When I was thinking about which DCC system to adopt, the most important considerations were keeping my entry costs as low as reasonably practicable whilst giving me a clear upgrade path that did not involve having to scrap stuff I’d bought earlier. I just hate having to throw things away, especially if they are not broken!
For the individual user, such as myself, the NCE PowerCab is the ideal entry system. From the outset, it gives 4-digit addressing, full control over two trains, programming on the main or on a program track, and full control of more than 2000 accessories. It comes with a comprehensive manual written in Plain English which is easy to understand. It will accept a second cab which can control another train and this can be plugged in at different points around the layout. Having three trains moving at once is probably enough for the average modeller on their own.
For someone who expects regular guests or who wishes to use computer control, the ProCab system would be the best starting point. A club would certainly need to start with the ProCab system. The PowerCab is a ProCab with the command station and a 2-amp power booster built into the handset and it allows relatively limited computer control.
NCE offer the SB3a Smart Booster as the first step to expand the PowerCab. It is a 5 amp booster and command station combined and the PowerCab handset then behaves as a ProCab and can control up to six trains. The SB3a can take up to four cabs and control up to twelve trains. Whilst the original range of “engineer’s cabs” can control only one or two trains, NCE have just released a new engineer’s cab, the Cab-06, which will be able to handle six trains just as the ProCab handset. This was first announced mid-2010 but the release date slipped until July 2011. NCE have a refreshingly old-fashioned policy on new products: they don’t release it until it’s ready. This is not the way a certain large software producer operates, releasing on schedule and then forever fixing bugs under the guise of “security updates”.
For the average home layout, this might be the only booster you would need to buy. A booster simply takes the low level DCC signal and delivers it to the track with sufficient power to drive the trains and anything else connected to that power district. We tend to refer to them as power districts to differentiate from the concept of sections as used for analogue DC control. A small layout can be split into sub-districts protected by circuit breakers, a larger-sized layout may need to be split into separate power districts by installing additional boosters, each with sub-districts protected by circuit breakers. Installing a number of circuit breakers means that only that sub-district goes out if you get a short circuit, the rest of the layout continues to run normally.
The Smart Booster can also drive any number of other standard boosters, which means that the system can be expanded as much as you would wish. True, it doesn’t have a programming track output but how often do you really need that? Any decent modern decoder can be fully programmed on the main after setting the address. There should be no need to read back CVs unless you have really got into a total mess, in which case you may need to reset and start again from scratch on the programming track.
I regard it as a safety feature, it must be a recurring nightmare for anyone who has reprogrammed every loco on the layout by accident! The Smart Booster is designed to complement the PowerCab, the original PowerPanel can remain connected to a test track on the workbench which then doubles as a programming track. The PowerCab can be plugged in to that when needed for setting up.
The PowerCab and Smart Booster allow only limited computer control, whereas the PowerPro system allows full monitoring and control. If the day should ever come when I wanted to upgrade further to the PowerPro system, then the Smart Booster can simply be reconfigured as a standard booster, so nothing becomes obsolete.
There seems to be a lot of confusion in some quarters over these two concepts. Some DCC systems (but not NCE) allow every loco to be entered into the system, often with a description, so that it can be selected from a menu rather than entering the number. This is the roster and it can be very useful for a club or multi-user system as it can also indicate whether or not the loco is allocated to a cab. However, it can mean a lot of button pressing and menu scrolling to find the loco you want.
On the other hand, the stack is the internal running memory of those locos that are currently moving on the layout under control. The stack is maintained by the command station and enables a controller to be unplugged and plugged back in somewhere else (within a reasonable time-frame) and still be controlling the same loco. If a system has a stack of two then, when a third loco is selected, the displaced loco will come to a halt. This is because it is no longer receiving updated instruction packets and all decoders are designed to come to a stop when they no longer detect regular instructions addressed to them. If a control system has a stack of six, the maximum that the ProCab and Cab-06 can handle, then you will need to scroll through the list to find the loco you want to control, whilst the others continue on their way. This is similar to scrolling through a roster but you are only scrolling through those locos allocated to that particular throttle.
So what’s the difference? For a club or multi-user setting, many people prefer the rule one cab per loco and one loco per cab, meaning that a stack of one per cab is enforced. A sole operator will want to have more than one train running at the same time even though it is only possible to simultaneously control two, one in each hand. However, a stack of several (and six seems a good practical limit) means that four or five trains can be set running whilst a sixth is under direct control. The train under control can then be left running or stopped somewhere safe and any other train then taken back by selecting it off the stack.
The question after the question: “How many wires?” The answer here is “three” – or more.
The Digitrax LocoNet wiring carries both the cab bus and the control bus in one cable so, although you might think there’s only one bus here, there are two electrically separate busses.
All of these busses carry a high-frequency digital signal and need to be kept apart to reduce cross-talk interference. In the worst case, this interference can mean that trains may not respond or they may start running away out of control, and signals and turnouts may switch at random without warning.
A simple way of immunising the cab bus from interference is to use CAT-5 network cable to daisy-chain between plug-in points. This is a twisted-pair cable which has a defined capacitance and impedance optimised for digital signals. The same can be used for the control bus between boosters. CAT-5 has eight wires (four pairs) whereas NCE’s cab bus and control bus both use four wires; the extra wires can simply be ignored or wired in parallel. For a larger layout, it is recommended that each track bus be terminated with a simple R-C snubber. It may also be necessary to terminate the cab bus lines with a 120Ω resistor (no capacitor) across the ends. No bus may ever be connected back onto itself in a ring.