Running bus wires

Model Railroader Electronics and DCC
1

My new layout is going to be basically a shelf around the room layout in half my basement. About mid way, there will be one section of track that peels off and cuts across the room, connecting to the other side. Picture looking from above and it looks like a digital 8 but no crossover tracks like a figure 8 would have.

This will be my first foray into DCC. From what Ive read, its best to run the bus wires underneath where the track goes. So if I start and run them under the part that goes around the room, what is the best practice to run them under the track that cuts across. My understanding is that the bus should be one continuous set of wires.

Hope what Im asking makes sense.

2

Hello All,

The term “bus” has been borrowed from the early days of the computer industry.

It is alive and well with the USB- -Universal Serial Bus, which can be used with all computers with these connectors.

Originally it referred to a “bus route”, where the “bus” would travel a specific “route” and pick up passengers and drop them off at various points along the continuous route.

The way this translates to computers is the “main ‘bus’” is the electrical path that the computer’s components are tied to- -disk drive, CPU, and other peripherals.

Signal packets travel this “route” and get on and off depending on their “destinations”.

For DCC it’s really not a complete circular or connected “route” it’s more of an out and back.

DCC manufacturers don’t recommend connecting the ends.

Because the rails of model track are not the best conductors of data, with the advent of DCC it has been recommended to run a set of wires underneath the track and tap into this “bus” at every other track section.

With sectional track that is a lot of feeders per 9-inch section. With uncut sections of flex track it’s about every 6-feet.

To answer your question…

Run an additional set of bus feeders; of the same gauge wire, under the crossover section.

This will create a “Y” section of the bus under the crossover section.

Do not tie these into the bus on the other side of the crossover section.

Also, do not make the bus a continuous loop- -connected at the ends.

The command station/booster should be placed approximately equal distance from each end of the bus wires.

Connect the bus via feeders to the track.

You did not mention the length of track you are considering.

Take a look at this thread for further discussion of signal and power strength over long distances.

3

Actually, ‘bus’ here means two different things, both of which are important.

As you know, NMRA DCC cleverly arranges the data modulation as part of the DC track power. To the extent we are concerned with correct reception of the DCC digital information, the advice previously given is correct, especially including the ‘no complete loops’ advice. (See other posts about using twisted-pair wiring for DCC.)

However, the other half of ‘bus’ is in the DC power sense, and it comes from ‘bus bars’ in electrical power: the use of relatively heavy copper sections to reduce losses. This is the principle on which the idea of using heavy (e.g. 12ga. solid) wire following under the track, with frequent ‘feeders’ going up to rail segments or other structures needing power, comes from.

I recommend (following advice obtained here) that each segment of rail get its own soldered ‘feeder’ diwn to a good undertrack bus: this eliminates concerns with rail-joiner integrity and potential signal interruptions on bad track joints. Depending on your benchwork and track construction you may need expansion jointing in the track, and the feeder system ensures you can do that with no potential (pun alert) electrical debility.

4

Thinking about a few details:

  1. The length of each split-bus section, plus the amps desired, will dictate the wire gauge recommended. One recommendation is to stay within 1/2 volt drop for HO. There are tables for amps desired (e.g., 5 amps for HO) and max run length for each awg wire size. I recall the table I used allowed 25’ max run for 16 awg wire at 5 amps.

  2. Each half of the outer loop will be longer than the cross-room track, so the longest of those half loops will determine the awg size to use there. Easiest to also use that gauge for the shorter run across the room. An example would be having a 10’ square room with the bus splitting at the middle of one side, where the cross room track diverges. So the 2 outer loop sections might be 20’ long and the cross track section 10’ long. So if needing 5 amps, 16 awg should do. If a larger room, and an outer portion exceeds 25’, then 14 awg needed, up to the lenght limit for that gauge. Note that different references suggest different gauges, so these are examples.

  3. A curiousity… ensuring you do not have a reversing loop, requiring isolation and a track power reversing mechanism. I presume your plan includes just an outer loop plus one turnout on each side to the cross-room track? If a train crosses mid room and re-enters the outer loop, if it is still going in the same direction, there is not a reverse loop. If it re-enters the outer loop and is going in the reverse direction due to the turnout orientation, you have a reverse loop requiring special attention. If you have a different arrangement, such as two turnouts (a wye) on each side of the loop, it’s a different story.

5

Definitions of “bus” aside, it makes the most sense to run bus wires under the track work as much as possible. For one thing, it saves on the use of feeder wires to have shorter lengths. For another, the shorter the length of the feeder wires, the less the voltage drop.

Rich

6

Thank you all for the responses. I guess I should have added more detail to my original post but didnt want it to drag on.

From my research and learning I do know that its not a continuous loop that connects.

Feeders my plan is every 3-6’ which may or may not be overkill but Ive read that is best practice.

I never thought of the strips to distribute the power from the cab or booster to different areas. The stuff I have watched on YT and read basically showed the wires coming from the cab/booster and running under the layout, about where the track was to facilitate connecting the feeders. Im my mind I was picturing having to somehow split off the main to run wires under the crossover section and couldnt picture how that was going to be easily done

And, there should be no reverse loop in my plan, the crossover will peel off the main, cut across to the other side and be going in the same direction when it reconnects.

Again I thank you all for your responses. I have alot to learn since Ive been out of the hobby since the late 80’s!

7

Having been in this hobby forever off and on and very recently into DCC, I have found there is a lot of imformation out there but a lot of it dose not mater. Just run the bus the length of you layout and drop feeders, always the more the better but every 3 feet or so is fine. If you end up needing a booster you can add one in but alot of that depends on how much power you need. Some here have layouts that double or tripple head and multiple trains at the same time, some just one or two at a time.

