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.
What are the pros and cons?
Rich
Alton Junction
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.
Larry
Conductor.
Summerset Ry.
"Stay Alert, Don't get hurt Safety First!"
Rich,
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.
Mike Lehman
Urbana, IL
mlehman 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 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 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.
-Crandell
Pro -Because you are running double wire you get half the voltage line loss.
Con -You are sending two signals. If one of the signals lags the other you will have problems with your decoders reading the signal.
The creators of DCC were proud of their robust signal so the con more then likely will not affect you. Just be aware of it if you do have problems.
Lee
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.
It takes an iron man to play with a toy iron horse.
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.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
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?
greg - Philadelphia & Reading / Reading
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.
gregcbesides, don't people connect DCC to tracks that are electrically connected together, and don't those track form loops and tees?
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.
mlehman 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.
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---<gap>--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.
rrinkerAnd 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. --Randy
Yeah, but think of all the Athearn tiny bulbs that will be saved.*
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.
rrinker 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---<gap>--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. --Randy
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.)
rrinker 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.
LOL
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.
rrinker 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.
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.
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.
You need a second booster to accomplish what I drew.
rrinker You need a second booster to accomplish what I drew. --Randy
I understand that. My only point was that the current booster is integral to the command station, so I need to figure a way to install that second booster and keep the two some distance apart.
The second booster needs only two connection to the Command Station/First booster.
A. A control bus connection (looks like a phone cord, but may be "special")
B. the grounding wire that runs from one case to the other. I put the spade at each end of it under one of the screws holding the case together on the two boxes. There is no internal connection, as the cases is already grounded internally.
Mine just happen to sit about a foot apart, but 80' is no problem once you have the wiring long enough. Maybe the connections don't have to be that long and can take a shortcut, though, since your layout loops back around?
On the front of your command station, there are those jacks labeled "control bus" - that's how you connect to additional boosters. Different than the cab bus, where you plug throttles in.
The long distance isn;t a problem, because the load placed on those lines by the booster to 'read' the signal is miniscule, plus it's a differential signal, which means the electronics int eh booster looks at the difference between the two wires and not the absolute voltage. This if there is say a 1V drop, both the 'high' and the 'low' will drop by 1V - the difference between them will be the same. It's also fairly immune to interference, say the wire gets run parallel to an AC power line for a segment - there will be an induced voltage on the wires from the parallel conductors, but both the 'high' and the 'low' will see an increase - again the difference between them remains the same.
OK more technical than you wanted, but that's another part of why you can run a thin phone cord 80 some feet and drive another booster and it's better than running 80 feet of bus wire.
Pages 21-23 of the current PH-Pro manual mention the control bus and adding more boosters. Not a lot of info and no picture, boo!
Rich.
I am a firm believer in Alan Gartners site. He even has scope traces that show ringing on the signal part. Also twisting long buss runs has been proven (seen it myself) to limit outside interferance from strong wirless signals. I know the debate about the track not being twisted and all. First the rail is nickle silver/ tin based metal and it is not round as in copper wire. The copper by it base element is more conductive to signals than any other base metal besides gold. Why do you supose they use so much inside antennas?
No never loop the buss. Ringing and feedback will result.
Any booster made in the past 15 years already has termination circuts built in. Early days of DCC suggested buss terminations before modern solid state boosters. Early boosters were not much more than tranformers that stepped up the command stations voltage and digital signal. My former club had an early Lenz booster (I think it was an LZ3) that was 3 amp and had no breaker in it. Any short and there was something fried. Then we wired in some 1156 bulbs. It was later replaced with a modern booster.
Pete
I pray every day I break even, Cause I can really use the money!
I started with nothing and still have most of it left!
mlehman The second booster needs only two connection to the Command Station/First booster. Mine just happen to sit about a foot apart, but 80' is no problem once you have the wiring long enough. Maybe the connections don't have to be that long and can take a shortcut, though, since your layout loops back around?
