en.wikipedia.org/wiki/Magneto
1 correction found
Dynamos and alternators require a source of power to drive their field coils.
This is too broad: permanent-magnet alternators do not use field coils, so they need no separate power source for field excitation.
Full reasoning
The sentence is incorrect as written because it treats all dynamos and alternators as machines with powered field coils.
Authoritative sources describe a major class of alternators/generators whose magnetic field is provided by permanent magnets instead of field windings:
- NREL explains that in a synchronous generator, the rotor's magnetic field "may be supplied either from permanent magnets or from direct current flowing in a wound field."
- Britannica likewise states that permanent-magnet generators "require no system for the provision of field current."
So the blanket claim that dynamos and alternators require a source of power to drive their field coils is false. That statement is only true for wound-field machines, not for permanent-magnet generators/alternators.
2 sources
- The History and State of the Art of Variable-Speed Wind Turbine Technology
A synchronous machine usually consists of a stator holding a set of three-phase windings ... and a rotor that provides a source of magnetic field. This may be supplied either from permanent magnets or from direct current flowing in a wound field.
- Electric generator - Permanent Magnet, Alternating Current, Direct Current | Britannica
Permanent-magnet generators are simple in that they require no system for the provision of field current.