CHAPTER 4ELECTRICAL AND HYDRAULIC SYSTEMSThe electrical and hydraulic systems are majorcomponents designed to perform a variety of functionsthat support the operation of equipment. These systemscontrol starting, charging, braking, steering, lifting, andthe movement of all attachments. This chapter coversthe basic components of the electrical and hydraulicsystems used in automotive and constructionequipment.ELECTRICAL SYSTEMSProper performance of pre- and post-operationalchecks and operator maintenance requires a basicunderstanding of the electrical systems used onautomotive and construction equipment. The basiccomponents of the electrical system are the following:a storage battery, a charging system, starting circuits, alighting system, and gauges.STORAGE BATTERYThe storage battery is the heart of the chargingcircuit. The type used in automotive, construction, andweight-handling equipment is a lead-acid cell type ofbattery. This type of battery stores energy in a chemicalform. It is not a storage tank for electricity.The battery acts as a stabilizer for the voltage of theelectrical system and may, for a limited time, furnishcurrent when the electrical demands of the vehicleexceed the generator output. The battery produces aflow of direct current when lights, starter motor, or othercurrent-consuming devices are connected to the batteryposts. This current is produced by a chemical reactionbetween the active materials of the plates and thesulfuric acid of the electrolyte.Part of your prestart and operator maintenanceresponsibilities are checking the battery water level andensuring the battery terminals are tight and free fromcorrosion. You can clean a battery thoroughly by usinga stiff brush and a water and baking soda solution. If thebattery terminals are corroded, disconnect and cleanthem. Clean the battery posts and the inside of theconnectors so they make good electrical contact. Aftercleaning, you should rinse off the battery with cleanwater. If the battery fails to supply sufficient power toturn the starter, document it and turn it in.Battery ConstructionA typical lead-acid storage battery is shown infigure 4-1. Like most batteries, it consists of a moldedcontainer with individual cell compartments, cellelements, cell connectors, cell covers, terminal posts,and vented filler caps.The container is made of molded hard rubber,plastic, or bituminous material. It must withstand shockand vibration as well as the heat of the enginecompartment, if so located. Each cell compartment hasrests to support the elements and space for an adequatesupply of electrolyte. An area between the element restsallows any material from the elements to settle withoutcontacting the elements and causing an internal short.The cell elements contain two types of lead plates,known as positive and negative. These plates areinsulated from each other by suitable separators madeof microporous, nonconductor material (usually porousrubber or spun glass) and are submerged in a sulfuricacid solution (electrolyte).Batteries are designed with a single cover thatextends over all cells. In many batteries, only the fillerFigure 4-1.—Typical storage battery.4-1
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