DCC IMPULSES |
3
the loop, the polarity must change to match the outgoing track.
This is handled in different ways, depending upon what power
source is being used.
With O-27, Marklin, and other 3-rail models, reversing sections
do not present an electrical complication. The outside rails are
always at the same polarity, so it doesn’t matter that they reverse.
However, with 2-rail DC or DCC, precautions must be taken
when the track work physically reverses a loco or train. Unless
the polarity of the loop reverses while the train is inside it, the
train won’t exit. Instead, it will short out the power being sup-
plied to it, as the leading wheels cross the interface.
In the DC world, folks frequently had a DPDT toggle switch that
reversed the power between the power-pack and the loop. In
operation, the operator would
stop the train in the loop.
Then the operator would use
the toggle switch to reverse
the polarity of the track and
then reverse the polarity of
the power pack that was feed-
ing the track. When the volt-
age was increased, the train
would continue in the same
direction as it had been going
before the stop.
The fact that DC has polar-
ity is pretty obvious -- that’s
how the trains know which
ADVERT I SEMENT
