REGULATOR, ALTERNATOR and BATTERY OPERATION
by Mark Hamilton
simple explanation is provided first, as not to leave out
readers who only want a sort of overall view of how a
system works, without getting too technical.
when explaining technical concepts, it’s good to use
parallel comparison with a more visible and simpler
working model. That
is why instructors and tutorial books often use
water-plumbing systems in attempt to explain various
electrical occurrences. (We cannot really see volts, and
amps, and ohms in wires.
We use meters and other equipment to check for
presence and levels of electricity, and to check up on
this author’s many years of experience while attempting
to explain functions of the alternator, voltage regulator,
battery, and electrical system power consumption; the
air compressor system has been the best parallel example
by far! That may be true because most people with at least limited
experience with cars will have worked around an air
possibly fewer people who work with cars will have
knowledge of hydraulic pressure differentials and pressure
loss with plumbing systems.
Once again, the air compressor system will be used
with attempt to explain this part of our auto electrical
(VOLT) is a measure of electrical pressure.
In the compressed air system, “PSI” (Pounds per
Square Inch) is the measure of pressure.
(AMP, or AMPERE) is a measure of electrical current flow. In the compressed air system cubic feet of air is the similar
measure of quantity.
is the measure of resistance to electrical current
flow–a resistance holds back the flow of electrical
the compressed air system, restriction, blockage, reduced
passage (metered orifice) are the terms most often used to
describe the same effect that resistance will have in an
COMPARISON (explanation of system functions)
battery is an electrical storage reservoir, similar in
function to the air tank for the compressed air system.
(Actually, the battery does not store electricity,
it would be more correct to say; “the
battery stores ingredients that can produce electricity.”) Both the battery and the air tank can store a source of
energy in reserve, keeping energy available for the times
we need it.
alternator produces electrical power, which can operate
devices that perform work for us.
And the compressor produces the compressed air,
which can be used as a source of power to operate tools or
voltage regulator limits the maximum voltage in the
electrical system. In
the compressed air system the pressure regulator limits
the maximum pressure.
The voltage regulator will also cause the
alternator to produce more output, when voltage (pressure)
at the electrical system is low.
And in the compressed air system, the pressure
switch will turn on the compressor when system pressure
ignition, and accessories use power from the electrical
time we switch an accessory ON, more power is drawn from
the system. Voltage
(electrical pressure) drops as power is drawn from the
system, and then the voltage regulator causes the
alternator to make more current.
And in the compressed air system an impact wrench,
blowgun, paint gun, or the fitting for filling a tire, can
all use power (compressed air) from the system.
When we use compressed air from the system, PSI
(air pressure) drops, and the regulator turns the
compressor ON. In
the electrical system, the voltage regulator “turns the
alternator ON,” or “turns OFF the alternator” as
needed to maintain voltage at the proper level.
And in the air compressor system the pressure
regulator stops and starts the compressor as needed to
maintain the proper level of pressure.
useful electrical system will require an alternator that
can produce an average
of more output than we use, and the regulator will limit
system voltage to the safe level we need.
Like most machinery, the alternator cannot stand to
work at maximum output for extended periods of time.
Short bursts at maximum output are okay, but normal
operation will require alternator operation at only a part
of full output potential, most of the time.
Alternators make heat as a by-product of making
electrical power, and the more power they supply the more
heat they make. Some models of alternators can stand to put out a much higher
percentage of their gross output rating than others,
during extended periods of operation.
compressors have “duty cycle” ratings.
The compressor also produces heat as a by-product,
and if it was called upon to run continuously while
maintaining high pressure, the compressor will burn out.
Some models of air compressors will have a greater
duty cycle than others.
Expect that a hobby shop model will not be intended
to run for the long time periods that a professional
workshop compressor is built for.
the electrical system needs more power than the alternator
can produce, for a short time, then the battery is already
connected to the system and the battery will contribute
the needed power. Entering
into this picture is that the alternator must spin at
sufficient RPM to produce power.
And there is an alternator power output/RPM curve,
where available output increases with RPM. There is also a minimum and maximum for practical alternator
RPM operating range.
