modular musings, part 3 (electrical)

If you can't get the control signals or power to the locomotives, all the mechanical construction effort is for nought. I will discuss electrical aspects with DCC in mind.

You need to have robust connectors, able to manage the high current draws:
i.e. Anderson, Cinch-Jones, trailer...
Each have their beneifts and drawbacks. Any one of them can be "bad" if they are not used properly.

What about power districts? Modern sound equipped locos can draw significant amounts of power, and having a short at one end of the modular layout should not disrupt activity at the other end.
- maximum track buss length for each booster should be less than 50'

Employ 'unique' connectors at the interfaces to prevent mix-ups. Throttle buss, track buss, and accessory power buss should NOT be able to be connected to each other. Throttle buss cabling is usually something like a Telco RJ12, so that's not too difficult to keep apart. However, you must bear in mind that there are 'straight through' and 'crossover' versions of typical Telco and Datacom cables - beware mixing them in a daisy-chain!


If you choose to use something like an Anderson Powerpoles for both the track and accessory wiring  harnesses, ensure that you use different dovetailed plug arrangements for each.

Hermaphrodite connections saves 1/2 your material costs for electrical hardware, and is especially useful in Free-mo 180° end-for-end flip situation.

Make troubleshooting provisions from the beginning. Nothing takes more time than tracing an electrical  fault. Employing quick disconnects, terminal blocks, and nicely dressed colour coded wiring will help but remember that each break in the wire (for a connector, plug or whatever) is another potential point of failure. Also, DO NOT make something that only one person can fix, and DO NOT rely on proprietary "gizmo" solutions.

- buzzer box
Radio Shack buzzer + 2 alligator leads for track laying
see "Testing" section of http://www.wiringfordcc.com/track.htm

- buss run AWG
Heavy, stranded, Landscape wire (designed for outdoor use, thick insulation, high amp/low volt)

- track buss taps
3M IDC Suitcase connectors,
Telegraphers "tap" slice (aka Western Union joint in some circles)

- track feeders AWG
light, short (less than 6"), solid

Keep accessory power draws OFF the DCC buss! DCC is for loco power & layout communication only! If you're wondering why you loco is behaving erratically, maybe you should disconnect the 'welding flicker' and 'telegraph sounder' from your track buss. Electrical noise coupled-in to the command signals is BAD. The decoders determine what to do through edge-detection in the DCC signal. Don't add to the noise by tacking on a bunch of animated elements. A DC or AC wall-wart adaptor, or an old PC power supply (with PWRGOOD mod) will run all your online accessories.

- Loconet buss termination
A properly sized resistor at the end of the track buss will help reduce or eliminate ringing & overshoot of the DCC signal. Early Tsunami decoders were susceptible to overvoltage/spikes, causing premature failure in some cases. Spikes can hit over 22V on a DCC system set for 16V output.

- communication buss
With the advent of full-duplex radio, it may be that you don't need this on the layout. However, there is no need for the expense of radio throttles at yard locations. Adding a few plug-in throttle jacks won't hurt, and may help to reduce radio interference at larger shows.

If you are going to add throttle jacks to your modules, put two at opposite diagonal corners of the module set. This ensures that, whatever the orientation, there are jacks at even spacings around the layout. You won't have far to move if you need one.

- DCC vs DC
will depend on # of simultaneous locos & operators

- getting power to the layout
anti-trip mats to run power cable through, do not daisy chain extension cords, multi-tap AC cords

- turnout power
local adaptors, low volt AC buss, low volt DC buss, Tortoises vs solenoids (CD, SwitchWitch or Circuitron), servos (TamValley, AneModel)

- turnout control
DCC throttles, momentary buttons, toggles, computer, hand thrown, Pete's panel

- cables
making your own, 3-pair telco, x-over vs straight through, proper crimping tools

- test equip
RRAMp meter, Telco cable tester, hooking up UP5 LEDs, buzzer box, Digitrax LT1

sites for further study:


Circuitron "Snapper" cap-discharge solenoid driver:

Tractronics "SwitchWitch" stall motor driver:

RRAmp meter for DCC testing:

series 302 Cinch connectors:

Anderson Powerpole connectors & accessories:

R/C servomotor controllers for turnouts:

IDC Scotchlok connectors:


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