I have a double main line, continuous loop layout, 160 linear feet of track on each main line. My operating system is an NCE PH-Pro 5 amp wireless set up, no additional boosters, no sub-districts. I run two short lengths of #14 AWG solid copper wires out of my command station. Each of these two short lengths of bus wire is connected in a plastic wire nut to the two ends of a much longer bus wire that runs under the double main line and back into the wire nut connector.
I have researched this issue and read that you should never form a continous loop of bus wire in a small layout. But I have a hard time finding anything that says you should, or you shouldn’t, have a continous loop of bus wire in a larger layout.
Rich,As you will recall I only had few loop layouts so,here is my limited thoughts.
On both of my HO 4X8 loopers I ran a boss wire and dropped 3 feeders…There was a slight power drop on the far side of the layout…On the second 4x8 footer I got lazy and just ran jumper from the front side to the back-the wire did run under the layout.Again there was a current drop.
I wised up on my N Scale loopers and used Atlas selectors for blocks.
I would either use a boss and feeders or Atlas sectors was I to build a 4x8 footer.
This is way over my head in knowledge of electrickery, but the lit I’ve seen indicates even a tree architecture of some kind for your bus can be controversial. There’s debate over whether it should be configured as a T or not, whether to use a terminating resistor, etc. Making a T is effectively required to do a loop. How else are you going to feed it? And there’s no place to put a terminating resistor on a continuous loop, either. Whatever issues people have with those would certainly be associated with using a continuous loop.
I guess the first thing I’d ask is, once the bus is run all the way around and come back into proximity with the other end of the bus, why hassle with joining them? I used #12 THNN wire (typically used inside conduit) for my bus, so it was a lot easier to just tie a knot in it to terminate than to solder the ends together, even presuming there are no issues with a loop.
I joined both ends together in the wire nut, rather than ending the bus wire run without joining the ends, to avoid a 160 length. If I didn’t join the ends together, wouldn’t I be better off running the wire as I have done, connected in the wire nut, but cut midway at the 80 foot mark?
It is sort of like the response an Anglican priest gave to the timid newcomer who asked him if she should kneel during prayer in an Anglican church.
“All may, some should, none must.”
It’s the same for looping buses on layouts. You may, and you may even gain a slight advantage in voltage at the far end of the loop. It might even be worth trying to see for yourself. Would there be harm in doing it? Absolutely not.
The only caution about this concept is one, and it goes like this:
You must NOT ever loop a bus wire between TWO terminals. They must only loop back to the same terminal FROM WHICH THEY ORIGINATE.
For a wider look we step back and consider that we could always have a single or double contiguous loop of rails, not gaps. That’s our track system right there. Why is it okay for our rails to channel electrons in an unbroken loop but not our bus wires? The logical response is that it is okay in both instances if we wouldn’t give the looped rail a second thought.
No, you shouldn’t form a bus loop for a DCC system. For a DC system, it doesn’t matter.
On DC, the voltage rises and falls all over the layout at the same time. I forget, though, if “DC” is true DC, or if it’s actually rectified 60 Hz AC. Anyone know? In any case, in terms of propagation speed along the wire, 60 Hz is very slow.
DCC is what’s called a “modulated square wave.” The voltage goes up and down much faster, and the way that it goes up and down is adjusted by the command station to send signals to the decoders. If you make a loop, these square wave patterns will collide at the end, and they will, in all likelihood, be slightly out of phase. The net result will be to “muddy” the waveform pattern, and make it just slightly harder for the decoder to figure out what’s going on.
For most layouts, this slight degradation of “coherence” of the DCC signal will not be noticed. The longer the loop, though, the more problems you’re likely to see.
Well, lets say you have a typicla 4x8 loop. Unless you put insulated joiners in the track, even if you don;t conenct the bus, you have a loop. It won;t matter.
Now if your layout is more linear, it would be completely pointless and a waste to join the far ends to make a loop. It shouldn’t hurt anything, but later on if you start breaking things up for signaling, you’ll end up confusing yourself because of that extra set of wires connecting the free ends.
i believe there is some degree of reflection at the end of all transmission lines. The signal, a change in voltage, propogates out at some fraction (~80%) of the speed of light (roughly 1 ft/ns), hits the trermination or impedance mismatch, and propogates backward. if you were transmitting a very hi frequency signal (i work with RF between 1-3 gHz), the reflected signal may not have reached the source before the signal changes again, and source and reflected signals may interfere (one positive while the other is negative).
for DCC signal frequencies (~10 kHz) having periods of a 100 us, and considering the speed of the reflection being < 1ft/ns, i believe the line would have to be something over 50,000 ft for there to be noticable problems. There would just be some very short duration ringing of the DCC signal due to reflections.
besides, don’t people connect DCC to tracks that are electrically connected together, and don’t those track form loops and tees?
There’s definitely some reflectivity off open-ended bus lines, it all depends on how well the booster can pull down the lines. Some systems seem to have more problems than others, but a simple RC snubber can be added to the end to stop that.
I think I’m following you here. You’re trying to avoid voltage drop at the far end of the line. That makes sense on DC, but doens’t sound right on DCC.
Mr. B put in words much better than I could one of the reasons why you don’t want it with DCC. Too much chance of garbling packets, which is why people avoid T’s and sometimes add resistors as snubbers on the end of long runs.
