45. MRH13-11-Nov2013-L - page 87

DCC Short detection - 4
6: At this point we discover that the short circuit current
is flowing in the branch feeder. Even in cramped spaces,
it is easy to follow the short circuit current without
disconnecting any wiring.
Wire a #1156 lamp in series with each booster output wire to
limit current and prevent the booster from tripping while testing
a short circuit. Wire a DPDT switch to switch from normal opera-
tion to the #1156 lamps for testing when a short circuit occurs.
Use a clamp-on ammeter to detect current flowing in one track
bus or feeder wire to isolate a short circuit.
Items required for this project:
Digital Clamp Meter. Harbor Freight Item 96308 or similar.
DPDT switch with a current rating sufficient to carry your booster's
2 each #1156 or #1157 automotive tail lamps. Solder one wire to
the brass lamp housing and the other wire to the tip. Be careful to
not stress the tip connection.
I suggest using short (4"-6") lengths of fine stranded #18 wire for
minimum strain and best results. You might want to make some sort
of mounting bracket by drilling 1" holes for the lamps, and a smaller
hole to fit your switch. Mount the lamps in the holes using silicon
caulk to hold them in place.
Dick Bronson has been modeling in HO
since the 1950's. His first layout was
three pieces of fiber tie flex track and
two cars on a leftover piece of plywood.
Dick is a life member of the NMRA and
has presented clinics (Signaling with
JMRI) at several national conventions
as well as other venues.
Work on his current layout, the Little
Mountain & Possum Hollow RR
slowed considerably when he and his
wife Karen moved their company RR-
CirKits, Inc.
from part-
time to full-time status.
It is much easier to track down elusive short circuits now that
we can 'see' the current flowing in a wire using the magic of a
clamp-on ammeter. Be sure to get a meter that has a 0.01A or
less minimum current reading so that you can read small varia-
tions in current as you track down your gremlins.
MRH-Nov 2013
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