DCC Command Unit Location

[Newbie2020]

Hi All, 

 

I have set up the DCC BUS for my layout and connected the DCC Command Unit (Digitrax) to one end. I based this on the early research I did on the topic. This means that I have about 4.5m of BUS from the command unit to the end. I note from further research that advice is, to get best results, to place the command unit approximately central - meaning I would have about 2.25m of BUS in either direction (terminating in DCC Concepts BUS Spike Suppressors). 

 

My Question is, is it worth the effort to change to a central position ? Inconvenient but quite do-able, or would the benefit be minimal?

 

Cheers

 

[Colin_McLeod]

IMHO benefit would be minimal.

Not worth the hassle so have fun doing something else.

[WIMorrison]

In a word - No

 

Place it where you operate the layout from most, or is most convenient for you.

[Newbie2020]

Thanks guys, thats great

[Ron Ron Ron]

1 hour ago, WIMorrison said:

.....Place it where you operate the layout from most, or is most convenient for you.

 

Unless the Command Station referred to, is a Zephyr (console based system), then where it's located should have no bearing on where you operate the layout from.

Throttle sockets can be located in convenient positions for the operator and the Command Station located wherever is most suitable for the layout wiring etc,.

 

 

 

1 hour ago, Newbie2020 said:

.......I have about 4.5m of BUS from the command unit to the end. I note from further research that advice is, to get best results, to place the command unit approximately central - meaning I would have about 2.25m of BUS in either direction (terminating in DCC Concepts BUS Spike Suppressors)......

 

 

4.5 metres should be perfectly OK.

At 9 or 10 metres  (30ft +) then certain advice says there may be some issues.

 

Do note that the furthest distance from the Command Station should take into account the track as well as the Power Bus wiring. 

That circuit isn't limited just to the bus wires.

 

 

.

[Crosland]

14 hours ago, Ron Ron Ron said:

Do note that the furthest distance from the Command Station should take into account the track as well as the Power Bus wiring. 

That circuit isn't limited just to the bus wires.

 

If it's wired correctly then the bus wires will be more or less the same length as the track. 

[Andymsa]

2 hours ago, Crosland said:

 

If it's wired correctly then the bus wires will be more or less the same length as the track. 

I think the point was from the location where the track feed is that track length from that point needs to be taken into consideration. Ie series wiring not parallel 

[Colin_McLeod]

Surely this is getting more complicated than it need be.  Just connect the command unit to the bus and stop worrying about the length of cable, track etc.

[RAF96]

My DCC bus goes down one side of a single garage, across the end and back down the other side.

Controller feeds one end of the bus and the far end sports a snubber/terminator/call-it-what-you-will.

[Crosland]

On 12/03/2021 at 14:43, Andymsa said:

I think the point was from the location where the track feed is that track length from that point needs to be taken into consideration. Ie series wiring not parallel 

 

If its wired correctly for DCC there is no one "track feed". The track is fed from the bus by multiple droppers. The length of the track will be more or less equal to the length of the bus.

[Andymsa]

1 hour ago, Crosland said:

 

If its wired correctly for DCC there is no one "track feed". The track is fed from the bus by multiple droppers. The length of the track will be more or less equal to the length of the bus.

Sorry I have to disagree, please see point 9 in the link. Layouts are not comprised of one track section fed by multiple feeders, by its very design a layout will be divided at some point. So a combination of track and bus length will be a factor. The dcc signal will degrade over a longer length regardless of how many droppers you have.

 

https://sites.google.com/site/markgurries/home/dcc-general-best-practices/wiring-planing/max-track-bus-lenght

 

also if you factor in track detection this 30 foot limit is even more important.

Edited March 13, 2021 by Andymsa

[Dungrange]

But point 9 in that article is just highlighting that the current flows from the command station along the red bus wire to the furthest part of the layout and then back to the command station station via the black bus wire, so when calculating the resistance of the wiring and therefore voltage drop, you need to remember to sum the resistance of both the red and black wires, but of course your bus length is the length of either or these (ie your red and black wires should be roughly the same length).  That is where his dividing by two factor comes from.  It has nothing to do with the length of track, droppers or parallel wiring.  In fact the author has deliberately ignored the fact that parallel track resistance would reduce the effective track bus resistance, as can be seen by footnote 1 in that article.  This would surely make the 30 foot limit less of an issue.

