I have a 4x6 basic loop of track with a few sidings. I read Alen Garders page discussing track wiring and he suggest putting insulated rail joiners in my track where the bus ends under the table so not to form an electrical loop. Why is this neccesary? I tested out my locomotives with just two feeders from the track plugged into my NCE power cab (continuous loop there...) and it worked fine. I forgot to put the insulated rail joiners in and the track is all secured down. I would have to cut the track now to insulate it.
It's not necessary.
It's discussed in this thread. The second page goes on to snubbers and the third to circuit breakers
http://cs.trains.com/mrr/f/744/t/225721.aspx?page=3
No one explains what happens when a loco truck bridges the insulated gap Seems to me it reconnects the loop.
Cutting the rail isn't that big a deal. Some people claim to have difficulty using a dremel tool and disk to cut a gap. Maybe they don't steady their hands, dunno. A razor saw makes quick work of it. most people fill the gap with a piece of styrene and super glue.
Henry
COB Potomac & Northern
Shenandoah Valley
I don't see the track making an "electrical loop".
It looks more to me like two parallel "wires". Which would halve the resistance. Nominally, half the power would go one way and half the other. Nominally.
In the cited topic above, someone dealt with the possibility of a phase shift because the DCC signal is sent down "two" wires. Turns out it takes about 10 miles of wire before there can be a problem.
I wouldn't cut the gap.
Ed
It is not necessary for this day and age. I have a very old article from the early 1960s somewhere and ( I stand to be corrected ) it said a closed loop could cause TV interference on TVs using bunny ears and possibly other electronics. In this digital age, I think it is just a "hanger on" out of date caution.
Brent
"All of the world's problems are the result of the difference between how we think and how the world works."
BATMAN It is not necessary for this day and age. I have a very old article from the early 1960s somewhere and ( I stand to be corrected ) it said a closed loop could cause TV interference on TVs using bunny ears and possibly other electronics. In this digital age, I think it is just a "hanger on" out of date caution.
Note that the article precedes DCC.
I think what they're talking about is the possibility of your trackwork having a overall length approximating the wavelength of a TV signal. Since a rabbit ear antenna was about 5', your layout would have to, somehow, conform to that dimension. If that were the case, it MIGHT interfere with the signal making it to the television.
Anyway, IF it were a problem, it wouldn't be DCC related. It would happen even if there were no power on the track at all.
Having been around in the days of rabbit ear antennae and b&w television, I don't recall this being a problem.
Similar situation . . .
I have two peninsulas and each is roughly 18 feet long. Both peninsulas have track along the outer edges that goes roundy-roundy and forms a hairpin curve where the track is about 35 feet (or more) in length. Underneath the deck are the normal white/black #12 buss wires. Nothing is laid as yet, but I am getting close to doing so. Really close.
Should I gap the track at the apex of the 180-degree curve? Should I gap (terminate) the buss? Both? Neither?
Robert
EDIT: Hang on a sec . . . I followed the link that BigDaddy provided. That might clear things up a bit.
EDIT #2: Nope. Interesting buggy ride, but it did not clear up anything.
LINK to SNSR Blog
Hello all,
As I read your post I believe you are talking about to two separate things...
The first is the track and it's polarity.
Second, is the bus or control wiring.
I am not familiar with the author and the article you sited.
Regarding the trackage, as long as you do not have a reverse loop, there is no need to use insulated rail joiners in either a DC or DCC system.
The caveat, if you are using DC and have block control each block needs to be electronically isolated.
If you are using DCC and have block detection or block circuits then you also need to separate these blocks with insulated rail joiners or physical gaps.
In regards to the control bus on a DCC system.
With digital signals there are two; extremely simplified types, self-terminating and non-terminating.
With a non-terminating signal a device; commonly known as a "dongle", is used to terminate the signal. This device "absorbs" the signal so signal bounce-back is eliminated.
This system can also be wired in a loop so the signal "terminates" at the source.
A self-terminating signal does not require a signal terminating device, nor should it be "looped" back to the source.
With DCC signals no termination device is necessary. The bus signal self-terminates.
