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.
4-1
