The big BUS debate

16114 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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61 - 80 of 90 Posts

ChrisE

· #61 · Jan 21, 2006 (Edited by Moderator)

QUOTE (Doug @ 21 Jan 2006, 01:28)On the subject of testing: When I'm constructing the track and installing the DCC signal and power BUS, Obviously I don't connect the power whilst I'm doing it, but I use a 9 volt battery - connected to a buzzer and a track power feed clip. I plug it in and if I get a wire crossed, the buzzer will go off as the track short-circuits.
<{POST_SNAPBACK}>

Sounds like a good idea. I know the way that you mean it is quite safe but can I just stress for the less electrically literate readers that this must be a dry battery - the sort you throw away when they run flat, Ever Ready, Panasonic, Duracell etc. If you use nicads, NiMh LiPolys or lead acid types the results could be burnt out wiring, fire or explosive - literally!!!!

Chris

Makemineadouble

· #62 · Jan 21, 2006

Why not connect up your droppers with the track power on. Your DCC control unit has built in protection, and gives you a very nice buzz if you make an accidential short, it then shuts down until you recify the situation, thats what it's designed to do. I always make a point to wire up with the track power on. Not that i make many mistakes, but then it only takes on lapse of concentration I suppose.

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Doug

· #63 · Jan 21, 2006 (Edited by Moderator)

My current DCC system (Arnold) doesn't buzz when a short occurs...

Anyway, I wouldn't be able to strip the wires with my teeth the then...

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Dynamite26

· #64 · Jan 21, 2006

Once i have put in the two wires for the power bus how many droppers do i need to put in and how far apart should they be,and also how long should i make the wires to connect the droppers to the power bus be.

As i have been reading a few sites and they give different lengths for the feed wire from the bus wire to the droppers on the track.

Doug

· #65 · Jan 21, 2006 (Edited by Moderator)

QUOTE (Dynamite26 @ 22 Jan 2006, 00:02)Once i have put in the two wires for the power bus how many droppers do i need to put in and how far apart should they be,and also how long should i make the wires to connect the droppers to the power bus be.

As i have been reading a few sites and they give different lengths for the feed wire from the bus wire to the droppers on the track.
<{POST_SNAPBACK}>

There are no hard and fast rules about this. I've heard that it is good to have droppers every 2 to 4 metres. If you are going to add feedback and block control later, put them closer together.

The droppers shouldn't be too long. I have my BUS under the baseboard and have the droppers roughly every metre and a half. The droppers themselves are about 20cm long - enough to easily manage the wires, connecting them to the terminal blocks.

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Dynamite26

· #66 · Jan 21, 2006 (Edited by Moderator)

I won't be having feed back or block control as i just want to run trains and thats all,would some droppers have to be longer as my layout is a two level layout which has four main tracks two upper and two lower with inclines connecting them together.

I think i might have to get a book on DCC as it seems they is alot to know about it.

Also does it make a difference if you use setrack for DCC as most of my layout will have hornby setrack as my layout was going to be just DC till i decided to wire it for DCC,i will also be using peco code 100 flexi track for my fiddle yard and station area.

ChrisE

· #67 · Jan 21, 2006

I have always either soldered my rail joints or put a dropper for every length of track on a non DCC layout.

I have also never used chocolate block connecters preferring to have one long length of wire & just strip the covering and then wrap & solder the drop to it. If I am looking at a number of connections close together I have used a tag strip.

As electrical problems nearly always begin at joints and appear insidiously over time this has always seemed the best way & is no extra work as long as you fix the wires to prevent shorts.

This method is why I asked about deliberately putting in breaks with DCC to help find faults. If I used blocks with all my sidings & points I could have an awful lot of chocolate blocks, breaks in the BUS & potential problems in my wiring. I would also have a lot of breaks in the track plan that Doug published.

Am I alone in my methods?

Chris

Branchliner

· #68 · Jan 21, 2006

Just a couple of queries,

1. somewhere in this subject a statement was made to the effect NOT to return the bus ends e.g, like a household ring main. Can anyone give me a rationale for this. Years ago when I worked with specialized equipment we had to take care when earthing to ensure that a loop was not formed, this was to minimise the possibility of induced current. I cannot see the same problem with a ring AC power circuit.

