Lesson 3/Learning Event 1
If the battery is charged and the load in this circuit is small, such as a small bulb, the meter should
indicate close to 24 volts. Notice this is about the center of this scale. Let us say you are checking
a defective 24-volt circuit with a heavy load, such as a starter. When you switch the selector to 50,
the meter indicates only approximately (about 12 volts). If you want to get a more exact
measurement, switch the selector to 20. You are now using the 0 to 20 scale, and it is easier to
read for this particular voltage.
CAUTION
You must turn the selector switch back to 50 or to OFF before this heavy load
is disconnected from the circuit. If you do not, the meter will be damaged if
the voltage jumps past 20 volts when the load is disconnected.
Notice that ranges for the selector switch start with the highest range 0 to 50. As the selector is
turned to the right, the ranges become smaller. This prevents burnout of the meter by the operator
having to go through the higher ranges first, once the operator leaves the OFF position.
Let us review what you have learned so far. We learned the automotive electrical system is in
many ways similar to a water system. We learned electrical pressure is measured with a voltmeter
as water pressure is measured with a pressure gage. We have also learned how a voltmeter is
connected to an electrical circuit. We know this is only one of many measurements that can be
made on the automotive electrical system. Let us next see how current can be measured with an
AMMETERS
If we want to find out how much water is flowing through a pipe in a water system, we install a
flowmeter, placed in the pipe in such a way that all of the water moving through the pipe goes
through the meter. The meter "counts" (measures) the gallons of water that move through it.
The ammeter does the same thing in an electrical circuit. The ammeter measures the amount of
current moving through the wire. While the flowmeter measures the water flow in gallons, the
ammeter measures the electrical current in amperes. The gallon is a unit of measure for water and
other liquids; the ampere is a unit of measure for electrical current. Amperes are often called
"amps" or "amps of current."
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