The modern
charging system hasn't changed much in over 40 years. It consists of
the alternator, regulator (which is usually mounted inside the alternator)
and the interconnecting wiring.
The purpose of the charging system is to maintain the
charge in the vehicle's battery, and to provide the main source of
electrical energy while the engine is running.
If the charging system stopped working, the battery's charge
would soon be depleted, leaving the car with a "dead battery."
If the battery is weak and the alternator is not working, the engine
may not have enough electrical current to fire the spark plugs, so the engine
will stop running.
If the battery is "dead", it does not necessarily mean
that there is anything wrong with it. It is just depleted of its charge.
It can be brought back to life by recharging it with a battery charger,
or by running the engine so that the alternator can charge it. For
more information on the battery, Click Here
.The main component in the charging system
is the ALTERNATOR. The
alternator is a generator that produces Alternating Current (AC),
similar to the electrical current in your home. This current is
immediately converted to Direct Current (DC) inside the alternator.
This is because all modern automobiles have a 12 volt, DC electrical
system.
A VOLTAGE REGULATOR
regulates the charging voltage that the alternator produces, keeping it between 13.5 and 14.5
volts to protect the electrical components throughout the vehicle.
There is also a system to warn the driver if something
is not right with the charging system. This could be a dash
mounted voltmeter, an ammeter, or more commonly, a warning lamp.
This lamp is variously labeled "Gen" Bat" and "Alt.". If this
warning lamp
lights up while the engine is running, it means that there is a problem
in the charging system, usually an alternator that has stopped working.
The most common cause is a broken alternator drive belt.
The alternator is driven by a belt that
is powered by the rotation of the engine. This belt goes around a
pulley connected to the front of the engine's crankshaft and is usually
responsible for driving a number of other components including the water pump, power
steering pump and air conditioning compressor. On some engines, there
is more than one belt and the task of driving these components is
divided between them. These belts are usually referred to as:
Fan Belt, Alternator Belt, Drive Belt, Power Steering Belt, A/C Belt,
etc. More common on late model engines, one belt, called a
Serpentine Belt will snake around the front of the engine and drive all
the components by itself.
On engines with separate belts for each component, the
belts will require periodic adjustments to maintain the proper belt
tension. On engines that use a serpentine belt, there is usually a
spring loaded belt tensioner that maintains the tension of the belt, so no
periodic adjustments are required. A serpentine belt is designed to last
around 30,000 miles. Check your owner's manual to see
how often yours should be replaced.
Alternator output is measured in both voltage and
amperage. To understand voltage and amperage, you must also know
about resistance, which is measured in ohms. An easy way to
picture this is to compare the movement of electricity to that of running water.
Water flows
through a pipe with a certain amount of pressure. The size
(diameter) of the pipe dictates how much resistance there will be to the
flowing water. The smaller the pipe, the more resistance.
You can increase the pressure to get more water to flow through, or you
can increase the size of the pipe to allow more water to flow using less
pressure. Since too much pressure can burst the pipe, we should probably restrict
the amount of pressure being used. You get the idea, but how is
this related to the flow of electricity?
Well, voltage is the same as water pressure.
Amperage is like the amount or volume of water flowing through, while
resistance is the size of the wire transmitting the current. Since too much voltage will
damage the electrical components such as light bulbs and computer circuits,
we must limit the amount of voltage. This is the job of the
voltage regulator. Too much water pressure and things could start
breaking. Too much voltage and things could start burning out.
Let's get
technical
Now, let's go a little deeper and see how these charging
system components actually work to produce the electrical power that a
modern automobile requires.
The alternator uses the principle of electromagnetism to
produce current. The way this works is simple. If
you take a strong magnet and pass it across a wire, that wire will generate a
small voltage. Take that same wire and loop it many times, than if
you pass the same magnet across the bundle of loops, you create a more
sizable voltage in that wire.
There are two main components that make up an
alternator. They are the rotor and the stator. The rotor
is connected directly to the alternator pulley. The drive belt spins
the pulley, which in turn spins the rotor. The stator is mounted to
the body of the alternator and remains stationary. There is just
enough room in the center of the stator for the rotor to fit and be able to spin
without making any contact.
The stator contains 3 sets of wires that have many loops each
and are evenly distributed to
form a three phase system. On some systems, the wires are
connected to each other at one end and are connected to a rectifier
assembly on the other end. On other systems, the wires are
connected to each other end to end, and at each of the three connection
points, there is also a connection to the rectifier. More on what
a rectifier is later.
