during peak operation, the battery helps the generatorsupply current; and (3) during normal operation, thegenerator supplies all current and recharges the battery.In both electrical systems, the battery starts theelectrical circuit that supplies the spark to start theengine.The engine then drives the generator oralternator that produces current to take over theoperation of the ignition, lights, and accessory loads.The battery also supports the generator or alternatorduring peak operation when the electrical loads areexcessive. But once the engine is started the generatoror alternator is the “work horse,” providing current tothe ignition and accessory circuits. The generatorsupplies current as long as the engine is at speed andrunning. When the engine slows down or stops, thebattery takes over part or all of the load.STARTING CIRCUITSHigh voltage is often necessary to ensure sufficientstarting power due to the high compression ratios ofsome diesel engines. Three systems are used to increaseeither the voltage or amperage to accomplish this taskThese are parallel, series, and series-parallel systems.Parallel SystemAn example of a parallel system, as shown in figure4-3, view A, is two 12-volt, 200-amp batteries areconnected from the starter to the positive terminal of onebattery to the positive terminal of the second battery.The negative side of the batteries are connected from theground to the negative terminal from one battery to thenegative terminal of second battery. This systemprovides 12 volts and 400 amps, providing moreamperage for starting.Series SystemAn example of a series system, as shown in figure4-3, view B, is two 12 volt, 200-amp batteries areconnected from the positive terminal of one battery tothe negative terminal of the second battery. Theremaining positive terminal is connected to the starterand the remaining negative temninal is connected to theground. This system provides 24 volt and 200 amps,providing more volts for starting.Series-Parallel SystemA series-parallel system provides a seriesconnection of the batteries for starting and a parallelFigure 4-3.—Starting circuits.connection for normal operation. An example of aseries-parallel system is when two sets of parallelbatteries, as shown in figure 4-3, view C, are connectedin series and the negative terminal from one set of thebatteries is connected to the positive terminal of theother set. This system provides 24 volts and 800 amps.This combination is used for cranking large constructionequipment.CAUTIONUse extreme care when jump starting isrequired. Hooking up jumper cables from a24-volt system to a heavy-duty 12-volt systemcan cause severe battery damage, starterdestruction, or even an explosion. If you areunsure of the starting circuit, get help from themechanic field crew for assistance.LIGHTING SYSTEMThe lighting system on automotive, construction,and weight-handling equipment includes the lamps andbulbs, clearance lights, side marker lights, reflectors,taillights and brake lights, auxiliary lights, and fuses.Standards for lights on vehicles are outlined in theFederal Motor Carrier Safety Regulations Pocketbook.The manufacturer provides equipment with anelectrical system that supports the lighting circuits. Partof your prestart responsibility is to ensure the lights onyour equipment work and are clean of dust and dirt. A4-3
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