Just completing my benchwork for an N-scale 3-wall shelf layout.
Will be running up to 4 locos / 20 switch machines / sound / various lights
Would like to install the DCC Wiring next & have come up with 2 (stupid) questions:
The control area & DCC Command Station will be on the middle of 3 walls (Central).
I plan to run the DCC Track Bus (12 gauge) wires underneath the middle of the layout & run Track Feeders (20 Gauge) every 3 - 6 feet.
Is a single straight run of the 12 Gauge wires with feeders running to the tracks on each side of the shelf appropriate or should the Track Bus run around the layout following the track (ie in a loop)?
What do you do with the ends of the Track Bus wires in either case? Enclose them separately in a Marr connector/wrap them with tape?
I run HO, usually have 6 -8 locomotives running at anyone time using Lenz DCC with a single power district. I have a RRamp meter and hardly ever pull more than .5 - 1.2 amps. I run NS flex track with most of the joints soldered and I do have a DCC bus but it is only 16 gauge stranded wire. No regrets, no issues with current and I have feeders every 6 - 8 feet.
My layout is using CTI block detection as well to provide computer automated operations and signalling.
I use 2 terminal barrier strips where ever I connect into my buss and I use crimp on spade connections.
IMHO, 12 or 14 gauge is overkill. Issue is usually track rail joiners
You could split the bus into a T, with the stem connected to the power source/controller, and the two arms going in opposite directions to each extreme of your layout. No probs.
Leave them tidied up wth a retainer of some sort, and there is no reason for them to be covered if they are held up tight to the nether side of something and are highly unlikely to come into contact with another bare wire. Wrapping a small piece of tape around the ends wouldn’t hurt, though.
Q2 - As I said, I use barrier strips with 2 postions, (terminal strips) for connections to the buss. This means that at the end of the buss is a terminal strip where the wires are terminated with a connection to the required block feeder(#20). When I expand the layout, I add a new piece of #16 wire.
Good luck and we look forward to pictures of your layout soon!
I am glad that 16 gauge wire works fine. 12 and 14 seem so big. I am beginning to wire my layout soon and plan to use 16 for the bus and 22 for feeders.
I also wondered about what to do with the end of the bus wire so this has been an informative thread for me.
I would also advise you to coil the bus wires, about 3 to 4 turns per running foot. DCC is an alternating signal in the 900 Mhz frequency range, as such, it is possible to pick up radiated interference. Is it common? No, Is it possible ? Yes…it is very easy prevent, but your choice. It is NOT necessary to coil the track drops, those runs are too short to cause any problems.
Driline & Jeff…buss wires are like antennas, and the longer they are, the more susceptable your layout is to problems. If you have an O scope, you can observe the waveforms of fast rising and falling pulses, and your booster can be considered as a transmitter. Decoders have been blown out by this sort of inductive reactance, and people attribute it to other causes, not knowing what caused the problem.
If you want to see some of these waveforms, check out “wiring for DCC”, by Bill Gartner I believe, he has good info on this subject on his web site.
Small layouts will probably never see a problem, however, as you buss length approaches 30 feet and greater, you now increase your chances of having this problem.
As for frequency, I was referring to RF freq of wireless transmitters from NCE or Digitrax, sorry for the confusion, my fault.
Yes, a bus line is an antenna, but I am exceedingly skeptical that anything picked u pin the air is going to blow a decoder, and it is going to have minimal impact on the signal. The specs and requirements on the waveform are such that a little noise on the edges doesn’t matter, and the signal is large enough that a little interference isn’t going to change it. The rails are not twisted, and are just as much an antenna as the bus lines. The biggest source of interference is the little motor spinning around right next to the decoder. I understand the thinking behind the twisting, but I remain absolutely convinced (as an EE) that for this type of signal it is not an issue.
The point of twisting isn’t to prevent the wires from picking up the interference, you can’t stop that. Twisting is done to try to get both wires to pick up the same interference, and to essentially cancel it out when it is received. That’s way more important at high speeds and lower signal levels (say a network cable). But, if you do twist, it isn’t going to hurt anything, so feel free.
Yes, this is urban legend. This has been discussed previously. There are a number of reasons why this doesn’t wash. First, the signals on the track bus are a mirror image of each other provided by opposite polarity of the DCC pulse stream. The height of the pulses is generally 10 volts and higher depending the booster, load, distance, wire gauge etc… So to induce a signal onto another wire at close range with enough amplitude to impact the DCC pulse stream already on the wire would take very large waveform that could not possibly be generated by a 10-12 v pulse on a wire. I am not going to post the math and show how much power would really be required but I assure you it is not trivial. Second, even if such an event were possible it would induce a signal of the same polarity as the source, which would be opposite of the wire
Wow…2…countem 2 double EE’s. And I was only a lowly electronic tech for 17 years in broadcasting.
Now that I’m working in Education, I will say that I use a lot of CAT5E cable and of course its twisted because of the long runs. Twisting there makes sense. Not on a train layout with 12 to 14 gauge wire in much shorter runs.
Best practices would keep the bus lines as short as possible - ie if you have a 20x75 room, don’t cluster all your boosters at one corner and tun hundreds fo feet of heavy bus wire. Distrubute the boosters and keep the bus runs as shoort as possible and there will be no issues with twisting or termination.
