Generators - Portable Generators
- Electric, Gasoline, Diesel
Inverter, RV Generators - On Sale!
GENERATORS - Portable,
Electric, Natural Gas, Diesel Inverter, RV
Generators - On Sale!
IS A GENERATOR?
is a latin word that means originator or maker.
In power industry, this term refers to a device
that produces electrical energy. Note that although
electricity does occur naturally, it does not exist
in the forms that currently can be practically used.
For practical use it is produced from other forms
of energy. Since energy cannot be created but can
only be transferred from one form to another, any
form of electricity generation obviously needs a
source of fuel. Technically speaking, in electric
generators electricity is generated from mechanical
energy. The mechanical energy in turn is produced
from so-called primary sources, such as chemical,
nuclear or thermal energy contained in various types
of fuel. It can also be obtained from renewable
resources such as sunlight, wind or falling water.
The machine that converts primary energy into mechanical
energy is called prime mover. Steam turbines, internal-combustion
engines, gas combustion turbines, water and wind
turbines are the common types of prime movers.
you've ever moved paper clips around with a magnet
or killed time arranging metal shavings into a beard
on a "Wooly Willy" toy, then you've dabbled
in the basic principles behind even the most complicated
electric generators. The magnetic field responsible
for lining up all those little bits of metal into
a proper Mohawk haircut is due to the movement of
electrons. Move a magnet toward a paper clip and
you'll force the electrons in the clip to move.
Similarly, if you allow electrons to move through
a metal wire, a magnetic field will form around
to Wooly Willy, we can see that there's a definite
link between the phenomena of electricity and magnetism.
A generator is simply a device that moves a magnet
near a wire to create a steady flow of electrons.
The action that forces this movement varies greatly,
ranging from hand cranks and steam engines to nuclear
fission, but the principle remains the same.
simple way to think about a generator is to imagine
it acting like a pump pushing water through a pipe.
Only instead of pushing water, a generator uses
a magnet to push electrons along. This is a slight
oversimplification, but it paints a helpful picture
of the properties at work in a generator. A water
pump moves a certain number of water molecules and
applies a certain amount of pressure to them. In
the same way, the magnet in a generator pushes a
certain number of electrons along and applies a
certain amount of "pressure" to the electrons.
an electrical circuit, the number of electrons in
motion is called the amperage or current, and it's
measured in amps. The "pressure" pushing
the electrons along is called the voltage and is
measured in volts. For instance, a generator spinning
at 1,000 rotations per minute might produce 1 amp
at 6 volts. The 1 amp is the number of electrons
moving (1 amp physically means that 6.24 x 1018
electrons move through a wire every second), and
the voltage is the amount of pressure behind those
form the heart of a modern power station. In the
next section, we'll take a look at how one of these
operation of electric generators is based on the
phenomenon of electromagnetic induction: whenever
a conductor moves relative to a magnetic field,
voltage is induced in this conductor. Particularly,
if a magnet is spinning inside a coil, AC voltage
is induced in the coil. For more information see
our tutorial on how generators work with an animation
that illustrates their basic operation.
induced voltage (called electromotive force or emf)
will create a current through an external circuit
connected to the coil terminals resulting in energy
being delivered to the load. Thus, the kinetic energy
that spins the source of the magnetic field is converted
into electricity. Note that the current flowing
through an external load in turn creates a magnetic
field that opposes the change in the flux of the
coil, so the coil opposes the motion. The higher
the current, the larger the force that must be applied
to the magnet to keep it from slowing down.
How An Electric Generator Works
electric generator is a device used to convert mechanical
energy into electrical energy.
generator is based on the principle of "electromagnetic
induction" discovered in 1831 by Michael Faraday,
a British scientist. Faraday discovered that if
an electric conductor, like a copper wire, is moved
through a magnetic field, electric current will
flow (be induced) in the conductor. So the mechanical
energy of the moving wire is converted into the
electric energy of the current that flows in the
practice, the magnetic field is most often induced
by an electromagnet rather then a permanent magnet.
