Setting up DCC for multiple tracks - beginner

[GSCR No.4]

Hello all!

I'm finally getting my railway started after a long period of not having one after my last was disassembled. One thing I want to do is make sure it's DCC this time for more interesting and complex train running.

Only problem is I'm not exactly certain how to make sure the DCC signal goes to the entire line, when there's multiple different lines anyway.

I'm a complete novice at this sort of thing. I know that with points I can use those funny metal clips to make sure the electric current goes through to both ends, but my concern is the signal will get really weak after a set distance.

So...how do you set up DCC for multiple long tracks? I think I saw in the DCC instruction book some kind of wire that connects multiple DCC power rails, but I don't recall seeing any specifics on it. Would I need to resort to manually wiring the rails to something?

[Bulleidboy]

Hi - probably the best way would be to install a "bus" cable under your board(??) and then attach your track to it. The bus can be created by stripping the blue and brown wires from a length of mains cable and attaching the two wires two or three inches apart to the bottom of the board - you can use chocblocks attached to the bottom of the board and thread the wires through the chocblock - no need to tighten the screws. The bus cable runs the length of your layout but does not need to be joined when the ends meet. Then using a slightly lighter cable again stripped down as before (blue and brown) create droppers, these are short lengths of wire, which are soldered to the outside of each rail, dropped through the board and then either soldered (best method) or using cable connectors, attached to your bus cables - brown to brown, blue to blue. Unless the end of your layout is out of sight, power reduction should not be an issue. You can use the wire clips for your points or if you have not bought the points yet, use electrofrog points. The power cable from your controller (the one that would normally connect to the track) is then attached (soldered) to the bus cable - usually at about half way point in the overall length of your layout.

My own layout is "U" shaped around three sides of a 10x7 room. My bus cables run from end-to-end, and every single piece of track, including points and crossings are soldered to the bus cable. I would not recommend the "droppers" that are attached to rail joiners.

I would advise some serious reading and/or watching YouTube videos on various aspects of getting started. I can highly recommend "The Newcomer's Guide to Model Railways: A Step-by-step Guide to the Complete Model Railway" by Brian Lambert - Check out Amazon Books.

BB

[Chrissaf]

The example schematic below takes BB's text description and presents it as a schematic for additional clarity. The key thing to note is that the dropper wires from the track rails to the BUS must always be the same way round to prevent short circuits. In the schematic, the brown dropper wire is shown always on the inside rail of the track. Although BB didn't mention it, the terminator filters are desirable to include as they protect the decoders from damage and corruption due to transient short circuits. Some layout builders place droppers on each and every track piece, relegating the metal track joiners to just being physical track joints that do not need to transfer power. However, as a minimum you only need a dropper on each side of every point.

Typically the BUS wires will be 32/0.2mm wires [32 strands of 0.2mm wire] in a single sheath, with droppers made from 7/0.2mm wire. The wire colours are arbitrary, I just used blue and brown to match in with BB's description.

[Bulleidboy]

Many thanks Chris for adding the schematic, it certainly adds clarity to what I was trying to explain. Also your adding the line about "terminators" - yes desirable, and yes I do have them fitted. BB

[Mac-_-]

I would use IRJ to split the track above where the bus wire's end. If you have a roundy layout with no lift out section.

Which reminds me i need too put the terminators on my bus wires, thanks Chis ;).

[Bulleidboy]

Why do you need to split the track on a DCC roundy??

[Chrissaf]

So that the break in the DCC BUS which is in effect a T BUS is not compromised [bypassed] by the continuity in the rails. Adding the IRJ in the loops just below where the terminators are located [blue squares], converts the 'roundy' layout electrically to an 'end to end' layout to match the T BUS configuration. Granted, the break is circumvented when rolling stock traverse the IRJs.

A niggly minor point, but something that I have done with my own DCC BUS configuration.

[Mac-_-]

I wouldn't have said a niggly minor point, when going to the bother of splitting the bus wire too then possibly bridge it with the tracks. Each too their own i suppose.