Alternator RPM is somewhat adjustable by changing
the ratio of the drive pulley at the crankshaft and
alternator pulley diameters.
But since the engine will run slowly at times, and
rev very high at other times, there is no “perfect”
pulley drive ratio for all applications.
The pulley drive ratio is a compromise; and
what’s acceptable at maximum RPM is the deciding point.
(An alternator can be damaged with excessive RPM.)
A pulley ratio that is good with 6,500 to 8,000
engine RPM on a circle track is far from ideal with the
in-line six engine in “Grandma’s grocery getter.”
low RPM, expect that early models of alternators often
produced much less available output than more modern
with many models of old alternators, electrical output at
engine idle speed was not
sufficient to support electrical demands.
But when sitting at a stoplight, the battery could
assist the alternator with support of the electrical
then when the light turned green we drove away with the
engine spinning the alternator fast once again.
The alternator soon replaced power used from the
battery while sitting at the stop light, no harm done.
System voltage will be low, when the alternator is
not keeping up. (Voltage
will be above 14 when the alternator is working, and about
twelve and falling when supported by the battery.)
of old cars were accustomed to the lights dimming at idle,
or the turn signals blinking slower–it was simply the
result of low voltage when the alternator did not keep up.
The older cars could get by with less than perfect
with fewer electrical items to support, then the voltage
did not drop off so quickly.
The old cars also did not have electronics that
would cease to operate at low voltage.
With the duration of city traffic jams in modern
times, the many accessories on a modern car, and
electronics that are sensitive to low voltage, of course
alternator output at engine idle speed had to get better.
The newer designs of alternators can produce a lot
more current at low RPM, even when the gross output rating
is nearly the same with the old model.
parallel to the electrical system, with the air compressor
at marginal capacity, there will be times when system
pressure gets low. As
when friends come over to help with a project on the
weekend, all armed with air tools to operate from the
small compressor in the garage.
(And as with electrical systems, this didn’t
likely happen back in the 1960’s!)
The small compressor cannot support an air ratchet,
an impact wrench, a blowgun, and a grinder with a cut-off
wheel all at once. During those times the reservoir (tank) would have to supply
power (compressed air).
When average use is more than the amount produced
by the compressor, then system pressure falls low.
electrical system behaves about the same.
If the average output from the alternator does not
keep up with electrical system power use, then the battery
falls to discharged condition, and system voltage falls
below acceptable level.
The table below shows about what to expect with
differences in alternators that are only one generation
type externally regulated compared to ‘70s type
About the same test results have been observed on
many occasions, when doing alternator up-grades.
The same “stock” pulley drive ratio was with
both types of alternators. (1969–1972, small block 350
engine, stock pulleys)
to 2500 RPM
to 1325 RPM
more aspect of the comparison between the electrical
system and the compressed air system, and that is
“PRESSURE DROP” with long “lines” used for
delivery. In the electrical system long lengths of wire will have
resistance, amounting to a restriction of electrical power
flow. And the
farther down the wire we check voltage, the lower the
voltage (electrical pressure) will be.
Also, with increased current flow, the voltage drop
(pressure drop) will increase.
In example, if we attempt to operate a really
powerful electrical device such as a starter, through a
long, small diameter wire, then starter performance will
be poor. The
starter motor will attempt to draw a large amount of
current through the long, small gauge wire, and voltage
will be weak at the starter end of the wire.
In another example, if wires from a headlight
switch all the way out to the front of the car are thin in
gauge size diameter, then voltage to the lights will be
low resulting with dim lights.
same can happen with compressed air systems.
In younger years, there were occasions where
working with air tools at low pressure was a constant
an old building, with a large compressor at the far end of
a long building. Back
in the 1940’s compressed air was mainly used to air-up
tires, but not to provide service for busy mechanics
wielding air ratchets and impact wrenches.
The building was equipped with very old, small
diameter steel tubing for the compressed air service.
In that facility, the mechanic farthest away from
the compressor did not receive air at full pressure.
If an air ratchet or tool requiring a large volume
of air was used, then the tool was down on power.
