The big BUS debate

16121 Views 89 Replies 13 Participants Last post by SPROGman, Jan 25, 2006

Rail-Rider

Discussion Starter · Jan 18, 2006

A few areas of uncertainty are emerging.
This is good because then, over time, we can sift through and sort out those that most obviously need clarification for more detailed FAQ, later.

For now, I am backtracking to "Two Wire?", but this sub-section should probably be headed

BUSSES?

The recent emergence of a new topic Wiring for DCC in the DCC section is opportune.
Opportune because I didn't pursue the subject of 'TWO WIRES' far enough at the time I first raised it and the link above should prove useful in this thread.

The point I didn't follow through, but perhaps should have and now must, is the terminology and principles used with regard to 'BUSSES'.
This is probably the most basic area of confusion for DCC beginners.
imho, the confusion is primarily created by unclear/ambiguous terminology and it is obvious that a digital beginner must be enabled to clearly understand the principles and terminology before any useful progress can be made (with anything but the most simple of layouts).

The previously mentioned topic "Wiring for DCC" starts out with enquiries about "The Bus".

THE Bus?
Here we hit maybe THE fundamental problem for beginners!
Mention of busses immediately makes it apparent that DCC may not be as simple as just buying a digital controller, a chipped loco or two, plug in and go. Sure, it CAN be, but the sheer volume of enquiries about busses and wiring is a dead giveaway that it is not really that simple in practice. If it were really that simple, those bus and wiring queries would have no need to exist!

To which, I must add and heavily emphasize that this topic is not aimed at someone making a fresh start with a clean slate (though it might be useful anyway), but is squarely aimed at modellers with well-established layouts who are contemplating its conversion to digital.

For these people, and there are probably thousands of them, it looks more and more certain that a simple 'two wire' setup just won't be adequate.

QUESTIONS
We were told, "all you need is two wires to the track", so why all this talk about 'busses' and wiring?
What, exactly, is a bus?
Why is a bus needed - what is it used for?
HOW MANY buses are needed?
What are the differences between busses?
How do we know which bus people are talking about?
Should we now forget the idealised 'TWO WIRE' principle as being far too simplistic for anything but the simplest layouts and therefore inadequate for converting anything more complex?
More questions?

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21 - 40 of 90 Posts

the volebender general

· #21 · Jan 19, 2006

Very good question ChriseE ,

Have a quick look at the post I first made to the question set. Ignore the rest.

Actually, a real fact did emerge from the discussion.

My idea for a second 'accessory decoder bus' (not my invention at all in fact, just a happy user of someone elses advice), it could have reasonably be said, was system specific. No need to do what TVBG suggests if you have a digitrax system etc, etc, etc. No need to run around the houses about it. Fair point.

So as I do use Lenz - If you are thinking about Lenz express net and their products on a large layout: it might be a good idea. If not, chuck the idea out.

I am happy, no proud, to say I know nothing about Digitrax as a system. But as I have gone on record here as saying I will not be involved in any of the 'my system is better than yours stuff' will not say anything about 'cheap', second rate and the like and suggest you ignore it.

As for wiring on a larger layout, and if you do build a feedback or points system etc with express net, then yes you may well be thinking about what your favourite colours are. My point always about saying the colour is too suggest order to the reader without spelling it out in a paragraph.

One extra point, it is certainly true if you look at the Lenz 'Product Overview' none of the static decoders are pictured with the required wiring coming in nor out. They are very wire sanitized images. You now know why!

TVBG

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ChrisE

· #22 · Jan 19, 2006 (Edited by Moderator)

QUOTE (LisaP4)Actually by your reckoning you need 5 BUSes, you missed out the Com BUS which the throttles plug into. However DCC only requires 2 BUSes;
The Track BUS
The Com BUS
<{POST_SNAPBACK}>

That is what I thought in the first place! Yes I did forget the COM bus as I have always intended to use wireless control but I am sure that I should install the BUS anyway. I am also pleased to note that a ring circuit is acceptable.