Here is a crude drawing of my layout, not exactly to scale. The existing booster is there in the center of the drawing. I added the likely location of the second booster at the midway point at the upper left of the drawing. The lines represent the bus wires.
Yeah, that's roughly it. Depending on how close it is to scale, if the second boosterwas moved to the bottom left loop, that would put it closer to halfway. Then the two sets of gaps would be roughly just above where the topmost AISLE is labeled.
Keeping the runs limited in length is really more important that keeping them any exact length or balanced in length. So if that proposed location is good for power supply or other reasons, it'll be fine. Another consideration is where are the more hevaily used locations. They might be shorter in length because you'll have more operators or locos going in them than elsewhere. There's also the case where you may want to split a yard, working one end off of one booster and the other off the other. That way only half the yard will be affected in the event of a short. The same thing applies to the breakers when you place them to protect different power districts.
The idea is to faciltate keeping as many different potential shorts as seprarated as possible with however many breakers you plan to use. Be sure and take them and their gaps and feeds into consideration when possible to save yourself any duplication or complications you can.
Depending on how things are wired into the bus, it'll be easier or harder to set up the power districts. Essentially, you'll want to tap into the bus, however you break it up only where it goes directly to the breaker, then everything it protects in its power district runs from it. If you have lots of individual drops off the bus already, this can get complicated. That's how my layout is, as there's a few places that it was just easier to leave dependent on the boosters to shut things down. As you noted earlier, plan on getting the yards and industrial areas protected first, as they cause the most issues.
mlehman Rich, Yeah, that's roughly it. Depending on how close it is to scale, if the second boosterwas moved to the bottom left loop, that would put it closer to halfway. Then the two sets of gaps would be roughly just above where the topmost AISLE is labeled.
Mike, you are correct. You are getting to know my layout better than I do - - - LOL. My mental math is as bad as my applied math.
The drawing is close to scale in all but one respect. The left side of the layout is longer than shown in the drawing. I used PowerPoint and didn't take the time to scale it correctly.
The second booster does belong at the bottom of the drawing, not at the upper left, as shown on that previous drawing. On this new drawing, I moved the second booster to the bottom, as you suggested. I then placed an X approximately 40' in either direction from the position of each booster. That is where I would cut gaps to divide the layout into two segments, with each segment being powered by its own booster.
I should note that this thread started out as a question about the advisability of a continuous loop of bus wire and then progressed into a discussion of an additional booster. I do like the idea of a second booster, but it does raise many complications for what I am contemplating. Right now, I have a single booster and no power districts. I have a RRampMeter wired in line with the booster to constantly monitor the voltage and amps on the layout. I am considering the addition of a PSX-4 to divide the layout into 4 sub-districts, each with its own circuit breaker. If I add a second booster, I will have to add a second RRampMeter. If I add a second booster, I will probably have to go with two PSX-2 circuit breakers, creating two sub-districts for each booster. Nuts, this is getting complicated.
I've found no problem looping a DCC bus on a small layout. An oval of track is a looped bus. What is a small layout? Well that's one that doesn't need aditional track power boosters. When you get to the point of adding booster districts, the question of looping the bus goes away because the other end of the bus is too far away to loop.
Martin Myers
rrinker On the front of your command station, there are those jacks labeled "control bus" - that's how you connect to additional boosters. Different than the cab bus, where you plug throttles in. OK more technical than you wanted, but that's another part of why you can run a thin phone cord 80 some feet and drive another booster and it's better than running 80 feet of bus wire. Pages 21-23 of the current PH-Pro manual mention the control bus and adding more boosters.
Pages 21-23 of the current PH-Pro manual mention the control bus and adding more boosters.
Randy, thank you very much for that explanation. I went back and read that portion of the manual and the relevant illustrations. It makes perfect sense to me. Using the circuitous route seen in my diagram above, I will need 93 feet of 4-wire RJ-H cable to connect the two boosters.
Thank you and everyone else responding to this thread. It has been a big help.