The rotor
contains the powerful magnet that passes close to the many wire loops
that make up the stator. The magnets in the rotor are actually electro magnets, not a permanent
magnets. This is done so that we can control how much voltage the
alternator produces by regulating the amount of current that creates the
magnetic field in the rotor. In this way, we can control the output of the
alternator to suit our needs, and protect
the circuits in the automobile from excessive voltage.
Now we
know that every magnet has a north and a south pole and electro magnets
are no exception. Our rotor has two interlocking sections of
electro magnets that are arranged so that there are fingers of
alternating north and south poles. that are evenly distributed on the outside
of the rotor.
When we spin the rotor inside the stator and apply current to the
rotor through a pair of brushes that make constant contact with two slip
rings on the rotor shaft. This causes the rotor to become
magnetized. The alternating north and south pole magnets spin past
the three sets of wire loops in the stator and produce a constantly
reversing voltage in the three wires. In other words, we are producing alternating
current in the stator.
Now, we have to convert this alternating current to
direct current current. This is done by using a series of 6
diodes that are mounted in a rectifier assembly. A diode allows current to flow only in one direction. If voltage tries to flow in the other direction, it is blocked. The
six diodes are arranged so that all the voltage coming from the
alternator is aligned in one direction thereby converting AC current
into DC current.
There are 2 diodes for each of the three sets of
windings in the stator. The two diodes are facing in opposite
directions, one with its north pole facing the windings and the other
with its south pole facing the windings. This arrangement causes
the AC current coming out of the windings to be converted to DC current
before it leaves the alternator through the B terminal. Connected
to the B terminal of the alternator is a fairly heavy wire that runs
straight to the battery.
Current to generate the magnetic field in the rotor
comes from the ignition switch and passes through the voltage regulator.
Since the rotor is spinning, we need a way to connect this current from
the regulator to the spinning rotor. This is accomplished by wires
connected to two spring loaded brushes that rub against two slip rings
on the rotor's shaft. The voltage regulator monitors the voltage
coming out of the alternator and, when it reaches a threshold of about
14.5 volts, the regulator reduces the current in the rotor to weaken the
magnetic field. When the voltage drops below this threshold, the
current to the rotor is increased.
There is another circuit in the alternator to
control the charging system warning lamp that is on the dash. Part of
that circuit is another set of diodes mounted inside the alternator
called the diode trio. The diode trio takes current coming from the
three stator windings and passes a small amount through three diodes so that only
the positive voltage comes through. After the diodes, the wires
are joined into one wire and sent out of the alternator at the L
connection. It then goes to one side of the dash warning lamp that
is used to tell you when there is a problem with the charging system.
The other side of the lamp is connected to the run side of the ignition
switch. If both sides of the warning lamp have equal positive
voltage, the lamp will not light. Remove voltage from one side and
the lamp comes on to let you know there is a problem.
This system is not very efficient. There are many
types of malfunctions of the charging system that it cannot detect, so
just because the lamp is not lit does not mean everything is ok. A
volt meter is probably the best method of determining whether the
charging system is working properly
The voltage regulator can be mounted inside or outside of
the alternator housing. If the regulator is mounted outside (common on
some Ford products) there will be a wiring harness connecting it to the
alternator.
The voltage regulator controls the field current applied to the
spinning rotor inside the alternator. When there is no current applied to the field, there is no voltage produced
from the alternator. When voltage drops below 13.5 volts, the regulator will apply current to the
field and the alternator will start charging. When the voltage exceeds 14.5
volts, the regulator
will stop supplying voltage to the field and the alternator will stop charging. This is
how voltage output from the alternator is regulated. Amperage or current is regulated by
the state of charge of the battery. When the battery is weak, the electromotive force
(voltage) is not strong enough to hold back the current from the alternator trying to
recharge the battery. As the battery reaches a state of full charge, the electromotive
force becomes strong enough to oppose the current flow from the alternator, the amperage
output from the alternator will drop to close to zero, while the voltage will remain at 13.5 to 14.5.
When more electrical power is used, the electromotive force will reduce and alternator
amperage will increase. It is extremely important that when alternator efficiency is
checked, both voltage and amperage outputs are checked. Each alternator has a rated
amperage output depending on the electrical requirements of the vehicle.
