Question: My mechanic says I have a bad voltage regulator,
and he has to replace my alternator. How come?
Answer: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 is replacement.
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 alternator.
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.