[melmerby]

My bus is much more than 4.5m* and I wired it with a snubber on the end. It was originally fed with a Lenz 100 system, now a Roco Z21

Out of interest I viewed the waveform at the end using a scope, with and without a snubber.

There washardly any visible difference!

The waveform straight out of a Digikeijs DR5000 was worse than when using either the Lenz or Roco kit at the far end of the bus!

 

*Probably nearer 10m, it runs all the way around a 20' x 12' layout, about 70cm in from the outer edge but there is a gap so that it is not a continuous circle.

 

[Andymsa]

10 hours ago, Dungrange said:

But point 9 in that article is just highlighting that the current flows from the command station along the red bus wire to the furthest part of the layout and then back to the command station station via the black bus wire, so when calculating the resistance of the wiring and therefore voltage drop, you need to remember to sum the resistance of both the red and black wires, but of course your bus length is the length of either or these (ie your red and black wires should be roughly the same length).  That is where his dividing by two factor comes from.  It has nothing to do with the length of track, droppers or parallel wiring.  In fact the author has deliberately ignored the fact that parallel track resistance would reduce the effective track bus resistance, as can be seen by footnote 1 in that article.  This would surely make the 30 foot limit less of an issue.

 

10 hours ago, Dungrange said:

 

9 hours ago, melmerby said:

My bus is much more than 4.5m* and I wired it with a snubber on the end. It was originally fed with a Lenz 100 system, now a Roco Z21

Out of interest I viewed the waveform at the end using a scope, with and without a snubber.

There washardly any visible difference!

The waveform straight out of a Digikeijs DR5000 was worse than when using either the Lenz or Roco kit at the far end of the bus!

 

*Probably nearer 10m, it runs all the way around a 20' x 12' layout, about 70cm in from the outer edge but there is a gap so that it is not a continuous circle.

 

 

you have to look at the whole picture here, not just about resistance. ie hardware used as I’m sure some manufacturers are better than others as melmerby showed with the Digikeijs system. How the layout is wired. Check the other sections of his website that covers such aspects of this, I followed these ideas and have never experienced any issues on my layout which is 70foot long with one section of running at least 140feet in length. Then the quality of the decoders used can be a factor. The 30 feet is probably not exact figure but a guide not to exceed, and all our layouts are unique so no two people will have the same issues as the link points out.
 

https://sites.google.com/site/markgurries/home/dcc-general-best-practices/wiring-planing/snubbers-rc-filter

Edited March 14, 2021 by Andymsa

[Crosland]

20 hours ago, Andymsa said:

Sorry I have to disagree, please see point 9 in the link. Layouts are not comprised of one track section fed by multiple feeders, by its very design a layout will be divided at some point. So a combination of track and bus length will be a factor. The dcc signal will degrade over a longer length regardless of how many droppers you have.

 

DCC layouts should be, ideally, fed from a bus using multiple feeders. It doesn't matter whether the track is continuous (linked by rail joiners) or isolated around every dropper. The track topology is largely irrelevant unless you have (which you shouldn't) a long spur relying on rail joiners and not connected to the bus.

 

The furthest distance from the command station is the furthest extent of the bus plus a few inches of track fed from the last dropper on the bus.

[Andymsa]

44 minutes ago, Crosland said:

 

DCC layouts should be, ideally, fed from a bus using multiple feeders. It doesn't matter whether the track is continuous (linked by rail joiners) or isolated around every dropper. The track topology is largely irrelevant unless you have (which you shouldn't) a long spur relying on rail joiners and not connected to the bus.

 

The furthest distance from the command station is the furthest extent of the bus plus a few inches of track fed from the last dropper on the bus.

But should be no more than 30 ft, which was the Op original question to centrally locate the command station

[Ron Ron Ron]

A lot of this argument is misplaced.

The recommended maximum distance isn't about the length of the DCC power bus wires, but about the distance to the furthest point on the layout, via the power bus, droppers and track combined, ....from not the Command Station, but from the power bus output, or outputs, of your system's Booster or Boosters (originally referred to as Power Stations).

n.b. The main system booster may be housed in the same box as the command station.

