Electrical Environment: Ac Vs. Dc - Craftsman 28906 Professional Shop Manual

ELECTRICAL SYSTEM
Electrical environment: AC Vs. DC
Most modern outdoor power equipment that has an
electrical system complex enough to require diagnosis
will be equipped with an alternator that produces alter-
nating current (AC). In most systems, this current is
immediately rectified to direct current (DC), and regu-
lated to a nominal 12 Volts. The presence of AC is very
limited. The primary concern of this section is 12 Volt
DC systems, though much of the theory and tech-
niques apply equally well to other DC systems.
1. Voltage: Pressure
Voltage is the "pressure" that electricity has. It is
the amount of force pushing electrons through a
circuit.
The unit of measurement for this pressure is
volts.
.
3.
The capital letter "V" is used to represent volts.
Most (not all) outdoor power equipment operates
on a nominal 12 volts. In practice, system volt-
age may run as high as 13.5V or 14V.
Amperes: Flow
Current is the "flow" of electricity. It is the amount
of electrons flowing in circuit.
The flow of current is measured in Amperes or
Amps for short.
The capital letter 'T' is used to represent Amps.
Ohms: Resistance
Resistance is the opposition to current flow. It is
a restriction that slows down the flow of current.
• Resistance is measured in Ohm's.
The greek letter omega "W", or the letter "R" for
Resistance is used to represent Ohm's.
Resistance creates heat. A circuit with too much
electrical load, or too much resistance for the
load placed on it will get hot.
,
Ohm's Law: relates voltage, amperage, and
resistance
Ohm's law states that voltage is the product of
resistance times current.
It is written as V = I x R.
In simplest terms, it goes like this:
It takes 1 volt to push 1 amp through a resis-
tance of 1 ohm (1 = 1 x 1).
This equation can be rearranged using algebra
to solve for any one variable.
Those who were traumatized by algebra can
represent Ohm's law as a triangle. When using
the triangle, cover the value to be found, and the
two values left exposed signify how to obtain that
value. See Figure 7.25.
I R
Figure 7.25
As an example if the "R" is covered, the "V" is
over the 'T' which means "V" divided by 'T' will
solve for the covered letter "R" (VII = R). If the
"V" is covered, "1"and "R" are exposed on the
same line, meaning that the product of 'T' times
"R" will solve for the unknown "V" (I x R = V).
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