Build Manual: Module Wiring Standards

Part two of the Build Manual preview covers wiring standards for Modutrak modules. Once again, please feel free to ask questions and help tailor this for eventual coverage in the Build Manual.

 

The wiring standards for Modutrak need to cover two main goals:
1) Easily run lots of trains with little effort at public shows.
2) Allow operating sessions when the layout is set up in private.

DCC is a must for both functions, and we're currently using Digitrax equipment for throttles and DCC command stations and boosters.

From the on-set, we've also been planning to have a fully functional signal system on the layout. An ABS system is the easiest, because unlike a CTC or other centralized system, wires do not have to run back to a central location. As you'll see in the wiring standards below, the signals on any given module only talk to their neighbors via two wires on a Cat5 cable. Otherwise, all detection and signal logic is contained within the module. This also allows us to rearrange the order of the modules without any programming of the signal system.

 

The corner module shown above just has two mainlines and no turnouts or block signals on it. With one track feeder for each rail, this is the most simple wiring example. On the module you can see the standard Modutrak bus wiring at the bottom (back or operator side) of the module. Four bus wires are then broken out into a Cinch terminal strip. Feeders then come off the terminal strip and feed the rails on top of the module.

The terminal strip has been a handy addition for trouble shooting and allows individual wires to be disconnected from the main bus without disconnection the whole module.

 

Here is an example of a more complex module, the Lakefront Depot, with Tortoise switch machines and related controls wired in place. This is an example of a module without any signaling installed.

Notice that wiring is run cleanly to each location. An extra foot of wiring is better than running a rats nest, so make 90 degree turns and bundle wires running to adjacent locations.

Again the bus is at the back side of the module, or top in this photo, and wires are broken out at a terminal strip. Then all the module wiring feeds into the terminal strip as well, utilizing a sub-bus to gather like feeder wires within the module. In other words, the 24ga feeders are collected on a sub-bus of 18ga wiring and then the 18ga feeds into the terminal strip.

 

These are some of the items that help keep the wiring clean. The Paduit cable tie mounts accept a #6 wood screw and allow wires to be bundled and strapped in place with standard 4" wire ties. The Cinch terminal blocks come in a number of terminal configurations down to 4 pairs for a basic module up to 14 pairs for a module with turnouts and signal control that need many wires broken out from the bus.

 

The main bus has 12 wires and utilizes Molex .093" 12-pin connectors. The housings and pins are shown at the left. Be sure to crimp and solder the pins before pressing them into the housing. We don't count on the crimp alone.

Wire is readily available in 10 colors. In order to get to 12, and in order to keep track of the three wires needed for each mainline (more information about this below) white and yellow heat shrink are used to mark a tracer on the detected mainline bus for each mainline. A short 1/8" piece is all that's needed to mark the end of the wire where it terminates.

Actual tracer wire is available, for example blue wire with a continuous white tracer, but it is very expensive through all sources we've found. The heat shrink color coding is cheap and effective.

Also, the Molex housings have the pin numbers molded into them if you get confused as to which side of the connector the diagram shows. Use those numbers.

And finally, Black pin 12 is a common ground for both the +12v (red) and +5v (gray) wires.

 

Back in my N-trak days I saw too many dangling cinch jones connectors get ripped off modules, or crushed during transport, because the long tails weren't secured up under the module during transport. In most cases the extra tails were just sort of wound around bus wires under the module, and could work loose and hang down.

In order to avoid this, we keep the connectors tight up under the modules, and keep the tails separate. These one foot long jumpers are used to plug in between modules during set-up. During tear down, they are all tossed in a bag from dangle-free transport to the next show.

 

Let's review a few diagrams in order to help explain the wiring convention on Modutrak. The main bus wiring is at the bottom of this diagram of the underside of the module. In order to help illustrate the feeder colors for each rail, those colors carry through in the diagram. A ghosted series of ties indicate which are rails versus feeder wires.

The terminal block we saw in the photos above is shown coming off the bus. Then the module wiring itself is broken out.

Main 1, or the blue main, is on the public (or shorter scenery side) of the module. Main 2, or the orange main, is on the operator (or wide scenery) side. The rail that is detected for signals is toward the public side on both mains, while the common rail is toward the operator side.

Cat5 cable is placed opposite the main bus wiring and covers Digitrax LocoNet and two wires for yellow signaling. More on that later.

Also shown on this diagram is the +12v (red) and ground (black) which powers the Tortoise switch machine.

