Page 17 - January February 2017

All decoders can have two addresses, a short one, which covers addresses 1 – 127, and a long one, which will take a number from 128 to, in most cases, 9983. CV29 is used to determine which of these addresses the loco responds to, among other things. The good news here is that with most DCC systems you just enter your chosen number, and the system determines how to program it into the decoder and how to set CV29 so that the loco responds to the correct address. From then on, assuming that you used the number on the loco’s cab side as the address, you just select that to run the loco.
Next up is the use of CV3 and 4 to control acceleration and deceleration. The larger the value in these, the longer the loco will take to accelerate or decelerate when the throttle speed setting is altered. You might want to enter settings between 5 and 20 in here, and watch the difference this makes to the way that the locomotive moves.
CV2 tended to be used on older decoders to be able to give the loco a kick to get it started. You’ll recall on DC, most locos required that the throttle know as turned a quarter or a third of the way round before the loco responded? Older DCC decoders sometimes were a bit like that too, needing the throttle wound up before the loco started, and then it might well spring into action, just like on DC. CV2 was used to get over this, but it’s been supplanted in more modern decoders by Back-EMF control. The Back-EMF control watches what the motor is doing and adjusts for speed and load changes such as going up and down grades automatically, as well as improving starting and smoothing out the slow-speed running. Back-EMF settings are, in the main, adjustable, but not via standardised CVs; these vary from decoder to decoder. Doing such adjustments is beyond the scope of this Back to Basics article.
But what is in scope is, as I mentioned, the need to be methodical about CV tuning, and also the need to record what changes you’ve made. As to the first of those, here’s what I’d suggest that you do.
First, work out and note down what you want to do in railroad as opposed to CV terms. Keeping things simple, for now, this might be:
 Set acceleration and deceleration for a switcher locomotive – which tend to accelerate quite quickly.
 Set up the lights. You might want special effects on a given light output, such as a rotary beacon on the cab roof.
 Determine what function keys you want to use for light and other functions. It’s a very good idea here to ensure that all locos use the same function key for the same function, and to note any special cases on the locomotive card.
Next, using the decoder documentation, work out what CVs you need to change, to what values, to achieve this.
Then, go and do the programming. This is where Ops mode comes in more than handy, because you can do this on the layout itself, with the loco running if need be, and instantly see the changes. But still, be methodical, change one CV at a time and check that the change has done what you expected.
DecoderPro
Again, probably a bit out of scope for this article, but we’ll mention DecoderPro here. This is a computer program that, among other things, makes programming decoders easy and straightforward, and enables you to store all the settings you’ve made. It’s open-source, and free to download and install. It does require a computer interface to your DCC system, but you’ll find that in some shape or form, that is available. Indeed, some DCC systems have a computer interface integrated into the system.
Next, you put the loco on the layout and put it to work.
The DCC Layout
Of course, to do that, you have to have wired the layout for DCC. If you're building a new layout, you'll find that DCC wiring is pretty simple; you just need to connect the system to the track, and then ensure that every piece of rail is powered. Again, this advice gets complicated by the type of points you use, dead or live frog, but the rule still is to make sure that each rail is powered, all the time. If you're using proprietary track, Peco, Atlas, ME or whatever, the manufacturer’s instructions on wiring their points will help you greatly.
You may also have an existing DC layout that you'd like to convert to DCC. This can often be as simple as connecting the DCC system in place of one of the cabs, switching all the block controls to that cab, and running the trains with the DCC system. What I would say here, though, is to resist any temptation to run both DC and DCC on the layout at the same time. However careful you are, you'll one day bridge the two, either by moving the wrong switch on the control panel, running a loco across a track break, or even through a derailment. When this happens, the usual result is that a lot of smoke comes out of one or usually both power systems - DC and DCC - and sometimes also the offending loco, with the end result that nothing then works, and a fair amount of swearing.
Now, we mentioned earlier that DCC offers more available power at the track, and the need to ensure that the DCC system's breaker is always able to detect and handle shorts. This means that the wiring on a DCC layout - a layout built for DCC - is usually differently done than for DC, and to be honest, DC layouts should really be converted to suit. DC layouts are wired with the expectation that only one loco will ever be on a piece of track, and so are often wired with quite small wire.
DCC layouts are different. All the track is powered, all the time. That enables us to simplify the wiring by running what's known as a track power bus or track bus, around the layout and also to be able to support the booster's ability to deliver 5 amps of power, or more. On bigger layouts, this track bus may be subdivided by the use of multiple boosters or power breakers, but the principle is the same. That bus need be nothing more than a pair of 1mm or so copper wires - bare - running an inch or so apart all around the layout. The solid conductors found in house mains wiring cables work well here with all the insulation stripped off. Then, you have short droppers of finer wire - the same size as used for DC wiring is Ok, if they're no more than a couple of feet long - connected to the rails. Like the DC layout, it's a good idea to try to power each piece of rail so that you're not carrying power through lots of rail joiners. You then check - the standard tool being a quarter dollar or 10p coin - that the booster reacts properly to a short on the rails, every few inches. If it doesn't, then either you don't have any power at all to one rail, or not enough power capacity in the wiring. Either way, you need to find and fix the issue. And then run trains.
Accessory Decoders
Check out, too, the choices you have for switching your points and their live frogs, because with DCC you do have a greater choice than is really the case with DC. You can of course use manually controlled points, with microswitches to change the point frog polarity and use the DCC system just to operate the trains. You can stick with tried and tested slow-motion point motors like Tortoises, or use Peco snap- actions, and still operate these with control panel switches.
Or you can use DCC accessory decoders to drive these point motors. DCC accessory decoders are available that will drive either slowmos like the Tortoise or snap action solenoid motors. Accessory decoders are also available that will operate servos, and there are even magic devices that will change the polarity of a point frog as and when it is needed by the trains running over it, no switches required!