Larger diameter tubing would have really improved
performance of the air tools. Especially so when other mechanics closer to the compressor
were using air before it gets to the end of the line.
situation with the long, small diameter tubing, for
compressed air, had the same effect as with a long small
wire used to operate many powerful accessories. The accessory farthest down the wire will receive power at
low voltage (pressure) level.
Larger wire diameter will improve performance by
delivering power at higher voltage (pressure.)
Or… Use a system design providing a shorter
length wire, which also will improve performance.
now for those who enjoy the technical aspects of how
things work, here is a more detailed explanation of system
operation with the
VOLTAGE REGULATOR and BATTERY.
alternator will generate power to operate the electrical
system plus keep the battery charged.
The purpose of the voltage regulator is to regulate
the amount of power output from the alternator.
(Of course! What
else do regulators do? Ha!)
The voltage regulator will allow the alternator to
make enough power to maintain proper voltage level, but
not allow system voltage to rise to a harmful level.
regulators for the alternator system, voltage limiting is
the means of controlling output.
(The older “generator” systems had a voltage
limiter and also a current limiter, plus a “cut-out
relay” that disconnected the system when the engine
the alternator was allowed to constantly produce all the
power it could, system voltage would rise to a damaging
level, the battery would overcharge, components would be
damaged, and the alternator would soon overheat and burn
a 100amp alternator installed, we do not drive around with
the alternator constantly producing 100amps.
When driving a simple car, in example a ’66
Chevelle, with no accessories switched on, stock ignition,
and the battery topped off with a charge, the alternator
produces only about 3amps to 5amps of current!
(No matter how powerful the alternator, output is
limited according to system demands.)
in case you are wondering, the amount of horsepower
used to spin the alternator changes with output.
When the alternators produce only a small amount of
current, the horsepower drag is very small (less than 1/3
amount of output causes more horsepower drag (about 3 or 4
horsepower to produce 120amps output).
textbooks tell us the ideal voltage regulator setting is
14.2 volts. A
range of about 14.0 to 14.6 volts is generally acceptable,
and various shop manuals will typically publish about that
system voltage is below the setting of the voltage
regulator, then the regulator causes the alternator to
produce power until voltage reaches the maximum setting of
the regulator. When
we first crank up the engine, battery voltage will be at
about 12.5 or 12.6 volts.
The regulator recognizes low voltage, and causes
the alternator to produce power.
Also when driving, every time we switch an
accessory ON, power is used from the system, voltage is
lowered, and the regulator restores voltage by causing the
alternator to make more power.
This action automatically allows the alternator to
provide power for the electrical system.
system does not need as much power output from the
alternator when accessories are not using power, and when
the battery is fully charged.
When voltage at the system rises to about 14.2
volts, the voltage regulator begins limiting alternator
we switch an accessory OFF, use of power from the system
is less, voltage quickly rises, and then the regulator
will cause the alternator to make less power.
of alternator output, by the voltage regulator, happens so
quickly that when using a meter to test the system, we see
function as smooth and constant. Even the old points type mechanical regulators could open and
close the points over 200 times per second!
Electronic voltage regulators have replaced the old
vibrating point type regulator, and electronic regulators
react even faster. With
a modern electronic voltage regulator, voltage at the
system will be very consistent.
battery serves as a big cushion in the system,
which also smoothes out voltage level.
The battery will provide momentary surges of power,
which are needed when devices are switched ON.
The battery also can absorb momentary excess of
power in the system as devices are switched OFF.
The battery prevents major and sudden voltage
changes in the system.
METHOD USED TO ADJUST ALTERNATOR OUTPUT
voltage regulator adjusts alternator output by controlling
the amount of power it will send to the magnetic field
winding in the alternator.
(Alternators work through the use of magnets.) More power delivered to the magnetic field winding in the
alternator will produce a stronger magnetic field, which
causes the alternator to produce more power output.
Alternator output is reduced when the voltage
regulator delivers less power to the magnetic field
winding in the alternator, as the strength of the magnetic
field will be reduced.
14.2VOLTS, BUT WE CALL IT A “12 VOLT SYSTEM?
14.2volt level is said to be the ideal voltage level for
the “12volt automotive system” because that’s the
amount required to fully charge a standard
By itself, without a battery charger, and without
cables connected, a typical, fully charged “12volt”
battery produces 12.6 volts.