I’d planned for this on my layout by locating my DC system in about the center of the layout as far as running a bus was concerned. I had two DC cabs, so two buses. When I intsalled DCC, I add a command station and a booster. The booster may have been overkill but it made splitting the T much easier. All I needed to do is cut the bus at the T and feed each side separately, one from the command station, one from the booster. So virtually no rewiring and all I need to do is leave the bloack power switches in the A cab position. The B cab bus is mothballed, but could be used for other things.
In your case an added booster may be needed or may be even more overkill than in mine. But it sounds like you’re mainly worried about voltage drop? The best solution for that is a fatter bus, but that would be a project at this point.
Are you experiencing any issues that lead you to believe that a non-loop 160’ run causes to happen? It’s be easy to test, just leave the wirenut on at the 80’ mark and disconnect one of the two loop ends.
Yeah, they do. And somestimes there are problems. The issue is these are hard to diagnose for the average home user. They tend to see it as random problems, whereas the equipment to actually analyze these things isn’t cheap and requires an exprienced user. And they’re very dependent on the exact length and interaction between lines, which varuies gretaly between layouts
So the tendency is to avoid netwrok configurations known to be associated with problems, the sfae not sorry solution. Doesn’t mean something other than the good ol’ reliable daisy chain config won’t work. It very well may. The next guy may run into a problem when he tries the same thing. Thus the cautions associated with Ts and loops. Proactive avoidance of problems is the strategy.
No, I do not have any issues at this time, but I am considering setting up some power districts, and in my reading, I came across some cautions about continuous loop bus wires.
As an experiment, I will cut the bus wires at the 80’ mark and see if I notice any difference.
Should I add a stubber on each end of the cut bus wires?
My busses are in the 40’ range and i have nothing – no snubber, no problems. It’s something I wouldn’t bother with unless you started having issues where it seems like commands are being garbled, etc.
Now as for the cautions about a continuous loop bus with multiple power districts, this has something to do with avoiding ground loops, which are generally bad no matter how they turn out as they lead to wierd voltages, etc. I know my NCE command station and booster are specifically grounded together to minimize that, but the caution about the loops is a way of avoiding that issue with wiring out on the layout itself.
It’s also the case with the protection circuits in power districts that the timing of the offending short drives how they deal with it, either trip and shut down or not. Avoiding a loop makes sure there’s only one path that the power district controls…
And with that, I’m sure someone who knows way more than me will probably step in and say that’s not quite right, but that is a plain language description of what’s going on…I hope.
80 feet, that’s a long bus run. Even with #12 wire. Even if you don;t need the extra amps, this is getting to the point where a second booster would make sense, then you could have no more than 40 feet:"
–40ft—Booster—40ft—–40ft----booster----40ft
With 80 feet out each way, snubbers might be needed, if there is any erratic control at the farthest ends, that would be it. Most importantly, do the quarter test at the far ends, make sure everything shuts down as it should. 80 feet, 160 feet total circuit, has a significant drop even with #12 wire. And of those long bus runs are #14 - there has to be noticeable slowing of locos at the farthest points, even a 1 amp load out there is almost half a volt drop with #14. At a full 5 amp load, there’s over 2 volts dropped.
Yeah, but think of all the Athearn tiny bulbs that will be saved.*[:D]
Yesh, that’s some significant voltage drop.
I actually run my NCE system at 12.5 volts. Athearn bulbs last longer than the first ops session. My Blackstone C-19s run cooler. And it softens those blinding LEDs. Not for everyone and it will mess with any previously installed resistance values. But you want to do it right, not via voltage drop.
Some time ago, many years in fact, I added snubbers about every 10 to 15 feet or so at the suggestion of other forum members on the Yahoo Groups NCE-DCC forum.
If I added a second booster, where would I place it to accomplish the diagram that you drew, Randy?
My operating system is an NCE PH-Pro 5 amp wireless set up.
Hmm, I don;t think snubbers every 10 feet do anything worthwhile, except possibly mess with the DCC signal. Definitely overkill there - they are only really needed, if at all, at the far ends of the bus to prevent ‘ringing’ - so called because using an oscilloscope you can see the echo return back into the line like the ringing of a bell.
To accomplish what I drew, you’d set it up, well, like I drew it. One booster about 40 feet in from one end of the layout, the other about 40 feet in fromt he opposite end. Midway along the 80 feet between them, gap both rails and cut the bus. It’s not super critical that all segments be eaxctly the same, if the middle of that 80 foot space isn’t convenient to cut the bus, shift it a few feet either way. Or say it’s in the middle of your yard - have one side continue and feed the yard, and have the other bus contiue to feed the main past the yard, so maybe each segment is 50 feet long instead of 40, they’d overlap there, one feeding the yard and one feeding the main. No big deal.
You can still add the PSX’s to further divide each segment into more sub districts so that a short in one place, like the yard, won’t shut down half of the layout (since there would be two boosters, a short in one half of the layout would not affect the other half, even without the extra breakers.)
I thought the same thing when I set them up but, at the time, snubbers were all the rage on the NCE-DCC forum, so I figured, what the heck, and I did it. Didn’t have problems before the snubbers were installed, didn’t have problems after the snubbers were installed.
That probably sounded like a dumb question, and maybe it was, but I have an NCE PH-Pro 5 amp system. The booster is contained in the same enclosure as the command station, so I cannot separate it from the command station by 40 feet.