Z Module Wiring

Overview

The wiring standard for modules has been around for a while, basically you feed the tracks from one end of the module to the other end. Since the wiring is separate for the 2 sets of main lines, you have 2 connectors at  each end of a module. Eventually a "chain" of modules is terminated with a "end module". This makes a large connected loop.

From a reliability standpoint, and really a power distribution standpoint, this is pretty weak. It works beause of the low current needed, but in larger layouts voltage drop will become significant.

One thing that is definitely lacking is isolation of power districts and using circuit breakers for them. One short anywhere can cause everything to stop.

The official Z-bend wiring standard is here: http://www.zbendtrack.com/Z-Bend_Track_Manual_2004.pdf

The standard uses DB 25 connectors (the original computer RS-232 "serial port")

• Pins 1-3 and 4-6 are used for the outer track feed
• Pins 8-10 and 11-13 are used for the inner track feed
• Pins 14-16 are + 12 v accessory and Pins 17-19 are the - 12v
• Pins 20 and 21 are reserved for the pushbutton power shutdown feature
• Pins 22 - 25 are for "user" defined operation.

So we have 4 pins to "play" with, or 6 if you give up the shutdown feature. More ideas about the "future" later.

Electrically connecting modules:

This connector has 25 pin

The standard calls for a DB25 connector, used on old serial ports on computers, two rows of pins, pins 1-13 on the "wider" row, and pins 14-25 on the narrower row:

If you are looking at the back side of a DB25 male: (you can see the gold pins), the pins are laid out thus:

13 ......   1  (wider)

25....14

If you are looking at the back side of a DB 25 female connector (you see holes, not pins), the pins are laid out thus:

1... 13  (wider)

14 ... 25

 Notice that virtually all DB25 connectors have the pin numbers molded in (very small)

Power is distributed thus:

• outer track + pins 1-3,
• outer track - pins 4-6
• inner track + pins 8-10
• inner track - pins 11-13
• 12v + pins 14-16 (intended as power bus)
• 12v - pins 17-19

Additional pin designations:

• emergency shutdown 20-21
• user defined 22-25

 By convention:

• The outer track pairs have a red piece of heat shrink on them, and red is the outer rail
• The inner track pairs have a black piece of heat shrink on them, a

The standard calls for a DB25 connector, used on old serial ports on computers, two rows of pins, pins 1-13 on the "wider" row, and pins 14-25 on the narrower row:

If you are looking at the back side of a DB25 male: (you can see the gold pins), the pins are laid out thus:

13 ......   1  (wider)

25....14

If you are looking at the back side of a DB 25 female connector (you see holes, not pins), the pins are laid out thus:

1... 13  (wider)

14 ... 25

 Notice that virtually all DB25 connectors have the pin numbers molded in (very small)

Power is distributed thus:

• outer track + pins 1-3,
• outer track - pins 4-6
• inner track + pins 8-10
• inner track - pins 11-13
• 12v + pins 14-16 (intended as power bus)
• 12v - pins 17-19

Additional pin designations:

• emergency shutdown 20-21
• user defined 22-25

 By convention:

• The outer track pairs have a red piece of heat shrink on them, and red is the outer rail
• The inner track pairs have a black piece of heat shrink on them, and red is the outer rail

Tips on making the DB-25 wiring harnesses

I normally use 16 or 18 gauge wire. The standard seems to embrace 18 gauge wire, but in larger modules, like the ZoCal-built yard module, which is 19 feet long and 28 tracks across, 16 might be a better choice.

One way to make harnesses is to just use the wire to bridge the 2 pins as seen below:

This is actually a bit hard to do, to get all 3 connections nicely done at the same time. Another way to do this, is to separate the stranded wire into 3 bundles. Twist and thin them and then bend the wires into 3 parallel groups, spacing them to match the 3 pins. This is very nice and looks much better, also the wires actually have a better connection, actually fitting into the "solder cups" on the pins, not just lying on top.

Another thing to watch for is shorting between the groups of wires. Notice how easy it would be to short between the 2 rows of pins:

Don Fedur came up with the idea of making a small insulator of styrene that fits between the rows, so shorting is impossible. (NEVER underestimate the crazy things people will do when setting up modules at a show).

Ideas for improving the electrical standard

One thing I think is a huge weakness is that a short anywhere on any track will stop all trains. In addition, a related problem is the reliance on the breaker in the DCC booster must sense a short properly at the extreme ends of the layout.

In modern DCC layouts, you distribute power through a bus with feeders and you isolate sections of track in to power districts, each protected by a breaker (solid state normally).

First comment is that this pushbutton feature for shutdown is not very practical because not all DCC systems have inputs to shut down, so the only reasonable method is to cause a short.

The second comment is that you are still forcing a shutdown of the entire layout for a problem in one isolated area.

As Z scale layouts become larger (one of the main advantages of modules) it's clear that the existing methods are dated.

So, what if we take 6 pins for a second power bus? Using 20-22 and 23-25 for a DCC "protected" power bus would allow this.

The idea is that every module could take power from the "main" and then power it's tracks via a circuit breaker. This of course could be done right now. But in addition, that module could "feed" the "protected bus" also. Adjoining modules then have 2 options. In either case, the main power continues to be fed "through" on the "original" bus.

Modules could still power their rails from the "original" bus.

But modules could also power their rails from the "protected bus", and then enjoy the protection of a separate power district.

If , in the future, all modules were "switched" to only power themselves from the "protected bus" then no module could shut down the power for the entire layout.

This idea is not completely worked out, but it does provide for backwards compatibility, flexibility, and a nice progressive path to a better power distribution and protection setup.

My thinking is to use these pins as a DCC distribution bus