 

Putting on my well worn pedant's hat, a Command Station usually, almost always, doesn't have a Power Bus output.

 

.

 

Edited March 14, 2021 by Ron Ron Ron

[Andymsa]

2 hours ago, Ron Ron Ron said:

A lot of this argument is misplaced.

The recommended maximum distance isn't about the length of the DCC power bus wires, but about the distance to the furthest point on the layout, via the power bus, droppers and track combined, ....from not the Command Station, but from the power bus output, or outputs, of your system's Booster or Boosters (originally referred to as Power Stations).

n.b. The main system booster may be housed in the same box as the command station.

 

Putting on my well worn pedant's hat, a Command Station usually, almost always, doesn't have a Power Bus output.

 

.

 

I certainly get this and agree about some understanding , apart from volt drop the dcc signal will degrade the longer the bus and track combined is at the furthest point from the, let’s say output source command station or booster as the case maybe. 
 

the point you make about the “not the command station” perplexes me because the same rule about distance applies equally to the command station. I must be an exception because my command station does have a power bus output, it is used to power my digital signals. But not to use a command station output for a power bus is a waste of resources.

[melmerby]

8 hours ago, Andymsa said:

 

the point you make about the “not the command station” perplexes me because the same rule about distance applies equally to the command station. I must be an exception because my command station does have a power bus output, it is used to power my digital signals. But not to use a command station output for a power bus is a waste of resources.

I think Ron means the thing you hold in the hand is the "command station", the thing that powers the track is the booster/amplifier and that's where the actual DCC signal to the track comes from.

Exceptions are  the all in ones like NCE Powercab, Hornby Elite and suchlike where it is all in one unit and the output to the track comes from the thing you do the control with.

[Ron Ron Ron]

8 hours ago, Andymsa said:

.....the point you make about the “not the command station” perplexes me because the same rule about distance applies equally to the command station. I must be an exception because my command station does have a power bus output, it is used to power my digital signals. But not to use a command station output for a power bus is a waste of resources.

Your Command Station will almost certainly be housed  in the same unit as the supplied system Booster.

The power bus output comes from the in-built booster.

 

Examples.

Lenz LZV100 & 200, NCE PowerPro, Roco Z21, Digitrax DCS series etc, ...all these are combined Command Station and Boosters, housed in one tin can.

Digitrax Zephyr series, ESU ECoS, Hornby Elite, ZTC, Sig-an Trak Ace etc, ....are console based systems that contain Command Station, Booster and throttle/cab user interfaces.

 

Whether it’s from a track output, or via LocoNet, or ECoSLink , in all cases, the power bus output is coming from the in-built Booster, not the Command Station.

 

Anyway, this is me being pedantic and a distraction from the topic of the OP.

My original point was that if there is a recommended max distance, before problems may start to occur (they may not in many cases), then it is from the power bus output, in whatever form, to the furthest point on the layout, where a mobile or stationary decoder could be located.

 

As Andrew said, if the layout is wired “properly”, there won’t be much difference between the length of the power bus wires and the furthest distance from the track output. At the most a few feet of additional distance along droppers and the track rails. The bus and feeder architecture has no bearing on this. It’s a simple measurement of distance, by any route.

.

Edited March 15, 2021 by Ron Ron Ron

[Ron Ron Ron]

6 minutes ago, melmerby said:

I think Ron means the thing you hold in the hand is the "command station", the thing that powers the track is the booster/amplifier and that's where the actual DCC signal to the track comes from.....

Sorry, no I don’t mean that.

Except for the PowerCab, where the Throttle, Command Station and Booster are all housed in the handset.

 

.

 

[WIMorrison]

Methinks that this topic has run its course and the answer for the OP was provided in the first few posts

[Nigelcliffe]

7 hours ago, WIMorrison said:

Methinks that this topic has run its course and the answer for the OP was provided in the first few posts

 Ah, spoilsport.   I was waiting to find out how many angels can dance on the end of a dropper wire....

 

 

[Ron Ron Ron]

1 hour ago, Nigelcliffe said:

 Ah, spoilsport.   I was waiting to find out how many angels can dance on the end of a dropper wire....

 

 

That must be scale dependent.

N gauge, 00 gauge or 0 gauge.

Gauge 1 wouldn’t work, as they’d probably fall off.

 

 

 

.