DCC Impulses Column - 3
Advantages of bulbs
Bulbs are inexpensive
Bulbs operate instantly, allowing even fast systems like the
NCE PowerCab to be separated into sections.
Disadvantages of bulbs
Bulbs generate light (distracting) and heat (possibly a haz-
ard) when they are protecting a short.
Bulb protection draws the bulb’s rated current from the
DCC system during a short.
The spike of current (seen as a spark) when a short occurs
can pit wheels or whatever is causing the short.
When you have a bulb in series with a track section, the
track voltage will vary a bit, depending upon power being
consumed in the section. Two locos or a power hungry loco
may change speed upon entering the protected section.
3. PM42 4-section power manager from Digitrax. Digitrax,
Inc. photo.
3
When the NCE PowerCab (all-in-one DCC system) was being
developed, there was no electronic circuit breaker that would
react fast enough to keep the protection circuitry in the Pow-
erCab from tripping. In response to the desire by users to sep-
arate districts, NCE developed the CP6 [2]. This circuit board
holds six bulbs, allowing a PowerCab user to split his pike into
six sections. The user has a choice of (standard) 1-amp bulbs
or (optional) 1.75-amp bulbs. The PowerCab can only supply
about 1.75 amps. So, consider the standard 1-amp bulbs. If
a short occurs in one district, the remaining five continue to
operate, but only have about ¾ amp remaining available. If a
second district has a short, the combined two bulbs will try
to draw 2 amps from the PowerCab (plus any current being
drawn in the remaining four districts) and the PowerCab will
still shut down.
Co
MRH-Nov 2014
