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General Information
Electrical Testing
For any electrical system to work, electricity must be able
to flow in a complete circuit from the power source (the
battery) via the components and back to the battery. No
circuit means no electrical flow. Once the power has left
the positive side of the battery and run through the
component it must then return to the battery on its
negative side (this is called earth or ground). To save on
wiring, connections and space, the negative side of the
battery is connected directly to the frame or engine.
Around the frame and engine will be various other
ground points to which the wiring coming from
components will be connected. In the case of the starter
motor it bolts directly to the engine, which is bolted to the
frame. Therefore the frame and engine also form part of
the earth return path.
Ohm's Law
The relationship between voltage, current and resistance
is defined by Ohm's Law.
•
•
•
The potential of a battery is measured in
VoltsM.
The flow of current in a circuit
(I)
is measured
in Amperes.
The power rating of a consumer is measured
in Watts <W>.
The resistance
(R>
of a circuit is measured in
Ohms
(W.
Ohms law, for practical work can be described as -
Voltage
.
C
t
=
ReSistance
urren
Power is calculated by mUltiplying Volts x Amps -
Watts
=
Volts x Amps
By transposing either of these formulae, the value of any
unit can be calculated if the other two values are known.
For example, if a battery of 12V is connected to a bulb of
60W:
•
the current flowing in the circuit can be
calculated by using -
W =1
60 =5
V
12
the bulb resistance can be calculated by
using -
Y
= R
1~
= 2.4
To use either of the following triangles, put your finger
over the value you want to find. Multiply the remaining
values if side-by-side, or divide if one is over the other.
Basic Electrical Circuits
1
1
Basic Circuit Diagram
In the above circuit an electrical reservoir (the battery) is
connected via a cable to a terminal on the controlling
device (the switch) whose contacts are either open or
closed. The other terminal on the switch is connected via a
cable to the consumer (the bulb), and the other side of the
bulb filament is connected to ground (earth) by another
cable. The ground point is usually a part of the frame or
engine, to which the battery negative terminal is also
connected.
When the switch contacts are open (as shown in the
diagram), the circuit is broken and no current flows. When
the switch contacts are closed the circuit is made and
current flows from the battery positive terminal through
the switch contacts and bulb filament to ground. The
frame completes the circuit to the battery negative
terminal and the bulb illuminates.
Although some circuits on the circuit diagram may at first
seem more complicated, it will generally be found that
they can be broken down into sections which do not differ
greatly from the basic circuit above.
1.14
SelVice Manual - Rocket III
I
Classic
I
Touring
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