Is there any advantage to connecting the ends of the bus lines for a continous run circle on a DCC layout, or should the terminal points just be left alone?
Hi there. What is the configuration of the layout? Can you post a plan?
Simon
it would reduce the wire resistance by half at the mid-point and presumably reduce reflections.
greg - Philadelphia & Reading / Reading
Hi Wil,
Conventional DCC wisdom and some DCC vendors specify that the ends of a DCC bus should not be joined. Specifically, Digitrax specifies that each end should either just be left empty or terminated with a device called a snubber. Not sure about other vendors but I have not seen any examples of joining the ends.
Checking Allan Gartner's DCC site, it suggests snubbers for terminating the ends of the bus but not connecting them.
Hope this helps.
Scott Sonntag
If there is one absolute about this question, it is this:
Do NOT close the loops crossed. That is, do not connect the 'positive', left, or red wire issuing out of one output post on the base station to the other wire issuing from the opposite output.
You can fashion a loop back to the same output post, but do it with the same wire.
As to whether-or-not it's a good idea, that part has been debated at lenght at least once a year in my 15 years in the hobby. I don't recall there ever being a consensus.
WilScarletMacaw Is there any advantage to connecting the ends of the bus lines for a continous run circle on a DCC layout, or should the terminal points just be left alone?
Rich
Alton Junction
Hello All,
In the September 2021 National Model Railroad Association (NMRA) magazine "The Pulse Of DCC" column; pg. 38-45, focuses on bus wire size and amperage drop.
Secondarily it addresses DCC signal distortion.
On pg. 42-45 it talks about the phenomenon of DCC signal "ringing" and "snubbers" or "Signal Termination Devices"- -RC (Resistor-Capacitor) Filters- -at the terminus of the bus wires.
A DIY schematic of an RC Filter is shown, along with a screenshot of an oscilloscope capturing the "ringing" effect.
If you are lucky enough to have a large pike most DCC manufacturers recommend using powered facia panels to "extend" the DCC command signal for optimum signal flow and eliminate the "ringing" effect.
These panels have auxiliary power supplies to help "boost" the DCC signal to the command station/boosters.
Adding powered facia panels is a cheaper alternative to adding command/power boosters, if your aim is to strengthen the DCC signal over long distances to the power booster(s).
They do not provide more amperage to the system to power more locomotives, as additional boosters do, or create power districts.
DCC signal distortion- -"ringing"- -is different than the loss of power over longer bus runs.
If you need increased amperage to run additional motive power and current drawing cars or, large power districts, then additional power boosters would be the way to go.
"Uhh...I didn’t know it was 'impossible' I just made it work...sorry"
gregcIt would reduce the wire resistance by half at the mid-point and presumably reduce reflections.
The DCC guru, and electrical engineer, I know has told me that on a large layout connecting the bus into a loop is advatageous for exactly the reasons Greg mentioned.
In actual application, I think Rich said it best. There will probably be no noticeable advatage.
-Kevin
Living the dream.
When I built my first large layout back in 2004, it was a continuous loop, 162 foot double mainline, built in an L-shape. The bus wires were also continuous loop directly under the double mainline. I never had a problem with that wiring arrangement, and I had plenty of feeders to avoid voltage drop.
Then, along came the notion of DCC snubbers. I saw no reason to install them, but I did anyhow because it was all the fashion. Later, the consensus seemed to be that snubbers weren't really required on home layouts.
When I built my new layout in 2018, I again built a continuous loop double mainline. But, my dear friend, the late Randy Rinker, convinced me to use power districts, each with its own bus wires, none longer than 50 feet. I skipped the snubbers.
My obeservations on the topic(s):
1) How many folks start out with a loop of track and a single set of feeders, which is what pretty much all DCC manufacturers tout as "how easy it is to get started"? Those are basically a just a circular bus, although with the track forming that bus instead of copper wire. It isn't a problem.
