Detection
How do the block detectors know that a train is in the detec-
tion district? They sense current flow into the district. Okay, the
locomotive with a DCC decoder will always draw current, but
how do you draw current with the rest of the train? Resistor
wheel sets.
“Huh?”, I hear you say. A high value resistor (typically 5 to 40
kohms; 5 kohms = 5,000 ohms) is connected between the two
tires on a single axle. This allows any wheel on the train to
draw some current, keeping the detector satisfied after the
loco leaves the detection district.
These wheel sets are commercially available through compa-
nies like Jay Bee (2).
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3: Drawing to build your own resistor wheel sets – from
the BD-20 manual. Courtesy of NCE Corporation.
Some hardy souls seek to make their own version with surface-
mount resistors and conductive paint. There are instructions
(3) on how to do this in NCE’s manual for their BD-20 block
detector. You can download the manual from their website
. Personally,
I would buy the commercial version and save my time for more
interesting things to do on my layout.
Where to locate resistor wheel sets?
“Okay, these little wheel sets are pretty expensive. Do I need to put
one on every car?”, I hear you cry. The answer is a definite “maybe.”
Some things are for certain. Since you want the end of the train to
be known, then an unlighted caboose needs one – preferably on
the last axle. A lighted caboose will be detected.
If you model a newer era, you have lighted FREDs on the end of
your train, don’t you? If they are track-powered, they may make
sure that the end of the train is detected. One popular FRED is made
4: Ring Engineering FRED – photo courtesy Ring
Engineering.
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DCC Impulses - 4
MRH-Aug 2013