[Rog RJ]

They are not terminators, they are filters and there is no need to split the bus.

DCC does not need to be terminated, unlike some other buses such as CAN bus which needs 120ohm resistors at each end. The DCC filters would work equally well on a circular track as they would on a T.

[Mac-_-]

Just wondering how many layout's out there that the owner thinks they have their bus wires terminated/split hushed. Though i do have mine split, and i'm happier with it split.

[Chrissaf]

I wouldn't have said a niggly minor point, ........

 

 

The reason I said 'minor niggly point' is that the effectiveness of breaking the track loop, would only be noticeable if the track length was 100's of metres long. Most domestic sized layouts would see little benefit. It's all to do with the theory of signal reflections and standing waves. At DCC frequencies, the wavelengths are too long to achieve standing waves where signal reflections can cancel out and distort the base DCC signal on domestic sized layouts. This kind of digital signal transmission theory was something I studied during my industry apprenticeship.

[Mac-_-]

Congrats on your apprenticeship Chis, i only queried your point of saying a niggly minor point, as in i would have thought splitting the wires below the board and then bridging them above a bit pointless, and not a niggly minor point at all, but as i said each too their own.

[Chrissaf]

I do actually agree with you Mac. I did say that it was something I had done with my own BUS arrangement for the very reason you have described. I acknowledge that although there is very little benefit to be gained on a domestic sized layout. I treat the concept as being 'Best Engineering Practice' [b.E.P]. And as Rog(RJ) says in his reply, the terminating filters can just as easily function on an unbroken BUS on the average domestic sized layout. I still chose to implement 'B.E.P' for my own layout.

I read 100's of posts each year on this forum where strange DCC operational issues are observed. I have never ever observed a single one of them on my own layout. I can only assume that it is the attention to detail in my DCC BUS implementation that is a contributory factor to that experience.

[Mac-_-]

I wouldn't argue with what Rog said in the last page, but i'm with you on your post above.

 

[Bulleidboy]

Interesting answers - and as said "each to their own". I read numerous books/articles about starting with DCC and planning your layouts before I started building my layout, and had never ever read what was suggested - but useful to know. BB

[pd91223]

Are there reasons to avoid a full ring bus rather than the radial one you all seem to prefer?

[Mac-_-]

Interesting answers - and as said "each to their own". I read numerous books/articles about starting with DCC and planning your layouts before I started building my layout, and had never ever read what was suggested - but useful to know. BB

 

 

The only right and wrong way to do something is if one works it's right, if it doesn't it's wrong, at least in my simple world ;).

The reason i split my bus wires.

Imagine your track as a clock, and only one hand on this odd clock, and your hand (power supply) is at six, and you don't have a split. You have a loco sitting at one, you have no control over the way the hand is going to go to that loco. It could go the shortest route, it might just as easily go the longest, might even split who knows.

Now introduce a split at twelve, same situation, loco at one, hand at six. Now your controlling the way the hand on the clock will go to that loco. As it can't go via twelve any-more.

That's why i split the bus wire.

[GSCR No.4]

Just popping back to say thank you all for your responses. I'd have been more involved but I briefly forgot about my own thread! T_T

I must admit, I am not particularly capable or informed when it comes to the details of wiring and electronics so I wasn't 100% certain what a "bus" cable was, although your comments have nonetheless proven very helpful in understanding how to manage things.

Thankfully I already understood the importance of avoiding short-circuits (having experienced several due to a wiring mistake on my original layout)!

Having read and re-read Bulleidboy's original response, I'd like to thank you very much for being so detailed. I'm getting a much better understanding now on how it'd work - and the bit with connecting the controller wire had been the biggest concern.

In regards to soldering the controller wire to the bus, does it matter which of the two wires is connected to which bus wire, or is it fine as long as they are connecting to different "colours"? Trying to envision it, I suspect the only thing it'd change is which "direction" the controller considers the track to be facing.