2 things come to mind.

1. The 5 amp supply - and many have less - that sounded so generous when I started all this is suddenly sounding very small if train lighting, building lighting & accessories are all to be powered from it and

2. As a result of this I am inclined to think a 12v BUS for non DCC based lighting etc might well be a good idea. I would also think that the less "junk" I have on my track BUS the less likely I am to compromise my proper control and power supply of trains & points etc.

I remember reading somewhere that as a matter of safety discipline it is a good idea to avoid mains cable colours when wiring a layout. As in the UK that would now include at least red, brown, blue, black, yellow, green and green/yellow stripes I am not kidding when I say my wholesaler doesn't have enough colours.

Chris

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the volebender general

· #23 · Jan 19, 2006 (Edited by Moderator)

Dear chrisE

Thanks for reading what I actually said.

Also thanks for seeing that I am tryng to get you to plan ahead. Once you have a few locos with sound decoders, for example, then your draw on five amps is massive. How about all your coaches and brake vans with lights and flasing lamps. Keep you track power for all of these in the future.

TVBG

Makemineadouble

· #24 · Jan 19, 2006

QUOTE I remember reading somewhere that as a matter of safety discipline it is a good idea to avoid mains cable colours when wiring a layout. As in the UK that would now include at least red, brown, blue, black, yellow, green and green/yellow stripes I am not kidding when I say my wholesaler doesn't have enough colours.

Its a defacto standard in DCC that the front bus is the A rail and is red, the rear rail or
B rail is black. This concept that one could confuse it for mains cable is crazy. It's another form of the nanny state. As I stated a long time ago I used bare earth wire on my last layout and this work really well, but you have to plan where and how you lay your bus. Try to avoid chocolate box connectors they are a scource of trouble. Automotive snap type cable connectors are far better and if your using sheafed bus you don't need to strip it. If you need a ring main type bus there's no reason at all why you can't do this.

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Edwin

· #25 · Jan 19, 2006

2

I thought I understood BUSes until I read this! Looks like you really do have to wait ages and then three come along at once

I notice people saying that Digitrax etc do not need a feedback bus. My understanding is that while this is true, that these systems use Loconet to provide feedback bus. So if you want to have feedback you have to wire a Loconet bus round the layout, though of course this will also allow you to plug in throttles at different places. Therefore which system needs fewest bus wires depends on which of these features you want.

There is also some discussion of running a separate bus to supply DCC signal to the accessory decoders. One reason to do this might be to run them from a separate booster so that they still work in the event of a short circuit on the track. Since the main cause of a short circuit is a train running onto an incorrectly set point, it is good if you are still able to change the point and fix the problem!

For what it's worth, I have chosen to use decoders which need a separate power supply, since their cheapness outweighs the need to provide extra wires, and sooner or later I'd probably need the separate supply in any case. I intend to run four high-current wires round my new layout: DCC track feed (red and black) and 15VAC (green and yellow). Low-current wires will go in a separate bus made from ribbon cable. These include accessory DCC feed (2), Xpressnet (4), emergency stop wire (1), but I'll probably run 16 cores as it isn't much extra effort or cost on a ribbon, and allows me to add more functions later if I need to.

Who was it that said you only needed two wires

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Brian

· #26 · Jan 19, 2006 (Edited by Moderator)

2

Edwin
Excellent choice of wiring colours

I fully go along with the Red/Black DCC BUS and Yellow/Green for ac permanent supply BUS. What needs to be remembered too is the output of the poor old 16v ac power unit (Transformer) will need to be in the region of at least 50va or better still 75va or even higher at 16volts ac output. These aren't cheap!