2. It was also recommended NOT to solder droppers to the track connectors due to the possibility of poor contact with the track. If this is the case it would be necessary to connect the bus to each section of track to avoid the same bad connections, I am aware that some modellers do this but I consider it overkill.

Brian

Dynamite26

· #69 · Jan 21, 2006

I couldn't connect the bus to each section of track as nearlly all my track is hornby setrack and would take forever to do it,plus i'm still thinking of sticking with DC as that seem far easier to me as i just connect two wire from each of the 5 controller to each loop and to my depot area and away i go controlling my trains.

And what wire i bought can be used to wire extra lighting in the loft.

ChrisE

· #70 · Jan 21, 2006

QUOTE (Dynamite26 @ 22 Jan 2006, 00:36)I couldn't connect the bus to each section of track as nearlly all my track is hornby setrack and would take forever to do it,plus i'm still thinking of sticking with DC as that seem far easier to me as i just connect two wire from each of the 5 controller to each loop and to my depot area and away i go controlling my trains.
And what wire i bought can be used to wire extra lighting in the loft.
<{POST_SNAPBACK}>

My way of doing it arose because of problems with non DCC - exactly what you are proposing as the easier solution. Track joints are a major weak spot & set track has lots of them. Even if they work well when new they degrade over time & running gets worse. Relco sold lots of units to pre DCC users - one per controller - to counter just this problem. If I were going to do what you suggest I would smear very sparingly Copperslip between all my rail joints as I assembled them. You could do this just as well for DCC as it makes no difference to a bad electrical contact which method of control you use.

Chris

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ChrisE

· #71 · Jan 21, 2006

QUOTE (Branchliner @ 22 Jan 2006, 00:22)Just a couple of queries,

1. somewhere in this subject a statement was made to the effect NOT to return the bus ends e.g, like a household ring main. Can anyone give me a rationale for this. Years ago when I worked with specialized equipment we had to take care when earthing to ensure that a loop was not formed, this was to minimise the possibility of induced current. I cannot see the same problem with a ring AC power circuit.

2. It was also recommended NOT to solder droppers to the track connectors due to the possibility of poor contact with the track. If this is the case it would be necessary to connect the bus to each section of track to avoid the same bad connections, I am aware that some modellers do this but I consider it overkill.

Brian
<{POST_SNAPBACK}>

1. Neither can I & others here have confirmed it.

2. I can well understand why you should not solder droppers to track connectors. The conductivity of the joint between the connector & the track is one of the major electrical weaknesses of model railways. If you solder to the connector it is distinctly possible that over time you could have a poor contact with the track both sides of the connector. Connectors are often not made of the same metal as the rail which of course makes the corrosion problem worse. As I posted above this is one of the problems that the Relco unit helped to minimise for non DCC. I guess it all depends how sure you want to be that you will not have poor conductivity in the future.

Chris

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Makemineadouble

· #72 · Jan 22, 2006

There appears to be a lot of lashing of teeth on this subject, it's no big deal.
The basic rule is have a pair of droppers for each length of track. If you can get away with less, and it works, fine. No DCC inspectors coming along to inspect your work. Your the customer, and your the one who need to be satisfied, so if you want less track feeds fine.
Do put a track feed at each section of track, IE before and after a turnout. Yes you can have a ring main if you want. If you have set track and you dont want to put in 100's of droppers fine, try it with a few droppers, after all you can always add a few more if running in an area becomes erractic.

This is hobby it supposed to be fun, so enjoy your Hobby and DCC it will be fun

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Doug

· #73 · Jan 22, 2006

When we say "length of track" - we are talking of yard-long flextrack, which is quite often used on larger layouts due to lower cost and ease of use.

Regarding the closed ring of the BUS, it is advisable not to close the ring, but to leave it open (with the command station or booster in the middle), terminating the ends with a resistance. More info about BUS length and termination can be found at Wiring for DCC.

the volebender general

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

One of the reasons I always suggest a large horse shoe around your layout is not for any electronics reason.

I have also heard loads of stuff about twisted wires, must end with an xxx across the gap, light bulbs, shut down units, god knows. Dont know anything about any of it myself. Read about it all five years ago and have since ignored it all quite happily.