If the track is a single loop, either DC or DCC; even with spurs, no insulated rail joiners are necessary.
Hope this helps.
"Uhh...I didn’t know it was 'impossible' I just made it work...sorry"
jjdamnitWith DCC signals no termination device is necessary. The bus signal self-terminates.
How exactly does it "self terminate"?
https://ncedcc.zendesk.com/hc/en-us/articles/204128735-Snubber-RC-Filter
https://ncedcc.zendesk.com/hc/en-us/articles/204633765-Wiring-Standards-for-Large-layouts
Also here is the source of the original posters questions.
http://www.wiringfordcc.com/track_2.htm#a47
On a small layout, you can probably get away with an unterminated bus. Large layouts will not work properly without RC filters and properly twisted wires, separation between the cab bus and dcc track bus, etc.
To the OP:
If you ever plan on expanding your layout, it might be a valuable idea to follow best practices. A simple Atlas track saw is all you need to gap. A snubber (RC filter) on a small layout is probably not necessary, unless you start having the problems listed on NCE's website. Except one of those problems is a blown decoder, a capacitor+resistor is probably cheaper than a sound decoder, so probably worth the trouble and investment ($5 for track saw+$1.00 for capacitor +$1.00 for resistor).
The snubber can be at any point on the bus - even inside the booster.
NCE seems to talk a lot about using snubbers - Digitrax tends to say they aren't needed. We don't have them on our 28x160 foot club layout, and never have any issues. Differences in the drive circuitry in the booster, I would say.
As for loops - 2 layouts ago, my layout was an 8x12 'donut' with a dounle track loop with crossovers plus a yard and some other sidings. The only palce I had insulated joiners was in the two crossovers between the loops, as my intent was to make them different power districts. Never had a problem with it. Maybe if it were 10x that size of a loop, there MIGHT be signal propogation issues. But there certainly weren't at 8x12, and there won't be with a 4x8.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
wish someone could explain what the electrical issue isd that an RC fixes.
i understand that twisting minimizes interference. But my understanding is that terminating the end of the bus is for high frequency signals producing standing waves.
greg - Philadelphia & Reading / Reading
gregc wish someone could explain what the electrical issue isd that an RC fixes. i understand that twisting minimizes interference. But my understanding is that terminating the end of the bus is for high frequency signals producing standing waves.
https://sites.google.com/site/markgurries/home/dcc-general-best-practices/wiring-planing/snubbers-rc-filter/rc-filter-name-why
Hope this provides the answers for which you are looking.
Sometimes I think Mark likes to actually make things MORE complicated. Every one of those circuits is an RC circuit, exactly as described, composed of a resistor and a capacitor of carefully chosen values. Main differnce in how each one works is the values of those resistors and capacitors.
There are a few issues with the DCC signal, First, a true sharp right angle square wave is pretty much impossible to generate. It may look nice and rectangular on a scope, but zoom in and there will always be some non-zero rise and fall time. Has to be - unless someone actually invents ideal electronic components that effectively ignore the laws of physics. But it's close enough to a square shape for our purposes.
Now, as the RLC factors (resistance, inductance, capacitance) change ont he transmission line (the bus), this will tend to distort the signal. Get too far awy from a nice sharp square wave and the decoder will have trouble interpreting the commands. Applying some RC at the far end of the bus can clean up the wave form.
Second, brushed permag motors are NOISY. Some of that noise gets back into the transmission line (track and bus). This can cause interference with the signal, and decoders to not be able to read the signal. Some RC on the line can filter this.
Third, the DCC bus IS a transmission line There are no rules that say a transmission line can only be under so many milliamps, and no more than 5 volts or something. As such, an open, unterminated end can cause a refection of the signal back into the line, out of phase with the original. Some R (and some C to block the DC component) can block those reflections. The design of the 'transmitter' (the booster) can also have an affect on how much end of line reflection you get. And how much the RLC of the line affects the signal waveform.
Long story short, call it what you will. I have not yet seen a need for them on either of my previous layouts, nor on the large club layout. I do not intend to connect anything besides track feeders and the boosters to my track busses as I build my basement size layout. I may take a peek with my scope to see what the signal looks like at the far end and go from there, but if I am not having problems with decoders going bonkers, I'm not going to add any components.
