2G Alternator Exploded
This type produces ~60~100A, and was typically used on early fuel-injected engines from the mid-80s to the early 90s. The 2G is famous for catching fire, usually due to the poor design of the 3-pin connector at the rectifier. The result of these fires was the development of a new Electrical Grease (not to be confused with Dielectric Grease). The greatest value of a 2G is as scrap metal.
All are wired similarly to this:
An alternator (generator) receives mechanical energy from the crankshaft through the belt (FEAD) and converts it to electrical energy, which is used to supply the vehicle's demands and charge the battery. To begin, the alternator must be supplied with electricity to generate the electromagnetic field within the Rotor windings. This is the main distinction between an alternator and a dynamo (which has permanent magnets & needs no electricity to begin working). An alternator might consume ~13A to produce 130A (net) output.
The case of the alternator must provide a solid ground to the voltage regulator & the stator, so its mounting points must be clean, and the engine block must be well-grounded to the battery (-) post.
The voltage regulator
Motorcraft GR821 detects the key on through the I (Indicator) terminal, and uses battery power from the A terminal (via the brushes, & the slip rings) to produce a magnetic field within the Rotor's Field windings.
The strength of this field is determined by the voltage regulator, based on the voltage between the A terminal and the alternator's case, which must be grounded to the battery (-) post to provide an accurate reading. The regulator controls output voltage by varying the ground signal applied to the F brush. Externally grounding this brush forces the alternator to its maximum output at that RPM (typically near 18V).
The pulley transfers mechanical energy from the belt to the Rotor's shaft (supported by 2 bearings), which causes the magnetic field to rotate through the Stator's 3 windings. This moving magnetic field induces an alternating current within the Stator windings, proportional to the strength of the field.
The Stator's alternating current passes through the Rectifier which lowers the voltage slightly and converts the AC to rough DC. The output is smoothed primarily by the battery (which is why a battery MUST be connected when the engine is running), and also by a capacitor (condenser) within the rectifier.
One of the Stator's windings is connected to the S terminal so the voltage regulator can monitor the alternator output. Voltage on this circuit is roughly 1/2 battery voltage.
The fan pulls hot air out of the case, causing cooler air to flow into the rear. The rear case & stator can be rotated (clocked) to 3 positions relative to the front case to orient the connectors for ease of installation.
Most failure modes result in the voltage regulator grounding the I terminal, which illuminates the ALT bulb in the dash. To maintain normal operation in the event of bulb failure (open I circuit), a 300 Ohm resistor must be wired in parallel with the bulb (typically a common 194).
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