Connecting DCC easily, to an existing layout in less than ½ hour.
Introduction There is no reason why modelers
with established small/medium sized layouts, that are operating on DC, but
would like to have all the extra features that DCC brings, especially the
flexibility and sound, cannot have this on their layouts without doing any
wiring changes. I have done this setup, not including adding a decoder to the
loco, in less than ½ hour. I maintain that any layout that runs ok on DC will
run ok on DCC with no modifications if you understand the limitations as set
out below. DCC lends itself by nature, to walk around layouts but there is no
reason that it cannot be used on basic oval design with a few sidings or end to
end shunting (switching) layouts, in fact in yards, is where DCC truly shines,
no isolating switches for block control.
There has been a lot said about DCC
to confuse a lot of people including me. I don’t care much about DCC packets
and how the system works internally, I accept it. (unusual for me, on any
account). I just want to run my layout more like the prototype and have sound
from my locomotives as I follow them around my layout. Note: Sound has to be at
the minimum volume level so everyone can enjoy operating trains.
DCC Background A DCC
system can output between 1.0 and up to 10 Amps, depending on which system you
have chosen. The reason that all DCC books say that wiring has to be of the
highest quality with the correct wire gauge depending on length of the power
bus, is that the booster provides the current for all the locos running on the
layout and must cut out quickly, due to the higher currents available with DCC,
when you have a short anywhere on the
layout which could be an operator running against an incorrectly
selected point.
The fact that booster must be able
to sense this short anywhere is why the wiring has to be thicker and depending
how big the layout is, determines the size (gauge). This booster cut out has to
happen quickly, so this makes DCC systems much more sensitive than DC.
A short of 5 amps at 14 volts is 70
watts, and this is the equivalent heat of large soldering iron and this could
cause some damage. For this reason the booster cuts out in a very short time.
In comparison a short in DC of 1 ½ amps at 14 volts is 21 watts (a very small
iron). This explains why operators have problems with points when having
converted to DCC. The problem was there with DC but did not show up due to the
fact that in DC, there was no fast acting circuit breakers and in DCC the
booster has the fast acting circuit breaker, typically 100 – 200 msecs,
therefore cutting of the power to layout and the fact that it takes 1 – 2
seconds to recover, this makes it a problem in DCC (whole layout power
interruption).
This makes DCC much more sensitive
than DC and this is why shorts are to be avoided in DCC. When operating in this manner it become very
annoying if you have a few operators or sound locos.
The complete shutdown of DCC system
can be avoided by using Electronic Circuit Breakers external to the booster,
but the trip current must be set lower than the booster’s trip current and
wiring the layout in separate power zones. More on this in a later topic.
One way to reduce layout shutdown
or zone shutdown is to reduce the number of shorts and these mainly happen at
points. Some of the shorts can be eliminated by checking that all wheel sets
are correctly gauged and the misalignment that happens at a lot a points, is
corrected by slight alignment repairs. Some modellers have modified their
points to be ”DCC friendly” by powering the closure rails the same polarity at
its adjacent stock rail at all times and powering the frog by auxiliary
contacts of point motors or similar manually operated switches connected to the
operating bar of the points.
On my code 100 layout, I have used
approximately 100 Peco points, mainly “Electrofrogs” and have not modified any
yet. I will only modify if and when they cause a problem. I could not stand the
thought of removing all the points and modifying them. I will wait and see, and
I suggest you do this also. Different if building a layout from scratch. I have
been operating DCC for over 3 years now.
On DC, these problems did not show
up because power was not removed because of a minor short due slow acting
breakers, and the loco just continued on due to its inertia, just slowed a
little and if no more short, continued on as if nothing happened. Obviously if
short was major the train would stop, due breaker tripping.
One of the misconceptions about DCC
is that when you have a short you can somehow damage the decoder. This is not
the case, nothing happens to the decoder, the short is a problem at the wheels,
before the decoder gets involved and all that happens to the decoder, is that
the power supplying the decoder is no longer available. After a decoder is
installed and programmed and loco runs, if a decoder fails it is because of an
internal failure or an external short on the function outputs or the motor
circuit.
