ELECTRICAL SYSTEM
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6. Kirchhoff’s voltage law:
• Kirchhoff’s voltage law deals with voltage drops.
A voltage drop is the amount of voltage used up
or “dropped” by resistance in a circuit. Ohm’s law
states that V = IxR, every component in a circuit
has resistance, even the wires. To push current
through resistance, it takes voltage. Kirchhoff’s
voltage law states that the sum of all the voltage
drops equals the source voltage.
• As an example, imagine a circuit that has a 12V
battery that produces 4 amps of current power-
ing a light bulb that creates 3 Ω of resistance.
The wires are assumed to have 0 Ω resis-
tance*. The light bulb uses 12 volts (4 amps x 3
ohms = 12 volts). The battery produces 12 volts
that equals the 12 volts used by the light bulb.
See Figure 7.27.
NOTE: * If the proper size wire is used and
there is no corrosion in the wire, the resistance
will be too small to worry about.
Figure 7.27
12 Volts
4 Amps
4 Amps flow
X
3 Ω resistance
=
12 Volts
7. How the system is wired together
The Rules: All circuits have some basic rules that
must be followed:
7a. All circuits must have at least one voltage
source. It could be a battery, an altenator
or both.
7b. All circuits must have a load. A circuit with-
out a load is the same as shorting out the
power source. Typical loads could be:
• lights
• a motor
• a solenoid
7c. All circuits must have a complete path
back to the voltage source. This is also
known as having continuity.
NOTE: On outdoor power equipment, the frame
of the machine is frequently used as the return
path to the battery. This is referred to as ground-
ing the machine. Any point on the frame should
be the same as the negative post of the battery
(Electrically) unless there is a bad connection
between the battery and the frame or between
the frame and the component or cable that is
assumed to be grounded to it.
7d. Most circuits have additional components
like switches and fuses.
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