The "AC generator", developed by Chrysler for 1960, which they called an "alternator" is physically incapable of developing more current that it is designed to produce, therefore, it is self-regulating in that aspect. The previous DC generator design needs to have its maximum current regulated to what the brushes and wiring can handle. That is done with the relay in your first photo. That is identified by the really fat wire wound around the relay's core. All generator output current flows through that coil.
As long as current stays below the maximum allowed, the electromagnetic field created by that coil isn't strong enough to pull the movable contact down. When current rises too high, the magnetic field becomes strong enough to move that arm, then the contacts break apart to affect current flow. That relay is probably not going to trip very often.
A different relay inside the regulator is for voltage regulation. First you have to understand how all electrical power is generated mechanically. Three things are required. You must have a wire, a magnetic field, and most importantly, movement between the two. A coil of wire is more efficient. We use another coil to make an electromagnet. The movement comes from the belt and pulley.
The "field" coil is easy to control. It makes its strongest magnetic field with as little as four to five amps of current. One of the biggest drawbacks to DC generators is the high output current is taken from the armature which is the spinning coil of wire. On a good day, roughly 30 amps is all you can hope for, and that all has to burn its way through the brushes sliding on the commutator. Those wear out very quickly.
There's more to an alternator, but one of the biggest differences is output current is taken off the stationary "stator" coil, and the brushes only send current to the very low-current spinning field coil. At most, those brushes have to pass only three amps, so they last a really long time.
In both designs, output current is adjusted to meet the needs of the electrical system by adjusting the strength of the magnetic field. Besides developing the first AC generator, Chrysler also developed the first electronic voltage regulator for 1970. Before that, everyone used another relay inside the voltage regulator. This one actually had three states, although the middle one didn't enter into the picture very often. Before the engine was running, or at low speeds when generator output voltage was low, this relay was released and the movable contact was connected to the 12-volt source, usually a tap on the ignition switch. That provided maximum field current of perhaps four amps, and the generator charged wide-open. Output current was limited by the speed of movement between the two coils, meaning engine speed. As the engine speed increased, and / or demands on the electrical system deceased, system voltage increased. With more voltage across the relay, it finally reached the strength where it could pull the movable contact away from its mating stationary contact. In between them is a wire-wound resistor that limited current flow through the field coils inside the generator. With reduced current, it caused reduced magnetic field strength, and that reduced output current and voltage.
Over time, as the battery charged back up after cranking the engine, system voltage continued to rise, even though that resistor had been switched into the field circuit. This is when the relay gets strong enough to pull the movable contact all the way until it contacts the second stationary contact. That second one is connected to ground, so it shorts out the field coil. Now there is no electromagnetic field, and no output current being generated. System voltage is strictly a factor of battery voltage. Within a few seconds that voltage will be seen as less than specified, the voltage regulator relay will relax, and field current will start to flow again.
The point is there are only three states the voltage regulator can be in. It will cause the generator to develop maximum, partial, or no output current, depending on the needs of the system, and it can switch between them many times per second. This is where you'll see the voltage regulator relay vibrating while the engine is running. A common problem used to be flickering head light brightness. That was caused by pitted contacts on the voltage regulator relay. Sometimes the arcing resulted in a poor contact, so field current would stick at a reduced level, or not switch smoothly between states.
Often you'll find a third relay inside the voltage regulator assembly. Since the generator's output is connected right to the battery, there is a direct short to ground when the engine is not running. This third relay opens that circuit to prevent that drain on the battery.
Both the generator and the alternator develop alternating current. It has to be converted to direct current to be stored in the battery. In the generator, that is done with segments on the rotating commutator bars. The polarity of the output current switches at the same time the place it's taken off the armature switches position, so only a pulsing direct current is developed. In the alternator, there are no brushes or spinning coils of wire involved in the output current. Instead, the switching of the currents' direction is done with "diodes". Those are one-way valves for electrical current flow. Due to the way they are placed in the circuit, they are backward, or "reverse-biased", meaning turned off, when the engine is not running. That is what blocks current from draining from the battery. No other switching is needed.
Adjusting mechanical voltage regulators is slightly before my time. The instructions can be found in service manuals. Every relay has a spring that pulls the movable contact away from one of the stationary contacts. By bending the tab that spring is hooked to, you can adjust how strong the electromagnetic coil has to become before that movable contact switches position.
Monday, June 22nd, 2020 AT 7:44 PM
