Booster connections

In my September 2017 DCC Corner column I talked about using a common between boosters on Digitrax and NCE command stations and boosters. This is especially important when dealing with both centralized and decentralized booster installations.  A centralized booster design is where all the boosters and command station are located together. A distributed design is just the opposite, with boosters located around the layout near the tracks they power.

I used to argue in favor of lining up the command station and all the boosters right next to one another, and in some cases I would still suggest doing it. If you have a layout where the command station and boosters can be placed in a central location and the power buses fan out from there to the tracks they serve, with minimal overlap, then that would be a good option. With all the components sitting next to one another it is easy to interconnect them, their wiring is kept short, plus it’s easy to trouble shoot when you can see any lights, and hear any warning and error sounds. The down side comes when you have to run parallel power buses next to one another to get from the central location out to all the track blocks on the layout. This results in overly long wire runs, increasing the chances of inductance related issues.

Now let’s look at the distributed arrangement. Many layouts have a pretty linear design with blocks located one after the other. If you run all your power buses out from a central point you’d have to run several of them alongside one another for at least part of the distance and that would be a waste of wire, and require some long runs. But what if you put a booster at the junction of two of those blocks? That way there would be no overlap and minimize power bus lengths. If you have two levels then you could run two power buses down to the lower lever and connect to two blocks there. Again, you’d have little overlap and shorter bus runs. You could locate your boosters at several points around the layout in this configuration and greatly reduce the lengths of all your runs. But how about interconnecting the command station and boosters?

When connecting boosters to a command station you have to have a cable, usually a flat telephone type cable, running between them. This cable sends out the basic low power DCC signal from the command station so the booster can boost it to final track power levels. Most manufacturers also suggest having a common wire running between them–this serves as a reference so that you don’t have problems crossing between power blocks, and autoreversing. So you would have to run a booster network around the layout but that’s a lot cheaper and easier than those longer power buses. And a single 14-12 ga wire can be used as the common wire. For optimal performance and to minimize electronic interference you would want to keep about 6″ between this network and any power bus running near it.

In the final analysis the important consideration in deciding which approach to use really comes down to picking the one that will give you the shortest power bus runs with as little overlap as possible.

5 comments

  • I have one command station and two boosters. The room is 20 by 25. The CS and boosters are co-located. Two PM42s are about 10 feet away and the third is on the opposite side of room about 24 feet away.
    I used regular 14 gauge 3-wire extension cables to reach each PM. The third one runs up to the ceiling across the room and down below the layout for about 40 foot run. No problem with voltage drops.
    The distributed PMs have no access/cooling/power problems. The central CS/Boosters are easy to monitor and operate, no cooling/power considerations.

  • Max- Excellent point. I have located all command and boosters centrally along with the PMs for the closest blocks. As the RR expands, further PMs will be located at the distant blocks. Thanks for bringing that important point to light. I’m sure Larry just forgot to include it.

  • Larry, your description of central and distributed networks is misleading. Clearly if you have multiple command stations/boosters, you also have dozens of (blocks) and widely dispersed at that. Distribution of the booster is not important, however, distribution of the required power managers is critical. A single 3-wire cable can go from central boosters to localized PMs far across the layout. This truely shortens and simplifies the layout block wiring while taking advantage of the central boosters monitoring as you stated. That is real distribution.

    • Max, there are folks who still get by using boosters alone and no power managers. Also it doesn’t make a lot of sense to keep your boosters together and distribute your power managers since you will introduce more potential for voltage drops and inductance issues. I feel it is better to place your boosters and power managers as close as possible to the tracks they feed.

      For example the Piedmont Southern is an around the walls design with about 100 linear feet of track. If I placed the command station and a second booster in the middle that means some points could be up to 50’ from the command station or booster. Keep in mind that the length of the wires from the booster to the power managers as well as the length from the power manager to the tracks are summed for the total length. So in some cases I would have 50’ of wire, well over the 30’ max for keeping inductance issues at bay. So I’d have to twist my wires and /or add snubbers.

      Instead by placing the command station at the midpoint on one side of the layout and the second booster at the midpoint on the other side it will not be more than 25’ from the tracks including the wires to and from each power manger. All I have to do is run a loconet cable from the command station to the booster and a 14 ga wire for the reference common. This reduces any voltage drop and inductance problems and simplifies the wiring as well.