What's the best way to solder the track pieces to the bus wire without risking distorting the track? Based on a couple of videos I've seen but not fully understood it seems like doing it on the outside of the track is better because the wheels don't interact with it, but then hiding the solder would also be more challenging.

Moving on to the addendum by Chrissaf with the diagram (thank you very much, that also helps a LOT!) I don't think I quite get what a terminator is. I think I'll need to look around for some DCC youtube videos to learn more.

[Chrissaf]

Q1 - In regards to soldering the controller wire to the bus, does it matter which of the two wires is connected to which bus wire, or is it fine as long as they are connecting to different "colours"? Trying to envisage it, I suspect the only thing it'd change is which "direction" the controller considers the track to be facing.

Q2 - What's the best way to solder the track pieces to the bus wire without risking distorting the track? Based on a couple of videos I've seen but not fully understood it seems like doing it on the outside of the track is better because the wheels don't interact with it, but then hiding the solder would also be more challenging.

 

 

A1 - The polarity of the DCC power connection to the track has absolutely no affect on train travelling direction. That is a DC Analogue concept and has no bearing on DCC operation. The controller wires can go either way round, it makes no difference. What you must do however is have all your droppers the SAME way round, else you will generate a 'short circuit.

A2 - The key to soldering is having the right tools for the job and cleanliness of the parts being soldered. Droppers must not be soldered to the inside of the track rails. The droppers are soldered to either the underside of the track as it is installed, or to the outside of the track if wired up after track installation.

How to Solder for model railways is covered by my tutorial here:

FAQ - How To Solder for Model Railways.

If you use the right tools, and the right solder [see tutorial] along with suitably sized dropper wires [i suggest 7/0.2mm wire] than the wires should be near invisible and any wire that does show can be hidden by 'ballast'.

My wires are soldered to the underside of my PECO flexitrack. Once ballasted, the wires will be covered. Even without the ballast I had to look hard to find the wire locations to take the photo below. The wires are 7/0.2mm wire in brown and blue.

If your track is modern 'Nickle Silver' then Solder will flow easily onto the rail. If your track is the much older 'Steel' rail then additional cleaning of the rail surface plus pre-tinning with flux and Solder will be needed. Steel rail is very much harder to solder to.

As far as YouTube videos are concerned, the gems are very few and far between. Most YouTubes I have seen make me despair at the misinformation they give out.

[GSCR No.4]

Thank you for the corrections there, Chris! You really are a bastion of information for a beginner!

I hadn't considered using the underside of the track. I'll have plenty of time to plan out the track locations first, so I'm definitely going to consider it over the more unsightly outside-type.

Luckily, I don't think I'll have to worry too much about steel-type track - most of my old steel track has become practically unusable due to age and poor storage conditions, or got warped in transit or when ripped up from the original garage layout. So at least it'll be easier to stick with the modern style. :D

[Chrissaf]

This is probably obvious, but I'll mention it anyway. When soldering to the underside of the rail as you install the track pieces. You will need to cut away a small section of plastic webbing between adjacent sleepers [PECO track], in order to reveal a bared piece of rail bottom to solder the wire to.

My method is to use the iron and solder to place a small blob of solder to the prepared rail area. Then tin the wire with solder as a separate activity. Then place the tinned wire against the rail solder and apply the iron to press the wire into the solder blob. Remove the iron and briefly hold the wire still until the solder has hardened. A good solder joint should look shiny. If it looks dull and slightly greyed with microscopic ridges, then the wire probably moved whilst the solder was still in a molten state and could be what is called a 'dry joint'. Dry joints can be resistive and not provide good electrical transfer of current. So if you suspect a 'dry joint' then redo it again.

[RDS]

This is probably obvious, but I'll mention it anyway. When soldering to the underside of the rail as you install the track pieces. You will need to cut away a small section of plastic webbing between adjacent sleepers, in order to reveal a bared piece of rail bottom to solder the wire to.

 

 

All but the shortest lengths of Hornby track feature an short section of bare track with the sleepers already cut away. This is where I have soldered all my connections. The curved track shown is Hornby item R607 and the straight one is Hornby R601.

David