In my easy hookup of DCC to
existing layout, I prevent the booster from cutting out, by using a 12V 21W
automotive lamp (use 1156s for slightly higher 2.1 amp current) to restrict
current. This reduction of current will allow us to operate on a layout whose
wiring is not up to the standard of “normal” DCC layouts. You will not have to
convert or modify points or wiring. Later on you will see that I can operate 10
or more locos on one booster even with sound by adding more light globes to
make power zones. You have to appreciate the limitations and work within the
lamp limitations, certainly not hard if your layout has 2 or 3 operators. It’s
all about power zones and light globes.
I strongly recommend wiring in an ammeter that is also shown in the second diagram to
monitor the layout’s current draw. This completely removes any doubt about how
many locos can be run of one booster and you will be surprised how little
current is drawn. Forget about the 1.0 amp per loco, if operating locos of the
last 15 or so years. Each loco’s current draw is in the range of 200 to 400 mAs
and this includes sound units. I have 12 sound locos on my layout, some double
headed, obviously not all running together, and I don’t have any problems using
the 1156 lamps for power division.
Easy hook up of DCC system using the existing transformer.
Transformer To setup DCC system quickly, you
can use existing transformer so long as it’s A.C. no load output
voltage is no greater than DCC system requirements and it can supply 1- 11/2
amps. If the transformer does not deliver enough current, this will effect how
many locomotives you can operate at one time. Using existing transformer, you must
use a 12V21W lamp in series and strategically placed as I have done
in a “local” line side building, will give a VERY bright visual warning, in one
of the track feeders. The lamp provides protection, because the booster will
not trip off when you have a short.
Connecting DCC System to
existing layout is really easy with no layout wiring changes now, if you add an automotive
stop lamp 12V 21W in series with one
lead from system to track. Remove existing throttle/s from control
panel, set cab switches, if any to removed cab selection (1, 2 etc) and connect
DCC system to control panel wiring where
previous DC throttle connected to, with the series 12V 21W lamp. This is
imperative for layout wiring protection. Make sure booster warning lights are
not flashing and 12V21W lamp is not illuminated. If all is ok, place your DCC
decoder equipped locomotive on the track and you are you are ready to run.
Select loco address and operate.
Walk around Operation If this
feature is available on your system, add a cab bus to layout so that you can
follow your loco around by plugging into appropriate plugs. See system manual
for details and do later after getting running.
Importance of 12V 21W Lamp (layout
protection) This is the “secret”. The cold resistance of the
tungsten filament is much less than when it is hot thus this works in our favour here
because as the more load current flows through lamp, it’s resistance does not
increase proportionally, so this allow us to run more locos until a certain
point, then it will start to illuminate. You can check what happens by checking
voltage at track as lamps gets brighter. The lamp reduces the operating current of
about 1.0 amp until the lamp starts to impact on the track voltage. With a
short there will be a 1.7 Amp current flowing that will not cause any problems
even with poorer wiring, if lot left too long unattended. Another reason to
locate the lamp at a very visual location, at operator eye level and not under
the layout.
The number of locos that can be run
at one time will depend on what type of motors in locos and if sound is fitted
to any locos. With later can motor equipped locos without sound, you will be
able to run about 4 or 5 locos without seeing and major drop off in performance
including a couple of 48s double headed. It is safe for now and you will see
the DCC results with it setup this way. Use an ammeter to monitor this.
With the 12V21W lamp, the booster
will never cut out. If poor
loco running, check for voltage drops at tracks. Check wiring. I actually use
12V21W lamps on my layout for power zones. That is layout is divided into power
zones like mainline, yard 1, yard 2 and so on with a lamp providing power zone
protection to each power zone. This is useful when having a few operators and
running more locos but all locos have to be spread across all power zones, not
in one zone. With a short, in say yard 1, the booster is capable of providing
current up to 5 amps and with this scenario, it is providing 11/2 amps to short
and what ever locos are using in other zones say 1 amp, this makes a total of
21/2 amps and with the output voltage still at 12 - 14 volts. This current is
well below limit of booster and this is why locos in yard 2 and mainline are
working as normal. You can use Electronic circuit breakers to replace lamps and
there is no voltage drop to track but power bus wiring must be adequate.
