Help understanding generators/alternators

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SUMMARY

This discussion clarifies the differences between DC generators and modern automotive alternators. DC generators were prevalent in vehicles until around 1970 due to the limitations of early rectifiers. Modern alternators utilize a DC-excited armature coil to generate a rotating magnetic field, producing a high-frequency AC output that is rectified to DC using solid-state diodes. This design significantly reduces voltage ripple compared to single-phase systems, enhancing battery charging efficiency.

PREREQUISITES
  • Understanding of DC generators and their historical context in automotive applications.
  • Knowledge of AC and DC electrical systems.
  • Familiarity with rectification processes and solid-state diodes.
  • Basic principles of electromagnetic fields and their applications in generators and alternators.
NEXT STEPS
  • Research the design and operation of modern automotive alternators.
  • Learn about the function and types of rectifiers used in electrical systems.
  • Explore the principles of voltage ripple and its impact on battery performance.
  • Investigate the materials used in the construction of stators and their significance in efficiency.
USEFUL FOR

Automotive engineers, electrical technicians, and anyone interested in the evolution of vehicle electrical systems and their efficiency improvements.

wall6ly
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Dumb question, inappropriate forum. Sorry
 
Last edited:
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This not an inappropriate question, and this is not an inappropriate forum.
Dc generators were used on cars up to about 1970, because the rectifiers for a high-current ac current (generated by an alternator) were not sufficiently compact or reliable. So the old generators had a stator excitation field coil, and the dc current output was taken off the armature via a commutator. These dc generators were often unable to produce a sufficient voltage and current at idle speeds to charge the battery.

In the modern automotive alternators, the armature coil is excited with a dc current via slip rings, producing a rotating dc multipole magnetic field. The alternator output is taken off the stator as a high frequency ac 3-phase current. Rectified 3-phase voltage has significantly less voltage ripple than recifiied single-phase voltage. Three pairs of rectifier solid-state diodes, usually inside the alternator case, convert the ac to dc. Because of the ac frequencies, the magnetic components (especially stator) have to be laminated.
Bob S
 
Last edited:

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