As far as signal reflection, I saw once where someone (an EE) used the DCC signal frequency, etc, to calculate the size of a loop needed for it to be an issue. The resulting loop size was roughly large enough to encircle a (US NFL) football field. But due to wire resistance, a loop that large would require electrical sections with separate boosters anyway, making signal reflection moot.
2) Snubbers: It depends. The subject regularly comes up on the NCE list on groups.io, usually with lots of discussion. Some folks swear by them and insist everyone needs them, others say they've never used them and never had an issue, etc. It goes back and forth, sometimes comically. On the Digitrax list it only occasionally comes up, usually by someone saying "I saw this big discussion about snubbers on the NCE list. What's a snubber?" My personal opinion: Unless you have a specific problem that has been identified (by use of an o'scope) as ringing, you don't need snubbers.
One thing you should NOT ever do is loop your control (throttle) bus. Digitrax specifically mentions this in one of their KB articles, although after a quick search I was unable to find anything there one way or the other about looping the track bus.
jjdamnitIf you are lucky enough to have a large pike most DCC manufacturers recommend using powered facia panels to "extend" the DCC command signal for optimum signal flow and eliminate the "ringing" effect. These panels have auxiliary power supplies to help "boost" the DCC signal to the command station/boosters. Adding powered facia panels is a cheaper alternative to adding command/power boosters, if your aim is to strengthen the DCC signal over long distances to the power booster(s).
I think you may be thinking of the Digitrax LNRP. While it is built into a fascia panel it is much more than just a powered fascia panel - it is a Loconet repeater module. Digitrax does sale powered fascia panels that are not Loconet repeaters (UP5, which can be powered or not depending on your needs), and they do nothing to boost the DCC signal. They can prevent devices from loading down the DCC signal because they can provide power to the devcies to keep it from drawing power from the DCC signal (in Loconet, Railsync is the DCC signaland is used to power throttles and other devices that are not powered separately).
Most other DCC systems don't even pass the DCC signal through the fascia panels in which case a powered fascia panel would have no effect on the DCC signal.
is this addressing ringing of the DCC signal on the track bus?
CSX Robert(in Loconet, Railsync is the DCC signal and is used to power throttles and other devices that are not powered separately).
huh? do they Railsync to connect the command station to boosters?
context?
Yes, they use Railsync to connect the command station and boosters. Railsync is the DCC signal before it gets boosted to track voltage and current. Loconet uses six wires, two for ground, two for Loconet data, and the last two are Railsync, the differential DCC signal. When you plug a throttle into a Loconet fascia panel, if the throttle does not have a battery and the panel is not powered separately, the throttle will use the Railsync lines for power. If you plug in too many throttles, you can place too much load on Railsync. By powering the fascia panel separately, the throttle draws its power from that power source instead of Railsync. While this does prevent the throttles from overloading Railsync, it is not boosting it.
thanks for the explanation.
is the reason they include the Railsync signal in the fascia panel bus to connect the command station to boosters? or are there DigiTrax devices that plug into the fascia panel that actually use the DCC data?
The answer is, both!
On a given layout**, there is usually only a single LocoNet instance. That LocoNet will connect the command station, additional boosters, BDL168's and whatever other devices need Railsync, as well as wired throttles***, your LocoNet interface device (PR3, PR4, LocoBuffer, etc) and other devices that don't need it. Various iterations of the UPx (fascia) panels available over the years have various combinations of jacks that do/don't propogate Railsync, so you need to have an idea of what you can plug where and still have it work.
**Some VERY large layouts run multiple LocoNets, separating different types of traffic (For example, throttle and booster on one and signaling on another), along with something like JMRI to logically bridge them. But since the LocoNet is event-driven rather than polled, and runs at roughly 19,200 baud, that's rarely needed.
