Co
If you want to use bulbs on your layout, consider these selec-
tion criteria:
The bulb must be rated for the track voltage of the DCC system.
Automotive systems are called 12 volt, but they actually push
15 volts with modern alternators. So automotive bulbs are
good for all but the highest voltage DCC systems (such as 20+
volt garden layouts).
The bulb current rating must be a fraction of the maximum
current the DCC system will supply. I recommend the bulbs
be rated at less than half the DCC system’s capabilities. That
way, two districts shorted at the same time may not take
down the system.
Given all of the above, I would stick with 1¾ amp automotive
bulbs on 5-amp rated DCC systems running track voltages up to
16 volts.
Relays
Some of the earliest circuit breakers were current sensors that
drove relays to interrupt the current flow to the track. The
sensing circuitry was pretty rudimentary on some versions,
resulting in some rather spectacular sparks and the resulting
wheel pitting.
The Digitrax PM42 four-section circuit breaker or auto-reverser
[3] was one of the first electronic units to achieve wide usage.
As low-on-resistance transistors have become more available
and less expensive, the relay-style circuit breakers have tended
to fade away. Given today’s technology, I would eschew relay
breakers on a new layout and suggest upgrading to fully elec-
tronic units on older layouts.
MRH-Nov 2014
