Practical Perspectives

The Use of Electric Circuit Elements

The extensive use of electric circuit elements including resistors, inductors, and capacitors in electric circuits making up manufacturing systems and engineering products and processes has led to a new integrated approach in the design of such engineering systems involving electrical, electronic, mechanical, and computer engineering.

In this section, we will describe for you how the above elements in addition to other elements are important for an automobile.

A model of automobile ignition circuit presents a good example of an electric circuit in engineering system.

An ignition circuit is made up of two sub-circuits:

1. The primary - carries low voltage
2. The secondary - carries high voltage

• The primary circuit is controlled by the ignition key.

• It releases 12 volts of electricity from the battery or alternator through the starter coil to a set of breaker points in the lower part of the distributor, or to the relay in electronic ignition applications.

• When the points or relay are closed, current flows through the chassis back to the battery, completing the circuit.

• When the points or relay are open, the flow stops, causing a high-voltage surge (from 20 to 40 kV) to pass from the coil through a rotor in the top of the distributor to the spark plugs in order to ignite a spark across the gap of the spark plug.

• The spark ignites the fuel-air mixture in the cylinder.

• Once the car has started, the voltage regulator protects the battery from being overcharged by the alternator.