DCC system & layout wiring & troubleshooting tips

Overview

Again, there are some myths to be debunked here, and some just common sense stuff.

My point of view is try to resist going "cheap". Like your track, the power to the layout is fundamental in importance. Poor wiring can lead to erratic operation.

So many people will brag "oh I only use this really cheap wire" or "I only need one connection to my layout", etc. are people that are either extremely lucky, or not telling the truth about how their system runs.

Like all things in the world, attention to details, quality work with quality "ingredients" works.

Also, please remember the "experts" you talk to may be using "HO" knowledge and insisting it is the same situation as your G scale layout. There are other factors besides the weather, notably the longer runs of wire, the heavier gauge and the higher current.

Determine your voltage and current needs

Just like different people have different needs of their locomotives, decoders and systems, your power requirements will vary.

Now, remember that I do run longer trains with more locos, so my current requirements will not be yours, ALTHOUGH if you build your layout like I did, you will be able to handle ANYTHING, current and future.

First, I do not recommend ANYTHING under 10 amps. Now all the people who can run an LGB loco on a 1 amp power supply are jumping up and down screaming. Tough, keep screaming. The Large Scale world consists of locos that pull a lot more current than a tiny plastic loco that pulls 5 cars.

A loaded locomotive (pulling a train) can pull about 2 to 2.5 amps easily. Lighted cars can draw up to an amp each. If you look at also connecting to the rails for some stationary decoders, you can see 5 amps does not make sense, 2 locos can take all your capability.

Specifically for DCC, voltage is important, since not all DCC systems can output the same voltages: If you run steam or narrow gauge, and mostly freight, the voltage to the rails of 19-20 volts will give you prototype speeds. But, if you run diesels or passenger trains, you may, on some locos, need 24 volts DCC on the rails. Also there are some other locos that need it too, like the LGB track cleaning loco, and some of the Accucraft and other brass models that have crappy gearing that will give you a low top speed.

Thus, I recommend that you have a system that can put a full 24v DCC on the rails.

Please remember that you CANNOT use an ordinary voltmeter on the AC setting to measure this AND various manufacturers don't always give the limitations or capabilities of their systems.

Here is the NMRA standard on DCC voltages: https://www.nmra.org/sites/default/files/standards/sandrp/pdf/s-9.1_electrical_standards_for_digital_command_control_2021.pdf

Take into account track material & construction

For track power, the less oxidation of the rail, the more reliable connections for power, between rail sections, and between the rail and your wheels on your locos.

Unfortunately, cost goes up as resistance to oxidation goes up. Read the section on track and rail material. Basically the more you spend, the more reliable and trouble free your layout and wiring will be. Using rail clamps instead of regular joiners, stainless steel rail instead of brass. Read the section on rail clamps.

If you use rail that oxidizes easily, then you need to take extra care in your wiring, using anti-oxidation paste in connections, larger contact areas, more feeders, better joiners.

Environment

If you live in an area with a large swing in temperatures, then you will have more movement with expansion and contraction. Add more feed points, better joiners, etc.

Some people have very alkaline or acidic soil, that can affect corrosion, or even "eat" metal connections.

Again, with a "tougher" environment, more attention to bulletproofing and providing redundant power paths.

Power districts / isolation

I have a bit different way to do things that helps debug conductivity problems.

My philosophy is to have a number of separate power districts, completely insulated from each other, and fed with a single feeder from the "middle" of these districts. If you have power problems, it's much easier to debug from a single feed point.

Many people connect everything together, and have multiple feeders. Makes sense from a reliability point of view until you have a problem. Now a bad "joint" can be fed from two different locations, so how to figure out where the bad feed is?

Having separate districts allows you to find these bad spots easily WITHOUT disconnecting wires. With all rails connected together and multiple feeders, you have to disconnect feeders.

The whole idea is to make it easy. Combine this idea with a load box and you can find problems right away.

Many people that "give up" on track power do so because they cannot keep the railroad conducting, and it can boil down to a single joint and frustration because of everything connected to everything, i.e. debugging the problem is too tough and frustrating. Take my advice and you can find issues quickly, and you will spend more time running trains than chasing a bad connection.

Plan autoreversing sections and locations of autoreversers

For people who have reversing loops, plan where it makes the most sense, and the basic rule is try to get the reversing section to fit the entire train, or at least the cars that pick up power. (Don't forget lighted passenger cars).

If you are using DC, then use the Massoth unit with the sensor "track sections". If you are using DCC, use the DCC Specialties PSX-AR series. Don't listen to the people who are worried that the short circuit sensing damages things, the autoreversers work so fast you are not damaging things. Yes there may be a small spark when it happens, but do me a favor, run your layout at night, get down to track level and look at all the sparks from your loco wheels under NORMAL running. You will see worrying about sparks from an autoreverser is foolish.

Feeders and wire gauge:

Here's where the "common wisdom" is normally a myth. There are people in HO and N and Z scale that insist you wire a feeder to EVERY piece of rail. Good for them, they could run with no joiners period. (Incidentally I run Z scale and solder my joiners).... I run feeders every 15 to 20 feet, and I run 10 amp trains... you can probably run fewer feeders depending on if you are running rail clamps or just stock joiners.

Now, since most people NEVER add wires later, do it right the FIRST time. I use all 10 gauge to the rails, no extra connections, no changing to a smaller gauge with a soldered joint that can corrode later.