You will need plenty of va output to allow all the points to multi gang operate, lights to be on in buildings, colour light signals (with grain of wheat lamps) and any station or street lights etc. Don't forget any dc needs too (Via a bridge rectifier connected across the 16v ac BUS.) to power LEDs in signals etc via dropping resistors. Yes , I know inverse diodes can be fitted across LEDs to enable them to work on ac, but how much easier it is to provide a 3 or 5 amp bridge rectifier to supply all the layouts LED (DC) needs and simply work in dc and use 470 or 560 ohm resistors!

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Edwin

· #27 · Jan 19, 2006

Thanks for your comments Brian.

I will be using the MERG point decoders which as well as being very good value have an on-board CDU so the peak current should not be too high. Also LEDs rather than bulbs in signals and wherever else I can, not just to save current but also as I don't fancy replacing them when they blow! I have 12Vdc in the Xpressnet bus but it won't drive very much else, so I'll just rectify the AC where I need to.

I have a 5-amp Lenz power supply but this is a bit excessive for N gauge so I may make this the auxiliary supply and buy a 3-amp for DCC.

My high current bus cables will be rated at 5 amps, but I plan to run the spurs to each baseboard through polyfuses so I can use thinner cable for the rest of the wiring avoid anything overheating.

I'm now having fun working out the core allocation on the low-current bus so the colour coding on rainbow ribbon cable can't get confused with anything else!

Doug

· #28 · Jan 19, 2006 (Edited by Moderator)

This should sort it out. Remember that your system may not have extra booster or feedback or accessories.

This is a complete system based on an Xpressnet command BUS. Perhaps Lisa can do a similar one for Loconet.

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ChrisE

· #29 · Jan 19, 2006

Doug,

I do know exactly what they mean but when I look at your diagram the "two wire" for DCC does seem to be marketing fluff & frankly would be better forgotten. Beyond the Bachmann market I suspect that it confuses more than it helps.

Actually my DCC layout will have more wiring than my non DCC layout partly at least because electrically it will do more - but isn't that why we go DCC?

Chris

the volebender general

· #30 · Jan 19, 2006

Edwin,

Three buses... very funny.

Doug,

Nice work. Certainly useful to put diagrams to what was being suggested.

My simple point. If you are wiring your layout with a DCC signal and power BUS (your diagram) then wire at the same time the (accessory power feed). Hence my four chock block idea! Thats all.

Reason; it will allow you to move the Lenz point decoder(your diagram) anyware on your layout and wire close to the points (horrid reality)- my point decoders are over 15 feet apart. It will save time and money.

p.s. I wasn't thinking so much of a typical Lenz feeback system. Your diagram catches the key point. In reality there are in fact three distinct modules that have to be wired if you buy into Lenz. Your notch in the track section is correct, but if only it were two wires. Leave as is though.

p.s. being a mod is a hard job, you three guys are doing well, despite what you may think your work is appreciated here. thanks for creating the space.

TVBG

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Doug

· #31 · Jan 19, 2006 (Edited by Moderator)

Yes, you are right, the point decoders are better located near to the points - less wiring. I have point decoders with 4 and 6 outputs so I position them in the most suitable location nearer to groups of points. I use keyboards for my point control. Each group of keys controls the points attached to one point decoder.

The Lenz feedback is slightly more complex than this, and also depends if you use occupancy detectors. With the Lenz Occupancy Detectors (LB101 ) and Feedback Modules (LR101). Each LR101 supports 4 LB101s which in turn support 2 track circuits, so for every one feedback module, you can monitor 8 track circuits or zones.

ChrisE

· #32 · Jan 19, 2006

QUOTE (Doug @ 19 Jan 2006, 15:57)The Lenz feedback is slightly more complex than this, and also depends if you use occupancy detectors. With the Lenz Occupancy Detectors (LB101 ) and Feedback Modules (LR101). Each LR101 supports 4 LB101s which in turn support 2 track circuits, so for every one feedback module, you can monitor 8 track circuits or zones.
<{POST_SNAPBACK}>

I feel confusion coming on again. I really do not understand the above quote at all. I am probably the only idiot who does not understand this but does it have any implications for how I electrically construct my railway or can it wait until/if I decide that I want occupancy detectors etc?