Operators in the US with large
layouts are using 12V21W or similar lamps at every loop and point for short
protection so as not to cause the booster to cut out, therefore shutting down
that area so they have acknowledged the problems of DCC and now are operating
the same way I have with a variation, but the lamp is the secret, so use it
correctly and it will hide a lot of DCC problems that were hidden in DC
layouts, nothing new, but a different way of doing things to make it all
easier.
Using meters The DCC voltage that is on the
track is approx 14 volts square wave A.C and to measure use a digital
multimeter set on A.C. volts, but slightly lower, less than 10%,adequate for
troubleshooting voltage drops in wiring and making comparative readings. To
measure current, you can make an ammeter by inserting a Bridge rectifier in one
track feeder as per last diagram. Note: There will be a 1.5 volts drop across
rectifier. Use switch to bypass ammeter if you have low volts at track, only
use for testing. A DCC digital meter can
be purchased from the
5 EASY STEPS to connect to Existing
Layout are:
1. Connect existing transformer to
DCC system so long as no load voltage is OK. Refer system manual.
2. Remove existing cab/throttle
and set all cab switches to removed cab/throttle number.
3. Connect DCC system in SERIES
with 12V21W lamp to the previous throttle connections.
4. Ensure warning lights on system
are not flashing and 12V21W lamp is NOT illuminated.
5. Convert large diesel to DCC and
operate. Now you’re into DCC.
Upgrade to full DCC operations with
Booster cutting out When you
have a few DCC converted locos running and you are enjoying DCC operation, you
will now have to determine how you are going to operate in the future. You will
have to buy a larger transformer greater than 5 amps output at 16 – 18 volts,
if you are going to operate more than say 3 or 4 locos at the same time (a few
operators) or you are going to use Electronic Circuit breakers or utilize the
DCC system cutout protection, but to do this you MUST have adequate wiring,
12-14 gauge. Don’t use the 12V21W lamp.
The layout will have to pass the
“quarter” test on every bit of track, that is when track anywhere is shorted
with a coin or screwdriver the system “cuts out” immediately. This can be the
booster or if Electronic Circuit breakers fitted, then these must cut out. When
you operate without the 12V21W lamp, you may find when you run across points
and crossings you may get shorts and this will shut down system or trip circuit
breakers and you will have to wait 2-3 seconds for system to reset. To reduce
this problem you will have to make your offending points, DCC Friendly.
I have been operating for over 2
years, progressively converting 22 locos (11 sound) with 12V21W lamps with 8
power zones and all the above works for me. I have not modified any of my 100
plus Peco points. You must understand limitations. I can operate with 4-5
operators, each with a throttle and really enjoy operating the layout with all
the DCC advantages, so can you.
I have fitted to my club layout
that has 29 modules, a 12 volt lamp to each module and now we never have a
complete layout shutdown that was ever so frequent before, we are all humans
and make the occasional mistake. At the club we operate with 6 to 10 operators
with up to 12 locos (some double headed) and some sound units and are still
using one 5A booster, no problems yet.
Now you have DCC connected to
layout and running a few locos, you probably will be busy converting most of
you locos, but this will take time. Convert your popular locos first, and
possibly consider sound.
Your first impression of sound may
be negative because you saw it on a large layout with the volume too loud. I
hate it when someone operates like that. I operate sound to just a level loud
enough that you would not hear it from 20 feet. It is only for the loco that
you are operating that give the loco a “sound identity” and not to annoy other
operators or onlookers. Once you have used sound this way you will be
impressed. I am mentioning this here because if you put a Soundtraxx DSD100LC
into a 45 or 421 etc, this is quite easy. I have put sound into 48s.
Don’t buy all decoders at once,
they are always improving with more features and getting smaller and cheaper.
Easy hookup of DCC system with DCC/DC changeover switch, Ammeter circuit
and Program Switch wiring.
With above diagram with a little more time, you will have a connection
that gives you a DCC/DC changeover switch so you can enjoy both types of locos
till you are a converted DCC modeller and have a facility to operate visitor’s
DC locos easily. The Program Track is controlled by a changeover switch.