In AC systems, usually the electromagnet is spinning,
and the power-producing armature is stationary.
The armature normally comprises of a set of coils
that form a cylinder. The electromagnet consists
of so called field coils mounted on an iron core.
A current flow in the field coils is required to
produce magnetic field. This current may be obtained
from an external source or from the system's own
armature. Most modern AC sources with field coils
are self-excited. In such devices the current for
field coils is supplied by an additional exciting
winding in the armature. The initial magnetic field
is produced by residual magnetism in the electromagnet's
cores. When the prime mover starts turning the armature,
at first the armature rotates in a very weak magnetic
field and produces small emf. This emf creates a
current in field coils, which increases magnetic
flux, which in turn increases emf in the armature.
This process continues until the rated output voltage
term "alternator," to describe what
we have been calling an alternator since the
late '50s, is now obsolete. Ever since the
'96 model year, we are supposed to call them
"generators." The name change more
accurately describes the function of what
we used to call an "alternator."
It is customary to describe
a voltage-generating source by the type
of voltage it provides; alternators produce
alternating current (AC) and generators
produce direct current (DC). To be technically
correct, it should be called a "generator"
since the output is DC.
A generator has two functions
in a vehicle. First, it provides the electrical
energy to operate the vehicle when the engine
is running; and second, it charges the battery
at the same time. This makes the generator's
performance during engine run important
so the computer-controlled engine gets the
power it needs to function properly to maximize
fuel economy and minimize emissions. The
battery is actually "off-line"
(not providing) when the generator is generating.
If the generator fails and cannot produce
electricity, the battery takes over and
runs the vehicle until the battery runs
down. Let's take a brief tour through a
generator to see how the internal components
work together to electrically power the
vehicle and charge the battery. A generator
contains several major components. Figure
1 shows the electronic voltage regulator,
a field/rotor winding and a stator coil.
The electronic voltage regulator controls
the generator output by controlling the
electron current flowing through the rotor.
The rotor is a large coil spinning inside
the stator winding. Transistor Q1 is a power
transistor located in the voltage regulator
to control rotor winding current. Current
flows up through ground, into emitter, out
Q1 collector through the rotor winding back
stator winding shown in Figure 1 is a delta
connection because the three windings are
connected to electrically form a triangle
like the Greek letter delta. Since a stator
has three windings the generator is said
to be a "three-phase system."
the rotor spins inside the stator winding,
electrical energy is induced in each of
the stator windings. Each of the outputs
from the three stator windings is called
a phase and is an AC voltage wave form called
a sine wave. The sine wave has a positive
alternation (+ peak) and a negative alternation
(- peak). Each of the phases reaches its
positive peak 120¯ after the previous
sine wave as the rotor continues to spin
inside the stator.
AC sine waves are presented to a diode bridge
inside the alternator to convert the AC
sine waves to DC (B+), as shown in Figure
2. To understand how the diode bridge converts
AC to DC, we need to understand how diodes
work. Generators use solid-state diodes
to do their job in converting AC to DC by
a process called rectification (converting
AC to DC).
diode lets electron current flow in one
direction but not the other. But how does
a diode respond to the voltage of the sine
wave? A diode lets electrons pass through
the opposite direction the diode's arrow
is pointing, as shown in Figure 3. Or, we
could say electrons only flow against the
arrow. For electron current to flow against
the arrow, the diode must be forward biased.
That means the diode anode is more positive
than the diode cathode. This is forward
bias and allows electrons to flow through
the diode in the direction against the arrow.
Heavy-duty diodes form a diode bridge inside
a generator to rectify (convert) the AC
produced inside the generator to DC at the
back at Figure 2, at the connections where
a stator winding connects to the diode bridge,
(P#1, P#2 and P#3), there are two diodes
in series from each connection point. There
is a diode connected to B+, and therefore
it is referred to as the positive diode.