***If you have batteries in your wired throttles, and/or provide external power via the UPx's, the throttles will use that power instead of drawing it from the Railsync lines.
gregc thanks for the explanation. is the reason they include the Railsync signal in the fascia panel bus to connect the command station to boosters? or are there DigiTrax devices that plug into the fascia panel that actually use the DCC data?
betamaxSo there are no devices that use the DCC/RailSync that would plug into the front (or side) jacks.
thanks for the clarification and describing the locations of the connectors. (another learning experience)
can't imagine any devices other than boosters or possibly stationary decoders that would connect to the Railsync bus.
It's a simple circle, about 14 feet.
SeeYou190 Thanks. gregc It would reduce the wire resistance by half at the mid-point and presumably reduce reflections. The DCC guru, and electrical engineer, I know has told me that on a large layout connecting the bus into a loop is advatageous for exactly the reasons Greg mentioned. In actual application, I think Rich said it best. There will probably be no noticeable advatage. -Kevin
Thanks.
gregc It would reduce the wire resistance by half at the mid-point and presumably reduce reflections.
WilScarletMacawI can't recall exactly when I bought my NCE Power Cab, but it was probably before 2010...I've been able to use my Power Cab successfully with my DCC locomotives on a simple circle of EZ track...
OK, knowing what DCC system you have and its age helps immensely.
According to the NCE website, "This 2 Amp system can operate up to 4 HO locomotives or 8 N scale locomotives running at the same time."
Has anything changed as far as power consumption- -have you added any locomotives or powered (lighted) cars lately?
Do your run DC and DCC locomotives simultaneously; even having the DC units parked on "live" track?
WilScarletMacawI have to suspect the over 10 year old wiring on my layout.
I'm not suggesting that it isn't the wiring.
However, unless you live in a highly corrosive environment and the pike has been stored outdoors I suspect it might be something else.
Your Power Cab might be due for an upgrade. Check out this link...
What Power Cab Version Do I Have.
WilScarletMacawI actually have four sidings which are have DPDT switches so that they could be turned off during DC days.
What you are describing now is more than just...
WilScarletMacaw...(A) simple circle, about 14 feet.
The DPDT switches could be suspect. But if they were only used for block selection of the sidings they might not be the reason for...
WilScarletMacaw...some type of electrical problem that resets my NCE Power Cab as I try to accelerate the engine.
Not knowing how many locomotives you are running and if they are sound equipped or not, I suspect you have exceeded the 2 Amps of the system.
Have you tried running only one locomotive on your "mainline" with no cars and without using the sidings, testing only one unit at a time (having removed all other powered units from the pike)?
Does this happen with all the locomotives or only one specific unit after testing?
Now, knowing more details on your particular situation can help the great folks on these forums.
Do you clean your track?
How often?
By what method? (Without opening the "Track Cleaning" can of worms debate.)
Thank you for your answers.
All of your responses have helped create a better picture of your situation.
Keep the answers and questions coming and...
I'm no expert but I can't see how a bus line, connected to form a circle, and feeding a 14 foot loop, could cause running issues. I can only see benefits as mentioned by others. And I can't imagine you running more than 4 engines on such a small loop.
What do you mean by the system "re-starting"? Would that mean that there is a short? If that is the case, you need to hunt that down. I would start by removing all the engines on the track, and checking the engines one by one and seeing what happens as it goes through the layout. It could also be a piece of rolling stock shorting in the switches.
snjroyI can't imagine you running more than 4 engines on such a small loop.
On my 4'x8' pike I run a consist of four (4) GP40s, and a consist of three (3) GP30s simultaneously.
A 44-tonner, 70-tonner, GP38-2, and an RS-3 are used for switching operations while the two (2) consists are running.
I use the NCE 5 Amp wireless system.
Track power is not through a bus. Track power, from the command station/booster, goes to a barrier strip.
From the barrier strip, track feeders radiate out.
The entire pike is protected by a single EB1 between the command station/booster and the barrier strip.
An MRC AD 520 auto-reversing unit powers the wye.
It is possible to run multiple locomotives, which may exceed the limitations of the power booster, on a small pike which could cause power fluctuations.
Until we hear back from the OP it's all speculation and presumption.
Impressive... I guess I was assumming a single loop.