60 Collectable Model Trains: Motor Design: The Can motor in operation
Description
This article is from the Model Trains FAQ, by Christopher D Coleman with numerous contributions by others.
60 Collectable Model Trains: Motor Design: The Can motor in operation
"Can" style motors are used in N, HO, G and some Lionel offerings use
a permanent magnet instead of an electric field coil. When DC is
applied, the current in the armature runs one way and the permanent
magnet substitutes for the field with current running one way. It
pushes the motor in a particular direction.
If the terminals of a can motor are reversed, only the armature is
reversed (remember the field never changes). The armature has changed
RELATIVE to the field so the motor direction reverses.
Now, if AC is applied, the field of the permanent magnet does not
change direction when the armature does. The RELATIVE directions
change with the AC. The motor tries to change direction 60 times a
second causing it to just shake violently.
Below is a table which tries to graphically show the different
behavior of these types of motors under AC and DC. 1 is a magnetic
field in one direction and 2 is in the opposite direction. When they
point in the same direction the motor will spin one way and the
opposite way for opposing fields (here I arbitrarily chose the
directions of rotation as clockwise CW and counter-clockwise CCW).
ELECTRIC FIELD COIL reverse motor leads
(universal) |
time (sec) 1/60 2/60 3/60 4/60 5/60...| 1/60 2/60 3/60 4/60
5/60...
DC supply |
field 1 1 1 1 1 | 2 2 2 2
2
armature 1 1 1 1 1 | 2 2 2 2
2
result CW CW CW CW CW | CW CW CW CW
CW
|
AC supply |
field 1 2 1 2 1 | 2 1 2 1
2
armature 1 2 1 2 1 | 2 1 2 1
2
result CW CW CW CW CW | CW CW CW CW
CW
|
PERMANENT MAGNET FIELD (can) |
DC supply |
field 1 1 1 1 1 | 1 1 1 1
1
armature 1 1 1 1 1 | 2 2 2 2
2
result CW CW CW CW CW | CCW CCW CCW CCW
CCW
|
AC supply |
field 1 1 1 1 1 | 1 1 1 1
1
armature 1 2 1 2 1 | 2 1 2 1
2
result CW CCW CW CCW CW | CCW CW CCW CW
CCW
DC can motors can be used with AC if it is converted into DC through a
rectifier or other means. This is done with many new offerings from
Lionel and MTH. However, this requires a slightly different type of
sequencer.
The cheapest Lionel offerings are equipped with non-rectified can
motors without sequencers. These are provided with DC power packs and
require a polarity change from the power pack to reverse, as in HO, N
and G scale. They are incompatable with the rest of the AC powered
line. (you get what you pay for)
Conversely, you can run universal motor equipped locomotives on DC.
However, since whistle, horn and bell activation relies on DC
signaling (except the TrainMaster System), DC power cannot be used on
a locomotive so equipped.
Also, smaller size can motors require less current to run and hence
smaller transformers. I have several HO transformers I use to run
lights and most do not generate enough current to run tinplate trains
with universal motors. The current limitation of DC power packs has
traditionally been linked to the inability to rectify large amounts of
AC house current to DC. Also, can motors have traditionally not been
as powerful as universal motors and only in the past 10 years have
they been considered to have enough power per size to use in the
better Lionel offerings.
As a result of all this, AC power and universal motors have been the
system of choice from the 1890's through the 1990's. Still today, many
of the best units have universal motors, albeit with five poles rather
than three.
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