 

I briefly mentioned that we need three wires per mainline. But why do we need three when there are only two rails to power? The answer lies in the breakdown of blocks for the detectors. Current detectors, such as the Bruce Chubb DCCOD that we use, need to have all power wires fed through the transformer on the detector. In order to accomplish this, we have both a detected and non-detected blue wire for Mainline 1. The non-detected bus wire (blue) is continuous around the layout. The detected bus wire (blue with white tracer) is split at signal blocks.

By doing this, the detectors can detect multiple modules worth of track without each module needing it's own detector. In other words, the insulated gaps in the track don't coincide with module joints. There might be basic modules with scenery only between two junctions, but those modules just tie into the detectors on either side of them in the layout.

It probably goes without saying, but that third wire is the common rail wire (white) and is also unbroken around the layout.

 

Main 2 is set up the same way, just with different colors. In this case the detected bus wire is orange with a yellow tracer.

 

Ok, so we have the three wires per mainline, and the mainline tracks are fed through detectors to drive the signals. But now what do we do about sidings? We certainly don't want a train parked at the coal dealer to cause the signals for that block to display red!

Easy enough, just wire the non-detected siding from the non-detected (blue or orange) wire depending on the main line that the siding comes off of! The break between detected and non-detected in this case should be at the fouling point of the siding.

 

Let's talk about Tortoise wiring for a bit. This is your friendly Tortoise switch machine motor. It has 8 traces at the bottom covering 2 power wires, and 2 sets of 3 contacts. We can use the contacts for powering a frog and for some signal control logic in special cases.

 

First lets wire up the control circuit to power the Tortoise and allow it to throw back and forth. Step one is to feed power to both pins 1 and 8, but do so through two 2.2K Ohm resistors. These are easy to remember as the color stripes should be red-red-red.

 

We use RCA jacks as push button control without the push button. The "push button" portion is simply a shorted out RCA plug, which provides a ground path through either the red or the white socket on the RCA jack panel. Red corresponds to a reverse throw on the turnout. White to a normal position.

The ground wire (black) is fed to both RCA jacks, and then one wire from each jack is fed to pin 1 and 8 as shown above. The Tortoise will throw toward the grounded pin, so consider this when wiring the RCA jack to correspond to the proper Tortoise throw.

In essence we're feeding resistored power to pins 1 and 8 at all times, and by grounding either pin, we allow the Tortoise to throw in one direction. This works based on the proper resistor value matching the motor resistance.

 

As everyone knows, the frog on a turnout needs to change polarity based on the direction the turnout is thrown. In the case shown above, a turnout on the blue main needs it's frog to change polarity from blue to white.

In order to accomplish this with one set of contacts on the Tortoise switch machine, first wire the frog feeder to one of the middle pins on the Tortoise. Use green wire for this, because frogs are green.

 

Then, hook up the blue and white wires to the corresponding pins for the frog contact.

I can never remember which contacts are which compared to the throw of the Tortoise, so I keep a disassembled Tortoise around so I can look at the inner circuit board when I'm wiring up the frog connections. You can also pull one apart and snap a photo.

 

Now we can start thinking about signals. Previously we looked at the mainline wiring with the detectors in place to detect current in a signal block. The current sensing detectors with detect anything from a locomotive, to a passenger car with lighting, to a single metal wheelset equipped with a 10k resistor. The latter work well for equipping freight cars and cabooses that don't generally draw current. One 10k resistor equipped wheelset at the extreme ends of each car is ideal, as a stranded car on the mainline will trip a red signal. Safety First!

 

So, if we put a train in the block farthest to the right, as shown above, then we want the signal entering that block to display a red indication when the corresponding detector detects. The block just prior should show a yellow, or approach, indication. And the third block down can display a clear green.

This is basic ABS signal logic. The signals are not being used to direct traffic, as a dispatcher on CTC controlled territory might do. Rather, the signals are just an extra layer of protection to keep trains spaced on the mainline. The permission to be on the main is governed by other paperwork.

 

So in order to make the signals work, the detector sensing the train need to talk to two signals through signal logic boards. These boards, as we'll explore later, accept a stop or approach indication from the detector boards. So the immediate signal at the detector is wired to a stop indication causing a red signal. But then we also need to run a wire back a block to cause the prior signal to display approach, yellow, as shown above.

 

Now that we understand the basics of what we're trying to accomplish with ABS signalling, lets take a look at the wiring and circuits involved with a simple intermediate block signal on a simple straight module.

The first thing we need to do is to gap the front (public or short side) rail on both mainlines in the location of the block signal installation. Remember that the common rail can remain un-gapped.