CHAPTER 4 ELECTRICAL AND HYDRAULIC SYSTEMS

The electrical and hydraulic systems are major components designed to perform a variety of functions that support the operation of equipment. These systems control starting, charging, braking, steering, lifting, and the movement of all attachments. This chapter covers the basic components of the electrical and hydraulic systems used in automotive and construction equipment.

ELECTRICAL SYSTEMS

Proper performance of pre- and post-operational checks and operator maintenance requires a basic understanding of the electrical systems used on automotive and construction equipment. The basic components of the electrical system are the following: a storage battery, a charging system, starting circuits, a lighting system, and gauges.

STORAGE BATTERY

The storage battery is the heart of the charging circuit. The type used in automotive, construction, and weight-handling equipment is a lead-acid cell type of battery. This type of battery stores energy in a chemical form. It is not a storage tank for electricity.

The battery acts as a stabilizer for the voltage of the electrical system and may, for a limited time, furnish current when the electrical demands of the vehicle exceed the generator output. The battery produces a flow of direct current when lights, starter motor, or other current-consuming devices are connected to the battery posts. This current is produced by a chemical reaction between the active materials of the plates and the sulfuric acid of the electrolyte.

Part of your prestart and operator maintenance responsibilities are checking the battery water level and ensuring the battery terminals are tight and free from corrosion. You can clean a battery thoroughly by using a stiff brush and a water and baking soda solution. If the battery terminals are corroded, disconnect and clean them. Clean the battery posts and the inside of the connectors so they make good electrical contact. After cleaning, you should rinse off the battery with clean water. If the battery fails to supply sufficient power to turn the starter, document it and turn it in.

Battery Construction

A typical lead-acid storage battery is shown in figure 4-1. Like most batteries, it consists of a molded container with individual cell compartments, cell elements, 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 shock and vibration as well as the heat of the engine compartment, if so located. Each cell compartment has rests to support the elements and space for an adequate supply of electrolyte. An area between the element rests allows any material from the elements to settle without contacting the elements and causing an internal short.

The cell elements contain two types of lead plates, known as positive and negative. These plates are insulated from each other by suitable separators made of microporous, nonconductor material (usually porous rubber or spun glass) and are submerged in a sulfuric acid solution (electrolyte).

Batteries are designed with a single cover that extends over all cells. In many batteries, only the filler

Figure 4-1.-Typical storage battery.

caps and the terminal post protrude from the cover. In other batteries, only the filler caps extend above the cover and the terminal posts extend through the side. The latest design of batteries is the so-called maintenance-free batteries that provide no means of checking the electrolyte or water level.

Battery Capacity

The capacity of a battery is measured in cold cranking amps (CCA). The CCA capacity is equal to the product of the current in amperes and the time in hours during which the battery is supplying this current when cranking a cold engine. The ampere-hour capacity varies inversely with the discharge current. The size of a cell is determined by its ampere-hour capacity. The capacity of a cell depends upon many factors. The most important of these factors are the following: (1) the area of the plates in contact with the electrolyte; (2) the quantity and specific gravity of the electrolyte; (3) the type of separators; (4) the general condition of the battery (degree of sulfating, plates buckled, separators warped, sediment in bottom of cells, etc.); and (5) the final limiting voltage.