I don't think that we have discussed track circuits & zones at all.

Edwin

· #33 · Jan 19, 2006

No you don't need to think about this until (if ever) you want to detect trains as they move round the layout. It just means that with Lenz kit you have to join a group of devices together to achieve this. At least one other supplier (LDT) does the whole lot in a single module.

HOWEVER, if you might want this, and haven't laid any track yet, it would be a good idea to decide where you detection section will be, include the necessary rail breaks and feeds as you lay it, and just join all the feeds together for the time being.

Which I suspect will start yet another discussion...

LisaP4

· #34 · Jan 19, 2006 (Edited by Moderator)

Here's the LocoNET verrsion

EDIT; wrong pic first time.

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the volebender general

· #35 · Jan 19, 2006

ChrisE,

know you are not an idiot.

I'm an idiot. I built an earlier dcc layout with the promise that i would have feedback and failed to do my research. And stripped it up when i found that it was no good for the job.

Carry on with your plans, you can build the layout of your dreams and carry them out with the ideas you have already read.

It really depends on what sort or type of occupancy detector system you want and why. A simpler signal stop, for example, will fit in with whatever you build.

A full blown computer control system (Rail Road and Co), for example, will take more forward planning.

They all, however, work on the isolated block system and you will find, for example, Peco code 75 track isolated at all exits provides a natural frame-work.

Do not get bogged down on this point, Doug put the F/B sytem into the diagram to cover all discussions. You will tend to install point decoders long before you worry about detection.

Just the humble opinion of one that is delaying this very job and enjoying the chat here instead.

mmmm

TVBG

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Doug

· #36 · Jan 19, 2006

QUOTE (ChrisE @ 19 Jan 2006, 17:10)I feel confusion coming on again. I really do not understand the above quote at all. I am probably the only idiot who does not understand this but does it have any implications for how I electrically construct my railway or can it wait until/if I decide that I want occupancy detectors etc?

I don't think that we have discussed track circuits & zones at all.
<{POST_SNAPBACK}>

Yes, leave it for a while. You can add it later. If you wish to make provision for it now, add an isolated section of track at the beginning and end of each track in your staging yard as well as any siding you may have. It also help to do this at the start and end of your platforms. These are the areas that you want trains to stop.

Link up all the track sections to your DCC signal/power BUS and enjoy your layout. Later if and when you would like to add feedback, you have the isolated sections of track ready for that.

Regarding the length of the isolated (feedback sections) - you can send a command to a train when it arrives into one of these zones. For example, if a train arrives at a station it can be detected and given the command to slow down. At the end of the platform it can be detected by another isolated section and it can be given the command to stop. This places the carriages in the right place for picking up and dropping off passengers. So the length depend on your trains, your zones and what you really want to do with the whole thing.

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ChrisE

· #37 · Jan 19, 2006

QUOTE (the volebender general @ 19 Jan 2006, 16:28)ChrisE,

They all, however, work on the isolated block system and you will find, for example, Peco code 75 track isolated at all exits provides a natural frame-work.

TVBG
<{POST_SNAPBACK}>

I now understand why you said in a post elsewhere to isolate all 6 rails in a turnout. At the time that I read it I couldn't see the reason when the outside two rails are continuous lengths. I thought that isolating the two that connect to the frog would be sufficient.

the volebender general

· #38 · Jan 19, 2006

Thanks,

there is a little method in my madness. You wont believe the pain of cutting through all your nicely soldered points.

I paid - you did some research in advance and put two and two together!

TVBG

Makemineadouble

· #39 · Jan 19, 2006

where did those two very nice circuit diagrams come from neither are my big book of DCC or in Digital command Control ? my compliments !

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Doug

· #40 · Jan 19, 2006 (Edited by Moderator)

Well I just spend a little while this afternoon drawing the first (Xpressnet), Lisa modified it for the second (Loconet).

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