Decoders built the the NMRA specs are quite robust in regards tot he signal they can handle and properly decode. There's a lot of margin built into the pecs between what the booster has to put on the rails and what the decoder has to accept in order to be compliant. A noisy environment was allowed for in the design.
will have to re-read these explanations. Do appreciate Mark's point that DCC is both a data and power bus, and i think, unlike DC, shared by multiple devices.
but not sure there is an explanation why an RC is needed for larger layout, unless it's assumed that in general, the various problems get worst with longer length. Maybe it's not length in general, but that larger layouts are more prone to construction and environmental problems.
i'm always wary of technical explanations that sound like "voodoo & mysticism". At work, some of us are not only interested in the solution, but also the root cause of the problem.
I sometimes wonder if we are over saturated with technical data. Sure, there are "rules" as to how some things should be wired, but is it taken to the extreme for the average user ?
My layout has been DCC of one form or another for over 20 years. When I built and wired it, there wasn't all this over abundance of technical information. I wired it to what made sense to me. My bus line is a pair of (not twisted) 14 gauge wires running around under the table and tied back in where they came from .... yes, a closed loop. I have upgraded through four different DCC systems over the years and the original wiring remains intact and still performs flawlessly.
Flawless you say ? Yes, flawless in regards to the DCC functionality. ANY, and I mean ANY problem that I have had can be traced directly back to operator error or neglected equipment maintenance. But .... it "shouldn't" work very well at all based on what the "experts" have to say today. Well, maybe it works as well as it does because, at the time, I didn't know it shouldn't.
Mark.
¡ uʍop ǝpısdn sı ǝɹnʇɐuƃıs ʎɯ 'dlǝɥ
Well think about it - the length of the run will affect all three - resistance, capacitance, and inductance - of the transmission line. The track too - what is track, two conductors held a precise distance apart, insulated with plastic (or wood, or a gap in a PC board tie) and air - a capacitor.
So it's fairly obvious that length of the bus run/track that is powered from said bus has an effect on this issue. The real question is, how big is big enough for it to matter?
rrinker So it's fairly obvious that length of the bus run/track that is powered from said bus has an effect on this issue. The real question is, how big is big enough for it to matter?
Rich
Alton Junction
rrinker So it's fairly obvious that length of the bus run/track that is powered from said bus has an effect on this issue. The real question is, how big is big enough for it to matter? --Randy
I remember reading somewhere, that someone did the actual calculations to find the loop size needed for propagation delay to affect the DCC signal at the far end.
IIRC, it didn't include the effects of voltage drop, capacitance, or any of that other stuff - Just the time and distance.
The loop required was roughly large enough to encircle a football field.
rrinkerWell think about it - the length of the run will affect all three - resistance, capacitance, and inductance - of the transmission line.
my guess ("voodoo") is that it's more about interference since some large layouts don't have problems requiring RC circuits.
length increases the amount of interference that the bus is susceptible to from both external sources like lights and furnace motors and internal sources such as the number of locos on the bus, the type of motors and loads on the motors. i think ("voodoo") that RC circuit may suppress some interference. Locos with keep alives may ("voodoo") help help reduce noise.
i'll also guess ("voodoo") that wiring: twisted, location next to other wiring, size (?) will affect susceptibility and propagation of interference.
if it depends on environment and wiring, then the length at which an RC is needed varies.
richhotrainAnd, I have yet to find a definitive answer.
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.
rrinkerNCE seems to talk a lot about using snubbers
Mike
Water Level Route rrinker NCE seems to talk a lot about using snubbers You know, I've heard this sort of comment a lot since getting my NCE system 3 years ago, but couldn't recall reading about it in the manual so went back to see. Indeed there is reference to snubbers in it, but all I found was a recommendation that IF you have bus runs longer than 50 feet AND IF you are having signal issues, then try a snubber of such and such design. In fact, if I recall correctly, it even states that they more than likely are not needed. Perhaps this approach was stressed more in previous iterations of NCE equipment, but it certainly isn't now.
rrinker NCE seems to talk a lot about using snubbers
You know, I've heard this sort of comment a lot since getting my NCE system 3 years ago, but couldn't recall reading about it in the manual so went back to see. Indeed there is reference to snubbers in it, but all I found was a recommendation that IF you have bus runs longer than 50 feet AND IF you are having signal issues, then try a snubber of such and such design. In fact, if I recall correctly, it even states that they more than likely are not needed. Perhaps this approach was stressed more in previous iterations of NCE equipment, but it certainly isn't now.
