I have what is a simple question for you guys but it isn't obvious to me.
I am running two bus wires under my layout, one for each rail. Let's just talk about one bus wire though. I start the bus wire and run it around the layout and when I get back to where I started do I tie in those two ends together for one continous bus wire? Or do I just keep the ends of the bus wire seperate and terminate at a strip or something? I feel like I should tie them together and then tie the power feed to the bus wire. What method to you guys use for that? Do you just solder them together?
ANy comments or pictures would be appreciated. Thanks
No, don't connect the other end of the bus wire to anything. It might feel wrong to have a wire just hanging out there connected to nothing, but the circuit is completed by the connection through the locomotive to the other rail and its bus wire, which is connected back to your base station. If you connect the bus wires to anything other than the track, you'll get a short circuit.
--Steven Otte, Model Railroader senior associate editorsotte@kalmbach.com
Yep, just what Steve says. I ran the last feeder wire to the track from the end of my bus wires. If yours are just hanging free, put a wire nut on the end, or tape.
Mike.
My You Tube
Steve is right, but not for the reason he states.
If, as you described, you connect the two ends of the "red" wire to make a loop, you will not get a short. The bus carries power which is no big deal and would actually be improved by the loop. But... the bus also carries the DCC signal, which is far more fragile than the power. Making a loop out of the bus can create signal issues.
I have the right to remain silent. By posting here I have given up that right and accept that anything I say can and will be used as evidence to critique me.
I agree that it is better not to form a complete loop. One other consideration, especially if the layout will be larger than smaller, would be to split the bus wire into two branches to keep the ends of the bus wire as close as possible to the command station/booster.
Rich
Alton Junction
I really appreciate the quick feedback guys. I feel much more confident in that part now.
Thanks!!
Lots of folks confuse the requirements of the DCC track bus vs. those of the DCC system's throttle bus.
The throttle bus should never be connected to form a loop around the layout.
However, there is no issue whatsoever with having your track bus loop around the layout.
I remember reading once that an EE had calculated how big of a loop would be necessary for propagation delay to actually degrade the DCC waveform. It was roughly the size of an (American) football field.
Just think of all those folks who have room-sized layouts with a loop of track that isn't gapped at the same point where their track bus ends. That upgapped stretch of track effectively loops their track bus, and their layouts still work just fine.
Is the track a contimuous loop? The bus can be as well. It really is your choice as either way will work.
As already stated, the size of a loop that would actually cause problems is far greater than any single booster power district would be. Once you get to those large sizes, you will have multiple booster districts and the bus (and track) won't be looped.
Do not loop the command bus.
Martin Myers
If I understand Allan Gartner correctly, in Wiring for DCC he says not to form the bus in a continuous loop.
"Even if your layout is a loop, don’t join the ends of your bus in a loop. If your loop is one big block, put one pair of insulated joiners in the track above where the ends of your bus are so that your layout doesn’t form an electrical loop with joined ends".
Rails make loops, but they are parallel and do not touch each other or there'd be a hard short. This is what happens when a metal tire bridges two rails.
So, too, can the wires of the bus form a loop. Just not with each other. That is to say, each bus wire CAN be looped back to its own output terminal from whence it comes. That loop is no different from the rail loop in the oval just above the bus. Taking each bus wire's end, bared, and winding them together, or using a Marrett, or using another type of mechanical connector to make them stay in good contact with each other will result in a short. Just like if you took the red wire and the black one in a light fixture box and joined them. Flick the switch and see what happens.
selectorRails make loops
Gartner's advice quoted by Rich, includes the suggestion that gap your rails to prevent them from forming a loop.