The on board charging system must exceed the 12.6
level for electrical current to flow through the battery
during charging. Electrical
current must flow through the battery during charging to
cause chemical reaction between the liquid acid and the
lead plates within the battery.
The 14.2volt level causes about the correct amount
of current flow through the battery to maintain a fully
charged condition. Extended
periods with higher than 14.2volt level will over-charge
the battery (at most temperatures).
and Operating Functions
interacts with the charging system.)
and negative metal plates within the battery, each made of
and with insulators between the plates.
Liquid acid within the battery (sulfuric acid) is
in contact with the plates, and the acid will chemically
react with material at the plates to produce electrical
the battery is called upon to produce power, as with
engine starting, the chemical reaction activity is greatly
the battery is stored, very little chemical reaction takes
place, however the elements are waiting in reserve and
available for use at any time.
battery must produce current for engine starting, and the
battery may also be called upon to supply power at times
when the alternator cannot keep up with electrical system
power use. When
we connect an electrical device to the battery, chemical
reaction takes place to deliver electrical power.
Throughout these periods when the battery must
supply electrical power, the battery is being discharged.
discharge of the battery, chemical reaction will produce
electrical power. And the chemical reaction between the acid and the plates
will convert material at the surface of the plates to a
new compound. And
as the chemical reaction changes the composition of
materials in the battery during discharge, material at the
positive and negative plates will eventually become the
sufficient material at the plates has been converted to
the same material at the positive and negative plates, the
assembly can no longer produce adequate power.
Then the battery is considered discharged.
reaction “takes apart” existing material, and
reassembles the original ingredients to form a new
The basic “ingredients” will all still be in
the new material, but after the chemical reaction has
taken place, the new material will be a different
compound. (It happens with manufacturing of plastics and polymers and
many things that we use and enjoy.)
applying energy to the new material, at least some
chemical reactions can be reversed, and the new material
will be converted back to its original form. This reverse
operation is exactly what happens when “recharging” a
battery. When recharging a battery, we apply electrical current
(energy), in reverse direction, which will cause the
chemical reaction needed to change materials in the
battery back to their original form. (Back to different materials at the positive and negative
recharge, chemical reaction changes compounds at the
positive and negative metal plates back to their original
current will flow through the metal plates in reverse
direction during charging, which causes a reverse chemical
reaction (compared to discharge).
When the battery becomes “charged,” the
compounds at the positive and negative plates in the
battery will once again be different.
With material at the plates restored back to
original compounds, the battery is again able to deliver
recharge the battery, we apply electrical power to the
amount of activity with chemical reaction during battery
charging will change according to the amount of electrical
current flow through the battery.
With voltage at proper level, the battery will only
accept the amount of current required for reasonable
activity with the chemical reaction.
little current flow will not cause enough activity with
the chemical reaction to completely charge the battery.
We need sufficient activity with the chemical
reaction to change the compounds at the plates back to
their original material.
Lack of sufficient activity with the chemical
reaction resulting from too little current flow may be
termed as an “under-charge” condition.
speed of activity with the chemical reaction during
recharge is of great concern!
The amount of activity is controlled by the amount
of current flow during recharge.
current flow during battery charging may be termed an
“over-charge” condition–the excessive current flow
causes too much activity with the chemical reaction.
The amount of activity with the chemical reaction
must be precisely controlled, and the perfect charge rate
is a thin line. It’s
a situation where too much charge rate is damaging, but
with not enough current flow the battery performance will
turns out that during charging, the amount of current flow
through the battery can be adjusted by regulating the
level of voltage as electrical power is applied to the
electrical current is supplied to the battery at proper
voltage level, the battery only accepts the amount of
current flow it wants.
And it’s current flow during charging that will
adjust the rate of chemical reaction activity within the
operation is summed up as “charge rate.”
In summary of charge rate,
voltage level will adjust the amount of current flow, and
the amount of current flow will affect the rate of the
chemical reaction. And
so with the alternator system serving as the onboard
battery charger, the regulator will control voltage, and
the rest will follow.
all quite simple, however,
the ideal amount of charge rate will change with
conditions. (There is always something to complicate matters!