Do you frequent the NCE Yahoo Group? The topic of snubbers comes up there like clockwork every few months. If there was ever a subject that could be made sticky on that list, it would be snubbers.
On the Digitrax group it comes up MUCH less frequently, and as often as not by a newer or less experienced user because they've seen/heard/read about it somewhere else.
Stevert Do you frequent the NCE Yahoo Group? The topic of snubbers comes up there like clockwork every few months. If there was ever a subject that could be made sticky on that list, it would be snubbers.
I am a member of that group. Great idea, Stevert, about making the snubber topic a sticky.
selector It's not necessary.
Technically yes.
Rio Grande. The Action Road - Focus 1977-1983
DCC isn't really at RF frequencies, but RF signal stuff is as much an art as it is a science. Voodoo may indeed be it. I just goggled at some of the things my friend showed me he built - he's a HF/Microwave guy. Components? What components? Circuit elements are made by adjusting the gap between two traces on the PC board. High pass filters, low pass filters, attentuators - there's not a physical resistor, capacitor, or coil to be seen.
StevertDo you frequent the NCE Yahoo Group? The topic of snubbers comes up there like clockwork every few months. If there was ever a subject that could be made sticky on that list, it would be snubbers. On the Digitrax group it comes up MUCH less frequently, and as often as not by a newer or less experienced user because they've seen/heard/read about it somewhere else.
Water Level Route Stevert Do you frequent the NCE Yahoo Group? The topic of snubbers comes up there like clockwork every few months. If there was ever a subject that could be made sticky on that list, it would be snubbers. On the Digitrax group it comes up MUCH less frequently, and as often as not by a newer or less experienced user because they've seen/heard/read about it somewhere else. No I don't. Maybe that's my problem! My longest bus run is only about 30' too. Never had the slightest issue. Maybe another 20' would change that? Still, doesn't change what is said (or not) in the manual.
Stevert Do you frequent the NCE Yahoo Group? The topic of snubbers comes up there like clockwork every few months. If there was ever a subject that could be made sticky on that list, it would be snubbers. On the Digitrax group it comes up MUCH less frequently, and as often as not by a newer or less experienced user because they've seen/heard/read about it somewhere else.
No I don't. Maybe that's my problem! My longest bus run is only about 30' too. Never had the slightest issue. Maybe another 20' would change that? Still, doesn't change what is said (or not) in the manual.
Well, I can speak from experience. My modular club has had instances of strange decoder issues (the ones listed on the NCE website linked). Installation of RC filters and not running the bus in a circle cured most of these issues. You cant fix human error with an RC filter.
As both Alan Gartner and Mark Gurries state each layout is unique like a fingerprint. Modular layouts especially can have wild variations in quality of work. You can probably get away with not following all of the recommendations by doing quality wiring work.
My previous layout did not have RC filters installed, but my longest wiring run was only 30ft, and I did twist the wires for the whole thing.
I have seen RC filters work, and its pretty easy to install them, why risk a blown decoder (its one of the stated symptoms). $80-120 vs $10 in parts and shipping.
In the digital world, you shouldn't have a loop. Signals crashing into each other can cause problems. On a small loop you probably won't see them.
Terminators are not required in most cases. Before installing them the waveform should be checked with a scope.
Twisting the bus wires is not an absolute requirement. All it does is keep them together in a neat fashion. Keeping the wires as close together as possible, even running them closely in parallel, reduces the impedance of the wire by minimizing the inductance. Since the rails are also consistently spaced, they have the same effect, while not as great. Inductors in parallel follow the same rule as resistors.