Alternator Symbol
Definition: The Alternator symbol represents an electromechanical AC generator — most commonly the automotive charging alternator — in circuit and wiring diagrams, denoting a rotating machine that converts mechanical energy into alternating current subsequently rectified to DC for battery charging and vehicle load supply, shown with three functional pins: B+ (battery positive / DC output), F (field winding excitation control), and GND (ground), as drawn per ANSI Y32.2 / IEEE 315-1975 generator symbol conventions.
Also known as: alternator symbol, automotive alternator, car alternator, AC generator, charging generator, vehicle charging system, automotive ACG, lundell alternator.
What the Alternator symbol means
The Alternator symbol in an automotive or power-system wiring diagram marks the source of on-board electrical power generation. In a motor vehicle, the alternator is belt-driven by the engine and produces three-phase AC internally; a built-in rectifier bridge (typically six diodes) converts this to DC, which is regulated to 13.5–14.8V and supplied through the B+ terminal to charge the battery and power all vehicle electrical loads. The F (field) terminal connects to the voltage regulator, which controls the field winding excitation current to maintain constant output voltage regardless of engine speed or load.
In power-system diagrams the alternator symbol more broadly represents any synchronous AC generator — from automotive to large grid-connected machines. The symbol indicates that mechanical rotation is converted to electrical power, and the associated annotations identify the rated output voltage, current, and frequency. In automotive wiring diagrams, the GND terminal is connected to the vehicle chassis ground.
How to identify the Alternator symbol
The Alternator symbol is drawn as a circle enclosing a sine wave or the letter 'G' (for generator) or 'AC' to indicate AC output. Three terminals emerge: B+ (typically shown at the top or right, representing the DC output after internal rectification), F (field excitation terminal, often with an arrow or separate small circle), and GND (chassis ground). Automotive wiring diagrams often show the alternator with additional connections for the warning light (L terminal) and sense terminal (S or sense). In IEC-style power system diagrams, the alternator is represented as a circle with the synchronous machine symbol inside.
Function in a circuit
The alternator rotor carries a DC-excited field winding that creates a rotating magnetic field as the rotor spins. The three-phase stator windings cut through this rotating field, inducing three AC voltages displaced 120° apart. A six-diode full-wave rectifier bridge (three positive diodes and three negative diodes) converts the three-phase AC to ripple DC on the B+ output. The internal voltage regulator measures output voltage via the S (sense) or B+ terminal and adjusts the field current (on the F terminal) to maintain the target regulated voltage (typically 13.8–14.4V in automotive systems). Alternator output capacity is rated in amps at a specified speed (e.g., 120A at 6000 rpm).
Standards: IEC vs ANSI
| IEC 60617 | IEC 60617-06 defines the synchronous generator / alternator symbol as a circle with 'G~' or 'G' inside, where '~' indicates AC output. For three-phase machines, three stator winding connections emerge from the circle. IEC 60034 series governs the performance characteristics of rotating electrical machines. |
|---|---|
| ANSI/IEEE 315 | IEEE 315-1975 / ANSI Y32.2 defines the AC generator symbol as a circle with a sine wave symbol or 'AC GEN' inside. Automotive wiring diagrams in North America typically use the simplified circle-with-G symbol. The reference designator 'G' is used for generators and alternators. |
| Key difference | IEC uses 'G~' or 'G' with a tilde for AC generators; ANSI/IEEE uses a circle with a sine wave or 'AC GEN'. Both show the same circular glyph shape. In automotive wiring diagrams both conventions are simplified to a plain circle with terminal labels. |
Terminals / pins
| Pin | Name |
|---|---|
| bat | B+ |
| field | F |
| gnd | GND |
Typical values
Automotive alternators: 60–220A output, 13.5–14.8V regulated DC output (after rectification), 12V field excitation. Industrial AC generators: voltages from 120V to 13.8kV, frequencies 50Hz or 60Hz, ratings from 1kVA to hundreds of MVA. Typical automotive alternator efficiency: 55–65%. Rotor field current: 2–5A.
