Voltage drops [in larger layout tracks]

In an ideal world all the track joiners would be tight fitting, clean and fitted to clean rails and offer excellent current transfer from one rail to the next. If one has an ideal world layout, then consider yourself lucky.

But the world is not ideal, particularly when deploying re-used older track products and mixed vendors as you plan to do.

For you and any readers of this thread, DO NOT be tempted to solder the track joints together to overcome any track electrical transfer issues. The track needs to be able to expand and contract with changes of temperature to prevent track buckling.

In order to get a voltage drop, you have to pass a current through a resistance. So let us assume that a loco is drawing 150mA and the controller is outputting 9 volts [i.e. not full speed], and 7 volts is measured across the rails at the location furthest away from the controller connection. This is a voltage drop of 2 volts when passing 150mA [0.15 Amps].

With this information we can calculate [using Ohms Law] what resistance is between the measurement point and the controller. For Resistance, Ohms Law is R = Voltage divided by Current.

So R = 2 volts divided by 0.15 amps = 13.34 Ohms

This resistance is the accumulative resistance of the whole track route between the measurement location and controller, so includes the resistance of the rails themselves and ALL of the track joins in-between.

If there are two or more track routes between the measuring location and controller connection, then that 13.34 Ohm resistance figure is the combined resistance of multiple resistances in parallel.

What this demonstrates, is the importance of the quality of the track and in particular track joiners. 13.34 Ohms is a relatively low value, the higher the resistance value is, then the greater the losses.

So what can be done to alleviate this. Firstly as stated above, do not be tempted to solder the track joints. The first task is to focus on the track and joints, track must be spotlessly clean, particularly on the ends, where the track joiners fit. The track joiners must also be clean. I would suggest if using old reused track that all brand new track joiners are fitted, and ensure that they fit very tightly. Crimping them on with pliers if required.

Don't forget the moving rails on points, the electrical transfer of current is totally reliant upon the pressure of the moving rail against the fixed rail and the cleanliness of the side of rail contact areas. Reusing old points, particularly the old steel variety, has been proven time and again on this forum to be the cause of electrical problems. Particularly with novice builders who buy cheap old track on ebay.

Even if not affected by excess resistance issues at the time of layout building, additional feeds from the controller to the track can be used as an insurance policy to reduce the number of track joints between any location on the layout and the connected location of the controller, to help with reducing future issues arising.

You are obviously an experienced DC modeller, so this next section is not aimed at you [I would be teaching grandmother to suck eggs], it is aimed at other more novice members who might be reading this thread.

But this needs careful design in a large Analogue DC layout as you have to remember that in DC Analogue you use the switching capability of the points to create purposely engineered dead track zones. So keep these multiple track power feeds to just the main loops of the layout. It may be necessary in extreme circumstances to include on/off switches in some or all of the additional feeds so that you can selectively remove power from certain sections. If deploying 'block working' for example. In deciding where to add additional controller connections consider how you are going to use the layout, where are the train movements going to be, start and end points. Ideally these might be run by the same controller in a layout using more than one controller.

Personally if it became neccessary, I would map out which track sections are going to be controlled by a controller and implement a BUS power distribution system dedicated for each controller. Thus there would be more than one BUS and these must not overlap, use Insulated Rail Joiners if needed in strategic locations to maintain BUS wiring electrical separation.

Going completely overboard, but I would consider making a BUS connection within each controller zone to each individual track piece, thereby relegating as many track joiners as possible to being there purely for physical track joining and alignment, thus removing their function of transferring controller current from the equation.

Hope this helps to answer your question to an adequate level.

Many thanks, Chrissaf. I have already laid in a stock of new fishplates and was wondering about the use of BUS connections. I shall follow your advice, particularly on the avoidance of soldered track connections. I shall lay one circuit and measure voltage drop before laying any others.

@threelink

"I shall follow your advice, particularly on the avoidance of soldered track connections."

Soldered track connections are good, soldered track joints (fishplates) are bad.

Noted, Rog. I presumed that Chrissaf was referring to rail joints, not power connections to the track - I shall certainly solder feed wires to the track but not solder up the fishplates. Thanks for your input - without experience of longer track runs I am keen to get as much advice as possible before starting the tracklaying and wiring. It has taken me forever to strenghten the loft joists, lay the floor, insulate the whole thing and get the baseboards properly built, so the last thing I want to do is make some schoolboy error in the tracklaying that will result in poor runnning.

I was indeed referring to not soldering the track joints. I wrote:

"For you and any readers of this thread, DO NOT be tempted to solder the track joints together to overcome any track electrical transfer issues."

No issues with soldering wired power feed connections to track. That is also preferred.

Note that if some of your older reused track is steel, that soldering wires to steel can be done but takes much more skill. Try to keep all soldered feeds on Nickle Silver track, which will easily solder.

I can only tell you that I've run a 14' x 9' layout with four loops for over a year now and have faced no such problems.

I rely on the fishplates, I don't have any wiring loom of any kind.

When I started this hobby two years ago on an 8' x 4' board [having never owned a model train in my life] I spent far too long listening to people on forums who, clearly experienced in their field, massively over-complicated this hobby.

I'm a little wiser now.

Nothing posted here is intended to complicate or over complicate any subject, rather being based on long experience of the subject at hand. If you are having better luck than most, it is just that, luck. R-

Threelink

By connecting in the centre of your 40' length you will reduce your track voltage drop by 1/2

Use a larger mm2 cable as possible this will also reduce volt drop . Bear in mind volt drop will also increase using larger current consuming locos .

Usual formula MV *MTR * I

@John, RogerB,Will Hay and Chrissaf,

Thank you all for your comments. All duly noted and will be more than helpful when I lay and wire the first circuit of track.

My layout is 8m x 6m. I run 4 DC circuits of lengths between 23 & 25m approx.

Each circuit is split into 4 sections of length 6m approx.

Each section has its own controller. I'm a firm believer in "minimum wiring" so each section has 1 +ve and 1 -ve wire attached, except for where point work dictates a second wire connected. I use 6-Core Alarm Cable (14/0.20mm).

For purposes of trying out different controllers, I have a setup whereby a single controller can be connected to each of the 4 sections in a circuit. When I do this, a slight drop in maximum train speed occurs over the whole circuit. This barely affects "train performance".