal. To avoid this, auto manufactures use a wiring style that involves using the vehicle's metal frame components as part of the return circuit.