ALTERNATOR, VOLTAGE REGULATOR and BATTERY.

The 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.

With 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 stopped.) If 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 out.

With 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.)

And, 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 amp). Large amount of output causes more horsepower drag (about 3 or 4 horsepower to produce 120amps output).

REGULATOR ACTIONS

Popular 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 range.

When 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.

The 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 output. When 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.

Adjustment 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.

The 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.

THE METHOD USED TO ADJUST ALTERNATOR OUTPUT

The 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.

WHY 14.2VOLTS, BUT WE CALL IT A “12 VOLT SYSTEM?

The 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 “twelve-volt” battery. 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).

VOLTAGE REGULATOR LIMITING

Most 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 duration. Corrosive vapors emitted from the battery during charging settle upon everything near the battery, resulting with severe corrosion at the battery area. (And I hate when that happens with a nice Hot Rod! Ha!)

Undercharge causes short battery life, and poor performance from the battery. During 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 discharged condition.) 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.

It’s a thin line between not enough voltage at under charge and too much voltage at overcharge. And ideal voltage level is different with various conditions. A good voltage regulator is a precisely operating piece of equipment! (And 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 precise. Batteries last longer, and expect less corrosion problems when using the Delco regulators.)

“12VOLT ELECTRICAL PARTS ARE ACTUALLY 14VOLT PARTS!

With 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.

PERFORMANCE

Although we always aim for the best, we are always likely to loose at least a small amount of voltage with long wiring circuits. What 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 part.

Voltage 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.

The 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 ON. Notice 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.

The 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.

THE 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.

If 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 electrical systems! (The “improvements” include more powerful alternators, and modern accessories to make good use of the electrical power.)

THE BEST PLAN

The 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.

See 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 SYSTEM.” Also see more about how severe voltage drop actually is with original wiring in our feature on “BRIGHTER HEADLIGHTS.”

In a nutshell, the alternator must charge above 12.6 volts to force the plates inside the battery to desulfate, thus restoring the acid's chemical and the plates' physical properties. And to supply the electrical needs of the vehicle. All this just to repeat the process of starting up your vehicle again.
So if the alternator is working properly, measuring voltage should and will suffice to test its performance. My rule of thumb has been that a steady 13 ( to 14.5) volts is an indication that Amperage is present to meet the electrical loads of the vehicle. Since one does not exist without the other. You can think of it this way: Voltage is the force or pressure behind the ‘flow’ (amperage) and that without this force or pressure (voltage) there wouldn't be any flow.
Put this test to practice, It works! Y'all come back, now...