Cub Cadet CC 500 EL - Manual (Page 8)

ELECTRICAL SYSEM
4
Kirchhoff’s current law
Kirchhoff’s current law deals with nodes. Nodes are the
junction of two or more wires or the junction of a wire to
a component.
Kirchhoff’s current law states that what ever current
goes into a node must come out.
As an example: Three wires are connected with a wire
nut. one wire has 5 amps going into the wire nut. The
sum of the current coming out of the other two wires
must equal 5 amps. That could be 3 amps in one wire
and 2 amps in the other or it could be 2.5 amps in each
wire, but the total must be the same as the current
coming in. See Figure 2.2.
Kirchhoff’s voltage law
Kirchhoff’s voltage law deals with voltage drops. A volt-
age drop is the amount of voltage used up or “dropped”
by a resistance in the circuit. Ohm’s law stated that V =
IxR, every component in a circuit has resistance, even
the wires. To push current through a resistance, it takes
voltage. Kirchhoff’s voltage law states that the sum of
all the voltage drops equals the source voltage.
An example: a circuit has a battery of 12V, a light bulb
that creates 3 ohms of resistance and there is 4 amps
of current in the circuit. The wires are assumed to have
0 ohms, if the proper size wire is used and there is no
corrosion in the wire, the resistance will be too small to
worry about. The light bulb uses 12 volts (4 amps x 3
ohms = 12 volts). the battery has 12 volts that equals
the 12 volts used by the light bulb.
AC electricity
AC electricity is used to provide electricity to homes
and businesses because it can be easily transmitted
over long distances. Some house hold products can
run on straight AC power while most will convert it to a
usable DC form internally.
AC or alternating current is a current or voltage value
that varies with time and has an average value of zero.
If the current or voltage is observed using an oscillo-
scope, the waveform will look like a sine wave. this
means it will be positive for awhile then it will be nega-
tive for awhile. The time spent positive will equal the
time spent negative. Since it spends just as much time
positive as negative, the positive values cancel out the
negative values leaving an average value of zero. See
Figure 2.3.
Since AC varies with time, the time or phase angle of
the waveform is needed to compute voltage and cur-
rent. This manual will not go into how to do this. AC is
only mentioned here as a reference. This mower is
plugged into AC electricity, but it will change the elec-
tricity to a DC waveform to power the motor.
Figure 2.2
5 Amps
3 Amps
2 Amps
Node
Figure 2.3
AC wave form
1 Cycle +
-