Battery state-of-charge condition, temperature, and
the duration of the charge (either long drives or short
drives), are all factors that will determine the ideal
charge rate. The
discharged battery does not produce as much voltage as the
fully charged battery.
When charging a “low” battery, the discharged
battery will accept a large amount of current flow, if
power is delivered at the full 14.2volt level.
Ideally, the voltage level would be slightly
reduced when a battery is accepting peak amount of current
during recharge. Current flow would then be optimized, which will cause the
correct rate of chemical reaction.
Then charge rate could remain optimized if voltage
could be slightly increased as the battery regains charge.
Eventually voltage must be limited as the battery
becomes fully charged, and then very little current flow
through the battery is required.
primary conditions are short drives in extreme cold
weather, the charge rate should be increased.
Internal resistance at the battery will change with
extreme cold. This
and other effects of the cold will contribute to slower
charge rates in cold temperatures.
Short drives with a slow charge rate may not allow
the battery to reach a fully charged condition in extreme
ideal voltage regulator setting should be slightly higher
for this type of usage.
author has lived in cold climates, and also where it is
hot much of the year. The hot weather is hard on batteries! In the hot climates, batteries typically have a much shorter
expect to find more corrosion at the battery area with hot
weather conditions (because the warm battery “accepts”
current at a higher charge rate).
voltage level must be precisely controlled during charging
to prevent excessive current flow.
Excessive current flow can damage the battery.
Excessive current flow is less efficient because
compounds at the surface of the plates will not have time
to disperse. Also
excessive amount of corrosive and very explosive gas will
be produced with over-charge rates.
And excessive charge rate heats the battery, which
changes internal resistance of the battery.
with “sealed batteries,”
over charging will destroy usefulness of the battery!
H2O (water) is one of the compounds
formed with the chemical reaction during battery charging.
Many of the so-called “sealed” batteries are
actually vented to surrounding atmosphere,
at least one very popular model of battery has a
pressure relief valve for venting.
The valve allows this popular model of battery to
be mounted in various positions.
However, these battery are “sealed” with regard
to access for adding water.
When these “sealed” batteries are charged at a
high rate, water and vapors will escape from the vents.
And we do not have opportunity to add more water to
this type of battery, when the liquid level becomes low.
we allow high rate charging, the “sealed” battery can
loose liquid that we cannot replace!
when charging these “sealed batteries with pressure
relief valve” at a rate high enough to cause the valve
to release; expect severe corrosion problems at the
battery area resulting from corrosive liquid and vapors
that will spew from the relief.
Unfortunately, the author has seen a few cars where
this unpleasant experience has occurred. (Every case was with expensive, high end, occasionally driven
cars. And in
every case the car was also equipped with a high output
“ONE-WIRE” alternator, which was connected directly to
the battery with a heavy cable.)
important of all, when a battery reaches fully charged
condition, then voltage must be precisely controlled, as
forcing a charge by allowing voltage to rise above ideal
level will result with all the previous mentioned
problems. (That applies to all batteries.)
And with extended periods of driving, all of the
previous mentioned problems will happen for longer time
vapors emitted from the battery during charging settle
upon everything near the battery, resulting with severe
corrosion at the battery area.
I hate when that happens with a nice Hot Rod! Ha!)
causes short battery life, and poor performance from the
charging the chemical reaction cleans the surface of the
lead plates within the battery. But insufficient charge rate (undercharging) allows a crust
of lead sulfate compound to accumulate on the surface of
the plates. (This
happens even more so when storing batteries in a
The crust will block access of the acid to the
active materials in the lead plates, and the crust also
changes internal resistance at the battery.
With too much crust build up the battery will no
longer be serviceable.
a thin line between not enough voltage at under charge and
too much voltage at overcharge.
And ideal voltage level is different with various
good voltage regulator is a precisely operating piece of
the author prefers and uses exclusively genuine Delco
voltage regulators. The
genuine item is more costly than some others, but it has a
lot more electronics within.
