An Alternator is a generator that produces alternating current (AC) by converting mechanical energy to electrical energy. The Process of rectifying the AC current into DC current is handled by diodes inside the alternator.

Alternators are generally simpler, more reliable, and can be more efficient than direct current generators. Alternators generate electricity by the same principle as DC generators. When magnetic field lines cut across a conductor, a current is induced in the conductor. Just like Generators, Alternators are used in automobiles to charge the battery and to power all the electrical systems when its engine is running. In the early 1960’s GM dumped their old generator system in favor of an alternator. The little 10DN alternator was much more compact than the old generator and used a small regulator that mounted to the firewall or one of the fenders. This early type of GM alternator was rated at around 61 AMPS and referred to as externally regulated.

By 1969 GM introduced the Delco 10-SI Delcotron alternator with its internal regulator on the Corvette and started offering it as an option on certain models. Within a few years the 10-SI was standard equipment on all GM cars and trucks and it too would eventually evolve into newer models.

The SI series alternators are typically found on cars of the 1970s and early 1980s and usually have a single grove pulley.

3-Wire vs. 1-Wire Alternators

Among the GM SI series alternators, there is both the 1-wire and 3-wire type with built in regulators.

For most applications, the advantages of a 3-wire alternator will far surpass a 1-wire installation. Both types have an internal regulator but it’s surprising how much stronger HEI ignition systems work at 14 volts compared to 11 or 12 volts. The same is true with a Vintage Air system, headlights and electric fans etc.

The 1-wire alternator only has a heavy gauge wire connected from the alternator output terminal to the battery. The one big advantage is that not much knowledge is needed to wire it into an electrical system. These alternators have been widely used on marine, agricultural and industrial applications such as boats, tractors and forklifts. They are best suited for applications that need the alternator for charging a battery only. The main difference between the 1-wire and 3-wire alternator is in the internal voltage regulator.

The voltage regulator for the 1-wire alternator is often referred to as self-exciting. After the engine has been started, and the alternator is spinning a small amount of current is developed to turn “on” the regulator. Sometimes the engine has to be revved up once or twice to excite the regulator.

Other advantages of a 3-wire alternator are, you can operate a warning or Idiot Lights on the dash, 3-wire alternator regulators use remote voltage sensing, availability is much better, and they cost less.

1957 Chevrolet 2 Door and 4 Door Hard Tops

I do not recommend using a 1-wire alternator on your 1957 Chevrolet or any classic 1950s or 1960s GM automobiles you may be converting from a generator to an alternator. When most if not all the factory wiring can be used in your generator to alternator conversion, why not use a 3-wire alternator. Even an intended up-grade to a 100 amp 1-wire alternator can result in dim lights, weak ignition and weak performance, all due to a lack of Remote Voltage Sensing.

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