DCC Bus and Rail Continuity on a Circular Layout?

[ATME]

I have read various options on how to wire a bus circuit on a circular layout but have not come across any opinion as to whether a pair of insulated fishplates are required - coinciding with the end of each bus circuit on an oval. 

Can anyone point me in the right direction for a known definitive guide to wiring a circular layout please?

 

Thanks

[WIMorrison]

Think of it like a ring main, you don’t need to insulate the ends, in fact depending on the type of turnouts you may not need to insulate anything.

[grriff]

As Iain has said, you don't need insulated fish plates on a simple oval. If you want to get into the subject in more detail try chapter 3 from 'Electronics for model railways' available, free, on www.merg.org.uk. 

[Steven B]

Splitting the bus and using rail joiner fails as a concept as soon as you run a train across the insulated gap. I've yet to see a layout there something bad happens when this occurs where it's implemented!

 

If you join the two ends you'll get track power being fed both ways around around the loop, reducing the resistance which is a good thing. If you've a dry solder joint one leg it can actually improve running (and short circuit protection).

 

Depending on size, breaking the layout into individually switchable circuits can help with fault finding (standard toggle switch or one of the numerous circuit breaker units that are available). These will need isolating from each other to work properly.

 

Steven B.

[dasatcopthorne]

Just as an aside.

 

The Track Bus as a circular thing is fine. It's just the same as having a circular layout.

 

However, DON'T have a circular Control Bus.

 

That's a no, no.

 

Dave.

[jamesed]

10 hours ago, dasatcopthorne said:

However, DON'T have a circular Control Bus.

 

That's a no, no.

 

 

That's a  myth which isn't supported by any half reasonable scientific justification. It's perfectly ok to wire your bus as a ring and, in fact, there is some scientific justification as to that being a good thing to do. 

[dasatcopthorne]

1 hour ago, jamesed said:

 

That's a  myth which isn't supported by any half reasonable scientific justification. It's perfectly ok to wire your bus as a ring and, in fact, there is some scientific justification as to that being a good thing to do. 

 

I stand corrected.

 

What is the scientific justification then please as we have a club layout that could benefit from it.

 

Dave

[dasatcopthorne]

1 hour ago, jamesed said:

 

That's a  myth which isn't supported by any half reasonable scientific justification. It's perfectly ok to wire your bus as a ring and, in fact, there is some scientific justification as to that being a good thing to do. 

 

I was going by this and others.

 

............

As mentioned above, the maximum length of the Cab Bus is 500' in a continuous run (daisy chain), any branches off the bus should be no more than 8 feet long. The Cab Bus and its throttle panels should be arranged in a daisy chain fashion, one feeding the next. Attempting to save wire by using stubs off the main bus to feed throttle panels will result in issues. If stubs are needed, they must be very short, no longer than the length of a coiled throttle cable.

It is important to arrange and wire the Cab Bus in a linear fashion. NCE does not recommend splitting the Cab Bus nor the use of stubs. As this is a serial protocol, it is meant to go point to point. It cannot be wired as a star, nor should it form a closed loop.

................................

 

Dave.

[Nigelcliffe]

1 hour ago, dasatcopthorne said:

 

I was going by this and others.

 

......

........  NCE does not recommend splitting the Cab Bus ..... nor should it form a closed loop.

.

 

 

Which is specific advice for one manufacturer's proprietary control bus.   Other control bus systems from other manufacturers might have different constraints.      You can't generalise from one manufacturer's proprietary arrangements.  

 

 

- Nigel

 

[Steven B]

Loconet can be connected as a line, star, tee (or any combination there of) but not in a complete circle: https://www.digitrax.com/tsd/KB714/loconet-overview/

Quote

LocoNet’s philosophy and architecture allow "free-form" wiring with no termination or "linear-bus" restrictions.  You can star, tee, branch, or expand LocoNet in any configuration. LocoNet can be used in any configuration except for a ring.  You should NEVER connect LocoNet back on itself, because pins 1 and 6 should not be connected.

 

 

Steven B.

[RFS]

8 minutes ago, Steven B said:

Loconet can be connected as a line, star, tee (or any combination there of) but not in a complete circle: https://www.digitrax.com/tsd/KB714/loconet-overview/

 

 

Steven B.

 

This refers to the Loconet bus not the DCC bus that connects to the rails. 

[jamesed]

As a general rule, the lower the impedance of the bus wire the better the quality of the dcc signal will be maintained. The nature of a ring circuit is that the impedance is reduced by up to half.  Most quality dcc controllers (but possibly not the one which recommends against a ring circuit) will have suppression circuitry built in to its output. Therefore, if both ends are terminated there they are both protected and there's no need to install snubbers as long as you have kept to a ring and don't have any spurs. 

 

There is some nonsense written around the web that says if the dcc signal is arriving from different directions that it can be out of sync and cause phase cancellation corruption but this would only be an issue where the bus wire is something like 3km long. Consequently that argument can be dismissed for virtually all model layouts.   There is also one particular uk manufacturer which likes to perpetuate this myth that ring circuits are bad and that it's much better to have a radial with snubbers fitted at each end point. However, despite them being challenged on this point a number of times I've never seen them come up with satisfactory scientific justification for that claim.  If one was being cynical then one might wonder whether the fact that they make and sell their own snubbers might be influencing their point of view. 