The Delco regulator is temperature compensating, it
does an excellent job of trimming off charge rate, it has
built-in back-up circuits, and voltage limiting is
last longer, and expect less corrosion problems when using
the Delco regulators.)
ELECTRICAL PARTS ARE ACTUALLY 14VOLT PARTS!
most applications, the battery likes about 14.2 volts from
the alternator and voltage regulator system, when driving.
Since the system must operate at about 14volts, electrical
parts are designed for best performance and longest life
when operating at about 14 volts.
The parts can generally withstand 15volts (or
more), although sometimes parts run hot or don’t last as
long at stress level voltages.
we always aim for the best, we are always likely to loose
at least a small amount of voltage with long wiring
really puts the hurt on performance is low voltage.
It turns out that with voltage about 10% low,
performance may be down by over 30%.
Electric motors, lights, ignition coils, and
various parts will all behave differently, but it’s
great when we connect the voltmeter with the part
powered-up and running, and find about 14volts at the
drop at wiring will only occur during current flow,
therefore testing must be done with the part connected,
powered-up, and operating.
In example, unplugging a wire connector at a part,
and then reading voltage at the wire harness connector is
not a valid test of circuit performance.
voltage test while a system is operating is the industry
standard electrical performance test.
It’s also very simple to do an approximate
performance comparison of parts running at low voltage to
parts running at full voltage, using only an ordinary car.
In darkness, with the engine running and headlights
ON, switch the ignition OFF while the headlights are left
that the lights dim considerably when the engine stops, as
the alternator will also be stopped and voltage drops
about 10%. Or
with radiator fans running, switch the ignition OFF and
notice the fans slow down.
significance of engine running and engine stopped, is that
when the engine is running the alternator will have
opportunity to maintain the system at about 14.2volts.
But with the engine stopped the battery will
deliver power at about 12volts.
This simple comparison with engine running and
engine stopped serves to give us a general feel for the
loss of performance we can expect with parts operating at
slightly low voltage.
In general, voltage drop at the wiring, with
delivery of power to parts, is the enemy to overcome.
WRENCH IN THE WORKS!
It all seems so simple just to use a quality
voltage regulator built by a major company that has the
overall picture all “scienced out.”
And install an alternator with more than enough
power rating to handle all the electrical loads on the
car. But in
the world of automotive wiring, voltage drop resulting
from long lengths of wire often prevents delivering power
at full voltage level to all parts of the system.
And especially with our older cars, as with
favorites from the Muscle Car period, voltage
drop in wiring is a lot worse than most people would guess. The problem often exists with design of the system, not with
age and deterioration of the wiring.
It happened when these cars were new, and it
happens when a new factory harness with the same original
design is installed.
So if voltage throughout the system is not the same
at all points, then we have a major problem with attempt
to use the voltage regulator to optimize performance!
The voltage drop only occurs with current flow.
Large amounts of current flow through a wire will
result with large amounts of voltage drop.
If current flow through a wire is reduced, then
resulting voltage drop will also be reduced.
we wire the voltage regulator to read and make adjustments
to the lowest part of the system, then the highest part of
the system might be dangerously high.
It would be safer and in better judgment to wire
the voltage regulator to the highest part of the system,
but then low voltage will cause poor performance at some
systems, and the battery might not even charge properly.
The best option will be to work with design
of the wiring layout, when making improvements to
(The “improvements” include more powerful
alternators, and modern accessories to make good use of
the electrical power.)
THE BEST PLAN
best plan for most systems is to route alternator power
output to a central power distribution hub.
Then send power from the hub to various parts of
the electrical system, and wire the voltage
regulator to maintain voltage at the main distribution hub.
The idea is very good, but cannot be claimed by the
author as an “original.”
It happens that Chevy did a very good example of
this design with ‘63 through ’71 models.
And the Chevy engineers did it well!
It’s also a system that we must be aware of when
installing more powerful alternators and when installing
wiring to power-up new accessories.
more about this design and function in our Tech Section
feature on “REMOTE VOLTAGE SENSING,” and also in our
feature on “THE CHEVY MAIN ELECTRICAL POWER DISTRIBUTION
Also see more about how severe voltage drop
actually is with original wiring in our feature on