My horse shoe starts in a choc box and runs around the room. The choc boxes do not also have feeders in (just the main bus): you solder the feeders in where ever you like too the bus wires. Screw choc boxes in once; solder anywhere as your layout grows Flexibilty is the key.

If you have lots of set track start with North, South East and west on each loop line and see how you get on. Problem areas get special feeder attention. Too many problem ares with your isolating points and old fish plates and you will need the attention!

Tripping system is the best diagnostic tool - second best; a coach with lights in.

Finally, so why a horse shoe shape for your power bus then TVGB?

Well you do have a door in the room dont you? If you start at one side and end at the other its a .....

KISS

TVBG

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ChrisE

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

Horseshoe v Ring Main BUS

There are definitely differences of opinion here. TVBG advocates a horseshoe (posts 2 & 74). Doug goes horseshoe + resistance (post 73). Lisa goes ring (post 19). There may well be others.

In a situation like this we all recommend what we have found works for us. In a newly developing sphere of expertise such as this many of us will not have tried all the alternatives. Can I thus ask this question the other way around.

1. Has anybody tried either a horseshoe or ring main BUS and found that it gave problems causing them to change? Did the change alone solve the problem?

2. Has anybody found problems with accessory or feedback BUS as above?

3. Which equipment manufacturers recommend which method?

If either horseshoe or ring has caused problems please be specific about the problem, the length of the main circuit, and the age & make/ model of the control system.

It has been suggested that with the current equipment there should be no problem with problems being confined to previous generation controllers only.

Chris

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dwb

· #76 · Jan 22, 2006

To ring or not to ring that is the question:-

The answer depends on the type of signal being carried by the wires you are considering and whether or not the sigalling method was designed with either a ring or open end in mind. The reason is that electrical signals behave differently in each case and this difference in behaviour will affect any receiver which is trying to observe those signals. If the difference in behaviour is large enough the receiver will fail to detect the signals correctly and refuse to work.

In general, almost all of the buses I can think of that have originated in the computing world - eg RS485, SCSI, IDE, Ethernet, USB are of the open ended type. You most definitely do NOT close the ring on these. Some of these buses require each end to be "terminated" with a resistor of an appropriate value in order to work correctly. SCSI and the original thick and thin versions of ethernet are examples of these.

In our world of DCC, the primary bus which is supplying power to the track along with the instructions to the locomotive decoders, is going to be a ring because this is the most likely circuit which buyers of a starter digital trainset will build. The last thing you want to say to a 7 year old is - "And don't forget to put this (magic) isolater track into the circuit or it won't work". The support calls and returns would probably bankrupt the company; so this primary (and only obligatory bus) was designed for connection to a ring.

It appears that the other signalling paths used in the DCC world have been "borrowed" from the computing world. As I have stated above, these are designed to be open ended and so should not be turned into rings.

Summary:
The primary DCC power supply / loco signalling path can be a ring.
All the other stuff most likely should not be.

I hope this helps. I could go into the bath water wave analogy but I take showers myself.

David

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Dynamite26

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

Well i have decided to leave DCC control for now and keep this layout as a DC layout as it's my first proper layout as my other layouts always got dismantled before i really got anywhere,so when i build another layout i will wire it for DCC as all track will peco code 100 streamline track.

Cheers for the help guys

Steven

ChrisE

· #78 · Jan 22, 2006

QUOTE (dwb @ 22 Jan 2006, 14:31)To ring or not to ring that is the question:-

Summary:
The primary DCC power supply / loco signalling path can be a ring.
All the other stuff most likely should not be.

I hope this helps. I could go into the bath water wave analogy but I take showers myself.

David
<{POST_SNAPBACK}>

Ah yes - I had been wondering about the speed of light amongst other issues. What you say suits me well. I can continue the power BUS accross my obligatory doorway crossing bridge and use it as the natural break for everything else.

Nobody has volunteered that their choice of BUS gave them a problem. Any takers?

Chris

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Makemineadouble

· #79 · Jan 22, 2006

My last layout was a horse shoe simply because thats what suited the layout. My only comment is that using a telephone in the railway room was impossible with the layout powered up. There was zero interferance outside the room, and zero interferance with the TV's.

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Doug

· #80 · Jan 22, 2006

I use a ring now on the DCC signal/power BUS (Arnold system).

I don't terminate my X-BUS command BUS.

No problems

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