Unit 13 Battery and Starting System英文.ppt

Unit 13 Battery and Starting System Unit 13 Battery and Starting System To understand the functioning of your cars electrical system, you should be aware of its major parts: Battery—supplies energy to operate the components which are needed when the engine is stationary or when the output from the charging system is low. Starting—enables the engine to be cranked over at a speed sufficient for it to fire. Unit 13 Battery and Starting System Charging—supplies the electrical energy when the engine is running. Also maintains the battery in a fully charged state. Ignition—provides a spark to fire the engine. Lighting—needed for exterior and interior illumination. Auxiliary—includes the various accessories such as windscreen wipers and washers, direction indicators etc. Unit 13 Battery and Starting System Battery and Battery MaintenanceFigure 13-1 Lead-acid battery 1. The Lead-acid Battery The purpose of the battery is to store electrical energy. It does this by converting the electrical energy supplied to it into chemical energy so that when an electrical current is required the energy change is reversed[1]. Unit 13 Battery and Starting System Unit 13 Battery and Starting System Most vehicles use a lead-acid battery: this type has lead plates which are immersed in an electrolyte of sulfuric acid and distilled water. As the battery discharges (gives up its energy) the lead in the plates undergoes a chemical change and the acid becomes weaker i .e. the relative density decreases[2]. Unit 13 Battery and Starting System To reverse the action an electrical charges the lead plates back to their original chemical for ms and strengthens the electrolyte. A charge current must pass through the battery in one direction only, so direct current (DC) is supplied with positive(+) terminal of the alternator connected to the positive terminal of the battery. Unit 13 Battery and Starting System 2. Battery Maintenance Battery maintenance focuses on several key task