8

To carry the main two wire bus wiring out along branching lines just consider the extension you need out under the branching line to be just another track feeder. You can run track feeders connected to other track feeders which are in turn connected to the main bus. The term “bus wire” is really intended to refer to the heavier gauge of wire used to power a number of track feeders. You can use the same heavier wire everywhere if you wish. The key aspect of a heavier gauge bus wire is it carries current to several locomotives running on widely separated track sections. A particular pair of track feeders need only supply current to the locomotives occupying track adjacent to that feeder connection. Conceptually. Electrically speaking all wires feed the whole layout all the time unless you have power districts or lots of bad rail electrical connections. The electrons don’t care how they get home.

9

As a small additional note: while you want two ‘rails’ of bus wire under the line of each track, you can arrange switches to cut particular sections off without disabling ‘the rest’. A number of posters want the ability to cut off locomotives with sound when not operating, or to allow power-up sequentially if engines or other loads have high momentary amp draw. A variant of this technique lets you switch a given section of track to be an isolated ‘program track’ if you want the effect and functionality of one without a special setup at the bench.

My ‘rule of thumb’ (again derived from other people’s experience and thought) is that every piece of separate rail gets a feeder. If you have a longer soldered length or a ‘common rail’ feed it every 3’ or so.

I would have been prepared to say this would solve any likely electrical contact problems… then up comes the current thread about glazed railhead surfaces which explicitly mentions he has feeders out the wazoo…

10

There’s no such thing as “too many” feeders from the bus to the rails. Nobody ever had layout problems from too good an electrical connection to the locomotive.

11

My recent layout performed great with soldered rail joiners (except at turnouts) and feeders to every rail piece. For feeder spacing, every 6 ft or less, which means a loco is never >3 ft from a feeder wire. Quite adequate IMHO, even for 4 loco consists.

My layout was indoors, climate controlled, and no track expansion / contraction issues. If concerned about significant temp or humidity swings, I would have soldered a fair number of joints but added a few expansion gaps occasionally. That would have added just a few additional feeders.

12

Nobody ever, in the history of evers!

[Y]

Too many is barely enough.

-Kevin

13

I’m also involved in my first foray into DCC. My layout was originally designed for DC, single cab control without blocks, but fairly robust for DC, with 18 gauge wires running between 6-foot detachable layout sections and several feeders to each section. I used power-routing Peco “Insulfrog” turnouts to park locomotives in small yards, but with DC obviously I was limited to one loco per yard, using the power routing switches to keep unused motive power “off” while one loco did the work. I finally took the leap into DCC in mid-December, and while my wiring was robust enough to handle a 5 amp Digitrax system, some of the switches had become electrically unreliable and the layout developed a few dead spots. I want to add a proper DCC electrical bus, improve electrical reliability by adding more , and add provision for future LocoNet wiring, and future animation and lighting.

Here’s a track plan with rudimentary plan for the bus wires; HO scale, 11’x24’ room. Approximate location of the bus wires is shown in red, with locations of associated feeder wires. Both wires (12 gauge solid copper) will be run along the back of each section, then drop down below the section a couple inches, attached between modules using “Wago” connectors. Each yard track, RIP and caboose tracks will have feeders, plus 1 extra feeder at each end of the yard. I’m keeping my existing 22-24 gauge feeders, but adding 20 gauge stranded copper. Overkill? No such thing! I’m also going to relocate my control station from its current location to the middle of the layout in the vicinity of X Street, which will mean no more than a 30 foot run in either direction. I’m not going to divide it into power districts yet (except for a reversing section at the wye near Westgate) but because each section can be electrically separated by opening the Wago connectors, it’ll be relatively simple to cut out sections to locate shorts, and easier

14

What type (brand) of electrical switches do you have that worked in DC but became unreliable in DCC?

I sometimes wonder if Atlas switches designed for DC have adequate amperage capacity to also work in a DCC environment.

15

Not electrical on-off switches, and not because of the DC/DCC change–my track switches (turnouts or points, depending on which side of the Atlantic you’re on) are Peco “Insulfrog” which are power routing–so it basically acts as an electrical switch as well as a track switch. Unfortunately, this is done via metal tabs under the track, and over time on a scenicked layout the tabs sometimes bend slightly or get covered with assorted grit & grime that affects their electrical properties. It wasn’t because of the DC/DCC switch, just routine wear and tear. But while Electrofrog turnouts are great because they’re DCC ready and don’t cause shorts due to live frogs (since the frogs are plastic), which greatly simplifies wiring, their original purpose (allowing me to spot locomotives in the yard where they wouldn’t move until the turnouts were routed for them, without the need for block control wiring) became redundant due to my change to DCC, although I’m also going to install some power cutout (electrical) switches that will let me turn off power in the two smaller yards where motive power lashes up in between runs (seen in the photos below) so I can still shut things down when needed–it won’t be necessary in my large freight yard posted above.

16

Here’s the underside of the layout after attaching feeders:

I used Wago connectors to connect the bus across sections. After adding 9 more track feeders across 2 sections and connecting the existing 3 feeders to the bus, I discovered I still had to re-solder one connection between two turnouts where there was a known dead spot in the track.

I probably overdid it with too-heavy wiring, as I’ll have to paint or otherwise disguise the wire to make it less visible. Won’t win any beauty contests, but at least there aren’t any dead spots! (Two sections down, eight to go…)