| When You Find
Your Vehicle Does Not Charge Properly
You need to check if your battery is dead,
or keeps running down or cranks your engine slowly.
If this is the case, you may have a charging problem.
Likewise, if the alternator or battery warning light
is on, or the amp or voltage gauge is reading low, that
too probably indicates a charging problem.
One quick way to check the charging system
is to start the car and turn on the headlights. If the
headlights are dim, it indicates the lights are running
off the battery and that little or no juice is being
produced by the alternator. If the lights get brighter
as you rev the engine, it means the alternator is producing
some current but may not be producing enough at idle
to keep the battery properly charged. If the lights
have normal brightness and don't change intensity as
the engine is revved, your charging system is functioning
You can also check the charging system
by connecting the leads of a voltmeter to the battery.
When the engine starts, the charging voltage should
jump to about 14.5 or higher. If the reading doesn't
change or rises less than a volt, you have a charging
problem that will require further diagnosis.
Alternators are pretty rugged, but can
succumb to excessive heat and overwork. They can also
be damaged by sudden voltage overloads (as when someone
attempts to jump start a dead battery and crosses up
the jumper connections or if someone disconnects a battery
cable from the battery while the engine is running).
Sometimes alternators can partially fail.
In the back of every alternator is a "diode trio"
that converts the alternators AC (alternating current)
output to DC (direct current). If one or more of these
diodes fail, the alternator's amperage output will be
reduced. It may continue to produce some current, but
not enough to keep the battery fully charged -- especially
at idle or low speed.
Most service facilities have test equipment
that can identify these kind of problems. So if you
suspect a weak alternator, you should have it tested
to see if it needs replacing.
Most service facilities do not repair
or rebuild alternators because it's too time consuming
and requires special parts. Most will replace your old
unit with a new or remanufactured unit. Your old alternator
is usually traded in or exchanged for a credit (so it
can be remanufactured and sold to someone else).
CAUTION: If you're replacing an
alternator yourself, always disconnect the battery before
unhooking the wiring on the alternator. This step will
eliminate the possibility of accidentally shorting out
a hot ware and damaging something or starting a fire.
The alternator drive belt should be inspected
at this time, and replaced if it is cracked, oil soaked,
glazed, badly worn or otherwise damaged. The belt should
be adjusted for proper tension following the vehicle
manufacturer's guidelines. Too much tension can overload
the alternator's bearings and shorten the unit's life
(as well as belt life), while too little tension may
allow the belt to slip.
For detailed instructions on installing
an alternator, see
When You Have A Bad
The voltage regulator controls or regulates
the alternator's output. Think of it as the brains of
the charging system. It senses how much voltage is needed
by your vehicle, then modifies the field current within
the alternator so it puts out just the right amount
of current. Too little current can allow the battery
to run down while too much can damage it and other electrical
and electronic components. When the regulator fails,
the charging system usually ceases to function -- except
in cases where the nature of the failure causes the
alternator to run wild and overcharge the battery. In
any event, the only cure for a dead or defective regulator
In older vehicles, the regulator was a
separate component usually mounted somewhere in the
engine compartment. If this type of regulator failed,
it could be easily replaced in a matter of minutes with
a new one. But for the last decade or more, most regulators
have been mounted in or on the alternator itself. This
was done by the vehicle manufacturers to simplify wiring
and assembly. It was also made possible by advances
in electronics that allowed the regulator to be reduced
in size to a small chip.
Charging systems that have a separate
regulator mounted away from the alternator are referred
to as "externally regulated" charging systems
while those that have the regulator in or on the alternator
are called "internally regulated" charging
systems. On some vehicles there is no regulator at all!
Voltage regulation is controlled by the engine computer.
Unfortunately, internally regulated alternators
are packaged as a unit -- which means that if either
component fails (alternator or regulator) both must
be replaced. This is because internal regulators are
not available separately (at least not to the general
public or the typical service facility). Electrical
shops and remanufacturers who rebuild alternators can
get them and can replace the regulator separately if
that's all that's wrong with the unit -- but they'll
usually charge you the same as if you bought a rebuilt
The truth is, the high cost of labor today
has made it impractical for most service facilities
to fool around trying to rebuild or repair components
like alternators, starters, carburetors, front-wheel
driveshafts, transmissions and even engines. It's faster,
easier and usually cheaper to simply replace the old
unit with a new or remanufactured one than to try to
overhaul or fix it. Besides, most new and remanufactured
parts come with a guarantee.
(Source: Larry Carley and Automotive
Information Center. )