58 Collectable Model Trains: Motor Design: Is my tinplate train motor AC or DC?
Description
This article is from the Model Trains FAQ, by Christopher D Coleman with numerous contributions by others.
58 Collectable Model Trains: Motor Design: Is my tinplate train motor AC or DC?
What follows is a technical description of the situation in as much
layman's terms as possible and still be accurate. There are three
basic types of electric machines in use today:
DC MACHINES: These have a non-moving field coil on the stator and a
moving armature on the rotor. It uses a commutator, which is a
segmented plate which constantly redirects the current direction in
the armature. This change in current causes a change in a magnetic
field so that it keeps pushing against the field produced by the field
coil. The more current, the more field, the more push, the faster the
motor goes and no matter how fast it goes the commutator keeps the
fields opposing each other, thus the variable speed.
SYNCHRONOUS AC MACHINES: These have a non-moving armature on the
stator and a moving field coil on the rotor. Since the field is
constant, it has a solid slip ring instead of a commutator and relies
on the change in the AC voltage supplied to it's stator to create the
changing field and hence the motion in the machine. Because of this IT
CAN TURN AT ONLY ONE SPEED at a given AC frequency for which it has
been designed, usually a factor of 60, the frequency of standard AC
current. (frequency can be varied by specialized electronics)
INDUCTION AC MACHINES: These are a variation on synchronous machines
that rely on induction to supply current to the rotor field from the
stator armature (slip rings are then not needed), but are otherwise
pretty similar.
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