Adapting DCC to Your Layout
Adapting Your Layout For DCC
The DCC system for your layout will consist of one or more throttles, one command station, and one or more boosters. The Functional Block Diagram [repeated below] shows multiple throttles attached to the throttle bus, and multiple boosters attached to the booster bus. How many you need depends on your goals. You'll select as many throttles as you want, and as many boosters as you need.
Boosters and Power Districts
Note on the Functional Block Diagram that all track on the layout is divided into districts; each district with its own booster. If on your layout only a few locomotives will be active at any time, then you may only need one booster, and the entire layout might be powered as one district. However, by dividing your layout into districts, and powering each district with its own booster, dozens or even hundreds of locomotives can be powered. Since all districts receive the identical signal at the same time [that is, every booster simply amplifies the common signal present on the booster bus], multiple districts and boosters are not needed for control, they are needed for load management. A booster can typically power a few locomotives. Though it might be possible to design a booster to power hundreds of locomotives, such a booster would resemble an arc welder, and would function as such... if anything ever went wrong, it could turn your fine brass import into a pile of molten metal and smouldering slag.
Districts are sized for the maximum number of locomotives to be powered in that district. As shown, Districts 1 and 2 are powering locos 9901 & 9902, and 9903 & 9904, respectively. On your layout, both districts might be long sections of mainline, on which only a few locomotives are active at any time. So the boosters for Districts 1 and 2 could be sized to power, for example five locomotives, allowing a 3-loco head and 2 pushers. However, if on your mainlines, you expect to run 100-car unit trains with 4-loco heads, 3 mid-assist locos, and 2 pushers, the boosters for Districts 1 and 2 must be able to power at least nine locomotives.
As shown, Booster N is wired to power three parallel tracks. On your layout District N might be a teardown yard for incoming trains, in which case, the Nth Booster might need to power only a few locomotives – the local yard switchers. However, if District N is a locomotive service and staging yard, its booster might need to power a dozen or more locos.
The electrical load that a locomotive presents to the DCC system is a function of physical size of its motor. For example, a Geep in 'N' scale draws less current than the same Geep in 'HO', which draws less current than the 'O' scale version. So your layout's scale will significantly impact the design of your DCC system, at least when sizing boosters. Current consumption of locomotives can vary widely, but the common rule of thumb is that a modern 'HO' locomotive will consume about 500 milliamps, and an 'N' scale loco will consume about 250 milliamps. At larger scales, locomotive current consumption varies widely; individual investigation is warranted. The addition of sound can add as much as 75 milliamps to a loco's consumption.