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 resis-
tance, even the wires. To push current through resis-
tance, 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 powering a
light bulb that creates 3 Ω of resistance. The wires are
assumed to have 0 Ω resistance*. The light bulb uses
12 volts (4 amps x 3 ohms = 12 volts). The battery pro-
duces 12 volts that equals the 12 volts used by the light
bulb. See Figure 7.17.
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 7.17
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 fol-
lowed:
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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