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.
dc charging system (fig. 4-2, view A) or an ac charging
system (fig. 4-2, view B). Both systems generate an
alternating current (at); however, the difference is the
way they rectify the ac current to direct current (de) for
charging the battery.
Dc Charging System
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.
CHARGING SYSTEM
The charging system performs two jobs: (1) it
recharges the battery and (2) it generates current during
operation. The two types of charging systems used on
automotive and construction equipment are a
A dc charging system has a generator and a
regulator. The generator supplies the electrical power
and rectifies its current mechanically by using
commutator bars and brushes. The regulator performs
three jobs: (1) it opens and closes the charging circuit,
(2) it prevents overcharging of the battery, and (3) it
limits the output of the generator to safe rates.
Ac Charging System
An ac charging system has an alternator and a
regulator. The alternator is really an ac generator. Like
the generator, it produces an ac current but rectifies it
electronically, using diodes. Most alternators are more
compact than generators of equal output and supply a
higher current output at low-engine speeds. The
regulator in an ac charging system limits the alternator
voltage to a safe, preset value.
Charging System
All charging systems operate in three stages: (1)
during starting, the battery supplies all load current; (2)
Figure 4-2.—Charging systems.
4-2