The charging system gauge or warning lamp monitors the health of the
charging system so that
you have a warning of a problem before you get stuck.
When a charging problem is indicated, you can still drive a short distance to find help
unlike an oil pressure or coolant temperature problem which can cause serious engine
damage if you continue to drive. The worst that can happen with a charging
system problem is that you get stuck in a bad
location.
A charging system warning lamp is a poor indicator of problems in that there are many
charging problems that it will not recognize. If it does light while you are driving, it
usually means the charging system is not working at all. The most common cause
of this is a broken
alternator belt.
There are two types of gauges used to monitor charging systems on
some vehicles: a voltmeter which measures
system voltage and an ammeter which measures amperage. Most modern cars that have gauges
use a voltmeter because it is a much better indicator of charging system health. A
mechanic's voltmeter is usually the first tool a technician uses when checking out a charging system
A modern
automobile has a 12 volt electrical system. A fully charged battery will read about 12.5
volts when the engine is not running. When the engine is running, the charging system
takes over so that the voltmeter will read 14 to 14.5 volts and should stay there unless
there is a heavy load on the electrical system such as wipers, lights, heater and rear
defogger all operating together while the engine is idling at which time the voltage may
drop. If the voltage drops below 12.5, it means that the battery is providing some of the
current. You may notice that your dash lights dim at this point. If this happens for an
extended period, the battery will run down and may not have enough of a charge to start
the car after shutting it off. This should never happen with a healthy charging system
because as soon as you step on the gas, the charging system will recharge the battery. If
the voltage is constantly below 14 volts, you should have the system checked. If the
voltage ever goes above 15 volts, there is a problem with the voltage regulator. Have the
system checked as soon as possible as this "overcharging" condition can cause
damage to your electrical system.
If you think of
electricity as water, voltage is like water pressure, whereas amperage is like the volume
of water. If you increase pressure, then more water will flow through a given size pipe,
but if you increase the size of the pipe, more water will flow at a lower pressure. An
ammeter will read from a negative amperage when the battery is providing most of the
current thereby depleting itself, to a positive amperage if most of the current is coming
from the charging system. If the battery is fully charged and there is minimal electrical
demand, then the ammeter should read close to zero, but should always be on the positive
side of zero. It is normal for the ammeter to read a high positive amperage in order to
recharge the battery after starting, but it should taper off in a few minutes. If it
continues to read more than 10 or 20 amps even though the lights, wipers and other
electrical devices are turned off, you may have a weak battery and should have it checked.
There are a number of things that can go wrong with a
charging system:
Insufficient Charging Output If one of the three stator windings failed, the alternator
would still charge, but only at two thirds of its normal output.
Since an alternator is designed to handle all the power that is needed
under heavy load conditions, you may never know that there is a problem
with the unit. It might only become apparent on a dark, cold rainy
night when the lights, heater, windshield wipers and possible the seat
heaters and rear defroster are all on at once that you may notice the
lights start to dim as you slow down. If two sets of windings
failed, you will probably notice it a lot sooner
It is more common for one or more of the six diodes in
the rectifier to fail. If a diode burns out and opens one of the
circuits, you would see the same problem as if one of the windings had
failed. The alternator will run at a reduced output.
However, if one of the diodes were to short out and allow current to
pass in either direction, other problems will occur. A shorted
diode will allow AC current to pass through to the automobile's
electrical system which can cause problems with the computerized sensors and
processors. This condition can cause the car to act unpredictably and cause all kinds of
problems.
Too much voltage A voltage regulator is designed to limit the voltage output
of an alternator to 14.5 volts or less to protect the vehicle's
electrical system. If the regulator malfunctions and allows
uncontrolled voltage to be released, you will see bulbs and other
electrical components begin to fail. This is a dangerous and
potentially costly problem. Fortunately, this type of failure is
very rare. Most failures cause a reduction of voltage or amperage.
Noise Since the rotor is always spinning while the engine is
running, there needs to be bearings to support the shaft and allow it to
spin freely. If one of those bearings were to fail, you will hear
a grinding noise coming from the alternator. A mechanic's
stethoscope can be used to confirm which of the spinning components
driven by the serpentine belt is making the noise.
The most common repair is the replacement of the alternator
with a new or rebuilt one. A properly rebuilt alternator is as
good as a new alternator and can cost hundreds less than purchasing a
brand new one.
Labor time to replace an alternator is typically under
an hour unless your alternator is in a hard to access location.