Where the Alternator symbol is used
- Automotive charging system wiring diagrams showing the alternator charging the battery and supplying the vehicle's electrical loads
- Marine wiring diagrams for engine-driven alternators charging the house bank and starter battery
- Recreational vehicle (RV) electrical system diagrams showing the engine alternator alongside solar and shore power charging sources
- Industrial standby generator schematics showing the AC generator connected to an automatic transfer switch
- Aircraft electrical system diagrams (engine-driven AC or DC generators)
- Power plant single-line diagrams showing large synchronous generators connected to transformers and the grid
- Hybrid and electric vehicle schematics showing the generator/motor integrated into the drivetrain
Example
In an automotive electrical system wiring diagram, the Alternator symbol connects B+ to the main positive battery cable (via a 100A fusible link), F to the voltage regulator (ECM or internal regulator), and GND to the engine block chassis ground; the alternator symbol and the battery symbol together form the core power source block of the vehicle electrical diagram, showing how the engine mechanically drives the charging system.
Key facts
- The Alternator symbol represents an AC generator that converts mechanical rotation to electrical power; in automotive applications the internal rectifier converts the AC output to regulated DC (13.5–14.8V) for battery charging.
- The three functional terminals on the automotive alternator symbol are B+ (battery/DC output), F (field winding excitation), and GND (chassis ground).
- The reference designator for a generator or alternator in IEEE 315-1975 / ANSI Y32.2 is 'G'.
- Automotive alternators use a Lundell (claw-pole) rotor design with a three-phase stator and a six-diode full-wave bridge rectifier integrated into the rear housing.
- The field current controlled through the F terminal regulates output voltage: higher field current produces more magnetic flux and raises output voltage; the regulator adjusts field current to maintain the set-point.
- The alternator symbol is drawn per IEC 60617-06 as a circle with 'G~' inside, or per ANSI Y32.2 / IEEE 315 as a circle with a sine wave, both indicating an AC source with the designator 'G'.
- Alternator output capacity is rated in amperes at a specific engine speed (e.g., 150A @ 6000 rpm); actual output falls significantly at idle speed (600–800 rpm engine = 1500–2000 rpm alternator).
Diagrams that use this symbol
- alternator connection diagram
- alternator diagram wiring
- car audio wiring diagram
- car stereo wiring diagram
- alternator circuit diagram
- alternator diagram
- car radio connection diagram
- car radio wiring diagram
Frequently asked questions
What does the alternator symbol mean in a wiring diagram?
The alternator symbol means an engine-driven AC generator is at that point in the circuit. In automotive wiring diagrams it represents the primary electrical power source that recharges the battery and powers all vehicle loads while the engine runs. The B+ terminal supplies regulated DC output (13.5–14.8V), the F terminal connects to the voltage regulator, and GND connects to the chassis.
What does the alternator symbol look like?
The alternator symbol is a circle containing a sine wave or the letter 'G' (IEC: 'G~'). Three terminals emerge: B+ (DC output), F (field excitation), and GND (ground). In IEC power system diagrams it is a circle labelled 'G~'; in automotive wiring diagrams it is often simplified to a circle with three labelled wire connections.
What is the difference between an alternator symbol and a DC generator symbol?
The alternator (AC generator) symbol shows a circle with a sine wave or '~' indicating AC output, with the reference designator 'G'. A DC generator symbol shows a circle with a straight line or 'DC GEN' inside, indicating direct current output. Automotive alternators produce AC internally but include a built-in rectifier, so they may be labelled with either convention depending on whether the symbol represents the internal AC machine or the external DC output.
What are the B+, F, and GND terminals on the alternator symbol?
B+ is the battery positive terminal — the main DC output after internal rectification, connected to the battery positive terminal via a high-current fusible link. F is the field terminal — carries the DC excitation current controlled by the voltage regulator to adjust the output voltage. GND is the chassis ground connection providing the return current path.
What standard defines the alternator symbol?
The alternator symbol is defined in IEC 60617-06 (power source symbols) as a circle with 'G~' for AC generator, and in ANSI Y32.2 / IEEE 315-1975 as a circle with a sine wave. The reference designator 'G' is used for all generator types. Performance standards for the machine itself are governed by IEC 60034 (rotating electrical machines).
Why does a car alternator output DC if it is called an AC generator?
An automotive alternator generates three-phase AC internally in its stator windings, but a built-in six-diode full-wave bridge rectifier (three positive and three negative diodes) converts the AC to DC at the B+ output terminal. The DC output is then regulated to 13.5–14.8V by the internal or external voltage regulator. The name 'alternator' refers to the internal AC generation principle, while the external electrical interface is DC.
How many pins does the alternator symbol have?
The basic alternator symbol has three pins: B+ (DC output to battery), F (field excitation input from regulator), and GND (chassis ground). Physical automotive alternators may have additional terminals: L (charge warning lamp), S (remote voltage sense), P (phase tap for tachometer), and IG (ignition enable), but the schematic symbol typically shows only the three functional signal connections.
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