There is a diode connected to ground, or
B-, and therefore it is referred to as the
negative diode. There is a positive and
negative diode in a series network for each
stator phase winding. Here is where diode
knowledge comes in handy. The positive diode
applies the positive alternation (+ peak)
into positive voltage to draw electrons
out of the positive post of the battery.
When the associated sine wave is in its
positive swing, the positive diode is forward
biased and draws electrons out of the battery
positive post. Electrons flow against the
arrow in the positive diode.
negative diode applies the negative alternation
(- peak) into negative voltage to force electrons
into the negative post of the battery. When the
associated sine wave is in its negative swing, the
negative diode is forward biased and sends electrons
into the battery negative post. Electrons flow against
the arrow in the negative diode. This establishes
a DC current through the battery to charge it. DC
current means the electrons always flow in one direction,
from negative to positive, through the battery and
electrical circuit on the vehicle is connected in
parallel to the battery between B+ and B-. Generator
current flows through each circuit as it does through
the battery. At no time does any diode network stop
contributing its share of electrical energy to charge
the battery or provide electron flow to vehicle
circuits. Each phase of the generator simply "peaks"
in numerical order as long as the rotor is energized
and turning. The end result is a constant DC voltage
and current source at the generator terminals.
DC current that runs the vehicle passes through
the diode bridge. The diode bridge generates a lot
of heat from all the hard work it must perform.
If the heat is not dissipated adequately, the diode
bridge will burn up and the generator fails - resulting
in no charging voltage and no charging current.
technicians have tried to take a weak or
dead battery and place it in a car with
the engine running to recharge the battery.
First of all, never disconnect a battery
cable while the engine is running if the
vehicle has any onboard electronics at all
(engine control module, power control module,
vehicle control module, body control module,
transmission control module, digital sound
system, etc.) The battery acts as a voltage
stabilizer to help the generator keep its
output below 15 volts. By disconnecting
one of the battery cables, the generator
loses the stabilizing action. The generator
then may go crazy and produce a major energy
dump (high voltage surge) into the electrical
system, possibly destroying the generator
itself but most assuredly a lot of electronics
in the car. Figure 4 shows the DC charging
voltage and the ripple voltage riding on
the output voltage as seen on a lab scope.
The ripple is created by each of the three
phases going through their positive peak
one after the other. The smaller the ripple
pattern the better. A generator is most
efficient when the ripple is less than 0.5
BACKUP GENERATORS FOR HOME USE
power plants the electricity generating devices
are most often driven by steam or hydraulic turbines
or by diesel engines. The same concept of converting
mechanical energy into electricity is widely used
in small consumer-grade units. In commercially available
models suitable for home use, an alternator is integrated
with an internal-combustion engine into a single
appliance. The resulting device is referred to as
an engine-generator set or a genset. It is the most
common type of a backup power source for the home.
A genset is often casually called just a generator
even though it also includes an engine. There are
two main types of such devices that differ by their
connection and activation methods: standby and portable.
Standby generators for home use are permanently
connected to the house wiring system and are also
hooked up to a fuel source, such as a natural gas
line or a large propane or diesel tank. They cost
more than portables and require professional installation
of a transfer switch and the fuel line. Their main
advantage is they can provide practically continuous
power for as long as the fuel is available. Portable
devices are intended primarily for a temporary connection
to several appliances via extension cords rather
than to the whole house. They are normally fueled
from an on-board tank and therefore need frequent
refueling. Some more expensive models can also be
connected to an external source for extended run
time. A portable unit is generally cheaper than
a standby, often sold at a discount and does not
require a professional installation. Of course you
want to connect it to the house wiring you need
to install a transfer switch. Choosing the best
device for your application involves selecting the
right type and a proper sizing based on the amount
of power you may need during an emergency