DCC layout wiring 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.

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. If you are running DCC and only run one loco ever, save your money, run DC.

A loaded locomotive can pull about 2 to 2.5 amps easily. Lighted cars can draw 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.

Now, to voltage, and this 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.

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.

Take into account track material & construction

 types of metals, types of joiners

 

Environment

 

Power districts / isolation

 

Plan autoreversing sections and locations of autoreversers

 

Implementation details

 bury wire / conduit

connections

soldering


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

meter

Since you are measuring AC voltage, the order of the probes does not matter, nor the exact accuracy of the meter. You will be measuring the relative voltage or pretty much go/no go situations. The technique will be explained, 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:

 resistor1

 

But they ARE big:

 

resistor2

 

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:

resistor bank

 

 Another way to build a load bank:

Cliff Jennings thought of a much less expensive way:

 

SAM 1266

SAM 1269

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.

 

So, another alternative is to use small halogen bulbs, and they can be found inexpensively, just protect yourself from touching the bulbs as they get hot.

 

 

 

 

 

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