Most alternators are easily accessible and visible on the top of the
engine.
Replacing an alternator is usually an easy task for a
backyard mechanic and rebuilt alternators are readily available for most
vehicles at the local auto parts store. The most important task
for the do-it-yourselfer is to be careful not to short anything out.
ALWAYS DISCONNECT THE BATTERY BEFORE REPLACING AN ALTERNATOR.
Alternators can be repaired by a knowledgeable
technician, but in most cases, it is not economical to do this.
Also, since the rest of the alternator is not touched, a repair job is
usually not guaranteed.
In some cases, if the problem is diagnosed as a bad
voltage regulator, the regulator can be replaced without springing for a
complete rebuild. The problem with this is that there will be an
extra labor charge for disassembling the alternator in order to get to
the internal regulator. That extra cost, along with the cost of
the replacement regulator, will bring the total cost close to the cost
of a complete (and guaranteed) rebuilt.
This is not the case when the regulator is not inside
the alternator. In those cases, the usual practice is to just
replace the part that is bad.
Notice: The information on this site is
not intended as a substitute for the advice of a professional who is
qualified to examine, diagnose and repair your vehicle.
A
Short Course on
The alternator is driven by a belt that
is powered by the rotation of the engine. This belt goes around a
pulley connected to the front of the engine's crankshaft and is usually
responsible for driving a number of other components including the water pump, power
steering pump and air conditioning compressor. On some engines, there
is more than one belt and the task of driving these components is
divided between them. These belts are usually referred to as:
Fan Belt, Alternator Belt, Drive Belt, Power Steering Belt, A/C Belt,
etc. More common on late model engines, one belt, called a
Serpentine Belt will snake around the front of the engine and drive all
the components by itself.
The alternator uses the principle of electromagnetism to
produce current. The way this works is simple. If
you take a strong magnet and pass it across a wire, that wire will generate a
small voltage. Take that same wire and loop it many times, than if
you pass the same magnet across the bundle of loops, you create a more
sizable voltage in that wire.
The rotor
contains the powerful magnet that passes close to the many wire loops
that make up the stator. The magnets in the rotor are actually electro magnets, not a permanent
magnets. This is done so that we can control how much voltage the
alternator produces by regulating the amount of current that creates the
magnetic field in the rotor. In this way, we can control the output of the
alternator to suit our needs, and protect
the circuits in the automobile from excessive voltage. 
There are 2 diodes for each of the three sets of
windings in the stator. The two diodes are facing in opposite
directions, one with its north pole facing the windings and the other
with its south pole facing the windings. This arrangement causes
the AC current coming out of the windings to be converted to DC current
before it leaves the alternator through the B terminal. Connected
to the B terminal of the alternator is a fairly heavy wire that runs
straight to the battery.
A modern
automobile has a 12 volt electrical system. A fully charged battery will read about 12.5
volts when the engine is not running. When the engine is running, the charging system
takes over so that the voltmeter will read 14 to 14.5 volts and should stay there unless
there is a heavy load on the electrical system such as wipers, lights, heater and rear
defogger all operating together while the engine is idling at which time the voltage may
drop. If the voltage drops below 12.5, it means that the battery is providing some of the
current. You may notice that your dash lights dim at this point. If this happens for an
extended period, the battery will run down and may not have enough of a charge to start
the car after shutting it off. This should never happen with a healthy charging system
because as soon as you step on the gas, the charging system will recharge the battery. If
the voltage is constantly below 14 volts, you should have the system checked. If the
voltage ever goes above 15 volts, there is a problem with the voltage regulator. Have the
system checked as soon as possible as this "overcharging" condition can cause
damage to your electrical system.
If you think of
electricity as water, voltage is like water pressure, whereas amperage is like the volume
of water. If you increase pressure, then more water will flow through a given size pipe,
but if you increase the size of the pipe, more water will flow at a lower pressure. An
ammeter will read from a negative amperage when the battery is providing most of the
current thereby depleting itself, to a positive amperage if most of the current is coming
from the charging system. If the battery is fully charged and there is minimal electrical
demand, then the ammeter should read close to zero, but should always be on the positive
side of zero. It is normal for the ammeter to read a high positive amperage in order to
recharge the battery after starting, but it should taper off in a few minutes. If it
continues to read more than 10 or 20 amps even though the lights, wipers and other
electrical devices are turned off, you may have a weak battery and should have it checked.