Here is something important: do NOT run a "bus" and tap off it every so often if you run DCC. This causes issues that our higher current helps make worse. (Stop listening to your HO DCC friend here). Run the wires as a "star" or "home run" system, i.e. every feeder goes directly back to your command station booster. Yes yes, it takes a lot more wire. But besides the electronic noise issues it creates (can you say "DCC runaway"?), it has far fewer connections. These soldered connections will fail and/or corrode over time. A single piece of wire from the track to your booster.

Don't run anything less than 12 gauge. Also read carefully about stranded vs. solid wire below.

Implementation details

Should bury the wire or put in conduit? By all means use conduit if you can. You can use less expensive wire and you can change out or add wire later. The cost in $$ is about the same between conduit and thin insulation indoor wire vs. the heavy thick direct burial landscape wire. Don't go less than 12 gauge, and I use 10 gauge.

When connecting wires, try to solder if you can, if the connection is underground, by all means solder and either encapsulate the joint or dip in "liquid rubber".

Also on wire, if you can use solid, it is more sturdy than stranded, especially against corrosion. Stranded wire will "suck in" moisture along the strands and can corrode inside the jacket. If you use stranded, then solder to connectors and make sure the solder wicks in under the insulation, although that will not completely prevent oxidation. Spray liquid rubber around where teh wire enters the insulation.

The issue here is while stranded is MUCH easier to handle, the thing strands can be much more easily "dissolved" than a single nice thick conductor, and the gaps between the strands can "wick" moisture way up inside an insulated wire.

Worse, the landscape wire is many more strands of finer copper, MUCH more susceptible to corrosion. You can use the indoor 120v stranded wire and it will last much longer.

When you connect to the wire, normally best practice is to use crimp on terminals. Do not get the insulated ones, because you ARE going to solder too. Get a GOOD crimping tool, not just something that squashes the barrel of the connector.

Solder! Yes, solder all connections, even crimped ones. Don't argue, do it.

Testing the system

Get a volt meter

Buy one. Honestly, don't whine they are too expensive, you can get the one below for $5 or even free on sale from Harbor Freight

On DCC, since you are measuring AC voltage, the order of the probes does not matter, nor the exact accuracy of the meter since a cheap meter cannot properly measure the DCC waveform. (You can however attach a full wave bridge to the track, and then measure the DC output - add a filter cap - this will give you an accurate reading of DCC voltage.

But for relative voltages or pretty much go/no go situations this meter is adequate. I also outline how to find "weak" connections easily, it is SIMPLE.

The need to test track voltage under load

This is the first concept you need to "get". Voltage can be affected by the load "against" the voltage. Let me give you an example you probably already know, but did not really understand. When a car fails to "turn over" when trying to start, do you remember being told to turn on the headlights, and see if they go out when trying to start?

The reason is that if the battery cannot supply enough juice (current) then when you try to crank the motor, the voltage will drop so low that the headlights will go out. Lights are very sensitive to voltage. But if you measured the voltage of the battery with everything off, it would probably be 12 volts.

So, putting a load on the battery will give a true test of the capacity (amperage / current) of the system.

Likewise you have the same situation on your layout. If there are no loads on the rails (locomotives running, lights), then the voltage can LOOK fine, but under load, the voltage can drop if you have bad connections, poor wiring, or a bad transformer.

Therefore you need a way to put a load on the rails and WHILE the load is applied, you measure the voltage in various spots. If the voltage is low, then you have a bad connection or wire. This low voltage is called "voltage drop", meaning the voltage "lost" between the transformer and the locomotive.

The "heavier" the load, the more voltage is dropped or lost in the bad wiring/connections.

So one way is to have a huge locomotive pulling a very long train... but of course it's moving so that makes it tough to measure. What you need is a way to put a load on the rails at any arbitrary point, and to draw a lot of amps.

Making a load with power resistors

This is the "neatest" way to do this, with power resistors. Unfortunately it takes big expensive resistors. For measuring 10 amps at 24 volts, you need to dissipate 240 watts, and that's a lot of wattage. You need 2.4 ohms also. Luckily I had these resistors already:

But they ARE big:

So combining two them in parallel gives 9 ohms, and paralleling 3 pairs gives 3 ohms, so that will draw 8 amps. Good enough to point out areas of resistance or bad connections.

Here's the assembled load box:

Another way to build a load bank:

Cliff Jennings thought of a much less expensive way:

Cliff found some 24 volt light bulbs, put them in parallel to make the load. A much less expensive way, but alas, the 24v screw base bulbs are getting more expensive and harder to find. Notice that Cliff used 4 little black things too. Those are thermistors, used to limit the inrush current, since light bulbs draw a ton of current when first turned on, and this could trip a circuit breaker.

I looked for these bulbs, and they are now hard to find, so a bi-pin halogen bulb, like 150 watts can be found at 24 volts. Just protect yourself from touching the bulbs as they get hot.

Below is a 150 watt, 24 volt halogen, use for fiber optic lighting for about $15 from amscope.com ..  this alone will put about 6.25 amps at 24v... you can also use lower wattage bulbs in parallel. 

150 watt 6.25 amps each.

250 watt 10.41 amps

70 watt  2.91 amps

G6.35 base

1000bulbs.com   SOCK-50275199