Lesson 4/Learning Event 3
Learning Event 3:
DESCRIBE PURPOSE AND OPERATION OF ELECTRICAL AUTOMOTIVE ACCESSORIES
The instrument panel usually is placed so that the instruments may be read easily by the driver.
They inform the driver of the approximate speed, engine temperature, oil pressure, rate of charge or
discharge of the battery, amount of fuel in the fuel tank, distance traveled, and the time. Certain
controls frequently are mounted on the instrument board, such as the throttle, choke, starter,
heater, and windshield wiper.
Battery Condition Gages
One of the instruments that almost always is included on an instrument panel is a battery condition
gage. It is a very important indicator because, if interpreted properly, it can be used to troubleshoot
or prevent breakdowns. The following are the three basic configurations of battery condition gages.
The ammeter indicates the amount of current flowing to and from the battery. It does indicate the
total generator output, because other units in the electrical system, besides the battery, are supplied
by the generator. If it shows a 10-ampere discharge, it indicates that a 100-ampere-hour battery
would be discharged in 10 hours; that is, 10 amperes flowing for 10 hours. Current flowing from
the storage battery to the starting motor is never sent through the ammeter, because the great
quantities used (200 to 600 amperes) cannot be measured on an instrument of such limited
capacity. In the typical ammeter, all the current flowing to and from the battery, except for
starting, actually is sent through a coil to produce a magnetic effect that deflects the ammeter
needle in proportion to the amount of current. This coil is matched to the maximum current
output of the generator and this varies with different applications. Some model wheeled vehicles
have replaced the ammeter with a battery generator indicator that does not give a calibrated
reading, but shows ranges by colors or bands.