[Steven B]

Basically:

 

Track feed buses can be circles

 

Control buses (Loconet, XpressNet, XBus, NCE Cab bus) - check with the manufacture!

 

 

Steven B

[dasatcopthorne]

We seem to have digressed on to Track Bus now.

 

My comment was about the Control Bus  which doesn't go anywhere near the track.

 

NOT the Track Bus.

 

Dave.

 

[WIMorrison]

The question was about the DCC track bus, it was you who digressed by quoting NCE as the definitive source for control busses, but NCE are only definitive for NCE equipment.

[two tone green]

4 hours ago, jamesed said:

As a general rule, the lower the impedance of the bus wire the better the quality of the dcc signal will be maintained. The nature of a ring circuit is that the impedance is reduced by up to half.  Most quality dcc controllers (but possibly not the one which recommends against a ring circuit) will have suppression circuitry built in to its output. Therefore, if both ends are terminated there they are both protected and there's no need to install snubbers as long as you have kept to a ring and don't have any spurs. 

 

There is some nonsense written around the web that says if the dcc signal is arriving from different directions that it can be out of sync and cause phase cancellation corruption but this would only be an issue where the bus wire is something like 3km long. Consequently that argument can be dismissed for virtually all model layouts.   There is also one particular uk manufacturer which likes to perpetuate this myth that ring circuits are bad and that it's much better to have a radial with snubbers fitted at each end point. However, despite them being challenged on this point a number of times I've never seen them come up with satisfactory scientific justification for that claim.  If one was being cynical then one might wonder whether the fact that they make and sell their own snubbers might be influencing their point of view. 

A more  modern version of the old ZTC who would sell people a box of tricks for over £100 that could be fixed for a tenner. 
 

The scam that makes me laugh the most at the moment is DCC track bus wire sold to counter problems you may encounter on modern fly by wire airliners. That’s the real aeroplanes not models. 
 

Utter rubbish, it’s a toy train don’t get conned. 

[Nigelcliffe]

7 minutes ago, two tone green said:

A more  modern version of the old ZTC who would sell people a box of tricks for over £100 that could be fixed for a tenner. 
 

The scam that makes me laugh the most at the moment is DCC track bus wire sold to counter problems you may encounter on modern fly by wire airliners. That’s the real aeroplanes not models. 

 

Don't forget to use green felt pen along the edge of the wire to optimise the signal quality - its essential now that sound decoders are offering "CD qualify" sound.  

 

 

- Nigel

 

[two tone green]

24 minutes ago, Nigelcliffe said:

 

Don't forget to use green felt pen along the edge of the wire to optimise the signal quality - its essential now that sound decoders are offering "CD qualify" sound.  

 

 

- Nigel

 

Yes, that one as well. Classic. 
 

The things get people get conned with. 

Actually I found red better. Gave a warmer sound. 🤣
 

[Crosland]

2 hours ago, Nigelcliffe said:

 

Don't forget to use green felt pen along the edge of the wire to optimise the signal quality - its essential now that sound decoders are offering "CD qualify" sound.  

 

 

- Nigel

 

 

Not to mention the special foil and magic water https://pwbelectronics.co.uk/images-of-our-products although we should not speak ill of the dead https://www.stereophile.com/content/peter-belt-1930-2017

[dasatcopthorne]

6 hours ago, WIMorrison said:

The question was about the DCC track bus, it was you who digressed by quoting NCE as the definitive source for control busses, but NCE are only definitive for NCE equipment.

 

I said this.

 

.....................

Just as an aside.

 

The Track Bus as a circular thing is fine. It's just the same as having a circular layout.

 

However, DON'T have a circular Control Bus.

 

That's a no, no.

 

Dave.

[Edward]

On 30/06/2022 at 22:45, dasatcopthorne said:

 

I said this.

 

.....................

Just as an aside.

 

The Track Bus as a circular thing is fine. It's just the same as having a circular layout.

 

However, DON'T have a circular Control Bus.

 

That's a no, no.

 

Dave.

So glad this was made clear as I have the unfortunate habit of misreading key words.  In this case it was "control" & "track"!  Was about to launch into an impassioned defence of circular buses too.  As my track uses a star system, you can imagine how confused I would have been!

My NCE cab bus does of course wend its way via the UTPs with the other cabs such as mini  panels & alpha units plugged into them.

[ATME]

What's the difference between a track bus and a control bus please?

[WIMorrison]

TBH I don’t think that there is. most people use the track bus to control their trains and accessories. 

 

some of us split off the track bus from an accessory bus to allow control of turnouts, signals, etc if there is a track short e.g. overrunning turnout.

 

however they are fundamentally just DCC busses and can be treated as such.
 

 

[Crosland]

Track bus: Can by used to run trains and control accessories (points, signals, etc).

 

Accessory Bus: Split off form the track bus in some way and used to control accessories. Usually done so that a short on the layout does not stop accessory control.

 

Control bus: Used to connect things such as cabs (throttles) and control panels, e.g., NCE Cab Bus, Loconet, ExpressNet. Can be used for feedback from occupancy detectors, etc. Can also often be used in place of an accessory bus to control accessories.

[WIMorrison]

I hadn't thought of Loconet, Xpressnet, etc as a Bus, rather a control protocol, but I guess they could also be called a Bus 😀